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Central Nervous System, Central Nervous System, Spinal Nerves, And Cranial Spinal Nerves, And Cranial

NervesNerves

Central Nervous System, Central Nervous System, Spinal Nerves, And Cranial Spinal Nerves, And Cranial

NervesNerves

Chapter 10

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Spinal Cord StructureSpinal Cord StructureProtection and CoveringsProtection and CoveringsSpinal Cord StructureSpinal Cord Structure

Protection and CoveringsProtection and Coverings

• Spinal cord in vertebral cavity-

Surrounded by bone• Wrapped in meninges-

3 layers of connective tissue

•Spinal cord meninges are continuous with brain meninges

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Spinal MeningesSpinal MeningesSpinal MeningesSpinal Meninges

• Epidural space lined with fat• Dura mater- tough ,dense connective

tissueExtends to 2nd sacral vertebra Well beyond spinal cord

• Arachnoid mater- collagen and elastic fibers

• Subarachnoid space- cerebral spinal fluid circulates in this space

• Pia mater- transparent layer adheres to surface of brain & spinal cordContains blood vessels

Figure 10.1

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Gross Anatomy Of Spinal Gross Anatomy Of Spinal CordCord

Gross Anatomy Of Spinal Gross Anatomy Of Spinal CordCord

• runs to 2nd lumbar vertebra• Roots of spinal nerves for lumbar,

sacral & coccygeal nerves in vertebral cavity before leaving = Cauda Equina

• Enlargements: cervical & lumbarInclude nerves for upper & lower limbs

• Each spinal segment gives rise to a spinal nerve – 31 pairs

Figure 10.2

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Internal Structure Of Spinal Internal Structure Of Spinal CordCord

Internal Structure Of Spinal Internal Structure Of Spinal CordCord

• Two grooves- left & right halvesAnterior median fissure & posterior median sulcus

• Gray matter- 3 horns on each sideAnterior, posterior, lateral

•Anterior- somatic motor neurons•Posterior- sensory neurons•Lateral- autonomic motor

neurons

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Internal Structure Of Spinal Internal Structure Of Spinal Cord (cont)Cord (cont)

Internal Structure Of Spinal Internal Structure Of Spinal Cord (cont)Cord (cont)

• White matter- organized into columnsAnterior, posterior & lateral white

columns

• Each column contains one or more tracts having a common destination

• Sensory = ascending tractsCarry information toward brain

• Motor = descending tractsCarry information down spinal cord

Figure 10.3

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Spinal NervesSpinal NervesSpinal NervesSpinal Nerves

• Serve particular area of body• Contain 2 bundles of axons = roots• Dorsal root- only sensory axons• Swelling called dorsal root ganglion

Contains Cell bodies of sensory neurons

• Ventral root- axons of somatic & autonomic motor neurons

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Spinal Nerves (cont)Spinal Nerves (cont)Spinal Nerves (cont)Spinal Nerves (cont)

• Named and numbered according to level of vertebra they emerge from

• C1-8, T1-12, L1-5, S1-5 & 1 coccygeal

• C1 from above atlas• Rest through intervertebral

foramina

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Spinal Nerve Spinal Nerve CompositionCompositionSpinal Nerve Spinal Nerve CompositionComposition

• Roots unite to form nerve at foramina

• Mixed sensory & motor axons• Each axon wrapped in

endoneurium• Axons grouped in fascicles

wrapped in perineurium• Outer covering = epineurium

Figure 10.4

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Distribution Of Spinal Distribution Of Spinal NervesNerves

Distribution Of Spinal Distribution Of Spinal NervesNerves

• After leaving vertebra nerves branch• Some join with axons from

neighboring nerves to form plexuses• Names then relate to area they are in

or region innervated• Spinal nerves T2-T11 do not form

plexuses= intercostal nervesSupply abdominal muscles, skin of chest

& back and muscles between robs.

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PlexusesPlexusesPlexusesPlexuses

• Cervical plexus- posterior head, neck, shoulders & diaphragm

• Brachial plexus-upper limbs & some neck & shoulder muscles

• Lumbar plexus- abdominal wall, external genitals & part of lower limbse.g. ilioinguinal, femoral, obdurator nerves

• Sacral plexus- buttocks, perineum & lower limbse.g. Gluteal, sciatic & pudendal nerves

Figure 10.2

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Spinal Cord FunctionsSpinal Cord FunctionsSpinal Cord FunctionsSpinal Cord Functions

• Routes signals along pathways• Gray matter integrates signals • Reflex = fast involuntary sequence

of actions in response to a stimulus• Inborn reflex e.g. withdrawal reflex• Can also have learned reflexes,

e.g. driving skills

• Can be spinal or cranial integration

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Reflex arc (patellar Reflex arc (patellar reflex)reflex)

Reflex arc (patellar Reflex arc (patellar reflex)reflex)

1. Sensory receptor- responds to stimulusTap below patella

2. Sensory neuron- to dorsal horn & brain3. Integrating center- e.g. single synapse

Sensory to motor neurons

4. Motor neuron- from center to effectorVia ventral horn

5. Effector- responder (muscle or gland)Patellar reflex- rectus femoris contracts

Figure 10.5

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Brain-major partsBrain-major partsBrain-major partsBrain-major parts

• Brain stem- continuous with spinal cordMedulla oblongata, pons, midbrain

• Diencephalon- above brain stemThalamus, hypothalamus & pineal gland

• Cerebrum- at top and largest partSurface covered with gray matter- cortexBeneath is cerebral white matter

• Cerebellum- back of brain stemMeans “little brain”

• Cranial meninges- dura mater, arachnoid mater & pia mater

Figure 10.6a

Figure 10.6b

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Brain blood supplyBrain blood supplyBrain blood supplyBrain blood supply

• Requires ~20% body’s oxygen supply4 min lack => permanent damage

• Requires continuous glucose supply• Protected by Blood-brain barrier

Allows lipid soluble materials: O2, CO2, alcohol, anesthetic agents but controls entry of other materials

• Created by tight capillaries and glial cells

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Cerebral Spinal Fluid Cerebral Spinal Fluid (CSF)(CSF)

Cerebral Spinal Fluid Cerebral Spinal Fluid (CSF)(CSF)

• Circulates through ventricles of brain and the subarachnoid space.

• 4 ventricles: 2 lateral, third & fourth• Formed in choroid plexuses

= Specialized capillary networks in wall of ventricles covered by ependymal cells

• Flows through ventricles then from 4th to central canal of spinal cord & subarachnoid cellsReabsorbed through arachnoid villi into

superior saggital sinus

Figure 10.7

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Brain Stem- MedullaBrain Stem- MedullaBrain Stem- MedullaBrain Stem- Medulla

• Medulla Oblongata- inferior part of brainstemwhite matter extending between spinal

cord & other parts of brain• several nuclei: cardiovascular

center (heart rate)

• Medullary rhythmicity area (respiratory rhythm)

• Other sensory & reflex motor areasSome related to cranial nerves

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Brain Stem- PonsBrain Stem- PonsBrain Stem- PonsBrain Stem- Pons

• Pons (bridge)- nuclei & tractsConnect left & right of cerebellum

• Ascending & descending tracts• Nuclei – motor relays from

cerebrum to cerebellum , respiration & cranial nerves V, VI, VII, VIII

Figure 10.8

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Brain Stem- MidbrainBrain Stem- MidbrainBrain Stem- MidbrainBrain Stem- Midbrain

• Connects pons to DiencephalonLarge tracts = cerebral peduncles

(motor)• Nuclei = substantia nigra, red

nuclei, cranial nerves III & IV• Superior colliculi – nuclei

involved in tracking visual stimuli• Inferior colliculi – auditory input

& startle reflex

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Reticular formationReticular formationReticular formationReticular formation

• Netlike arrangement of gray and white mater

• Ascending part = Reticular Activating System (RAS)

• Projects to cerebral cortex & helps maintain consciousness

• Inactivation => sleep

Figure 10.9

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DiencephalonDiencephalonDiencephalonDiencephalon

• Thalamus- critical relay for sensory inputTransmits motor information from cerebellum &

basal nuclei to cerebrum

• Hypothalamus- important for homeostasisControl of ANS-regulation of many activitiesControl of pituitary and hormone productionRegulation of emotional & behavior patternsRegulation of eating & drinkingControl of body temperatureRegulation of circadian rhythms & states of

consciousness

• Pineal gland- secretes melatonin

Figure 10.10

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CerebellumCerebellumCerebellumCerebellum

• Two cerebellar hemispheresPosterior to medulla and pons,

below cerebrum

• Cerebellar cortex –gray matter• Tree like white matter & nuclei• Attached to brain stem via

cerebellar peduncles

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Cerebellar functionCerebellar functionCerebellar functionCerebellar function

• Gets wide range of sensory input• Compares with programmed motor

activity from cerebral cortex• Smoothes & coordinates complex

activities• Regulates posture & balance• Required for skilled motor activities

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Cerebrum- StructureCerebrum- StructureCerebrum- StructureCerebrum- Structure

• Cerebral cortex• Internal white mater• Deep gray nuclei• Surface folds = gyri• Grooves between = sulci•Longitudinal Fissure- divides

it into left & right hemispheres• Connected by corpus collosum

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Cerebrum- Structure Cerebrum- Structure (cont)(cont)

Cerebrum- Structure Cerebrum- Structure (cont)(cont)

• Each hemisphere has 4 lobesFrontal, parietal, temporal, occipital

• Central sulcus separates frontal & parietalPrecentral gyrus anterior to sulcus= primary

motor areaPostcentral gyrus = primary sensory area

• Deep gray = basal nuclei (basal ganglia)Globus palladus, putamen, caudate

nucleus

Figure 10.11a

Figure 10.11b

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Limbic SystemLimbic SystemLimbic SystemLimbic System

• Ring of structures on inner border of cerebrum and floor of diencephalon

• “emotional brain” – pain , pleasure, anger, affection, docility

• Involuntary activity related to survival

• Important in memory development

Figure 10.12

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Function areas of CortexFunction areas of CortexFunction areas of CortexFunction areas of Cortex

• Specialized areas anatomically located

•Sensory areas receive input and responsible for perception

•Motor areas- initiate movements

•Associative areas- complex integration: e.g. memory, emotion, reasoning, etc.

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Sensory AreasSensory AreasSensory AreasSensory Areas

• Primary somatosensory area- postcentral gyrus.input includes: touch, proprioception, pain,

itching, tickle, temperature • Primary visual area- occipital lobe• Primary auditory area- temporal

lobe• Primary gustatory area – base of

postcentral gyrus• Primary olfactory area- medial

aspect of temporal lobe

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Motor AreasMotor AreasMotor AreasMotor Areas

• Mainly from anterior part of hemisphere

• Primary motor area- precentral gyrus

• Broca’s speech area- interacts with premotor area &

primary motor area to regulate breathing and speech muscles

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Association AreasAssociation AreasAssociation AreasAssociation Areas

• Adjacent to sensory & motor areas• connected with tracts- interpret

information• E.g. somatosensory association area

Posterior to primary somatosensory areaIntegrates sensation- exact shape & texture

of object compares with stored memories• Wernike’s area- left temporal &

parietal lobesInterprets meaning of speechRight hemisphere adds emotional content

Figure 10.13

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Sensory PathwaysSensory PathwaysSensory PathwaysSensory Pathways

• Relay information from periphery to cerebral cortex

• 3 neurons in each pathway.• Posterior column- medial

lemniscus pathwayFine touch- body location, texture, sizeProprioception- position & motion of body

partsVibratory sensations- fluctuating touch

stimuli

Figure 10.14a

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Sensory Pathways (cont)Sensory Pathways (cont)Sensory Pathways (cont)Sensory Pathways (cont)

•Spinothalamic pathways-• anterior & lateral spinothalamic

tracts• Relay impulses for pain, tickle,

itch & thermal sensations.

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Somatic Motor PathwaysSomatic Motor PathwaysSomatic Motor PathwaysSomatic Motor Pathways

• Signals converge on lower motor neurons

• Lower motor neurons stimulate muscles directly

• Input comes from:Local interneurons- e.g. reflexesUpper motor neurons- corticospinal tractsBasal ganglia- help with muscle toneCerebellum- coordination

Figure 10.15

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LateralizationLateralizationLateralizationLateralization

• Left gets input from & sends output to right side of body and vice versa

•Left important for spoken & written language, numerical & scientific skills & reasoning

•Right more involved with spatial and pattern recognition and emotional content

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MemoryMemoryMemoryMemory

• Process for storing & retrieving information

• Involves structural & functional changes

• Involves association areas, parts of limbic system & diencephalon

• Skill memory also involves cerebellum & basal ganglia

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Cranial NervesCranial Nerves (table 10.2) (table 10.2)Cranial NervesCranial Nerves (table 10.2) (table 10.2)

• I Olfactory- special sensory• II optic- special sensory -eye• III oculomotor-Motor eye• IV trochlear- motor eye• V trigeminal- Mixed

sensory around eyes & upper mouth motor to chewing

• VI abducens- motor eye• VII facial- mixed

sensory to front of tongue & motor to facial expression, lacrimal and some salivary glands

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Cranial NervesCranial NervesCranial NervesCranial Nerves

• VIII vestibulocochlear- special senses- ear• IX glossopharyngeal-mixed

Sensory for rest of tongue, pharynx & palate, blood pressure

Motor to pharyngeal muscles, parotid salivary gland

• X vagus-mixed (major visceral nerve)Sensory from pharynx, ear, diaphragm, visceral

organs in ventral cavityMotor to palatal & pharyngeal muscles & organs in

ventral cavity

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Cranial Nerves (Cont.)Cranial Nerves (Cont.)Cranial Nerves (Cont.)Cranial Nerves (Cont.)

• XI Accessory-Motor to voluntary muscles including sternocleidomastoid and trapezius

• XII hypoglossal.- motor to tongue

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AgingAgingAgingAging

• Rapid growth during first few years• Size of neurons & proliferation of

neuroglia• Increases development of

dendritic branches & synaptic contacts

• Decline in brain mass from early adulthood on