Chapter 12: The Central Nervous System

Transcript 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

1. 3 week embryo- ectoderm thickens along dorsal midline of body = neural plate 2. Neural tube invaginates – forms groove flanked by neural folds 3. Groove deepens – superior ridges fuse forming neural tube – detached from ectoderm and sinks into a deeper position 4. Neural tube differentiates into CNS – brain anterior and spinal cord - caudal

Embryonic Development

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  (hindbrain) telencephalon (endbrain) + diencephalon - Hindbrain constricts – metencephalon “afterbrain” - Metencephalon – “spinal brain”

Embryonic Development

• • • • • 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

Head Tail 1 The neural plate forms from surface ectoderm.

Neural plate Surface ectoderm Figure 12.1, step 1

2 The neural plate invaginates, forming the neural groove, flanked by neural folds.

Neural folds Neural groove 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

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

Neural

tube

Figure 12.1, step 4

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

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

Regions of Brain

1. Cerebral Hemispheres 2. Diencephalon 3. Brain stem (pons, midbrain, and medulla)

Central cavity Cortex of gray matter Migratory Inner gray pattern of matter neurons Cerebrum Outer white Cerebellum matter Region of cerebellum Gray matter Central cavity Inner gray matter Outer white matter Brain stem Gray matter 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 Lateral aperture Interventricular foramen Third ventricle Inferior horn Cerebral aqueduct Fourth ventricle Central canal (a) Anterior view Median aperture Lateral aperture (b) Left lateral view Figure 12.5

Lateral Ventricles

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

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 – 5 th its floor lobe – deep in lateral sulcus – forms

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

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

Anterior

Longitudinal fissure Cerebral veins and arteries covered by arachnoid mater Left cerebral hemisphere (c)

Posterior

Frontal lobe Parietal lobe Right cerebral hemisphere Occipital lobe Figure 12.6c

Brain stem (d) Left cerebral hemisphere Transverse cerebral fissure Cerebellum 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 – – 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

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

Motor map in precentral gyrus

Posterior

Motor

Anterior

Jaw Tongue Swallowing Primary motor cortex (precentral gyrus) Toes 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

• 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 Anterior

Sensory Sensory map in postcentral gyrus Genitals Primary somato sensory 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 Anterior

Sensory Sensory map in postcentral gyrus Genitals Primary somato sensory 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

Multimodal Association Areas

• • • • 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

Multimodal Association Areas

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

Multimodal Association Areas

• • • • • 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

Longitudinal fissure Lateral ventricle Basal nuclei • Caudate • Putamen • Globus pallidus Thalamus Third ventricle Pons Medulla oblongata (a)

Superior

Commissural fibers (corpus callosum) Association fibers Corona radiata Fornix Internal capsule Gray matter White matter Projection fibers Decussation of pyramids 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 Corpus striatum Lentiform nucleus • Putamen • Globus pallidus (deep to putamen) (a) Projection fibers run deep to lentiform nucleus Thalamus Tail of caudate nucleus Figure 12.11a

Diencephalon

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

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

Diencephalon - Thalamus

• • • • • • Bilateral egg shaped nuclei Superolateral walls of 3 rd 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 3 rd ventricle Extends from optic chiasma to mammillary bodies Infundibulum – stalk of hypothalamic tissue connects pituitary Main visceral controlling center of body

Diencephalon - Hypothalamus

• Homeostatic roles – 1. Autonomic Control Center – influences BP, rate and force of heart beat, digestive tract motility, pupil size, etc.

2. Emotional response – perception of pleasure, fear, and rage, biological rhythms and drives 3. Body temperature – monitor blood temperature and other thermoreceptors 4. Food Intake – hunger and satiety in response to changing blood levels 5. Water balance and thirst – osmoreceptors, ADH 6. Sleep – wake Cycles 7. Endocrine System functioning – releasing and inhibiting hormones

Diencephalon - Hypothalamus

• • • 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 3 rd ventricle Pineal gland – secrets hormone melanin – sleep signal and antioxidant

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

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

Pons

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

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

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

Cerebellar peduncles • Superior • Middle • Inferior Medulla oblongata (b) Anterior lobe Cerebellar cortex Arbor vitae Flocculonodular lobe Posterior lobe Choroid plexus of fourth ventricle 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 1. Cerebral cortex motor areas notify cerebellum of intent to initiate voluntary muscle control 2. Receives info from proprioceptors throughout the body – body position and momentum 3. Cerebellar cortex – calculated best way to coordinate force, direction, and extent 4. 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 1.

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

1. 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

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 – 1. Simultaneous activity of large areas of cerebral cortex 2. It is superimposed on other types of neural activity 3. 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 1. Non-rapid eye movement (NREM) 2. Rapid Eye movement (REM) - Defined by EEG patterns

Sleep

• • • •

1 st

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 (a) Typical EEG patterns 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: occur.

EEG is dominated by delta waves; arousal is difficult; bed-wetting, night terrors, and sleepwalking may 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 1 st REM – 5-10 minutes long Final REM – 20 -50 minutes long • Wake – hypothermic neurons release peptides (exins) “wakeup” chemical

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 – 1. Broca’s area – can’t speak, but can understand 2. 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 1. 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 -

1. 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 Automatic memory Data selected for transfer Short-term memory (STM) Forget Forget Retrieval Long-term memory (LTM) Data transfer influenced by: Excitement Rehearsal Association of old and new data 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

Superior sagittal sinus Subdural space Subarachnoid space Skin of scalp Periosteum Bone of skull Periosteal Meningeal Dura mater Arachnoid mater Pia mater Arachnoid villus Blood vessel 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

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

Superior sagittal sinus Choroid plexus Interventricular foramen 3 Third ventricle Cerebral aqueduct Lateral aperture Fourth ventricle Median aperture Central canal of spinal cord (a) CSF circulation 4 1 Arachnoid villus 2 Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle 1 CSF is produced by the choroid plexus of each ventricle. 2 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.

3 CSF flows through the subarachnoid space. 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi. 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

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

Homeostatic Imbalances of the Brain

• 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

Homeostatic Imbalances of the Brain

• 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

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

Spinal Cord

• • Location – Begins at the foramen magnum – Ends as conus medullaris at L 1 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

T 12 L 5 L 4 L 5 Inter vertebral disc S 1 Arachnoid matter Ligamentum flavum Lumbar puncture needle entering subarachnoid space Supra spinous ligament Filum terminale Dura mater Cauda equina in subarachnoid space Figure 12.30

Cervical enlargement Dura and arachnoid mater Lumbar enlargement Conus medullaris Cauda equina Filum (a) The spinal cord and its nerve roots, with the bony vertebral and arachnoid mater are cut open and reflected laterally.

terminale arches removed. The dura mater Cervical spinal nerves Thoracic spinal nerves Lumbar spinal nerves Sacral spinal nerves Figure 12.29a

Spinal Cord

• • • Spinal nerves – 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

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

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

Ascending tracts Dorsal white column Fasciculus gracilis Fasciculus cuneatus Dorsal spinocerebellar tract Ventral spinocerebellar tract Lateral spinothalamic tract Ventral spinothalamic tract Descending tracts Ventral white commissure Lateral reticulospinal tract Lateral corticospinal tract Rubrospinal tract Medial reticulospinal tract Ventral corticospinal 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)

Dorsal tract (axons of second-order neurons) Axon of first-order neuron Muscle spindle (proprioceptor) (a) 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)

Cervical spinal cord

Fasciculus gracilis (axon of first-order sensory neuron)

Lumbar spinal cord

Touch receptor Figure 12.34a (2 of 2)

(a) Primary somatosensory cortex Axons of third-order neurons Thalamus

Cerebrum Midbrain Cerebellum Pons

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

Medulla oblongata

Lateral spinothalamic tract (axons of second-order neurons) Pain receptors

Cervical spinal cord Lumbar spinal cord

(b) Spinothalamic pathway Axons of first-order neurons Temperature receptors Figure 12.34b (2 of 2)

Primary somatosensory cortex Axons of third-order neurons Thalamus

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

Medulla oblongata

Fasciculus cuneatus (axon of first-order sensory neuron) Joint stretch receptor (proprioceptor)

Cervical spinal cord

Fasciculus gracilis (axon of first-order sensory neuron)

Lumbar spinal cord

Touch receptor Figure 12.34a (2 of 2)

(a) Primary somatosensory cortex Axons of third-order neurons Thalamus

Cerebrum Midbrain Cerebellum Pons

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: 1. Upper motor neurons • Pyramidal cells in primary motor cortex 2. 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 corticospinal tract Skeletal muscle

Medulla oblongata Cervical spinal cord Lumbar spinal cord

(a) Somatic motor neurons (lower motor neurons) 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

Indirect (Extrapyramidal) System

• 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

Indirect (Extrapyramidal) System

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

Cerebrum Midbrain

Red nucleus

Cerebellum Pons

(b) Rubrospinal tract Figure 12.35b (1 of 2)

Rubrospinal tract

Medulla oblongata Cervical spinal cord

(b) Rubrospinal tract Figure 12.35b (2 of 2)

Spinal Cord Trauma

• Functional losses – Parasthesias • 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 T 1 and L 1 – 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

Developmental Aspects of the CNS

• • • 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

Developmental Aspects of the CNS

• • • 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