1

Chapter 11

Nervous System II

Nervous System ReviewCentral Nervous System

• brain & spinal cord

Peripheral Nervous System

• contains nerves connecting CNS to all other body parts

• Cranial nerves arising from the brain

• Spinal nerves arising from the spinal cord

• ÷÷÷÷ into somatic & autonomic nervous systems• Somatic fibers connect to skin & skeletal muscles & control conscious activities; voluntary • Autonomic fibers connect to viscera, glands & control subconscious activities; involuntary

Central Nervous System

Brain and spinal cord

2

Central Nervous System

• Brain & spinal cord connected by brainstem

Spinal Cord

2 way communication

between CNS & PNS

Protected by vertebral

column

Brain

Largest, most complex

part of nervous system

Consist of 2 hemispheres,

diencephalon, cerebellum & brainstem

Protected by cranium

• Membranes surrounding & protecting CNS• 3 layers

• dura mater – tough, outer CT attached to periosteum. Contain many blood vessels & nerves.• arachnoid mater – middle, web-like membrane w/out blood vessels• pia mater – inner, delicate membrane w/ many nerves & blood vessels to nourish cells of CNS; a band of pia mater called the denticulate ligamentattaches dura mater to spinal cord

• subarachnoid space between arachnoid & pia contains cerebrospinal fluid (CSF)

Meninges

3

Ventricles

• interconnected cavities within cerebral hemispheres & brain stem

• continuous with central canal of spinal cord• filled with cerebrospinal fluid (CSF)

� lateral ventricles – largest; ventricles 1 & 2� third ventricle – w/in midline of brain� fourth ventricle – w/in brainstem, in front of cerebellum� cerebral aqueduct – connects 3rd & 4th ventricles� interventricular foramen – connects laterals & 3rd

ventricle

4

Cerebrospinal Fluid• secreted by choroid plexus located in pia mater• circulates in ventricles, central canal of spinal

cord, & subarachnoid space• completely surrounds brain and spinal cord• clear nutritive liquid

• mechanical protection (cushions)• helps maintain stable ion conc. in CNS• reabsorbed into blood stream by arachnoid

granulations• ventricles lined w/ cilia from ependymal cells; cilia aids in movement of CSF; ependymal cells regulate

composition of CSF (selective)

FYI

• Meningitis – inflammation of meninges; (pia

& arachnoid are most common)

• Subdural hematoma – accumulation of blood between dura mater & arachnoid space

• Spinal tap – measures CSF pressure

• Hydrocephalus - ↑ CSF pressure w/in

brain; developing cranial sutures allow

excess swelling. Shunt drains excess fluid away

• Continuous nerve tissue from brain thru vertebral column

• 31 segments starting w/ foramen magnum

• Cervical enlargement – nerves to upper limbs

• Lumbar enlargement – nerves to lower limbs

• Conus medullaris – tapered area below lumbar E.

• Filum terminale – distal portion of tail; thin cord of

CT

• Cauda equina – area below conus medullaris; consist of spinal nerves & filum terminale

Spinal Cord Structure

5

Spinal Cord Structure• foramen magnum to 2nd lumbar vertebra

• Cross section resembles butterfly (gray mater) surrounded by white mater

• Cross section shows spinal cord ÷÷÷÷ by 2 grooves– Anterior median fissure

– Posterior median sulcus

• Gray matter– Posterior horns – upper wing

– Anterior horns – lower wing

– Lateral horns – side protrusion

• Gray commissure – area surrounding central canal; connects R & L wings

• Central canal – lined w/ependymal cells; contains CSF

Spinal Cord Structure

Cross Section of Spinal Cord

6

• White matter – 3 areas surrounding gray

matter

– Anterior funiculi (ventral)

– Posterior funiculi (dorsal)

– Lateral funiculi

• Ventral root

• Dorsal root

– Dorsal root ganglion – a bundle of cell bodies outside CNS

– Fusion of dorsal & ventral root forms spinal nerve that passes thru intervertebral foramen

Spinal Cord Structure

Cross Section of Spinal Cord

Spinal Cord Functions

•Center for spinal reflexes

•Carries nerve impulses to & from brain

7

Reflex Arcs

•Reflexes – automatic, subconscious

responses to stimuli. Helps maintain homeostasis

•Consist of receptors, sensory neurons,

interneurons, motor neurons & effectors•Examples

– sneezing, blinking, knee jerk, withdrawal

Withdrawal Reflex

Protective

8

Tracts of the Spinal Cord

• Ascending tracts conduct sensory impulses

(afferent) to brain

• Descending tracts conduct motor impulses

(efferent) from brain to motor neurons reaching

muscles & glands• Provides a 2-way communication

• Located in white matter

BrainFunctions

• interprets sensations

• determines perception• stores memory• reasoning

• makes decisions• coordinates muscular

movements

• regulates visceral activities• determines personality

• controls emotions

Major Parts• cerebrum

• 2 hemispheres• diencephalon• brain stem

• cerebellum

Cerebrum

• Largest part of brain

• Develops from forebrain

• Consist of 2 hemispheres

9

Structure of Cerebrum• corpus callosum

• nerve fibers connecting hemispheres

• convolutions or gyri

• ridges caused by infolding

• sulci -shallow grooves• fissure – deep grooves• longitudinal fissure

• separates hemispheres

• transverse fissure• separates cerebrum from cerebellum

Lobes of CerebrumEach hemisphere is ÷÷÷÷ into lobes named after bones covering them

• Frontal

• Parietal

• Temporal

• Occipital

• Insula – lobe located w/in lateral sulcus; covered by frontal,

parietal & temporal lobes

Functions of Cerebrum

• interpretation

• initiating voluntary movements• storing & retrieving memory

• reasoning

• intelligence• personality

10

Functional Regions of Cerebral Cortex

Cerebral Cortex – thin layer of gray matter on surface of cerebrum;

Divided into motor, sensory & association areas

Motor Areas• Primary Motor Areas

• frontal lobes;anterior to central sulcus• controls voluntary muscles; skeletal

• Broca’s Area• anterior to motor area• left hemisphere• controls muscles needed for speech

• Frontal Eye Field• above Broca’s area• controls voluntary movements of eyes & eyelids

Sensory Areas

• Visual Area• occipital lobe• interprets vision

• Auditory Area• temporal lobe• interprets hearing

Sensory fibers cross over; R hemisphere interprets info from L hemisphere• Sensory Area

• parietal lobe; posterior to central sulcus• interprets sensations on skin

11

Association Areas• regions of cortex that are not primary motor or sensory areas• analyze & interpret sensory experiences• provide memory, reasoning, verbalization, judgment, emotions

Frontal Lobe Association Areas• concentrating• planning• problem solving• consequences of behavior

Association AreasParietal Lobe

• understanding speech• word expression• feelings

Temporal Lobe• remember visual scenes, music & complex patterns

Occipital Lobe• analyze visual patterns &recognition

Hemisphere Dominance• both analyze impulses & send impulses to opposite side of body

• in over 90% of population, left hemisphere is dominant in right handed people

• In most Left hemisphere controls

• speech• writing• reading• verbal skills• computational skills

• Nondominant hemisphere controls

• nonverbal tasks• motor tasks• provides emotions

12

Memory

Short Term• working memory

• closed circuit• circuit is stimulated over and

over• when impulse flow stops, memory

disappears

Long Term• repeated stimulation

changes neuron structure • strengthens

synaptic transmission

Consequences of learning & being able to access it later

Basal Nuclei

• basal ganglia • masses of gray matter

deep within cerebral hemispheres• forms from forebrain

• known as caudate nucleus, putamen, & globus pallidus

• produce dopamine• control certain motor activities

Diencephalon• between cerebral hemispheres & brainstem• surrounds 3rd ventricle• mostly gray matter• contains the following

– thalamus– hypothalamus– optic tracts– optic chiasm– infundibulum– posterior pituitary– mammillary bodies– pineal gland

13

DiencephalonThalamus

• receives & directs sensory impulses to appropriate part of cerebral cortex for interpretation

Hypothalamus• maintains homeostasis by regulating visceral activities • links nervous & endocrine systems

Limbic System

• Located in diencephalon

• Functions

• controls emotions• produces feelings • recognizes life threating condition

Brainstem

• Consist of midbrain, pons, medulla

oblongata

• Attaches brain to spinal cord

14

Midbrain

• between diencephalon & pons

• contains bundles of fibers that join brainstem & spinal cord w/ higher brain• contains gray matter that acts as reflex centers

• cerebral aqueduct – connects 3rd & 4th ventricles• cerebral peduncles – bundles of nerve fibers• corpora quadrigemina – 4 dome protrusions that

are centers for visual & auditory reflexes

Brainstem

Pons• rounded bulge on underside of brainstem• between medulla oblongata & midbrain

• regulate rate & depth of breathing

15

Medulla Oblongata• enlarged continuation of spinal cord• conducts ascending & descending impulses between brain and spinal cord• contains cardiac, vasomotor, & respiratory control centers• contains various nonvital reflex control centers (coughing, sneezing, swallowing & vomiting)

Reticular Formation• network of nerve fibers w/in brain stem• connects to hypothalamus, basal nuclei, cerebellum, & cerebrum• filters incoming sensory information • arouses cerebral cortex into state of wakefulness• injury causes unconsciousness

Types of SleepSlow Wave

• person is tired• decreasing activity of reticular formation• restful• dreamless• reduced blood pressure & respiratory rate• ranges from light to heavy• alternates with REM sleep• between 70-90 minutes

Rapid Eye Movement (REM)• some areas of brain active• heart and respiratory rates irregular• dreaming occurs• 5-15 minutes

16

Sleep Disorders

• Insomnia – inability to sleep

• Narcolepsy – extreme daytime sleepiness

• Sleep apnea – upper airway collapses during sleep; blocks breathing; snoring

• Parasomnias – sleep walking & sleep talking

• Restless leg syndrome – repetitive leg jerks;

leg pain at night

• Sleep paralysis – inability to move a few

minutes after waking

Cerebellum• 2 hemispheres inferior to occipital lobes• posterior to pons & medulla oblongata• vermis connects hemispheres• cerebellar cortex – gray matter• arbor vitae – white matter• cerebellar peduncles – allows communication between other parts of CNS• coordinates skeletal muscle activity• maintains posture

Peripheral Nervous System

• Nerves that branch from CNS and connect

to other body parts

17

Structure of Peripheral Nerve

• CT surrounding bundles of nerve fibers

• Epineurium – outer most layer

• Perineurium – surrounds each fascicle

•Endoneurium –

surrounds each axon

•Blood vessels located in

epineurium & perineurium

Nerve Fiber Classification

• Sensory Nerves – conduct impulses to CNS• Motor Nerves – conduct impulses from CNS to

muscles & glands• Mixed Nerves – contain both sensory & motor nerve fibers; most nerves

•Review terms

•Afferent – towards•Efferent - away

• Nerve fibers ÷÷÷÷ into 4 general groups

Nerve Fiber Classification

– General somatic efferent fibers• carry motor impulses from CNS to skeletal muscles

– General visceral efferent fibers• carry motor impulses away from CNS to smooth muscles & glands

– General somatic afferent fibers• carry sensory impulses to CNS from skin & skeletal muscles

– General visceral afferent fibers• carry sensory impulses to CNS from blood vessels & internal organs

18

Nerve Fiber Classification•Nerve fibers ÷÷÷÷ into 3 specialized groups

– Special somatic efferent fibers •carry motor impulses from brain to muscles used in

chewing, swallowing, speaking, & facial expressions–Special visceral afferent fibers

•carry sensory impulses to brain from olfactory & taste receptors

–Special somatic afferent fibers• carry sensory impulses to brain from receptors of sight, hearing, & equilibrium receptors

Cranial Nerves

• 12 pairs

• 1st & 2nd pair

originate w/in cerebrum

• others form from brainstem

Cranial Nerves• Oh Olfactory

• Oh Optic

• Oh Oculomotor

• To Trochlear

• Touch Trigeminal

• And Abducens

• Feel Facial

• Very Vestibulocochlear

• Good Glossopharyngeal

• Velvet Vagus

• AH Accessory & Hypoglossal

19

Cranial Nerves I and IIOlfactory (I)

• sensory only• impulses associated w/smell• receptors located in upper nasal cavity

Optic (II)• sensory only• impulses associated w/vision

Cranial Nerves III and IV

Trochlear (IV)• smallest cranial nerves• motor impulses to superior oblique muscles that moves the eye downward

Oculomotor (III)•motor impulses to eye muscles that

• raise eyelids• move the eyes• focus lens• adjust pupil

Cranial Nerve VTrigeminal (V)

• largest cranial nerve• mixed nerves; sensory to face

& motor to chewing muscles

• opthalmic division• sensory from surface of

eyes, tear glands, scalp,

forehead, & upper eyelids• maxillary division

• sensory from upper jaw,

teeth, lip, palate, & skin of face

• mandibular division

• sensory from scalp, skin of jaw, lower teeth, gum, & lip

• motor to muscles of

mastication

20

Cranial Nerves VI and VIIAbducens (VI)

• motor impulses to lateral rectus muscles

that move eyes to outside

Facial (VII)• mixed• sensory from taste receptors• motor to muscles of facial expression, tear glands, & salivary glands

Cranial Nerves VIII and IXVestibulocochlear (VIII)

• sensory• forms 2 branches• Vestibular - sensory from equilibrium receptors of ear• Cochlear - sensory from hearing receptors of inner ear

Glossopharyngeal (IX)• mixed• sensory from pharynx, tonsils, tongue, & carotid arteries• motor to salivary glands & muscles of pharynx

Cranial Nerve XVagus (X)

• mixed• somatic motor to muscles of speech & swallowing• autonomic motor to viscera • sensory from pharynx, larynx, & esophagus,

21

Cranial Nerves XI and XIIAccessory (XI)

• 2 branches • cranial- motor to muscles of soft palate, pharynx, larynx• spinal – motor to muscles in neck & back

Hypoglossal (XII)•motor to muscles of the tongue• controls speaking, chewing, & swallowing

Spinal Nerves• mixed nerves• provides 2-way communication between brain & limbs• 31 pairs

• 8 cervical (C1 to C8)• 12 thoracic (T1 to T12)• 5 lumbar (L1 to L5)• 5 sacral (S1 to S5)• 1 coccygeal (Co)

• Adult spinal cord ends between L1-L2 vertebrae• lumbar, sacral & coccygeal nerves form cauda equina & are called descending nerves• each spinal nerve forms from fusion of 2 roots

Spinal NervesDorsal root

• posterior branch of axons of sensory neurons

Dorsal root ganglion• lateral enlargement cell bodies of sensory neurons

Ventral root• anterior branch of axons of motor neurons;cell bodies are in spinal cord

22

Nerve Plexus

Nerve plexus – branching networks formed by spinal nerves;

not in T2-T12

–Cervical Plexus

• C1-C4

• supply muscles & skin of the neck

• contributes to phrenic nerve associated w/diaphragm

–Brachial plexuses

• C5-T1

• supply impulses to upper limbs

–Lumbosacral plexuses

•T12-S5

• supply impulses from lumbar region to pelvic cavity

Brachial Plexus

Lumbosacral Plexus

23

Autonomic Nervous System• functions w/out conscious effort• controls visceral activities• regulates smooth & cardiac muscles, & glands

• efferent fibers typically lead to ganglia outside CNS• 2 Divisions

• sympathetic – prepares body for fight or flight situations; stress• parasympathetic – functions under normal restful conditions; maintains homeostasis

Autonomic Nerve Fibers• all are motor (efferent)• includes 2 neurons• preganglionic fibers

• axons of preganglionic neuronsleave CNS to synapse with

• postganglionic fibers• axons of postganglionic neurons synapse w/viscera effector

Control of Autonomic Activity

• Controlled largely by CNS• Medulla oblongata regulates cardiac, vasomotor & respiratory activities• Hypothalamus regulates visceral functions; renal & digestive• Limbic system & cerebral cortex control emotions

24

Life-Span Changes

• Brain cells begin to die before birth• Over average lifetime, brain shrinks 10%• Most cell death occurs in temporal lobes• By age 90, frontal lobe has lost half its neurons• Number of dendrites ↓↓↓↓• Decreased levels of neurotransmitters• Fading memory• Slowed responses and reflexes• Changes increase risk of falling• Sleep problems common; decrease in REM sleep

Diseases or Disorders

• Lou Gehrig’s disease – amyotrophic lateral

sclerosis (ALS)

– Motor neurons degenerate & replaced w/ fibrous tissue; decline of muscle function

– Genetic; abnormal enzyme doesn’t break

down O 2 free radicals

• Anencephaly – fetus w/brainstem but lacks

upper brain structures

• Lissencephaly – smooth brain; lack of

convolutions causes retardation & seizures

• Cerebral palsy – motor impairment caused

by blocked cerebral blood vessels

• Parkinson disease – dopamine producing

neurons degenerate; leads to tremors; muscle rigidity

• Dementia

• Alzheimer

Diseases or Disorders

25

Cerebral Injuries

Concussion• brain jarred against cranium

• loss of consciousness• temporary loss of memory• headache

• recovery usually complete

Cerebrovascular Accident• stroke

• sudden interruption in blood flow• brain tissues die