Chapter 12: The Central Nervous System

Chapter 12: The Central Nervous System

Central Nervous System
Brain and Spinal Cord Body’s supercomputer Cephalization – elaboration towards rostal “towards the snout” or anterior portion of CNS Also increase in the number of neurons

Brain Adult male – 1600 g (3.5 lbs) Adult female – 1450 g (3.2 lbs)
Brain mass per body mass - equal

Embryonic Development
3 week embryo- ectoderm thickens along dorsal midline of body = neural plate Neural tube invaginates – forms groove flanked by neural folds Groove deepens – superior ridges fuse forming neural tube – detached from ectoderm and sinks into a deeper position Neural tube differentiates into CNS – brain anterior and spinal cord - caudal

5. Neural crest forms – gives rise to some neurons 6. Neural tube – anterior end expands 3 primary brain vesicles – 1. prosencephalon – forebrain 2. mesencephalon – midbrain 3. rhomben cephalon – hindbrain 7. Week 5 – primary vesicles secondary vesicles Forebrain  telencephalon (endbrain) + diencephalon (hindbrain) Hindbrain constricts – metencephalon “afterbrain” Metencephalon – “spinal brain”

8. 5 – secondary vesicles – develop into major structures of adult brain 2 cerebral hemispheres – cerebrum Diencephalon – hypothalamus Thalamus Epithalamus Retina Mesencephalon = midbrain Metencephalon = pons Myelencephalon = cerebellum Midbrain and hindbrain = spinal cord

1 Surface ectoderm Head Neural plate Tail
The neural plate forms from surface ectoderm. Figure 12.1, step 1

2 Neural folds Neural groove
The neural plate invaginates, forming the neural groove, flanked by neural folds. 2 Figure 12.1, step 2

Neural crest 3 Neural fold cells migrate to form the neural crest, which will form much of the PNS and many other structures. Figure 12.1, step 3

4 Head Surface ectoderm Neural tube Tail
The neural groove becomes the neural tube, which will form CNS structures. 4 Figure 12.1, step 4

(b) Primary brain vesicles
Neural tube (b) Primary brain vesicles Anterior (rostral) Prosencephalon (forebrain) Mesencephalon (midbrain) Rhombencephalon (hindbrain) Posterior (caudal) Figure 12.2a-b

(e) Adult neural canal regions (c) Secondary brain vesicles
(d) Adult brain structures Cerebrum: cerebral hemispheres (cortex, white matter, basal nuclei) Lateral ventricles Telencephalon Diencephalon (thalamus, hypothalamus, epithalamus), retina Diencephalon Third ventricle Cerebral aqueduct Mesencephalon Brain stem: midbrain Metencephalon Brain stem: pons Fourth ventricle Cerebellum Brain stem: medulla oblongata Myelencephalon Spinal cord Central canal Figure 12.2c-e

Regions of Brain Cerebral Hemispheres Diencephalon
Brain stem (pons, midbrain, and medulla)

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

Pattern Central cavity surrounded by gray matter (neuron cell bodies)
External – white matter (myelinated fiber tracts) Outer layer of gray matter – cortex – dissapears as you move down the brain stem

Ventricles Arise from expansions of lumen (cavity) of embryonic neural tube Filled with cerebral spinal fluid Lined by ependymal cells

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

Lateral Ventricles Deep in cerebral hemisphere
Large C – shaped chambers separated by septum pellucidum Communicate with 3rd ventricle – in diencephalon Channel – intraventricular foramen 3rd ventricle continuous with 4th – canal cerebral aqueduct 4th ventricle – 3 openings – 2 lateral apertures and median aperture

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 Superior part of brain 83 % of brain’s mass
Cover and obscure diencephalon and top of brain stem Surface – gyri – elevated ridges Sulci – grooves Fissures – deeper grooves Longitudinal fissure – separates cerebral hemispheres Transverse cerebral fissure – separates cerebral from cerebellum

Cerebral Hemisphere Divided into 5 lobes by sulci
Central sulcus – frontal plane – separates frontal lobe from parietal lobe Percentral gyrus and postcentral gyrus – border – central sulcus Occipital lobe – separate from parietal by parietocciplital sulcus Lateral sulcus – outlines temporal lobe Insula – 5th lobe – deep in lateral sulcus – forms its floor

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

Brain Fits snuggly in skull
Frontal lobes – lie in anterior cranial fossa Middle cranial fossa – temporal lobe Each hemisphere – 3 regions 1. cerebral cortex – gray 2. internal white matter 3. basal nuclei

Cerebral Cortex “executive suite” of NS conscious mind
Enables awareness of ourselves, our sensations, and enables us to communicate, remember, and understand Also voluntary movement Composed of gray matter – neuron cell bodies, dendrites, glial and blood vessels

Cerebral Cortex Billions of neurons – arranged in 6 layers
2-4 mm thick – 40 % of total brainmass 52 cortical areas – Broadman areas

Cerebral Cortex 3 functional areas – All neurons – interneurons
1. motor area 2. sensory area 3. association area All neurons – interneurons Each hemisphere – sensory and motor functions of opposite sides of body Hemispheres – not entirely equal in function Lateralization or specialization of cortical functions No functional area acts alone Conscious behavior involves the entire cortex

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

Motor Areas Control voluntary movement
Posterior part of frontal lobes: primary motor cortex, premotor cortex, Broca’s area, and frontal eye field

Motor Area – Primary Motor Cortex
Primary (somatic) motor cortex – Located in precentral gyrus of frontal lobe Large neurons – pyramidal cells Allow control of precise or skilled voluntary movements Long axons – project into spinal cord – pyramidal tracts Somatotrophy – control of body structures mapped to places Muscles controlled by multiple spots

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

Motor Area – Premotor Cortex
Just anterior to precentral gyrus Controls learned motor skills of repetitious pattern or nature Coordinates movements of several muscle groups Memory bank for skilled motor activites

Motor Area – Broca’s Area
Lies anterior to inferior region of premotor area Considered to be 1. present in one hemisphere only (usually the left) 2. special motor speech area – directs muscles involved in speech production Recently shown to “light up” as we prepare to think or even think about voluntary activities other than speech

Motor Area – Frontal Eye Field
Located partial in and anterior to premotor cortex and superior to Broca’s area Controls voluntary movement of eyes

Damage Damage to areas of primary motor cortex – paralyzes the body muscles controlled by those areas Voluntary control lost, muscles can still contract reflexively Premotor cortex - damage results in a loss in motor skills programmed in that region, but muscle strength and ability to perform movements are not

Sensory Areas Occur in parietal lobe, insular, temporal, and occipital lobes 1. Primary Somartosensory Cortex – In post central gyrus of parietal lobe Neurons receive info from general (somatic) sensory receptors in the skin and proprioceptors (position sense receptors) in skeletal muscle, joints and tendons Neurons identify body region being stimulated – spatial discrimination Right hemisphere – receive input from left side of body Face & fingertips – most sensitive – largest part

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

Sensory Areas 2. Somatosensory Association Cortex – posterior to primary somatosensory cortex Integrates sensory inputs – temp, pressure, etc. – relayed to produce understanding of object being felt – size, texture, relationship

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

Sensory Areas 3. Visual Areas – primary visual (striate) cortex
Extreme posterior tip of occipital lobe Most buried deep in calcarine sulcus Largest Receives visual input from retina Visual association areas – surround primary – uses past visual experiences to interpret stimuli

Sensory Areas 4. Auditory Areas – primary auditory cortex – superior margin of temporal lobe Impulses from ear transmitted here – interpreted as pitch, loudness, location, etc. Auditory Association area – permits perception of sound Memories of past sounds

Sensory Areas 5. Olfactory cortex – Medial aspect of temporal lobes
Small region – piriform lobe Smell receptors send impulses

Sensory Areas 6. Gustatory Cortex – taste stimuli
Insula just deep to temporal lobe

Sensory Areas 7. Visceral Sensory Area – conscious perception of visceral stimulation Upset stomach, full bladder, lung bursting – holding breath to long

Sensory Areas 8. Vestibular (equilibrium) cortex – difficult to find
Imaging – shows it in the posterior part of insula and adjacent parietal cortex

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

Multimodal Association Areas
Cortex – complex Input from multiple senses and outputs to multiple areas Meaning to info we receive, stores memories, ties to previous experiences, and decide actions Sensations, thoughts, and emotions

1. Anterior Association Areas – frontal lobe – prefrontal cortex Most complicated Intellect, complex learning abilities (cognition), recall, and personality Working memory – abstract ideas, judgment, reasoning, persistence, and planning Abilities develop slowly in children – region of the brain that matures slowly

2. Posterior Association areas – large region encompassing part of temporal, parietal, and occipital lobes Recognizes patterns and faces

3. Limbic Association Areas – cingulate gyrus Parahippocampal gyrus Hippocampus Part of limbic system Emotional impact Sense of danger

Lateralization of Cortical Functioning
Division of labor Each hemisphere has unique abilities not shared by its partner – lateralization Cerebral dominance – designates hemisphere – dominant for language Left hemisphere – 90 % - language, math, and logic Right – more free spirited – visual-spatial skills, intuition, emotion, artistic and musical skills Remaining 10 % of people – roles reversed Typically – male and left handed

Cerebral White Matter White matter – deep to cortical gray matter – responsible for communication between cerebral area and cerebral cortex and lower CNS centers Consists of – myelinated fibers classified according to the direction they run – 1. Commissural fibers – connect gray area of 2 hemispheres 2. Association fibers – connect different parts of same hemisphere 3. Projection fibers – cortex to rest of NS

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

Cerebral White Matter Basal nuclei - Subcortical nuclei
Deep within cerebral white matter Input from entire cerebral cortex Functions overlap with those of cerebellum Part in regulating attention and cognition

Fibers of corona radiata Caudate nucleus Thalamus Lentiform Tail of
• Putamen • Globus pallidus (deep to putamen) Tail of caudate nucleus Corpus striatum Projection fibers run deep to lentiform nucleus (a) Figure 12.11a

Diencephalon Central core of forebrain
Surrounded by cerebral hemispheres 3 parts – thalamus, hypothalamus, and epithalamus

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

Diencephalon - Thalamus
Bilateral egg shaped nuclei Superolateral walls of 3rd ventricle 80 % of diencephalon Relay station for info Nuclei – each functional specialty receives from a specific area Info sorted and edited

Diencephalon - Hypothalamus
Below thalamus Caps brain stem and forms infolateral walls of 3rd ventricle Extends from optic chiasma to mammillary bodies Infundibulum – stalk of hypothalamic tissue connects pituitary Main visceral controlling center of body

Homeostatic roles – Autonomic Control Center – influences BP, rate and force of heart beat, digestive tract motility, pupil size, etc. Emotional response – perception of pleasure, fear, and rage, biological rhythms and drives Body temperature – monitor blood temperature and other thermoreceptors Food Intake – hunger and satiety in response to changing blood levels Water balance and thirst – osmoreceptors, ADH Sleep – wake Cycles Endocrine System functioning – releasing and inhibiting hormones

Number of Disorders – Obesity, sleep disturbances, dehydration, emotional impulses Infant failure to thrive – delay child’s growth or development when deprived of a warm, nurturing relationship

Diencephalon - Epithalamus
Most dorsal Roof of 3rd ventricle Pineal gland – secrets hormone melanin – sleep signal and antioxidant

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 Midbrain, pons, medulla oblongata 2.5 % of total brain mass
Deep gray matter surrounded by white fibers Automatic behaviors Pathway Innervation of head

Midbrain 2 cerebral peduncles – “little feet” Cruscerbui – “leg”
Fight or flight Reflexive responses – startle response

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

Pons Bulging brainstem region Conduction tracts
Deep fibers – longitudinal Superficial – transverse and dorsal Cranial nerves

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

Medulla Oblongata Medulla Inferior part of brain stem
Visceral motor nuclei Cardio center – adjusts heart rate Vasomotor center – changes blood vessel diameter Respiratory = respiratory rhythm Various others – vomiting, coughing, swallowing, hiccupping , and sneezing

• 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

Cerebellum Cauliflower like 11 % of total brain mass
Under occipital lobes Input from – cerebral motor cortex, brain stem, and sensory receptors Coordinated movement – driving, typing, etc

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

Cerebellum Anatomy – bilateral symmetry 2 apple sized hemispheres
Fola – pleat-like gyri Deep fissures Outer cortex – gray matter and deeply situated paired mass of gray matter Neurons – Purkinje cells

Cerebellum Cerebellar Processing – functional scheme
Cerebral cortex motor areas notify cerebellum of intent to initiate voluntary muscle control Receives info from proprioceptors throughout the body – body position and momentum Cerebellar cortex – calculated best way to coordinate force, direction, and extent Superior peduncles – dispatches “blue print” for coordinated movement

Functional Brain Systems
Network of neurons that work together but span large distances in brain Cannot be localized to specific regions

Limbic System Group of structures located in medial aspect of each cerebral hemisphere and diencephalon Cerebral structures that encircle upper part of brain stem Emotional or affective (feelings) brain Odors – trigger emotional reactions – rhinencephalon – “smell brain” Interacts with prefrontal lobes – intimate relationship between feelings and thoughts

Reticular Formation Extends central core of medulla oblongata, pons, and midbrain Loosely clustered neurons Midline raphe neuclei Medial (large cell) group Lateral (small cell) group flung axonal connections Reticular activating system (RAS) – impulses from great ascending sensory tracts – keep them active and enhance effect on cerebrum Filter sensory inputs Inhibited sleep centers Depressed by alcohol, sleep aid drugs, and tranquilizers

Higher Mental Functions
Brainwaves reflect the electrical activity of higher mental functions Electroencephalogram – record some aspects of activity Electrodes on scalp measure potential energy differences Brainwaves – generated by synaptic activity at surface of cortex

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

Brain Waves –4 categories Alpha Waves – 8-13 Hz Regular rhythmic
Low amplitude Synchronous waves Brain – ‘idling’ – calm, relaxed state of wakefulness

Brain Waves 2. Beta Waves – 14-30Hz – rhythmic, but not as regular, occur when mentally alert 3. Theta Waves – 4-7 Hz – irregular, common in children, uncommon in adults 4. Delta Waves – 4 Hz or less – high amplitude waves, deep sleep – reticular activating system is damped – anesthesia - Indicated brain damage in awake adults

Brain Waves Change with age, sensory stimuli, brain disease and chemical state of body Flat EEG – clinical evidence of brain death Epilepsy – seizures – torrent of electrical charges of groups of brain neurons Uncontrolled activity – no other messages can get through

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

Consciousness Encompass conscious perception of sensations, voluntary initiation and control of movements and capabilities associated with higher mental functioning Defined by behavior in response to stimuli Alertness Drowsiness or lethargy Stupor coma

Consciousness Difficult to determine Current suppositions –
Simultaneous activity of large areas of cerebral cortex It is superimposed on other types of neural activity Is it holistic and totally interconnected

Consciousness Fainting or Syncope – brief loss of consciousness
Most often from inadequate cerebral blood flow due to low BP Coma – total unresponsiveness Not deep sleep – oxygen level lower than deep sleep Blows to head – widespread cerebral or brain stem trauma Tumors or infections, hypoglycemia, drug overdose, kidney failure Brain Death – irreparable damage to brain

Sleep and Sleep Wake Cycles
Sleep – state of partial unconsciousness from which a person can be aroused by stimulation Coma – cannot be aroused

Types of Sleep 2 major types that alternate throughout the sleep cycle
Non-rapid eye movement (NREM) Rapid Eye movement (REM) - Defined by EEG patterns

Sleep 1st 30 -45 minutes – 2 stages of NREM
Then stage 3 and 4 – NREM- slow wave sleep Deeper sleep – EEG wave declines – amplitude increase 90 minutes – NREM stage 4 – changes rapidly – appears to backtrack until alpha waves appear – onset of REM sleep Increase in heart rate Increase respiratory rate Increase in blood pressure Decrease in gastrointestinal activity Increase in oxygen use Eyes move rapidly, skeletal muscles limp, dreams

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 patterns of sleep and wakefulness
Natural circadian, or 24 hour, rhythm Hypothalamus response Suprachaismatic nucleus – biological clock regulates preoptic nucleus – sleep inducing center

Sleep Patterns Young/middle aged adult – 4 stages of NREM then alternate with occasional partial analysis REM ~ every 90 minutes 1st REM – 5-10 minutes long Final REM – minutes long Wake – hypothermic neurons release peptides (exins) “wakeup” chemical

(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 – restorative – neural activity winds down REM – deprived – moody and depressed Analyze days events Get rid of meaning less communication Alcohol and sleep meds – suppress REM but not slow wave sleep Tranquilizers – suppress slow wave more than REM

Importance of Sleep Requirements – infant – 16 hrs
7 ½  8 ½ - early adulthood REM – ½ sleep time in infants – declines until 10 years old Stabilizes ~ 25% Stage 4 – declines steadily – often disappears by age 60

Sleep Narcolepsy – lapse into REM from an awake state
Lasts ~ 15 min, can occur at any time, most often triggered by a pleasurable event Fewer cells in hypothalamus that secrete orexins Insomnia – inability to obtain amount or quantity of sleep needed to adequately function Varies – 4 -9 hrs/day Sleep Apnea – temporary cessation of breathing during sleep Victim wakes due to hypoxia Associated with obesity Made worse by alcohol Must wear a mask when sleeping

Language Involves almost all of association cortex on left side
2 important areas – Broca’s area – can’t speak, but can understand Wericke’s area – can speak but can’t understand - Areas work together to form a single implementation system

Memory Storage and retrieval of information essential for learning and incorporating experiences Stages Short term Memory (STM) – working memory Limited to 7 or 8 chunks of information 2. Long term Memory (LTM) – limitless capacity Can be forgotten Memory bank changes with time Ability to store and retrieve information declines with age

From STM to LTM - Emotional state – we learn when surprised, alert, motivated, or aroused Norephinephrine released when excited 2. Rehearsal – repetition – enhances memory 3. Association – tying new info to old info already stored 4. Automatic Memory – not all impressions are consciously formed - Memory consolidation – fitting new facts into knowledge already stored

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

Categories of Memory Declarative (fact) memory – learning explicit info – names, faces, dates Non-declarative memory – less conscious Procedural (skills) memory – ex. Playing the piano Motor Memory – riding a bike Emotional memory – pounding heart when see a rattlesnake

Brain Structures Visual memories – stored in occipital cortex
Music – temporal cortex Damage to hippocampus and medial temporal lobe result in slight memory loss Bilateral destruction - amnesia

Protection of Brain Nervous tissue – soft and delicate
Brain – protected by bone, membranes, and CSF Harmful substances – blood-brain barrier

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

Meninges 3 connective tissue membranes that lie external to CNS organs
Functions: Cover and protect CNS Protect blood vessels and enclose venous sinuses Contain cerebral spinal fluid Form partitions in skull

Meninges Dura Matter “tough mother’ Strongest meninx
Surround brain – 2 layered sheet of fibrous CT Dura septa –dura matter extends into brain, limit excessive movement of brain Arachnoid Matter Middle meninx Loose brain covering

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

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

Meninges Pia Mater – “gentle matter” Delicate connective tissue
Clings to brain Meningitis – inflammation of meninges Serious threat – can spread to CNS Encephalitis – brain inflammation

Cerebrospinal Fluid CSF – found in and around the brain Liquid cushion
Prevents brain from crushing itself Protects against trauma Watery “broth” similar to blood plasma – less proteins and plasma CSF contains more Na, Cl, and H, and less Ca and K

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

Blood Brain Barrier Protective mechanism that helps maintain a stable environment for brain If brain exposed to chemical variations in blood – neurons would fire uncontrollably Blood born substances must pass through 3 layers before they reach neurons – 1. epithelium of capillary walls 2. relatively thick basal lamina surrounding capillaries 3. bulbous “feet” of astrocytes clinging to capillaries - Barrier is selective – nutrients pass, wastes can not

(a) Astrocytes are the most abundant CNS neuroglia.
Capillary Neuron Astrocyte (a) Astrocytes are the most abundant CNS neuroglia. Figure 11.3a

Homeostatic Imbalances of the Brain
Traumatic brain injuries Concussion—temporary alteration in function Contusion—permanent damage Subdural or subarachnoid hemorrhage—may force brain stem through the foramen magnum, resulting in death Cerebral edema—swelling of the brain associated with traumatic head injury

Cerebrovascular accidents (CVAs)(strokes) Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral artery by a blood clot Typically leads to hemiplegia, or sensory and speed deficits Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia Tissue plasminogen activator (TPA) is the only approved treatment for stroke

Degenerative brain disorders Alzheimer’s disease (AD): a progressive degenerative disease of the brain that results in dementia Parkinson’s disease: degeneration of the dopamine-releasing neurons of the substantia nigra Huntington’s disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex

The Spinal Cord: Embryonic Development
By week 6, there are two clusters of neuroblasts Alar plate—will become interneurons; axons form white matter of cord Basal plate—will become motor neurons; axons will grow to effectors Neural crest cells form the dorsal root ganglia sensory neurons; axons grow into the dorsal aspect of the cord

Dorsal root ganglion: sensory neurons from neural crest
Alar plate: interneurons White matter Basal plate: motor neurons Neural tube cells Central cavity Figure 12.28

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

Spinal Cord: Protection
Denticulate ligaments: extensions of pia mater that secure cord to dura mater Filum terminale: fibrous extension from conus medullaris; anchors the spinal cord to the coccyx

Ligamentum flavum Lumbar puncture needle entering subarachnoid space
Supra- spinous ligament L5 Filum terminale S1 Inter- vertebral disc Cauda equina in subarachnoid space Arachnoid matter Dura mater Figure 12.30

(a) The spinal cord and its nerve roots, with the bony vertebral
Cervical spinal nerves Cervical enlargement Dura and arachnoid mater Thoracic spinal nerves Lumbar enlargement Conus medullaris Lumbar spinal nerves Cauda equina Filum terminale (a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Sacral spinal nerves Figure 12.29a

Spinal Cord Spinal nerves Cervical and lumbar enlargements
31 pairs Cervical and lumbar enlargements The nerves serving the upper and lower limbs emerge here Cauda equina The collection of nerve roots at the inferior end of the vertebral canal

Cross-Sectional Anatomy
Two lengthwise grooves divide cord into right and left halves Ventral (anterior) median fissure Dorsal (posterior) median sulcus Gray commissure—connects masses of gray matter; encloses central canal

(a) Cross section of spinal cord and vertebra
Epidural space (contains fat) Pia mater Arachnoid mater Spinal meninges Subdural space Dura mater Subarachnoid space (contains CSF) Bone of vertebra Dorsal root ganglion Body of vertebra (a) Cross section of spinal cord and vertebra Figure 12.31a

(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

White Matter Consists mostly of ascending (sensory) and descending (motor) tracts Transverse tracts (commissural fibers) cross from one side to the other Tracts are located in three white columns (funiculi on each side—dorsal (posterior), lateral, and ventral (anterior) Each spinal tract is composed of axons with similar functions

Pathway Generalizations
Pathways decussate (cross over) Most consist of two or three neurons (a relay) Most exhibit somatotopy (precise spatial relationships) Pathways are paired symmetrically (one on each side of the spinal cord or brain)

Ventral corticospinal tract Ventral spinothalamic tract
Ascending tracts Descending tracts Fasciculus gracilis Ventral white commissure Dorsal white column Fasciculus cuneatus Lateral reticulospinal tract Dorsal spinocerebellar tract Lateral corticospinal tract Rubrospinal tract Ventral spinocerebellar tract Medial reticulospinal tract Lateral spinothalamic tract Ventral corticospinal tract Ventral spinothalamic tract Vestibulospinal tract Tectospinal tract Figure 12.33

Ascending Pathways Consist of three neurons First-order neuron
Conducts impulses from cutaneous receptors and proprioceptors Branches diffusely as it enters the spinal cord or medulla Synapses with second-order neuron

Ascending Pathways Second-order neuron Interneuron
Cell body in dorsal horn of spinal cord or medullary nuclei Axons extend to thalamus or cerebellum

Ascending Pathways Third-order neuron Interneuron
Cell body in thalamus Axon extends to somatosensory cortex

Ascending Pathways Two pathways transmit somatosensory information to the sensory cortex via the thalamus Dorsal column-medial lemniscal pathways Spinothalamic pathways Spinocerebellar tracts terminate in the cerebellum

Dorsal Column-Medial Lemniscal Pathways
Transmit input to the somatosensory cortex for discriminative touch and vibrations Composed of the paired fasciculus cuneatus and fasciculus gracilis in the spinal cord and the medial lemniscus in the brain (medulla to thalamus)

Medial lemniscus (tract) (axons of second-order neurons)
Dorsal spinocerebellar tract (axons of second-order neurons) Medial lemniscus (tract) (axons of second-order neurons) Nucleus gracilis Nucleus cuneatus Medulla oblongata Fasciculus cuneatus (axon of first-order sensory neuron) Joint stretch receptor (proprioceptor) Axon of first-order neuron Cervical spinal cord Fasciculus gracilis (axon of first-order sensory neuron) Muscle spindle (proprioceptor) Lumbar spinal cord Touch receptor (a) Spinocerebellar pathway Dorsal column–medial lemniscal pathway Figure 12.34a (2 of 2)

Primary somatosensory cortex Axons of third-order neurons Thalamus
Cerebrum Midbrain Cerebellum Pons (a) Spinocerebellar pathway Dorsal column–medial lemniscal pathway Figure 12.34a (1 of 2)

Anterolateral Pathways
Lateral and ventral spinothalamic tracts Transmit pain, temperature, and coarse touch impulses within the lateral spinothalamic tract

Lateral spinothalamic tract (axons of second-order neurons)
Medulla oblongata Pain receptors Cervical spinal cord Axons of first-order neurons Temperature receptors Lumbar spinal cord (b) Spinothalamic pathway Figure 12.34b (2 of 2)

Cerebrum Midbrain Cerebellum Pons (b) Spinothalamic pathway Figure 12.34b (1 of 2)

Spinocerebellar Tracts
Ventral and dorsal tracts Convey information about muscle or tendon stretch to the cerebellum

Medial lemniscus (tract) (axons of second-order neurons)
Dorsal spinocerebellar tract (axons of second-order neurons) Medial lemniscus (tract) (axons of second-order neurons) Nucleus gracilis Nucleus cuneatus Medulla oblongata Fasciculus cuneatus (axon of first-order sensory neuron) Joint stretch receptor (proprioceptor) Axon of first-order neuron Cervical spinal cord Fasciculus gracilis (axon of first-order sensory neuron) Muscle spindle (proprioceptor) Lumbar spinal cord Touch receptor (a) Spinocerebellar pathway Dorsal column–medial lemniscal pathway Figure 12.34a (2 of 2)

Cerebrum Midbrain Cerebellum Pons (a) Spinocerebellar pathway Dorsal column–medial lemniscal pathway Figure 12.34a (1 of 2)

Descending Pathways and Tracts
Deliver efferent impulses from the brain to the spinal cord Direct pathways—pyramidal tracts Indirect pathways—all others

Descending Pathways and Tracts
Involve two neurons: Upper motor neurons Pyramidal cells in primary motor cortex Lower motor neurons Ventral horn motor neurons Innervate skeletal muscles

The Direct (Pyramidal) System
Impulses from pyramidal neurons in the precentral gyri pass through the pyramidal (corticospinal)l tracts Axons synapse with interneurons or ventral horn motor neurons The direct pathway regulates fast and fine (skilled) movements

Pyramidal cells (upper motor neurons) Primary motor cortex
Internal capsule Cerebrum Midbrain Cerebral peduncle Cerebellum Pons (a) Pyramidal (lateral and ventral corticospinal) pathways Figure 12.35a (1 of 2)

Ventral corticospinal tract Pyramids Decussation of pyramid Lateral
Medulla oblongata Pyramids Decussation of pyramid Lateral corticospinal tract Cervical spinal cord Skeletal muscle Lumbar spinal cord Somatic motor neurons (lower motor neurons) (a) Pyramidal (lateral and ventral corticospinal) pathways Figure 12.35a (2 of 2)

Indirect (Extrapyramidal) System
Includes the brain stem motor nuclei, and all motor pathways except pyramidal pathways Also called the multineuronal pathways

These pathways are complex and multisynaptic, and regulate: Axial muscles that maintain balance and posture Muscles controlling coarse movements Head, neck, and eye movements that follow objects

Reticulospinal and vestibulospinal tracts—maintain balance Rubrospinal tracts—control flexor muscles Superior colliculi and tectospinal tracts mediate head movements in response to visual stimuli

Red nucleus Cerebrum Midbrain Cerebellum Pons (b) Rubrospinal tract
Figure 12.35b (1 of 2)

Rubrospinal tract Medulla oblongata Cervical spinal cord (b)
Figure 12.35b (2 of 2)

Spinal Cord Trauma Functional losses Parasthesias Paralysis
Sensory loss Paralysis Loss of motor function

Spinal Cord Trauma Flaccid paralysis—severe damage to the ventral root or ventral horn cells Impulses do not reach muscles; there is no voluntary or involuntary control of muscles Muscles atrophy

Spinal Cord Trauma Spastic paralysis—damage to upper motor neurons of the primary motor cortex Spinal neurons remain intact; muscles are stimulated by reflex activity No voluntary control of muscles

Spinal Cord Trauma Transection
Cross sectioning of the spinal cord at any level Results in total motor and sensory loss in regions inferior to the cut Paraplegia—transection between T1 and L1 Quadriplegia—transection in the cervical region

Poliomyelitis Destruction of the ventral horn motor neurons by the poliovirus Muscles atrophy Death may occur due to paralysis of respiratory muscles or cardiac arrest Survivors often develop postpolio syndrome many years later, as neurons are lost

Amyotrophic Lateral Sclerosis (ALS)
Also called Lou Gehrig’s disease Involves progressive destruction of ventral horn motor neurons and fibers of the pyramidal tract Symptoms—loss of the ability to speak, swallow, and breathe Death typically occurs within five years Linked to glutamate excitotoxicity, attack by the immune system, or both

Developmental Aspects of the CNS
CNS is established during the first month of development Gender-specific areas appear in both brain and spinal cord, depending on presence or absence of fetal testosterone Maternal exposure to radiation, drugs (e.g., alcohol and opiates), or infection can harm the developing CNS Smoking decreases oxygen in the blood, which can lead to neuron death and fetal brain damage

The hypothalamus is one of the last areas of the CNS to develop Visual cortex develops slowly over the first 11 weeks Neuromuscular coordination progresses in superior-to-inferior and proximal-to-distal directions along with myelination

Age brings some cognitive declines, but these are not significant in healthy individuals until they reach their 80s Shrinkage of brain accelerates in old age Excessive use of alcohol causes signs of senility unrelated to the aging process

Chapter 12: The Central Nervous System

Similar presentations

Presentation on theme: "Chapter 12: The Central Nervous System"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Chapter 12: The Central Nervous System

Similar presentations

Presentation on theme: "Chapter 12: The Central Nervous System"— Presentation transcript:

Similar presentations

About project

Feedback