Central Nervous System (CNS)

Central Nervous System (CNS)
CNS consists of the brain and spinal cord Cephalization Evolutionary development of the rostral (anterior) portion of the CNS Increased number of neurons in the head Highest level is reached in the human brain

Regions and Organization of the CNS
Adult brain regions Cerebral hemispheres Diencephalon Brain stem (midbrain, pons, and medulla) Cerebellum

Cerebral hemisphere Diencephalon Cerebellum Brain stem • Midbrain
• Pons • Medulla oblongata (d) Birth Figure 12.3d

Spinal cord Central cavity surrounded by a gray matter core External white matter composed of myelinated fiber tracts

Brain Similar pattern with additional areas of gray matter Nuclei in cerebellum and cerebrum Cortex of cerebellum and cerebrum

Central cavity Cortex of gray matter Migratory pattern of neurons
Inner gray matter Cerebrum Outer white matter Cerebellum Gray matter Region of cerebellum Central cavity Inner gray matter Outer white matter Gray matter Brain stem Central cavity Outer white matter Inner gray matter Spinal cord Figure 12.4

Ventricles of the Brain
Connected to one another and to the central canal of the spinal cord Lined by ependymal cells

Ventricles of the Brain
Contain cerebrospinal fluid Two C-shaped lateral ventricles in the cerebral hemispheres Third ventricle in the diencephalon Fourth ventricle in the hindbrain, dorsal to the pons, develops from the lumen of the neural tube

Lateral ventricle Septum pellucidum Anterior horn Posterior horn
Inferior horn Interventricular foramen Lateral aperture Median aperture Third ventricle Inferior horn Lateral aperture Cerebral aqueduct Fourth ventricle Central canal (a) Anterior view (b) Left lateral view Figure 12.5

Cerebral Hemispheres Surface markings
Ridges (gyri), shallow grooves (sulci), and deep grooves (fissures) Five lobes Frontal Parietal Temporal Occipital Insula

Cerebral Hemispheres Surface markings Central sulcus
Separates the precentral gyrus of the frontal lobe and the postcentral gyrus of the parietal lobe Longitudinal fissure Separates the two hemispheres Transverse cerebral fissure Separates the cerebrum and the cerebellum PLAY Animation: Rotatable brain

Parieto-occipital sulcus (on medial surface of hemisphere)
Precentral gyrus Central sulcus Postcentral gyrus Frontal lobe Parietal lobe Parieto-occipital sulcus (on medial surface of hemisphere) Lateral sulcus Occipital lobe Temporal lobe Transverse cerebral fissure Cerebellum Pons Medulla oblongata Fissure Spinal cord (a deep sulcus) Gyrus Cortex (gray matter) Sulcus White matter (a) Figure 12.6a

Central sulcus Frontal lobe Gyri of insula Temporal lobe (pulled down)
Figure 12.6b

Anterior Longitudinal Frontal lobe fissure Cerebral veins and arteries
covered by arachnoid mater Parietal lobe Left cerebral hemisphere Right cerebral hemisphere Occipital lobe (c) Posterior Figure 12.6c

Left cerebral hemisphere Transverse cerebral fissure Brain stem
Cerebellum (d) Figure 12.6d

Cerebral Cortex Thin (2–4 mm) superficial layer of gray matter
40% of the mass of the brain Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding Each hemisphere connects to contralateral side of the body There is lateralization of cortical function in the hemispheres

Functional Areas of the Cerebral Cortex
The three types of functional areas are: Motor areas—control voluntary movement Sensory areas—conscious awareness of sensation Association areas—integrate diverse information Conscious behavior involves the entire cortex

Motor Areas Primary (somatic) motor cortex Premotor cortex Broca’s area Frontal eye field

Sensory areas and related association areas Primary motor cortex
Motor areas Central sulcus Sensory areas and related association areas Primary motor cortex Primary somatosensory cortex Premotor cortex Somatic sensation Frontal eye field Somatosensory association cortex Broca’s area (outlined by dashes) Gustatory cortex (in insula) Taste Prefrontal cortex Working memory for spatial tasks Wernicke’s area (outlined by dashes) Executive area for task management Working memory for object-recall tasks Primary visual cortex Visual association area Vision Solving complex, multitask problems Auditory association area Hearing Primary auditory cortex (a) Lateral view, left cerebral hemisphere Primary motor cortex Motor association cortex Primary sensory cortex Sensory association cortex Multimodal association cortex Figure 12.8a

Primary Motor Cortex Large pyramidal cells of the precentral gyri Long axons  pyramidal (corticospinal) tracts Allows conscious control of precise, skilled, voluntary movements Motor homunculi: upside-down caricatures representing the motor innervation of body regions

Posterior Motor Motor map in precentral gyrus Anterior Toes Jaw Tongue Primary motor cortex (precentral gyrus) Swallowing Figure 12.9

Premotor Cortex Anterior to the precentral gyrus Controls learned, repetitious, or patterned motor skills Coordinates simultaneous or sequential actions Involved in the planning of movements that depend on sensory feedback

Broca’s Area Anterior to the inferior region of the premotor area Present in one hemisphere (usually the left) A motor speech area that directs muscles of the tongue Is active as one prepares to speak

Frontal Eye Field Anterior to the premotor cortex and superior to Broca’s area Controls voluntary eye movements

Sensory Areas Primary somatosensory cortex
Somatosensory association cortex Visual areas Auditory areas Olfactory cortex Gustatory cortex Visceral sensory area Vestibular cortex

Primary Somatosensory Cortex
In the postcentral gyri Receives sensory information from the skin, skeletal muscles, and joints Capable of spatial discrimination: identification of body region being stimulated

Posterior Sensory Anterior Sensory map in postcentral gyrus Genitals Primary somatosensory cortex (postcentral gyrus) Intra- abdominal Figure 12.9

Somatosensory Association Cortex
Posterior to the primary somatosensory cortex Integrates sensory input from primary somatosensory cortex Determines size, texture, and relationship of parts of objects being felt

Primary visual (striate) cortex
Visual Areas Primary visual (striate) cortex Extreme posterior tip of the occipital lobe Most of it is buried in the calcarine sulcus Receives visual information from the retinas

Primary auditory cortex
Auditory Areas Primary auditory cortex Superior margin of the temporal lobes Interprets information from inner ear as pitch, loudness, and location Auditory association area Located posterior to the primary auditory cortex Stores memories of sounds and permits perception of sounds

Medial aspect of temporal lobes (in piriform lobes)
OIfactory Cortex Medial aspect of temporal lobes (in piriform lobes) Part of the primitive rhinencephalon, along with the olfactory bulbs and tracts (Remainder of the rhinencephalon in humans is part of the limbic system) Region of conscious awareness of odors

Primary somatosensory cortex
Cingulate gyrus Primary motor cortex Premotor cortex Central sulcus Corpus callosum Primary somatosensory cortex Frontal eye field Parietal lobe Somatosensory association cortex Prefrontal cortex Parieto-occipital sulcus Occipital lobe Processes emotions related to personal and social interactions Visual association area Orbitofrontal cortex Olfactory bulb Olfactory tract Primary visual cortex Fornix Temporal lobe Uncus Calcarine sulcus Primary olfactory cortex Parahippocampal gyrus (b) Parasagittal view, right hemisphere Primary motor cortex Motor association cortex Primary sensory cortex Sensory association cortex Multimodal association cortex Figure 12.8b

Limbic Association Area
Part of the limbic system Provides emotional impact that helps establish memories

Lateralization of Cortical Function
Division of labor between hemispheres Cerebral dominance Designates the hemisphere dominant for language (left hemisphere in 90% of people)

Lateralization of Cortical Function
Left hemisphere Controls language, math, and logic Right hemisphere Insight, visual-spatial skills, intuition, and artistic skills Left and right hemispheres communicate via fiber tracts in the cerebral white matter

Myelinated fibers and their tracts Responsible for communication
Cerebral White Matter Myelinated fibers and their tracts Responsible for communication Commissures (in corpus callosum)—connect gray matter of the two hemispheres Association fibers—connect different parts of the same hemisphere Projection fibers—(corona radiata) connect the hemispheres with lower brain or spinal cord

Commissural fibers (corpus Longitudinal fissure callosum) Superior
Lateral ventricle Association fibers Basal nuclei • Caudate Corona radiata • Putamen • Globus pallidus Fornix Internal capsule Thalamus Gray matter Third ventricle White matter Projection fibers Pons Decussation of pyramids Medulla oblongata (a) Figure 12.10a

Three paired structures
Diencephalon Three paired structures Thalamus Hypothalamus Epithalamus Encloses the third ventricle PLAY Animation: Rotatable brain (sectioned)

Cerebral hemisphere Septum pellucidum Corpus callosum Interthalamic
adhesion (intermediate mass of thalamus) Fornix Choroid plexus Thalamus (encloses third ventricle) Interven- tricular foramen Posterior commissure Pineal gland (part of epithalamus) Anterior commissure Corpora quadrigemina Mid- brain Hypothalamus Cerebral aqueduct Optic chiasma Arbor vitae (of cerebellum) Pituitary gland Fourth ventricle Mammillary body Choroid plexus Pons Cerebellum Medulla oblongata Spinal cord Figure 12.12

Thalamus 80% of diencephalon Superolateral walls of the third ventricle Connected by the interthalamic adhesion (intermediate mass) Contains several nuclei, named for their location Nuclei project and receive fibers from the cerebral cortex

Dorsal nuclei Medial Lateral dorsal Lateral posterior Pulvinar
Anterior nuclear group Medial geniculate body Reticular nucleus Lateral geniculate body Ventral postero- lateral Ventral anterior Ventral lateral Ventral nuclei (a) The main thalamic nuclei. (The reticular nuclei that “cap” the thalamus laterally are depicted as curving translucent structures.) Figure 12.13a

Thalamic Function Gateway to the cerebral cortex
Sorts, edits, and relays information Afferent impulses from all senses and all parts of the body Impulses from the hypothalamus for regulation of emotion and visceral function Impulses from the cerebellum and basal nuclei to help direct the motor cortices Mediates sensation, motor activities, cortical arousal, learning, and memory

Forms the inferolateral walls of the third ventricle
Hypothalamus Forms the inferolateral walls of the third ventricle Contains many nuclei Example: mammillary bodies Paired anterior nuclei Olfactory relay stations Infundibulum—stalk that connects to the pituitary gland

(b) The main hypothalamic nuclei.
Paraventricular nucleus Anterior commissure Dorsomedial nucleus Fornix Preoptic nucleus Posterior hypothalamic nucleus Anterior hypothalamic nucleus Lateral hypothalamic area Supraoptic nucleus Ventromedial nucleus Supra- chiasmatic nucleus Mammillary body Arcuate nucleus Optic chiasma Pituitary gland Infundibulum (stalk of the pituitary gland) (b) The main hypothalamic nuclei. Figure 12.13b

Hypothalamic Function
Autonomic control center for many visceral functions (e.g., blood pressure, rate and force of heartbeat, digestive tract motility) Center for emotional response: Involved in perception of pleasure, fear, and rage and in biological rhythms and drives

Hypothalamic Function
Regulates body temperature, food intake, water balance, and thirst Regulates sleep and the sleep cycle Controls release of hormones by the anterior pituitary Produces posterior pituitary hormones

Cerebral hemisphere Septum pellucidum Corpus callosum Interthalamic
adhesion (intermediate mass of thalamus) Fornix Choroid plexus Thalamus (encloses third ventricle) Interven- tricular foramen Posterior commissure Pineal gland (part of epithalamus) Anterior commissure Corpora quadrigemina Mid- brain Hypothalamus Cerebral aqueduct Optic chiasma Arbor vitae (of cerebellum) Pituitary gland Fourth ventricle Mammillary body Choroid plexus Pons Cerebellum Medulla oblongata Spinal cord Figure 12.12

Brain Stem Three regions Midbrain Pons Medulla oblongata

Brain Stem Similar structure to spinal cord but contains embedded nuclei Controls automatic behaviors necessary for survival Contains fiber tracts connecting higher and lower neural centers Associated with 10 of the 12 pairs of cranial nerves

Frontal lobe Olfactory bulb (synapse point of cranial nerve I)
Optic chiasma Optic nerve (II) Optic tract Mammillary body Midbrain Pons Temporal lobe Medulla oblongata Cerebellum Spinal cord Figure 12.14

Oculomotor nerve (III) Trochlear nerve (IV)
View (a) Optic chiasma Optic nerve (II) Diencephalon Crus cerebri of cerebral peduncles (midbrain) • Thalamus • Hypothalamus Thalamus Mammillary body Diencephalon Hypothalamus Oculomotor nerve (III) Midbrain Pons Brainstem Trochlear nerve (IV) Medulla oblongata Trigeminal nerve (V) Middle cerebellar peduncle Pons Facial nerve (VII) Abducens nerve (VI) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Hypoglossal nerve (XII) Pyramid Vagus nerve (X) Ventral root of first cervical nerve Accessory nerve (XI) Decussation of pyramids Spinal cord (a) Ventral view Figure 12.15a

Superior cerebellar peduncle Pons Middle cerebellar peduncle
Crus cerebri of cerebral peduncles (midbrain) Thalamus View (b) Infundibulum Superior colliculus Pituitary gland Inferior colliculus Trochlear nerve (IV) Trigeminal nerve (V) Superior cerebellar peduncle Pons Middle cerebellar peduncle Facial nerve (VII) Inferior cerebellar peduncle Abducens nerve (VI) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Olive Hypoglossal nerve (XII) Thalamus Vagus nerve (X) Diencephalon Hypothalamus Accessory nerve (XI) Midbrain Pons Brainstem Medulla oblongata (b) Left lateral view Figure 12.15b

• Superior cerebellar peduncle Pons • Middle cerebellar peduncle
Thalamus View (c) Diencephalon Midbrain • Superior colliculus Corpora quadrigemina of tectum • Inferior colliculus • Trochlear nerve (IV) Pineal gland • Superior cerebellar peduncle Pons • Middle cerebellar peduncle Medulla oblongata Anterior wall of fourth ventricle • Inferior cerebellar peduncle • Facial nerve (VII) • Vestibulocochlear nerve (VIII) Choroid plexus (fourth ventricle) • Glossopharyngeal nerve (IX) • Vagus nerve (X) • Accessory nerve (XI) Dorsal median sulcus Thalamus Dorsal root of first cervical nerve Diencephalon Hypothalamus Midbrain Pons Brainstem (c) Dorsal view Medulla oblongata Figure 12.15c

Located between the diencephalon and the pons
Midbrain Located between the diencephalon and the pons Cerebral peduncles Contain pyramidal motor tracts Cerebral aqueduct Channel between third and fourth ventricles

Superior Tectum Dorsal colliculus Periaqueductal gray matter
Cerebral aqueduct Oculomotor nucleus (III) Reticular formation Medial lemniscus Red nucleus Substantia nigra Fibers of pyramidal tract Ventral Crus cerebri of cerebral peduncle (a) Midbrain Figure 12.16a

Pons Forms part of the anterior wall of the fourth ventricle
Fibers of the pons Connect higher brain centers and the spinal cord Relay impulses between the motor cortex and the cerebellum Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial) Some nuclei of the reticular formation Nuclei that help maintain normal rhythm of breathing

Fourth ventricle Reticular formation Superior cerebellar peduncle
Trigeminal main sensory nucleus Trigeminal motor nucleus Middle cerebellar peduncle Pontine nuclei Trigeminal nerve (V) Fibers of pyramidal tract Medial lemniscus (b) Pons Figure 12.16b

Medulla Oblongata Inferior olivary nuclei—relay sensory information from muscles and joints to cerebellum Cranial nerves VIII, X, and XII are associated with the medulla Vestibular nuclear complex—mediates responses that maintain equilibrium Several nuclei (e.g., nucleus cuneatus and nucleus gracilis) relay sensory information

Autonomic reflex centers Cardiovascular center
Medulla Oblongata Autonomic reflex centers Cardiovascular center Cardiac center adjusts force and rate of heart contraction Vasomotor center adjusts blood vessel diameter for blood pressure regulation

Medulla Oblongata Respiratory centers Generate respiratory rhythm
Control rate and depth of breathing, with pontine centers

Additional centers regulate
Medulla Oblongata Additional centers regulate Vomiting Hiccuping Swallowing Coughing Sneezing

Hypoglossal nucleus (XII) Dorsal motor nucleus of vagus (X)
Fourth ventricle Solitary nucleus Choroid plexus Hypoglossal nucleus (XII) Dorsal motor nucleus of vagus (X) Vestibular nuclear complex (VIII) Inferior cerebellar peduncle Cochlear nuclei (VIII) Lateral nuclear group Nucleus ambiguus Medial nuclear group Reticular formation Inferior olivary nucleus Raphe nucleus Pyramid Medial lemniscus (c) Medulla oblongata Figure 12.16c

The Cerebellum 11% of brain mass Dorsal to the pons and medulla Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction

Anatomy of the Cerebellum
Two hemispheres connected by vermis Each hemisphere has three lobes Anterior, posterior, and flocculonodular Folia—transversely oriented gyri Arbor vitae—distinctive treelike pattern of the cerebellar white matter

Anterior lobe Cerebellar cortex Arbor vitae Cerebellar peduncles
Posterior lobe • Superior • Middle Choroid plexus of fourth ventricle • Inferior Medulla oblongata Flocculonodular lobe (b) Figure 12.17b

Anterior lobe Posterior lobe (d) (d) Vermis Figure 12.17d

Cerebellar Processing for Motor Activity
Cerebellum receives impulses from the cerebral cortex of the intent to initiate voluntary muscle contraction Signals from proprioceptors and visual and equilibrium pathways continuously “inform” the cerebellum of the body’s position and momentum Cerebellar cortex calculates the best way to smoothly coordinate a muscle contraction A “blueprint” of coordinated movement is sent to the cerebral motor cortex and to brain stem nuclei

Cognitive Function of the Cerebellum
Recognizes and predicts sequences of events during complex movements Plays a role in nonmotor functions such as word association and puzzle solving

Functional Brain Systems
Networks of neurons that work together and span wide areas of the brain Limbic system Reticular formation

Limbic System Structures on the medial aspects of cerebral hemispheres and diencephalon Includes parts of the diencephalon and some cerebral structures that encircle the brain stem

Diencephalic structures of the limbic system Corpus callosum •Fornix
Fiber tracts connecting limbic system structures Septum pellucidum Diencephalic structures of the limbic system Corpus callosum •Fornix •Anterior thalamic nuclei (flanking 3rd ventricle) •Anterior commissure Cerebral structures of the limbic system •Hypothalamus •Mammillary body •Cingulate gyrus •Septal nuclei •Amygdala •Hippocampus •Dentate gyrus •Parahippocampal gyrus Olfactory bulb Figure 12.18

Emotional or affective brain
Limbic System Emotional or affective brain Amygdala—recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict Puts emotional responses to odors Example: skunks smell bad

Limbic System: Emotion and Cognition
The limbic system interacts with the prefrontal lobes, therefore: We can react emotionally to things we consciously understand to be happening We are consciously aware of emotional richness in our lives Hippocampus and amygdala—play a role in memory

Reticular Formation: RAS and Motor Function
RAS (reticular activating system) Sends impulses to the cerebral cortex to keep it conscious and alert Filters out repetitive and weak stimuli (~99% of all stimuli!) Severe injury results in permanent unconsciousness (coma)

Reticular Formation: RAS and Motor Function
Helps control coarse limb movements Reticular autonomic centers regulate visceral motor functions Vasomotor Cardiac Respiratory centers

(touch, pain, temperature)
Radiations to cerebral cortex Visual impulses Auditory impulses Reticular formation Descending motor projections to spinal cord Ascending general sensory tracts (touch, pain, temperature) Figure 12.19

Electroencephalogram (EEG)
Records electrical activity that accompanies brain function Measures electrical potential differences between various cortical areas

(a) Scalp electrodes are used to record brain wave activity (EEG).
Figure 12.20a

Brain Waves Patterns of neuronal electrical activity Generated by synaptic activity in the cortex Each person’s brain waves are unique Can be grouped into four classes based on frequency measured as Hertz (Hz)

Types of Brain Waves Alpha waves (8–13 Hz)—regular and rhythmic, low-amplitude, synchronous waves indicating an “idling” brain Beta waves (14–30 Hz)—rhythmic, less regular waves occurring when mentally alert Theta waves (4–7 Hz)—more irregular; common in children and uncommon in adults Delta waves (4 Hz or less)—high-amplitude waves seen in deep sleep and when reticular activating system is damped, or during anesthesia; may indicate brain damage

Alpha waves—awake but relaxed
1-second interval Alpha waves—awake but relaxed Beta waves—awake, alert Theta waves—common in children Delta waves—deep sleep (b) Brain waves shown in EEGs fall into four general classes. Figure 12.20b

Brain Waves: State of the Brain
Change with age, sensory stimuli, brain disease, and the chemical state of the body EEGs used to diagnose and localize brain lesions, tumors, infarcts, infections, abscesses, and epileptic lesions A flat EEG (no electrical activity) is clinical evidence of death

Consciousness Conscious perception of sensation Voluntary initiation and control of movement Capabilities associated with higher mental processing (memory, logic, judgment, etc.) Loss of consciousness (e.g., fainting or syncopy) is a signal that brain function is impaired

Consciousness Clinically defined on a continuum that grades behavior in response to stimuli Alertness Drowsiness (lethargy) Stupor Coma

Two major types of sleep (defined by EEG patterns)
State of partial unconsciousness from which a person can be aroused by stimulation Two major types of sleep (defined by EEG patterns) Nonrapid eye movement (NREM) Rapid eye movement (REM)

Sleep First two stages of NREM occur during the first 30–45 minutes of sleep Fourth stage is achieved in about 90 minutes, and then REM sleep begins abruptly

Awake REM: Skeletal muscles (except ocular muscles and diaphragm) are actively inhibited; most dreaming occurs. NREM stage 1: Relaxation begins; EEG shows alpha waves, arousal is easy. NREM stage 2: Irregular EEG with sleep spindles (short high- amplitude bursts); arousal is more difficult. NREM stage 3: Sleep deepens; theta and delta waves appear; vital signs decline. NREM stage 4: EEG is dominated by delta waves; arousal is difficult; bed-wetting, night terrors, and sleepwalking may occur. (a) Typical EEG patterns Figure 12.21a

Sleep Patterns Alternating cycles of sleep and wakefulness reflect a natural circadian (24-hour) rhythm RAS activity is inhibited during, but RAS also mediates, dreaming sleep The suprachiasmatic and preoptic nuclei of the hypothalamus time the sleep cycle A typical sleep pattern alternates between REM and NREM sleep

(b) Typical progression of an adult through one night’s sleep stages
Awake REM Stage 1 Stage 2 Non REM Stage 3 Stage 4 Time (hrs) (b) Typical progression of an adult through one night’s sleep stages Figure 12.21b

Importance of Sleep Slow-wave sleep (NREM stages 3 and 4) is presumed to be the restorative stage People deprived of REM sleep become moody and depressed REM sleep may be a reverse learning process where superfluous information is purged from the brain Daily sleep requirements decline with age Stage 4 sleep declines steadily and may disappear after age 60

Sleep Disorders Narcolepsy Insomnia Sleep apnea
Lapsing abruptly into sleep from the awake state Insomnia Chronic inability to obtain the amount or quality of sleep needed Sleep apnea Temporary cessation of breathing during sleep

Storage and retrieval of information Two stages of storage
Memory Storage and retrieval of information Two stages of storage Short-term memory (STM, or working memory)—temporary holding of information; limited to seven or eight pieces of information Long-term memory (LTM) has limitless capacity

Outside stimuli General and special sensory receptors Afferent inputs Temporary storage (buffer) in cerebral cortex Data permanently lost Data selected for transfer Automatic memory Forget Short-term memory (STM) Forget Data transfer influenced by: Retrieval Excitement Rehearsal Association of old and new data Long-term memory (LTM) Data unretrievable Figure 12.22

Transfer from STM to LTM
Factors that affect transfer from STM to LTM Emotional state—best if alert, motivated, surprised, and aroused Rehearsal—repetition and practice Association—tying new information with old memories Automatic memory—subconscious information stored in LTM

(a) Declarative memory circuits
Thalamus Basal forebrain Touch Prefrontal cortex Hearing Smell Vision Taste Hippocampus Sensory input Thalamus (a) Declarative memory circuits Association cortex Medial temporal lobe (hippocampus, etc.) Prefrontal cortex ACh ACh Basal forebrain Figure 12.23a

Brain Structures Involved in Nondeclarative Memory
Procedural memory Basal nuclei relay sensory and motor inputs to the thalamus and premotor cortex Dopamine from substantia nigra is necessary Motor memory—cerebellum Emotional memory—amygdala

(b) Procedural (skills) memory circuits
Sensory and motor inputs Association cortex Basal nuclei Premotor cortex Thalamus Dopamine Premotor cortex Substantia nigra Basal nuclei Thalamus Substantia nigra (b) Procedural (skills) memory circuits Figure 12.23b

Protection of the Brain
Bone (skull) Membranes (meninges) Watery cushion (cerebrospinal fluid) Blood-brain barrier

Meninges Cover and protect the CNS Protect blood vessels and enclose venous sinuses Contain cerebrospinal fluid (CSF) Form partitions in the skull

Meninges Three layers Dura mater Arachnoid mater Pia mater

Skin of scalp Periosteum Bone of skull Dura Periosteal mater Meningeal
Superior sagittal sinus Arachnoid mater Pia mater Subdural space Arachnoid villus Blood vessel Subarachnoid space Falx cerebri (in longitudinal fissure only) Figure 12.24

Dura Mater Strongest meninx Two layers of fibrous connective tissue (around the brain) separate to form dural sinuses

Dural septa limit excessive movement of the brain
Dura Mater Dural septa limit excessive movement of the brain Falx cerebri—in the longitudinal fissure; attached to crista galli Falx cerebelli—along the vermis of the cerebellum Tentorium cerebelli—horizontal dural fold over cerebellum and in the transverse fissure

Superior sagittal sinus Falx cerebri Straight sinus Crista galli
of the ethmoid bone Tentorium cerebelli Falx cerebelli Pituitary gland (a) Dural septa Figure 12.25a

Arachnoid Mater Middle layer with weblike extensions Separated from the dura mater by the subdural space Subarachnoid space contains CSF and blood vessels Arachnoid villi protrude into the superior sagittal sinus and permit CSF reabsorption

Skin of scalp Periosteum Bone of skull Dura Periosteal mater Meningeal
Superior sagittal sinus Arachnoid mater Pia mater Subdural space Arachnoid villus Blood vessel Subarachnoid space Falx cerebri (in longitudinal fissure only) Figure 12.24

Pia Mater Layer of delicate vascularized connective tissue that clings tightly to the brain

Cerebrospinal Fluid (CSF)
Composition Watery solution Less protein and different ion concentrations than plasma Constant volume

Cerebrospinal Fluid (CSF)
Functions Gives buoyancy to the CNS organs Protects the CNS from blows and other trauma Nourishes the brain and carries chemical signals

Right lateral ventricle (deep to cut)
Superior sagittal sinus 4 Choroid plexus Arachnoid villus Interventricular foramen Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle 3 Third ventricle CSF is produced by the choroid plexus of each ventricle. 1 Cerebral aqueduct Lateral aperture Fourth ventricle CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. 2 Median aperture 2 Central canal of spinal cord CSF flows through the subarachnoid space. 3 (a) CSF circulation CSF is absorbed into the dural venous sinuses via the arachnoid villi. 4 Figure 12.26a

Spinal Cord Location Functions Begins at the foramen magnum
Ends as conus medullaris at L1 vertebra Functions Provides two-way communication to and from the brain Contains spinal reflex centers

Spinal Cord: Protection
Bone, meninges, and CSF Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater CSF in subarachnoid space

(b) The spinal cord and its meningeal coverings
Dorsal median sulcus Gray commissure Dorsal funiculus Dorsal horn White columns Ventral funiculus Gray matter Ventral horn Lateral funiculus Lateral horn Dorsal root ganglion Spinal nerve Central canal Dorsal root (fans out into dorsal rootlets) Ventral median fissure Ventral root (derived from several ventral rootlets) Pia mater Arachnoid mater Spinal dura mater (b) The spinal cord and its meningeal coverings Figure 12.31b

Gray Matter Dorsal horns—interneurons that receive somatic and visceral sensory input Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots Lateral horns (only in thoracic and lumbar regions) –sympathetic neurons Dorsal root (spinal) gangia—contain cell bodies of sensory neurons

Dorsal horn (interneurons)
Dorsal root (sensory) Dorsal root ganglion Dorsal horn (interneurons) Somatic sensory neuron Visceral sensory neuron Visceral motor neuron Spinal nerve Ventral horn (motor neurons) Ventral root (motor) Somatic motor neuron Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons Figure 12.32

Central Nervous System (CNS)

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Central Nervous System (CNS)

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