13 The Brain and Cranial Nerves.

13 The Brain and Cranial Nerves

Section 1: Functional Anatomy of Brain and Cranial Nerves
Learning Outcomes 13.1 Name the major regions of the brain, and describe their functions. 13.2 Explain how the brain is protected and supported, and how cerebrospinal fluid forms and circulates. 13.3 List the components of the medulla oblongata and pons, and specify the functions of each. 13.4 List the main components of the cerebellum, and specify the functions of each.

Learning Outcomes 13.5 List the main components of the midbrain, and specify the functions of each. 13.6 List the main components of the diencephalon, and specify the functions of each. 13.7 Identify the main components of the limbic system, and specify the locations and functions of each. 13.8 Describe the structure and function of the basal nuclei of the cerebrum. 13.9 Identify the major superficial landmarks of the cerebrum, and cite the locations of each.

Learning Outcomes Identify the locations of the motor, sensory, and association areas of the cerebral cortex, and discuss the functions of each. Discuss the significance of the white matter of the cerebral cortex. CLINICAL MODULE Discuss the origin and significance of the major categories of brain waves seen in an electroencephalogram. Identify the cranial nerves by name and number, and cite the functions of each.

Brain characteristics Equals ~97% of body’s neural tissue in adults “Typical” brain Weighs 1.4 kg (3 lb) Has volume of 1200 mL (71 in.3) Size varies among individuals Male are ~10% larger than female Owing to differences in overall body size No correlation between size and intelligence Functional normal individuals with smallest (750 mL) and largest (2100 mL) brains

Brain development at 4 weeks Neural tube is present Hollow cylinder that is beginning of CNS Has internal passageway (neurocoel) Cephalic portion enlarges into three portions (primary brain vesicles) Prosencephalon (proso, forward + encephalos, brain) “Forebrain” is at tip of neural tube Mesencephalon “Midbrain” is an expansion caudal to prosencephalon Rhombencephalon “Hindbrain” most caudal portion, continuous with spinal cord

A lateral view of the brain of an embryo after
4 weeks of development showing the neural tube Diencephalon (covered by cerebrum) Mesencephalon (covered by cerebrum) Mesencephalon Rhombencephalon Cerebrum Spinal cord Prosencephalon Neurocoel A lateral view of the brain of a 5-week-old embryo Prosencephalon Rhombencephalon Pons Metencephalon Myelencephalon Medulla oblongata Diencephalon Figure 13 Section 1 The Functional Anatomy of the Brain and Cranial Nerves Cerebellum Spinal cord Telencephalon Spinal cord Brain development in a child, showing the cerebrum covering other portions of the brain Figure 13 Section 1 7

Brain development at 5 weeks Primary brain vesicles change position and prosencephalon and rhombencencephalon subdivide to form secondary brain vesicles Prosencephalon Diencephalon (dia, through + encephalos, brain) Becomes major relay and processing center for information to/from cerebrum Telencephalon (telos, end) Becomes cerebrum in adult brain

Brain development at 5 weeks (continued) Secondary brain vesicles (continued) Rhombencephalon Metencephalon (meta, after) Adjacent to mesencephalon Forms cerebellum and pons in adult brain Myelencephalon (myelon, spinal cord) Becomes medulla oblongata in adult brain

Module 13.1: Major brain regions
Cerebrum Divided into pair of large cerebral hemispheres Surfaces covered by superficial layer of gray matter = Cerebral cortex (cortex, rind or bark) Functions Conscious thought Memory storage and processing Regulation of skeletal muscle contractions

Superficial cerebral structures Fissures Deep grooves that subdivide hemispheres Gyri (singular, gyrus) Folds in cerebral cortex that increase surface area Sulci (singular, sulcus) Shallow depressions in cerebral cortex that separate adjacent gyri

Cerebellum Partially hidden by cerebral hemispheres Second largest structure of brain Functions Coordination and modulation of motor commands from cerebral cortex

A diagrammatic view of the brain
showing its major regions and their general functions Cerebrum Is divided into a pair of large cerebral hemispheres whose surfaces are covered by a superficial layer of gray matter called the cerebral cortex Fissures Gyri Sulci Diencephalon Is the structural and functional link between the cerebral hemispheres and the rest of the CNS. Thalamus Spinal cord Not visible in this view; the hypothalamus, or floor of the diencephalon Figure Each region of the brain has distinct structural and functional characteristics Cerebellum Functions in coordination and modulation of motor commands from the cerebral cortex Brain stem Includes three structures Midbrain Pons Medulla oblongata Figure 13

Diencephalon Structural and functional link between cerebral hemispheres and rest of CNS Two parts Thalamus Relay and processing centers for sensory information Hypothalamus (hypo-, below) Floor of diencephalon Contains centers involved with Emotions Autonomic function Hormone production

Brain stem (3 parts) Midbrain Contains nuclei that coordinate visual and auditory reflexes Contains centers that help to maintain consciousness Pons (pons, bridge) Connects cerebellum to brain stem Has tracts and relay centers Contains nuclei that function in somatic and visceral motor control

Brain stem (3 parts, continued) Medulla oblongata Relays sensory information to other areas of brain stem and thalamus Contains major centers that regulate autonomic function Examples: heart rate, blood pressure Animation: Brain

Ventricular system, lateral view Ventricular system, anterior view
Two views of the ventricles, which are filled with cerebrospinal fluid Cerebral hemispheres Cerebral hemispheres Ventricles of the Brain Lateral ventricle Interventricular foramen Third ventricle Aqueduct of midbrain Fourth ventricle Pons Figure Each region of the brain has distinct structural and functional characteristics Medulla oblongata Central canal Central canal Cerebellum Spinal cord Ventricular system, lateral view Ventricular system, anterior view Figure 17

Ventricles of the brain Fluid-filled cavities Filled with cerebrospinal fluid Lined with ependymal cells Formed during development as neurocoel expands within cerebral hemispheres, diencephalon, and metencephalon Connected by narrow canals

Four ventricles 1. & 2. Lateral ventricles Contained within each cerebral hemisphere Each connected to third ventricle by interventricular foramen Separated medially by septum pellucidum “Roof” partially formed by thick white matter tract connecting hemispheres (corpus callosum) Then narrows to become central canal of spinal cord

Four ventricles (continued) Third ventricle Contained within diencephalon Connected to fourth ventricle by aqueduct of the midbrain Fourth ventricle Begins in metencephalon and extends into superior portion of medulla oblongata Then narrows to become central canal of spinal cord

Ventricles of the Brain
Cerebral hemispheres Ventricles of the Brain Lateral ventricle Interventricular foramen Third ventricle Aqueduct of midbrain Fourth ventricle Figure Each region of the brain has distinct structural and functional characteristics Pons Medulla oblongata Central canal Spinal cord Ventricular system, lateral view Figure 21

Ventricles of the Brain
Cerebral hemispheres Ventricles of the Brain Lateral ventricle Interventricular foramen Third ventricle Aqueduct of midbrain Fourth ventricle Figure Each region of the brain has distinct structural and functional characteristics Central canal Cerebellum Ventricular system, anterior view Figure 22

Two views of the ventricles, which are filled with cerebrospinal fluid
Corpus callosum Lateral ventricles Interventricular foramen Septum pellucidum Third ventricle Inferior tip of lateral ventricle Aqueduct of midbrain Figure Each region of the brain has distinct structural and functional characteristics Fourth ventricle Cerebellum Central canal Figure 23

Module 13.1 Review a. Name the major regions of the brain and the distinct structures of each. b. Describe the role of the medulla oblongata. c. Compare the corpus callosum to the septum pellucidum.

Module 13.2: Cranial meninges and cerebrospinal fluid
Dura mater Consists of two layers Separated by slender fluid-filled gap containing fluids and blood vessels Outer (endosteal) layer Fused to cranial bones (no epidural space) Inner (meningeal) layer

Cranial meninges (continued) Arachnoid mater Consists of Arachnoid membrane Provides smooth covering that does not follow brain’s underlying folds Subarachnoid space lies below Arachnoid trabeculae Connect to pia mater

Cranial meninges (continued) Pia mater Bound to brain surface by astrocyte processes Extends into every fold and accompanies cerebral blood vessels extending into surface brain structures

Arachnoid mater Dura mater Pia mater
The three layers of the cranial meninges: the dura mater, arachnoid mater, and pia mater Subdural space Cranium (skull) Arachnoid mater Dura mater Arachnoid membrane Dura mater (endosteal layer) Subarachnoid space Dural sinus Arachnoid trabeculae Dura mater (meningeal layer) Pia mater Cerebral cortex Is bound to the surface of the brain by astrocytes Figure The brain is protected and supported by the cranial meninges and the cerebrospinal fluid Figure 28

Dural folds and sinuses Dural folds Dip into cranial cavity and return Provide additional stabilization and support to brain Falx cerebri (falx, sickle shaped) Projects between cerebral hemispheres Inferior attachment to crista galli (anteriorly) and internal occipital crest (posteriorly) Superior and inferior sagittal sinuses lie within

Dural folds and sinuses (continued) Dural folds (continued) Tentorium cerebelli (tentorium, a tent) Separates cerebrum from cerebellum Falx cerebelli Separates cerebellar hemispheres along midsagittal line Inferior to tentorium cerebelli

The dural sinuses and dural folds
Inferior sagittal sinus Superior sagittal sinus The dural sinuses and dural folds Tentorium cerebelli Falx cerebri Figure The brain is protected and supported by the cranial meninges and the cerebrospinal fluid Falx cerebelli Figure 31

Cerebrospinal fluid (CSF) Completely surrounds and bathes CNS exposed surfaces Materials diffuse between CSF and interstitial fluid of CNS across ependymal walls Total volume = ~150 mL Entire volume replaced in ~8 hours

Cerebrospinal fluid (continued) Choroid plexus (choroid, vascular coat; plexus, network) Consists of ependymal cells and capillaries Produces CSF ~500 mL/day Found in all ventricles

Cerebrospinal fluid circulation Created and circulates between ventricles From fourth ventricle, CSF can circulate Down central canal of spinal cord Out single median aperture and lateral apertures into subarachnoid space Down around spinal cord and cauda equina Up around brain Absorbed back into venous circulation through arachnoid granulations within superior sagittal sinus

The sites of cerebrospinal fluid production,
circulation, and absorption into the venous system Superior sagittal sinus Third ventricle Aqueduct of the midbrain Figure The brain is protected and supported by the cranial meninges and the cerebrospinal fluid Central canal of spinal cord Dura mater Arachnoid Subarachnoid space Figure 35

Cerebrospinal fluid in third ventricle
The sites of cerebrospinal fluid production, circulation, and absorption into the venous system Nutrients, O2 Interstitial fluid in thalamus Capillaries Waste products, CO2 Neuron Astrocyte Choroid plexus cells Ependymal cells Removal of waste Figure The brain is protected and supported by the cranial meninges and the cerebrospinal fluid Cerebrospinal fluid in third ventricle Production of CSF Choroid plexus Figure 36

An arachnoid granulation, the site at which
Dura mater Superior sagittal sinus Cranium Arachnoid granulation CSF movement Subdural space Arachnoid membrane Cerebral cortex Figure The brain is protected and supported by the cranial meninges and the cerebrospinal fluid Pia mater An arachnoid granulation, the site at which cerebrospinal fluid is absorbed into the venous circulation Figure 37

Module 13.2 Review a. From superficial to deep, name the layers that constitute the cranial meninges. b. What would happen if the normal circulation or reabsorption of CSF became blocked? c. How would decreased diffusion across the arachnoid granulations affect the volume of cerebrospinal fluid in the ventricles?

Module 13.3: Medulla oblongata and pons
All communication (sensory and motor) between brain and spinal cord passes through Center for coordination of relatively complex autonomic reflexes and control of visceral functions Major anatomical features Olive (prominent bulge and anterolateral surface) Pyramids (contain descending/motor tracts from cerebral cortex) Some fibers cross over to other side of spinal cord = Decussation (decussation, crossing over)

Structure of the medulla oblongata
The anterior surface of the medulla oblongata Pons Pyramids Figure The medulla oblongata and the pons contain autonomic reflex centers, relay stations, and ascending and descending tracts Site of decussation Figure 40

Medulla oblongata components Autonomic centers (controlling vital functions) Reticular formation Cardiovascular centers Respiratory rhythmicity center Solitary nucleus Relay stations Olivary nucleus Nucleus cuneatus Nucleus gracilis

Respiratory rhythmicity
Structure of the medulla oblongata Olive Autonomic centers Reticular formation Attachment to membranous roof of fourth ventricle Cardiovascular centers Two views of the structure of the medulla oblongata showing its landmarks and structures Respiratory rhythmicity center Solitary nucleus Relay stations Posterior median sulcus Olivary nucleus Nucleus cuneatus Spinal cord Figure The medulla oblongata and the pons contain autonomic reflex centers, relay stations, and ascending and descending tracts Nucleus gracilis Anterior view Posterolateral view Figure 42

Figure The medulla oblongata and the pons contain autonomic reflex centers, relay stations, and ascending and descending tracts Figure 43

Figure The medulla oblongata and the pons contain autonomic reflex centers, relay stations, and ascending and descending tracts Figure 44

Links cerebellum with midbrain, diencephalon, cerebrum, medulla oblongata, and spinal cord Contains: Tracts (ascending and descending) Respiratory centers (pneumotaxic and apneustic) Reticular formation Loosely organized mass of gray matter containing centers that regulate vital autonomic functions Extends from medulla oblongata to mesencephalon

The pons, which links the cerebellum with the midbrain, diencephalon,
cerebrum, medulla oblongata, and spinal cord Tracts Respiratory Centers Ascending tracts Descending tracts Pneumotaxic center Apneustic center Transverse fibers Cerebellum Midbrain Fourth ventricle Pons Medulla oblongata Olivary nucleus Reticular formation Figure The medulla oblongata and the pons contain autonomic reflex centers, relay stations, and ascending and descending tracts Spinal cord Figure 46

Module 13.3 Review a. What is the function of the ascending and descending tracts in the medulla oblongata? b. Name the medulla oblongata parts that relay somatic sensory information to the thalamus. c. Describe the pyramids of the medulla oblongata and the result of decussation.

Module 13.4: Cerebellum Cerebellum
Is an automatic processing center that monitors proprioceptive, visual, tactile, balance, and auditory sensations Has two primary functions Adjusting postural muscles Programming and fine-tuning movements controlled at conscious and subconscious levels Ataxia (ataxia, lack of order) Disturbance of muscular coordination from trauma, stroke, or drugs such as alcohol

Module 13.4: Cerebellum Components (posterior view)
Anterior and posterior lobes Separated by primary fissure Two hemispheres Separated by vermis (worm) Surface of gray matter (cerebellar cortex) Contains huge, highly branched Purkinje cells that form many sensory and motor synapses Has folds (folia)

Structural features of the cerebellum Posterior view
The posterior, superior surface of the cerebellum Vermis Anterior lobe Primary fissure Posterior lobe Figure The cerebellum coordinates learned and reflexive patterns of muscular activity at the subconscious level Folia Left Hemisphere of Cerebellum Right Hemisphere of Cerebellum Figure 50

Purkinje cells of the cerebellar cortex
Dendrites Cell body of Purkinje cell Purkinje cell axons project into the white matter of the cerebellum. Figure The cerebellum coordinates learned and reflexive patterns of muscular activity at the subconscious level Purkinje cells LM x 400 Purkinje cells of the cerebellar cortex Figure 51

Module 13.4: Cerebellum Components (sagittal section)
Cerebellar cortex Arbor vitae “tree of life” Branching pattern of inner cerebellar white matter Cerebellar peduncles Link cerebellum to brain stem Three on each side Superior Middle Inferior

Cerebellar Peduncles Lateral view
A sagittal section through the vermis showing the internal organization of the cerebellum and the locations of the three cerebellar peduncles Midbrain Anterior lobe Arbor vitae Cerebellar Peduncles Pons Superior cerebellar peduncle Middle cerebellar peduncle Cerebellar nucleus Inferior cerebellar peduncle Cerebellar cortex Posterior lobe Figure The cerebellum coordinates learned and reflexive patterns of muscular activity at the subconscious level Choroid plexus of the fourth ventricle Medulla oblongata Spinal cord Lateral view Figure 53

Figure The cerebellum coordinates learned and reflexive patterns of muscular activity at the subconscious level Figure 54

Module 13.4 Review a. Identify the components of the cerebellar gray matter. b. Describe the arbor vitae, including its makeup, location, and function. c. Describe ataxia.

Module 13.5: Midbrain Midbrain
Most complex and integrative portion of brain stem Can direct complex motor patterns at subconscious level Influences activity level of entire nervous system

Module 13.5: Midbrain Midbrain components Corpora quadrigemina
Superior colliculus (colliculus, hill) Receives visual inputs from thalamus Controls reflex movements of eyes, head, and neck in response to visual inputs Inferior colliculus Receives auditory data from nuclei in medulla oblongata and pons Controls reflex movements of head, neck, and trunk in response to auditory inputs

Module 13.5: Midbrain Midbrain components (continued)
Reticular activating system (RAS) Specialized part of reticular formation Stimulation to RAS makes you more alert/attentive Damage to RAS causes unconsciousness Red nucleus Receives information from cerebrum and cerebellum Issues commands that affect upper limb position and background muscle tone Substantia nigra (nigra, black) Dark cells that adjust basal nuclei activity in cerebrum

A posterior view of the midbrain showing the major
superficial landmarks and the underlying nuclei Posterior view of brain stem and diencephalon Pineal gland Thalamus Red nucleus Corpora Quadrigemina Superior colliculus Substantia nigra Figure The midbrain regulates auditory and visual reflexes and controls alertness Inferior colliculus Cerebral peduncles Reticular activating system (RAS) Figure 59

Two views of the brain stem showing the anatomy of the midbrain in relation to the brain stem as a whole Midbrain Cerebral peduncle Cranial Nerves of Brain Stem Superior colliculus Inferior colliculus III IV IV Cerebellar Peduncles V Superior cerebellar peduncle Pons Middle cerebellar peduncle VI Inferior cerebellar peduncle VII VIII IX Choroid plexus in roof of fourth ventricle X Medulla oblongata Medulla oblongata XI XII Figure The midbrain regulates auditory and visual reflexes and controls alertness Spinal nerve C1 Dorsal roots of spinal nerves C1 and C2 Spinal nerve C2 Spinal cord Spinal cord Ventral root Dorsal root Lateral view Posterior view Figure 60

Module 13.5: Midbrain Midbrain components (continued) Tectum Tegmentum
Roof of midbrain Region posterior to aqueduct of midbrain Tegmentum Area anterior to aqueduct of midbrain

A superior view of a horizontal section through the midbrain Posterior
Superior colliculus Tectum Red nucleus Aqueduct of the midbrain Substantia nigra Tegmentum Cerebral peduncle Figure The midbrain regulates auditory and visual reflexes and controls alertness Anterior Figure 62

Figure 13.5.3 The midbrain regulates auditory and visual reflexes and controls alertness
63

Module 13.5 Review a. Cranial nerves III to XII arise from which structure? b. Identify the sensory nuclei contained within the corpora quadrigemina. c. Which area(s) of the midbrain control reflexive movements of the eyes, head, and neck?

Module 13.6: Diencephalon Diencephalon components Epithalamus Thalamus
Hypothalamus

Module 13.6: Diencephalon Epithalamus
Roof of diencephalon, superior to third ventricle Anterior portion Marked by: Anterior commissure (tract interconnecting cerebral hemispheres) Optic chiasm (where optic nerves connect to brain) Contains extensive area of choroid plexus that extends into interventricular foramina

Module 13.6: Diencephalon Epithalamus (continued) Posterior portion
Pineal gland Secretes melatonin (hormone regulating day-night cycles and some reproductive functions)

Module 13.6: Diencephalon Thalamus
On each side of brain, superior to midbrain Final point for ascending sensory information to be relayed or projected to cerebral cortex Acts as a filter, only passing on small portion of sensory information Has regions that contain nuclei or groups of nuclei that connect to specific regions of cerebral cortex

V e n t r a l g r o u p Left thalamus
The regions of the thalamus, each of which contains nuclei or groups of nuclei that connect to specific regions of the cerebral cortex Anterior group Medial group Lateral group Posterior group Pulvinar V e n t r a l g r o u p Note: colors indicate the associated areas of the cerebral cortex Medial geniculate nucleus Figure The diencephalon consists of the epithalamus, thalamus (left and right), and hypothalamus Lateral geniculate nucleus Left thalamus Figure 69

Module 13.6: Diencephalon Thalamus (continued) Components
Interthalamic adhesion Connects thalamic hemispheres, but no neural fibers cross Lateral geniculate (genicula, little knee) nucleus Receives visual information over optic tract and relays signals to midbrain and occipital lobe Medial geniculate nucleus Relays auditory information from inner ear receptors to appropriate cerebral cortex area

left thalamus and midbrain
The thalamus and important landmarks made visible by the removal of the cerebral hemispheres and cerebral peduncles Lateral geniculate nucleus Thalamus Medial geniculate nucleus Optic chiasm Optic tract Figure The diencephalon consists of the epithalamus, thalamus (left and right), and hypothalamus Cerebral peduncle (midbrain) Lateral view of the left thalamus and midbrain Figure 71

Figure The diencephalon consists of the epithalamus, thalamus (left and right), and hypothalamus Figure 72

Module 13.6: Diencephalon Hypothalamus
Contains important control and integrative centers Centers may be stimulated by: Sensory information from cerebrum, brain stem, and spinal cord Changes in CSF and interstitial fluid composition Chemical stimuli from blood because this area lacks blood–brain barrier

Module 13.6: Diencephalon Hypothalamus (continued) Components
Infundibulum Connects to pituitary gland Mamillary bodies Control feeding reflexes like licking and swallowing Hormonal centers Secrete chemical messengers that control endocrine cells in anterior pituitary Secrete two hormones released by posterior pituitary

Module 13.6: Diencephalon Hypothalamus (continued) Components
Nuclei (autonomic centers that control cardiovascular and vasomotor centers of medulla oblongata) Preoptic area Regulates body temperature through adjustments in blood flow and sweat gland activity Suprachiasmatic nucleus Coordinates day-night cycles of activity/inactivity

Hypothalamic Nuclei A sagittal section of the brain showing the
structure of the hypothalamus Hypothalamic Nuclei Thalamus Autonomic centers Preoptic area Suprachiasmatic nucleus Hypothalamus Hormonal centers Figure The diencephalon consists of the epithalamus, thalamus (left and right), and hypothalamus Pons Infundibulum Mamillary body Anterior pituitary gland Posterior pituitary gland Figure 76

Module 13.6 Review a. Name the main components of the diencephalon.
b. Damage to the lateral geniculate nuclei of the thalami would interfere with what particular function? c. Which component of the diencephalon is stimulated by changes in body temperature?

Module 13.7: Limbic system The limbic system
Includes nuclei and tracts along border of cerebrum and diencephalon Is a functional grouping rather than anatomical Through experimental stimulation, many functional areas/centers identified Emotional areas for rage, fear, pain, sexual arousal, and pleasure Areas that produce heightened alertness/generalized excitement, generalized lethargy, and sleep

Module 13.7: Limbic system Also known as motivational system Functions
Establishing emotional states Linking conscious, intellectual functions of cerebral cortex with unconscious and autonomic functions of brain stem Facilitating memory storage and retrieval

Module 13.7: Limbic system Cerebral components (also called limbic lobe) Cingulate gyrus (superior portion) Parahippocampal gyrus (inferior portion) Hippocampus Diencephalon components Anterior group of thalamic nuclei Hypothalamus Mamillary bodies

A diagrammatic sagittal section showing the position and
orientation of the major components of the limbic system Central sulcus Corpus callosum Pineal gland Fornix Components of the Limbic System in the Cerebrum Limbic lobe (shown in green) Figure The limbic system is a functional group of tracts and nuclei located in the cerebrum and diencephalon Cingulate gyrus (superior portion of limbic lobe) Parahippocampal gyrus (inferior portion of limbic lobe) Components of the Limbic System in the Diencephalon Hippocampus Anterior group of thalamic nuclei Temporal lobe of cerebrum Hypothalamus Mamillary body Figure 81

Module 13.7: Limbic system Specific functional areas
Anterior group of thalamic nuclei Relay information from mamillary body to cingulate gyrus on same side Hippocampus Shaped like a sea horse (hippocampus) Important in learning, especially in storage and retrieval of long-term memories

Module 13.7: Limbic system Specific functional areas (continued)
Fornix (arch) White matter tract connecting hippocampus with hypothalamus Amygdaloid (amygdale, almond) body Interface between limbic system and cerebrum and various sensory systems Plays a role in regulation of heart rate, control of “fight or flight” response, and linking emotions to specific memories

A sectional view of important limbic system components and nuclei
Cingulate gyrus Corpus callosum Anterior group of thalamic nuclei Fornix Mamillary body Hypothalamic nuclei Olfactory tract Figure The limbic system is a functional group of tracts and nuclei located in the cerebrum and diencephalon Amygdaloid body Parahippocampal gyrus Hippocampus Figure 84

Module 13.7 Review a. List the primary functions of the limbic system.
b. Which region of the limbic system is particularly important for the storage and retrieval of long-term memories? c. Damage to the amygdaloid body would interfere with the regulation of which division of the autonomic nervous system?

Module 13.8: Basal nuclei of cerebrum
Also known as basal ganglia Are masses of gray matter within each hemisphere deep to lateral ventricle floor Provide subconscious control of skeletal muscle tone and help coordinate learned movement patterns Normally do not initiate movement, but provide general pattern and rhythm

Module 13.8: Basal nuclei of cerebrum
Basal nuclei of cerebrum components Caudate nucleus Lentiform (lens-shaped) nucleus Medial globus pallidus (pale globe) Lateral putamen Axon bundles connecting cerebral cortex to diencephalon and brain stem pass around and between basal nuclei = Internal capsule

Lateral view A lateral view of the brain showing the locations of the
caudate and lentiform nuclei, which constitute the basal nuclei Head of caudate nucleus Lentiform nucleus Tail of caudate nucleus Amygdaloid body Thalamus Figure The basal nuclei of the cerebrum perform subconscious adjustment and refinement of ongoing voluntary movements Lateral view Figure 88

Horizontal section, dissected
A dissected horizontal section showing the locations of the caudate nuclei Caudate nucleus Internal capsule Putamen Thalamus Choroid plexus Third ventricle Lateral ventricle Head of caudate nucleus Lentiform nucleus Pineal gland Figure The basal nuclei of the cerebrum perform subconscious adjustment and refinement of ongoing voluntary movements Fornix Tail of caudate nucleus Horizontal section, dissected Amygdaloid body Thalamus Lateral view Figure 89

A frontal section of the brain showing the locations of the basal nuclei
Head of caudate nucleus Lentiform nucleus Tail of caudate nucleus Amygdaloid body Thalamus Lateral view Lateral ventricle Corpus callosum Septum pellucidum Basal Nuclei Internal capsule Figure The basal nuclei of the cerebrum perform subconscious adjustment and refinement of ongoing voluntary movements Claustrum Caudate nucleus Lateral sulcus Putamen Lentiform nucleus Globus pallidus Anterior commissure Tip of lateral ventricle Amygdaloid body Frontal section Figure 90

Module 13.8 Review a. Define the basal nuclei.
b. Describe the caudate nucleus. c. What clinical signs would you expect to observe in an individual who has damage to the basal nuclei?

Module 13.9: Cerebral superficial landmarks
Help to divide each cerebral hemisphere into lobes Central sulcus Deep groove dividing anterior frontal lobe from more posterior parietal lobe Precentral gyrus Anterior to central sulcus Contains primary motor cortex Postcentral gyrus Posterior to central sulcus Contains primary sensory cortex Receives sensory information from body

Parieto-occipital sulcus Separates parietal and occipital lobes Lateral sulcus Separates frontal and temporal lobes Insula (island) An “island” of cortex Medial to lateral sulcus

The lobes of the cerebral cortex in the left
A lateral view of the brain showing the lobes of the cerebral cortex in the left cerebral hemisphere The lobes of the cerebral cortex in the left cerebral hemisphere, shown in lateral view Central sulcus Precentral gyrus Postcentral gyrus Frontal lobe Parietal lobe Lateral sulcus Occipital lobe Temporal lobe Figure Superficial landmarks can be used to divide the surface of the cerebral cortex into lobes Cerebellum Pons Medulla oblongata Figure 94

A lateral view of the brain showing the lobes of the
cerebral cortex in the left cerebral hemisphere Retraction of the superficial cerebral cortex along the lateral sulcus to expose the insula Figure Superficial landmarks can be used to divide the surface of the cerebral cortex into lobes Insula Figure 95

Figure Superficial landmarks can be used to divide the surface of the cerebral cortex into lobes Figure 96

(Structures outside of the cerebrum are labeled in italics.)
A midsagittal view showing the inner boundaries of the lobes of the cerebral cortex (Structures outside of the cerebrum are labeled in italics.) Precentral gyrus Central sulcus Postcentral gyrus Limbic lobe Parietal lobe Frontal lobe Corpus callosum Parieto-occipital sulcus Occipital lobe Thalamus Pineal gland Hypothalamus Corpora quadrigemina Figure Superficial landmarks can be used to divide the surface of the cerebral cortex into lobes Aqueduct of the midbrain Optic chiasm Fourth ventricle Pons Temporal lobe Cerebellum Mamillary body Medulla oblongata Figure 97

Figure Superficial landmarks can be used to divide the surface of the cerebral cortex into lobes Figure 98

General facts about cerebral hemispheres to remember Each hemisphere receives sensory information from and sends motor information to the opposite side of body Has no known functional significance Hemispheres may look identical but may have different functions Mapping of specific functions to specific areas is imprecise Boundaries are indistinct and areas may overlap Some functions (like consciousness) may be found in multiple regions

Module 13.9 Review a. Identify the lobes of the cerebrum and indicate the basis for their names. b. Describe the insula. c. What effect would damage to the left postcentral gyrus produce?

Module 13.10: Specialized functional regions in cerebral hemispheres
Motor cortex Neurons here are called pyramidal cells because of their shape Somatic motor association area Responsible for coordination of learned movements

Sensory areas Sensory cortex Receives somatic sensory information from receptors for touch, pressure, pain, vibration, taste, or temperature Somatic sensory association area Monitors activity in primary sensory cortex Gustatory cortex Area within insula that receives taste receptor information Olfactory cortex Receives olfactory receptor information

Sensory areas (continued) Auditory cortex Primary auditory cortex Monitors auditory (sound) information Auditory association area Monitors sensory activity in auditory cortex and recognizes sounds, such as spoken words

Sensory areas (continued) Visual cortex Primary visual cortex Receives information from lateral geniculate nuclei Visual association area Monitors activity in visual cortex and interprets results Example: recognizing “c” “a” “r” together is the word “car”

The motor and sensory cortexes and the association areas for each
Central sulcus Motor Cortex Somatic motor association area Sensory Cortex PARIETAL LOBE Somatic sensory association area Gustatory Cortex Olfactory Cortex OCCIPITAL LOBE FRONTAL LOBE Visual Cortex Primary visual cortex Figure The lobes of the cerebral cortex contain regions with specific functions Visual association area Auditory Cortex Lateral sulcus Primary auditory cortex TEMPORAL LOBE Auditory association area Figure 105

Integrative centers Concerned with performance of complex processes such as speech, writing, mathematics, and spatial relationships Restricted to either right or left hemisphere

Integrative centers (continued) General interpretive area Also known as the Wernicke area Receives information from all sensory association areas Present only in one hemisphere (typically the left) Plays an essential role in personality by integrating sensory information and accessing visual and auditory memories Speech center Also known as the Broca area or motor speech area Lies in same hemisphere as general interpretive area Regulates patterns of breathing and vocalization needed for normal speech

Integrative centers (continued) Frontal eye field Controls learned eye movements such as scanning text Prefrontal cortex Coordinates information relayed from association areas Performs abstract intellectual functions such as predicting consequences of events or actions

Locations of some integrative centers, which are concerned with the
Frontal eye field Locations of some integrative centers, which are concerned with the performance of complex processes Speech center (Broca area) General interpretive area (Wernicke area) Prefrontal cortex Figure The lobes of the cerebral cortex contain regions with specific functions Figure 109

Hemisphere lateralization (specialized functions of each hemisphere) Left cerebral hemisphere Contains general interpretive and speech centers Is responsible for language-based skills such as reading, writing, speaking Premotor cortex controlling hand movements is larger for right-handed individuals Important in performing analytical tasks such as mathematics and logic

Hemisphere lateralization (continued) Right cerebral hemisphere Analyzes sensory information and relates body to sensory environment Examples: recognize faces, understanding 3-D relationships Important in analyzing emotional context of conversation Example: “Get lost!” or “Get lost?”

Hemisphere lateralization (continued) Left-handedness Represents about 9% of population Controlled by primary motor cortex of right hemisphere In an unusually high percentage of musicians and artists Primary motor cortex and association areas on right cerebral hemisphere are near spatial visualization and emotion association areas

Left Cerebral Hemisphere Right Cerebral Hemisphere
A schematic representation of hemispheric lateralization Left Cerebral Hemisphere Right Cerebral Hemisphere In most people, the left hemisphere contains the general interpretive and speech centers and is responsible for language-based skills. Reading, writing, and speaking, for example, depend on processing done in the left cerebral hemisphere, in addition, the premotor cortex that functions in the control of hand movements is larger on the left side for right-handed individuals than for left-handed individuals. The left hemisphere is also important in performing analytical tasks, such as mathematics and logic. The right cerebral hemisphere analyzes sensory information and relates the body to the sensory environment. Interpretive centers in this hemisphere enable you to identify familiar objects by touch, smell, sight, taste, or feel. For example, the right hemisphere plays a dominant role in recognizing faces and in understanding three-dimensional relationships. It is also important in analyzing the emotional context of a conversation—for instance, distinguishing between the threat “Get lost!” and the question “Get lost?” LEFT HAND RIGHT HAND Prefrontal cortex Prefrontal cortex Speech center Anterior commissure C O R P U S A L M Figure The lobes of the cerebral cortex contain regions with specific functions Writing Analysis by touch Auditory cortex (right ear) Auditory cortex (left ear) General interpretive center (language and mathematical calculation) Spatial visualization and analysis Visual cortex (right visual field) Visual cortex (left visual field) Figure 113

Module 13.10 Review a. Where is the primary motor cortex located?
b. Which senses are affected by damage to the temporal lobes? c. Which brain part has been affected in a stroke victim who is unable to speak?

Module 13.11: White matter in the brain
Functional groups of white matter in inner cerebrum Association fibers Interconnect areas of neural cortex within a hemisphere Shortest fibers connect one gyrus to another (= arcuate fibers) Longest fibers are organized into bundles or fasciculi and connect frontal lobe to other lobes of same hemisphere (= longitudinal fasciculi)

Lateral view The locations of association fibers,
which interconnect areas of neural cortex within a single cerebral hemisphere Arcuate fibers Longitudinal fasciculi Figure White matter interconnects the cerebral hemispheres, the lobes of each hemisphere, and links the cerebrum to the rest of the brain Lateral view Figure 116

Functional groups of white matter in inner cerebrum (continued) Commissural (commissura, crossing over) fibers Interconnect cerebral hemispheres Corpus callosum Most substantial and important of commissural fibers Contains more than 200 million axons carrying more than 4 billion impulses per second Anterior commissure Importance increases if corpus callosum is damaged

Functional groups of white matter in inner cerebrum (continued) Projection fibers Link cerebral cortex to other CNS areas Includes both sensory (ascending) and motor (descending) fibers All must pass through diencephalon Entire mass known as the internal capsule

The locations of important commissural fibers, which interconnect the cerebral
hemispheres, and projection fibers, which link the cerebral cortex to the rest of the brain Corpus callosum Longitudinal fissure Projection fibers of internal capsule Anterior commissure Figure White matter interconnects the cerebral hemispheres, the lobes of each hemisphere, and links the cerebrum to the rest of the brain Anterior view Figure 119

Module Review a. What special names are given to axons in the white matter of the cerebral hemispheres? b. What is the function of the longitudinal fasciculi? c. What are fibers carrying information between the brain and spinal cord called, and through which brain regions do they pass?

CLINICAL MODULE 13.12: Brain activity and electroencephalograms
Neural function depends on electrical impulses Electrical activity changes as certain areas are stimulated or quieted down Electrical activity at any time generates an electrical field that can be measured using electrodes on the scalp A printout of that activity = electroencephalogram (EEG) Electrical patterns observed = brain waves

The four types of brain waves as they
appear on an electroencephalogram (EEG) Figure Brain activity can be monitored using external electrodes; the record is called an electroencephalogram, or EEG Figure 122

Brain waves Alpha waves Occur in brains of healthy awake adults that are resting with eyes closed Vanish when sleeping or concentrating on a specific task Beta waves Higher-frequency waves Typical of people concentrating on a task or in a state of psychological tension

Brain waves (continued) Theta waves May appear transiently during sleep in normal adults Most often observed in children and in intensely frustrated adults In certain circumstances, may indicate presence of brain disorder such as a tumor Delta waves Very large amplitude, low frequency waves Normally seen during sleep in all ages Also seen in infants and awake adults with brain damage from a tumor, vascular blockage, or inflammation

The four types of brain waves as they appear on an electroencephalogram (EEG)
Alpha waves Beta waves Theta waves Figure Brain activity can be monitored using external electrodes; the record is called an electroencephalogram, or EEG Delta waves Figure 125

Abnormal brain activity Electrical activity in each hemisphere is generally synchronized by thalamus Asynchrony may indicate localized damage or cerebral abnormalities Seizures Temporary cerebral activity disorder accompanied by Abnormal movements Unusual sensations Inappropriate behaviors Some combination of above symptoms Can start in one area and spread across cortical surface

Abnormal brain activity (continued) Epilepsies Clinical conditions characterized by seizures Also known as seizure disorders

CLINICAL MODULE 13.12 Review
a. Define electroencephalogram (EEG). b. Describe the four wave types associated with an EEG. c. Differentiate between a seizure and epilepsy.

Module 13.13: Cranial nerves
Can be classified as: Sensory Special sensory Motor Mixed Innervate head, neck, and some torso regions

The branches of the 12 cranial nerves, their functions (motor, sensory, or mixed), and the structures they innervate Optic nerve (II) Abducens nerve (VI) Oculomotor nerve (III) Trochlear nerve (IV) Olfactory nerve (I) Motor nerve to muscles of mastication Motor nerve to facial muscles Ophthalmic branch Maxillary branch Mandibular branch Sensory nerve to tongue and soft palate Trigeminal nerve (V) Olfactory bulb Facial nerve (VII) Olfactory tract Pituitary gland Vestibulocochlear nerve (VIII) Cochlear branch Semilunar ganglion (V) Pons Superior ganglion (IX) Vestibular branch Geniculate ganglion (VII) Glossopharyngeal nerve (IX) Inferior ganglion (IX) Superior ganglion (X) Medulla oblongata Inferior ganglion (X) Figure The twelve pairs of cranial nerves can be classified as sensory, special sensory, motor, or mixed nerves Vagus nerve (X) Hypoglossal nerve (XII) Accessory nerve (XI) Sensory nerve to posterior tongue Motor nerve to pharyngeal muscles To tongue muscles KEY Sensory nerves Motor nerves To sternocleidomastoid and trapezius muscles Figure 13.13 130

Figure The twelve pairs of cranial nerves can be classified as sensory, special sensory, motor, or mixed nerves Figure 13.13 131

Figure The twelve pairs of cranial nerves can be classified as sensory, special sensory, motor, or mixed nerves Figure 13.13 132

Module 13.13 Review a. Identify the cranial nerves by name and number.
b. Which cranial nerves have motor functions only? c. Which cranial nerves are mixed nerves?

Section 2: Sensory and Motor Pathways
Learning Outcomes Explain the ways in which receptors can be classified. List the types of tactile receptors, and specify the functions of each. Identify and describe the major sensory pathways. Describe the components, processes, and functions of the somatic motor pathways.

Learning Outcomes Describe the levels of information processing involved in motor control. CLINICAL MODULE Describe the roles of the nervous system in referred pain, Parkinson disease, rabies, cerebral palsy, amyotrophic lateral sclerosis, Alzheimer disease, and multiple sclerosis.

General senses Our sensitivity to temperature, pain, touch, pressure, vibration, and proprioception Receptors that respond to these stimuli are found throughout the body Are relatively simple in structure Size of the area each receptor monitors (= receptive field) varies Can be as large as 7 cm (2.5 in.) as on general body surfaces or as small as 1 mm as on tongue or fingertips Size of receptive field is inversely related to ability to accurately describe location of stimulus

Receptive fields, the areas monitored by a single receptor cell
Figure 13 Section 2 Sensory and Motor Pathways Figure 13 Section 137

General senses (continued) Sensory pathways begin at peripheral receptors and often end at diencephalon and/or cerebral hemispheres Much sensory information does not reach primary sensory cortex and our awareness Sensation Information carried by sensory pathway Perception Conscious awareness of sensation

Basic events occurring along sensory and motor pathways Sensory pathway Depolarization of receptor Stimulus produces graded change in transmembrane potential of receptor (= transduction) Action potential generation If depolarized to threshold, initial segment develops action potentials Greater degree of sustained depolarization = higher frequency of action potentials

Basic events occurring along sensory and motor pathways (continued) Sensory pathway (continued) Propagation over labeled line = Information about one type of stimulus (touch, pressure, temperature) carried on axons Brain processes sensory information based on what type of axons are transmitting information CNS processing Occurs at every synapse along labeled line May occur at multiple nuclei and centers in CNS

Basic events occurring along sensory and motor pathways (continued) Motor Pathways (one of two responses) Immediate involuntary response Processing centers in spinal cord or brain stem respond before sensations reach cerebral cortex Voluntary Perception (only ~1% of sensations) Voluntary response Can moderate, enhance, or supplement simple reflexive response

Module 13.14: Receptor classification by function and sensitivity
Free nerve endings Can be stimulated by many different stimuli Examples: chemical, pressure, temperature changes, trauma Sensitivity and specificity may be altered by location and presences of accessory structures Are simplest receptors, being the dendrites of sensory neurons Have branching tips that are unprotected

Free nerve endings, the branching tips
of the dendrites of sensory neurons Free nerve endings Figure Receptors for the general senses can be classified by function and by sensitivity Figure 143

Module 13.14: General sense receptor classification by function and sensitivity
Functional classes Nociceptors Pain receptors Free nerve endings with large receptive fields and broad sensitivity Two axon types carry pain information Type A fibers (fast pain) Such as from injection or deep cut Quickly reach CNS and trigger fast reflexive responses Relayed to primary sensory cortex for conscious attention Stimulus can be located to an area within a few cm

Functional classes (continued) Nociceptors (continued) Two axon types carry pain information (continued) Type C fibers (slow pain) Such as burning or aching Cause generalized activation of thalamus and reticular formation Individual aware of pain but only general location

Functional classes (continued) Thermoreceptors Temperature receptors Free nerve endings in dermis, skeletal muscles, liver, and hypothalamus 3–4× more cold receptors than warm receptors No structural differences Chemoreceptors Respond to water-soluble and lipid-soluble substances dissolved in body fluids (interstitial fluid, plasma, CSF)

Functional classes (continued) Mechanoreceptors Sensitive to stimuli that distort plasma membrane Contain mechanically gated ion channels that open or close in response to: Stretching Compression Twisting Other distortions of membrane

Functional classes (continued) Mechanoreceptors (continued) Three main types Proprioceptors Monitor position of joints and muscles Most complex of general sensory receptors Example: muscle spindle Baroreceptors (baro, pressure) Detect pressure changes in blood vessels and portions of digestive, reproductive, and urinary tracts

Functional classes (continued) Mechanoreceptors (continued) Three main types (continued) Tactile receptors Provide sensations of touch (shape or texture), pressure (degree and frequency of distortion), and vibration Fine touch and vibration receptors give detailed information Crude touch and pressure receptors provide poor localization and give little information

A Functional Classification of General Sensory Receptors
Nociceptors Thermoreceptors Chemoreceptors Mechanoreceptors Pain receptors Temperature receptors Respond to water-soluble and lipid- soluble substances dissolved in body fluids Sensitive to stimuli that distort their plasma membranes Figure Receptors for the general senses can be classified by function and by sensitivity Myelinated Type A fibers (carry sensations of fast pain) Unmyelinated Type C fibers (carry sensations of slow pain) Proprioceptors (monitor the positions of joints and muscles) Baroreceptors (detect pressure changes) Tactile receptors (provide the sensations of touch, pressure, and vibration) Figure 150

Receptor classes based on stimulation response Tonic receptors Always active Frequency of action potentials generated reflects background stimulation level As stimulation changes, AP frequency changes accordingly Phasic receptors Normally inactive Become active transiently in response to changing conditions

Classification of receptors based on the nature of their response to stimulation
Increased Increased Normal Normal Stimulus Stimulus Normal Normal Frequency of action potentials Frequency of action potentials Time Time Tonic receptors are always active and generate action potentials at a frequency that reflects the background level of stimulation. When the stimulus increases or decreases, the rate of action potential generation changes accordingly. Phasic receptors are normally inactive, but become active for a short time in response to a change in the conditions they are monitoring. Figure Receptors for the general senses can be classified by function and by sensitivity Figure 152

Adaptation Reduction in sensitivity in the presence of a constant stimulus Two types Peripheral adaptation Occurs at receptor Receptor activity decreases with time Central adaptation Occurs along CNS sensory pathways Generally involves inhibition nuclei along pathway

Adaptation, a reduction in sensitivity in the presence of a constant stimulus
Receptor Labeled line Arriving stimulus CNS processing center Site of peripheral adaptation Site of central adaptation Figure Receptors for the general senses can be classified by function and by sensitivity Figure 154

Module Review a. List the four types of general sensory receptors based on function, and identify the type of stimulus that excites each type. b. Describe the three classes of mechanoreceptors. c. Explain adaptation, and differentiate between peripheral adaptation and central adaptation.

Module 13.15: Structural receptor classes in skin
Free nerve endings Most common receptors in skin Root hair plexus Monitor distortions and movements of hair follicle Adapt rapidly Tactile discs and Merkel cells Fine touch and pressure receptors Are extremely sensitive tonic receptors Have very small receptive fields Merkel discs are large epithelial cells in stratum germinativum closely associated with tactile discs

The types of receptors in the skin
Hair Figure General sensory receptors are relatively simple in structure and widely distributed in the body Sensory nerves Figure 13.15 157

Free Nerve Endings Are the branching tips of sensory
neurons; are unprotected and nonspecific; can respond to tactile, pain, and temperature stimuli Free nerve endings Figure General sensory receptors are relatively simple in structure and widely distributed in the body Sensory nerve Figure 158

Tactile (Meissner’s) corpuscles Are sensitive to fine touch, pressure, and low frequency vibration Adapt quickly Fairly large (~100 µm in length and ~50 µm in width) Most abundant in eyelids, lips, fingertips, nipples, and external genitalia Dendrites are highly coiled and interwoven Surrounded by modified Schwann cells Anchored in dermis by fibrous capsule

Lamellated (lamella, thin plate) corpuscles Also known as pacinian corpuscles Sensitive to deep pressure Fast adapting Most sensitive to pulsing or high-frequency vibrating stimuli Very large receptors May reach 4 mm in length and 1 mm in diameter Surrounded by layers of collagen fibers separated by interstitial fluid Shield dendrite from other stimuli Found in dermis of fingers, mammary glands, external genitalia, in fasciae, joint capsules, and viscera

Ruffini corpuscles Sensitive to pressure and distortion of reticular dermis Are tonic and show little (if any) adaptation Surrounded by capsule that is continuous with dermis Within is a network of dendrites and collagen fibers

Module Review a. Identify the six types of tactile receptors located in the skin, and describe their sensitivities. b. Which types of tactile receptors are located only in the dermis? c. Which is likely to be more sensitive to continuous deep pressure: a lamellated corpuscle or a Ruffini corpuscle?

Module 13.16: Three major somatic sensory pathways
Spinothalamic pathway Neural path First-order neuron From receptor to synapse in spinal cord posterior gray horn Second-order neuron From posterior gray horn, crosses spinal cord and reaches thalamus Third-order neuron From thalamus to primary sensory cortex Sensory homunculus (“little man”) maps somatic sensations to discrete areas in cortex

Spinothalamic pathway (continued) Anterior spinothalamic tracts Carry crude touch and pressure sensations from body Lateral spinothalamic tracts Carry pain and temperature sensations from body

Posterior column pathway Carries sensations of highly localized “fine” touch, pressure, vibration, and proprioception Begins at peripheral receptor and ends in primary sensory cortex Sensory axons ascend in fasciculus gracilis and cuneatus Medial lemniscus (tract) leads to thalamus

Spinocerebellar pathway Carries proprioceptive information about position of skeletal muscles, joints, and tendons to cerebellum Posterior axons do not cross sides of spinal cord Pass through cerebellar peduncles of same side Anterior axons do cross over to opposite side of spinal cord

A cross section through the spinal cord showing the
locations of the somatic sensory pathways Posterior column pathway Spinocerebellar pathway Spinothalamic pathway Figure Three major somatic sensory pathways carry information from the skin and musculature to the CNS Figure 167

Module 13.16 Review a. Define sensory homunculus.
b. Which spinal tracts carry action potentials generated by nociceptors? c. Which cerebral hemisphere receives impulses conducted by the right fasciculus gracilis of the spinal cord?

Module 13.17: Somatic motor pathways
Always involve at least two motor neurons Upper motor neuron Cell body in a CNS processing center Lower motor neuron Cell body in a nucleus of brain stem or spinal cord Upper motor neuron synapses on lower, which then innervates a single motor unit of skeletal muscle

Corticospinal pathway Provides voluntary control over skeletal muscles Sometimes called the pyramidal system Begins at pyramidal cells in primary motor cortex Upper axons descend into brain stem and spinal cord Synapse with lower motor neurons that control muscles

Corticospinal pathway (continued) Upper motor neurons begin along specific areas of the primary motor cortex that map to muscles in specific areas of the body (= motor homunculus) Motor homunculus pattern varies with number of motor units innervated and degree of motor control available Synapses with lower motor neurons occur in two tracts Corticobulbar (bulbar, brain stem) tracts Synapses occur in motor nuclei of cranial nerves Provide conscious control over skeletal muscles that move eye, jaw, face, and some muscles of neck and pharynx

Corticospinal pathway (continued) Synapses with lower motor neurons occur in two tracts (continued) Corticospinal tracts Visible along ventral surface of medulla oblongata as pair of thick bands (pyramids) ~85% of corticospinal axons cross midline to enter lateral corticospinal tracts ~15% descend uncrossed as anterior corticospinal tracts (crossing over occurs through anterior white commissure at specific spinal segment) Provide conscious control over skeletal muscles that move various body areas

Lateral corticospinal tract Anterior corticospinal tract
The corticospinal pathway, which provides voluntary control over skeletal muscles Motor homunculus To skeletal muscles Corticobulbar tract Motor nuclei of cranial nerves Cerebral peduncle To skeletal muscles Midbrain Motor nuclei of cranial nerves Pyramid Figure The somatic nervous system controls skeletal muscles through upper and lower motor neurons Lateral corticospinal tract Medulla oblongata Anterior corticospinal tract KEY To skeletal muscles Spinal cord Upper motor neuron Lower motor neuron Figure 173

Two main pathways for subconscious motor commands Lateral pathway Primarily concerned with muscle tone and precise movements of distal limb parts Red nucleus (primary nucleus of lateral pathway) Receives information from cerebrum and cerebellum Adjusts upper limb position and background muscle tone Axons cross to opposite side of brain and descend through rubrospinal (ruber, red) tracts

Two main pathways for subconscious motor commands (continued) Medial pathway Primarily concerned with muscle tone and gross motor control of neck, trunk, and proximal limb muscles Upper motor neurons located in three areas Superior and inferior colliculi Tectospinal tracts pass axons down to direct reflexive movements of head, neck, and upper limbs to visual/auditory stimuli Reticular formation Reticulospinal tracts conduct impulses down spinal cord

Two main pathways for subconscious motor commands (continued) Medial pathway (continued) Upper motor neurons located in three areas (continued) Vestibular nucleus (of CN VIII) Receive information from inner ear about position and movement of head Issue motor commands through vestibulospinal tracts to adjust muscle tone in neck, eyes, head, and limbs

Nuclei of the Medial Pathway
The locations of centers in the cerebrum, diencephalon, and brain stem that may issue somatic motor commands as a result of processing performed at a subconscious level Motor cortex Thalamus Basal nuclei Red nucleus Cerebellar nuclei Nuclei of the Medial Pathway Figure The somatic nervous system controls skeletal muscles through upper and lower motor neurons Superior and inferior colliculi Reticular formation Medulla oblongata Vestibular nucleus Figure 177

Lateral Pathway Medial Pathway
A cross section of the spinal cord showing the locations of the medial and lateral pathways Lateral corticospinal tract Lateral Pathway Involved primarily with the control of muscle tone and the more precise movements of the distal parts of the limbs Medial Pathway Involved primarily with the control of muscle tone and gross movements of the neck, trunk, and proximal limb muscles Rubrospinal tract Reticulospinal tract Vestibulospinal tract Figure The somatic nervous system controls skeletal muscles through upper and lower motor neurons Tectospinal tract Anterior corticospinal tract Figure 178

Module 13.17 Review a. Define corticospinal tracts.
b. Describe the role of the corticobulbar tracts. c. What effect would increased stimulation of the motor neurons of the red nucleus have on muscle tone?

Module 13.18: Levels of somatic motor control
Many brain areas are involved in controlling body movements Generally, the closer the motor center to the cerebral cortex, the more complex the motor activity Cerebellum is the exception as it is involved at multiple levels

Brain areas involved in increasing levels of motor complexity (as indicated by increasing numbers) Brain stem and spinal cord Simple cranial and spinal reflexes Pons and medulla oblongata Balance reflexes and more complex respiratory reflexes Hypothalamus Reflex motor patterns related to eating, drinking, and sexual activity; also modifies respiratory reflexes Thalamus and midbrain Reflexes in response to visual and auditory stimuli

Brain areas involved in increasing levels of motor complexity (continued) Basal nuclei Modify voluntary and reflexive motor patterns at subconscious level Cerebral cortex Plans and initiates voluntary motor activity Cerebellum Coordinates complex motor patterns through feedback loops involving cerebral cortex, basal nuclei, and nuclei of medial and lateral pathways

Figure 13.18.1 There are multiple levels of somatic motor control
The brain structures involved in increasing levels of motor complexity (as indicated by the numbers); the cerebellum is involved in coordinating motor activities at multiple levels Basal Nuclei Modify voluntary and reflexive motor patterns at the subconscious level Thalamus and Midbrain Cerebral Cortex Control reflexes in response to visual and auditory stimuli Plans and initiates voluntary motor activity Hypothalamus Controls reflex motor patterns related to eating, drinking, and sexual activity; modifies respiratory reflexes Figure There are multiple levels of somatic motor control Pons and Medulla Oblongata Cerebellum Control balance reflexes and more complex respiratory reflexes Coordinates complex motor patterns through feedback loops involving the cerebral cortex and basal nuclei as well as nuclei of the medial and lateral pathways Brain Stem and Spinal Cord Control simple cranial and spinal reflexes Figure 183

Preparing for movement Once a decision to move has been made, information is relayed Frontal lobes  motor association areas  basal nuclei & cerebellum

The path of information flow when
an individual makes a conscious decision to perform a specific movement Motor association areas Cerebral cortex Decision in frontal lobes Basal nuclei Cerebellum Figure There are multiple levels of somatic motor control Figure 185

Performing a movement As movement begins, responses are relayed from motor association areas Motor association areas  primary motor cortex  medial and lateral pathways Basal nuclei adjust movement patterns in two ways Alter pyramidal cell sensitivity, adjusting corticospinal output Change excitatory or inhibitory output of medial and lateral pathways Cerebellum monitors somatic sensory input and adjusts motor output as necessary

The flow of information as an individual begins a movement
Primary motor cortex Motor association areas Cerebral cortex Basal nuclei As the movement proceeds, the cerebellum monitors proprioceptive and vestibular information and compares the arriving sensations with those experienced during previous movements. It then adjusts the activities of the upper motor neurons involved. The basal nuclei adjust patterns of movement in two ways: 1. They alter the sensitivity of the pyramidal cells to adjust the output along the corticospinal tract. 2. They change the excitatory or inhibitory output of the medial and lateral pathways. Other nuclei of the medial and lateral pathways Cerebellum Corticospinal pathway Figure There are multiple levels of somatic motor control Lower motor neurons Motor activity Figure 187

Effects of primary motor cortex damage Individual loses ability to exert fine control of skeletal muscles Some voluntary movements can still be controlled by basal nuclei Cerebellum cannot fine-tune movements because corticospinal pathway is inoperative An individual can stand, balance, and walk All movements are hesitant, awkward, and poorly controlled

Module Review a. The basic motor patterns related to eating and drinking are controlled by what region of the brain? b. Which brain regions control reflexes in response to visual and auditory stimuli that are experienced while viewing a movie? c. During a tennis match, you decide how and where to hit the ball. Explain how the motor association areas are involved.

CLINICAL MODULE 13.19: Nervous system disorders
Referred pain Sensation of pain in part of body other than actual source Examples: Heart attack pain felt in left arm Strong visceral pain causing stimulation of interneurons in specific spinal cord segment of spinothalamic pathway causing pain at body surface

Figure Nervous system disorders may result from problems with neurons, pathways, or a combination of the two Figure 191

Parkinson disease When substantia nigra neurons are damaged or secrete less dopamine Basal nuclei become more active, increasing muscle tone and producing stiffness and rigidity Starting movements is difficult because antagonistic muscle groups do not relax (must be overpowered) Movements controlled through intense effort and concentration

Diminished substantia nigra in Parkinson patient
The substantia nigra from individuals with and without Parkinson disease Normal substantia nigra Diminished substantia nigra in Parkinson patient Figure Nervous system disorders may result from problems with neurons, pathways, or a combination of the two Figure 193

Rabies Bite from rabid animal injects rabies virus into peripheral tissues Virus spreads to synaptic knobs and is relayed up axons into CNS through retrograde flow Many toxins, pathogenic bacteria, and other viruses also bypass CNS defenses through retrograde flow

A member of the dog family, common vectors of the rabies virus
Figure Nervous system disorders may result from problems with neurons, pathways, or a combination of the two Figure 195

The movement of rabies viruses in a peripheral axon
Retrograde flow Synaptic knob Figure Nervous system disorders may result from problems with neurons, pathways, or a combination of the two Figure 196

Cerebral palsy (CP) Refers to a number of disorders that affect voluntary motor performance Appears during infancy or childhood and persists throughout life Cause may be: Trauma associated with premature or stressful childbirth Maternal exposure to drugs (including alcohol) Genetic defect that causes improper motor pathway development

An individual with cerebral palsy, a number of disorders that
affect voluntary motor performance Figure Nervous system disorders may result from problems with neurons, pathways, or a combination of the two Figure 198

ALS (amyotrophic lateral sclerosis) Commonly known as Lou Gehrig disease (famous Yankees player who died from disorder) Noted physicist Stephen Hawking also is afflicted Progressive, degenerative disorder that affects motor neurons in spinal cord, brain stem, and cerebrum Affects both upper and lower neurons Causes atrophy of associated skeletal muscles Thought to be related to a defect in axonal transport

Lou Gehrig, the most famous person afflicted with amyotrophic lateral
sclerosis (ALS), a progressive, degenerative disorder that affects motor neurons Figure Nervous system disorders may result from problems with neurons, pathways, or a combination of the two Figure 200

Alzheimer disease (AD) Progressive disorder characterized by loss of higher-order cerebral functions Most common cause of senile dementia Symptoms may appear at ages 50–60 years but can affect younger individuals Estimated 2 million affected in United States ~15% of those over 65 ~50% of those over 85 Causes ~100,000 deaths per year AD patients have intracellular and extracellular abnormalities in hippocampus

The appearance of a neuron from an individual with Alzheimer
disease (AD), a progressive disorder characterized by the loss of higher-order cerebral functions Abnormal dendrites, axons, and extracellular proteins form complexes known as Alzheimer plaques. Figure Nervous system disorders may result from problems with neurons, pathways, or a combination of the two Figure 202

Multiple sclerosis (MS; sklerosis, hardness) Disease characterized by recurrent incidents of demyelination in axons within optic nerve, brain, and spinal cord Common signs and symptoms include: Partial vision loss Problems with speech, balance, general motor coordination (including urinary and bowel control) In ~1/3 of cases, disease is progressive with more functional impairment with each incident First attack often in individuals 30–40 years old 1.5× more common in women

Damage to a neuron from an individual with multiple
sclerosis (MS), a disease characterized by recurrent incidents of demyelination that affects axons Demyelinating neuron Figure Nervous system disorders may result from problems with neurons, pathways, or a combination of the two Figure 204

CLINICAL MODULE 13.19 Review
a. Define referred pain. b. Describe how rabies is contracted. c. Describe amyotrophic lateral sclerosis (ALS).

13 The Brain and Cranial Nerves.

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