THE NERVOUS SYSTEM

Chapter 7

• Monitors changes-__________________________--inside and outside the body

• Processes and interprets input-________________________________

• Effects a response by activating muscles or glands(effector)via_____________________________________

Stimuli and gathered info is sensory input

integration

Motor output

Organization of the Nervous System

• Divided by structure and activities• Structural classification• _____________________________________-consists of brain and

spinal cord and is integrating command center• __________________________________-part of system outside CNS-

nerves extending beyond the brain and SC• _______________________________-carry messages to and from SC

and• ______________________________-carry impulses to and from brain

CNS

Peripheral nervous system

Spinal nerves

Cranial nerves

Functional classification

• Divides peripheral nervous sytem into 2 divisions• __________________or afferent division consists

of nerves conveying info to CNS via sensory receptors in the body

• __________________________-bring in impulses from skin,skeletal muscles and joints

• ________________________________bring in messages from inside and outside the body

sensory Somatic sensory fibers

Visceral or sensory fibers or afferents

• Motor or efferent division carry impulses from CNS to effector organs-muscles and glands-They _________a motor response

• a)______________________allows us to consciously,or voluntarily control skeletal musces-so this sytem is also called ______________________________/some skeletal responses are initially involuntary

• b) __________________ regulates autonomic or involuntary-like smooth muscle ,cardiac muscle and glands…..commonly called ______________________,which has 2 parts :1)sympathetic-opposes parasympathetic-associated w/ flight or fight 2)parasympathetic division-opposes sympathetic and craniosacral division

effect Somatic nervous system

Voluntary nervous sysyem

Autonomic nervous system

Involuntary NS

Nervous Tissue:Structure and Function

• Either supporting cells or neurons• Supporting Cells-limped together as neuroglia

and includes cells that generally support,insulate and protect delicate neurons---glial cells have special functions:

• ______________________________-abundant star shaped cells-swollen ends that cling to neurons,bracing them and anchoring to nutrient supply:________________________/They form a living barrier between capillaries and neurons and help make exchange between the 2-help protect neurons from harmful substances in the blood and also help control brain chemical environment by “mopping”up leaked K ions and recapturing released neurotransmitters

• _____________________________-spider like phagocytes to dispose of debris-like dead brain cells and bacteria

astrocytes

capillaries

microglia

• _____________________________-glial cells that line the central cavities of the brain and SC …..beating of cilia to distribute cerebrospinal fluid for those cavities and provide a cushion

• _________________________________-glia that wrap flat extensions tightly around nerve fibers-producing fatty myelin sheath(an insulation)

• 2 major varieties in PNS:______________________form myelin sheath and ______________________________-positive cushioning cells

ependymal

oligiodendrocytes

Schwann cells Satellite cells

Neurons-- anatomy-all have cell body,which contains nucleus and is metabolic center and one or slender extending processes

• Neurons-- anatomy-all have cell body,which contains nucleus and is metabolic center and one or slender extending processes

• Cell Body-metabolic center• Transparent ________________ w/ a conspicuous nucleolus• Cytoplasm has usual organelles except centrioles• Rough ER is called______________________________and

_____________________________(intermediate filaments used in maintaining cell shape)

nucleusNissal substance

neurofibrils

• Processes-or fibers- vary greatly in length from microscopic - ~3-4 ft.Our longest reach from lumbar to large toe

• ________________________-convey incoming messages(electrical signals) towards cell body-may be many of these for one nerve cell

• _____________________- carry messages AWAY from cell body-only 1 axon,but branch much 2 end w/hundreds of axon _____________________________.-they contain 100’s of tiny vesicles,or membranous sacs w/___________________________chemicals-released into extracellular space

dendritesaxons Axon

terminals

neurotransmitters

• _____________________________tiny gap that separates axon terminal from next neuron(synapse)

• _____________________________-whitish ,fatty material w/waxy appearance.It functions by insulating or protecting fibers and Increases transmission rate

Synaptic cleftMyelin sheath

• Axons outside CNS are myelinated by ____________________________,which is gradually squeezed tightly enclosing axon

• External to Schwann cell is neurilemma-

Schwann cells

• Gaps between Schwann cells are called __________________________

• Myelinated fibers also in CNS as ___________________________-around small segment of 1 nerve fiber-coiling around as many as 60 fibers at one time…Since they lack neurilemma that contributes to non –regeneration property

Nodes of Ranvier

oligodendrites

• __________________________________is a neurological disorder causing visual or speech problems as wel as increasingle degenerating muscle …This is all due to an autoimmune response that destroys a protein in the myelin and cause nerves to short ciruit----Interferon is used

Multiple sclerosis

Terminology-

• -• cell bodies in CNS are usually called ______________--

carrying out metabolic functions/not regenerated • __________________small collections of cell bodies outside

CNS-in PNS• ________________________ are bundles of nerve fibers

running through CNS• _____________________________________ are bundles of

nerve fibers running through PNS• _________________________-collections of myelinated fibers

in CNS• ________________________CNS unmyelinated fibers

nuclei ganglia

tracts nerves

White matter

Gray matter

Classification

• Functionally groups neurons according to direction of nerve transmission relative to CNS…if carrying impulse from receptor to CNS-____________________________neurons-found in a ganglion outside CNS;dendrite endings of sensory neurons are usually associated with specialized recptors activated by specific nearby changes-cutaneous sense organs and_____________________________in muscle and tendons

Sensory or afferent

proprioreceptors

• _________________(efferent)neurons carry impulses from CNS to visceraan/or muscles or glands-cell bodies in CNS

• ________________________or association neurons connect motor and sensory neurons in neural pathways-cell bodies always in CNS

• Structurally based on # of processes extending from cell body---if several:____________________________-inc. all motor and association neurons/__________________neurons have 2 processes-rare in adults/_____________________neurons have single process –sensory neurons in PNS

motor interneurons multipolarneuron

bipolarUnipolar neurons

6-Physiology

• NERVE INPULSES:Neurons have 2 major properties-___________________________________________

• __________________________refers to inactive or resting plasma membrane(fewer + ions on inner face(K+ions)-outside are Na+ ions …if the inside is more - ,it is inactive

Irritability and conductivity

polarized

• Action Potential and generation:…many different stimuli excite neurons—eg.light,sound,pressure-most excited by neurotransmitters released by other neurons….changes permeability of membrane changes briefly-gates of Na channels open---changing polarity-_________________________-inside now more +--graded potential

• If this strong enough it initiates an_________________________(nerve impulse)-all-or none response

• An outflow now of K+ ions will restore resting state-__________________________________

depolarization

repolarizationAction potential

• UNTIL REPOLARIZATION HAPPENS<A NEURON CANNOT CARRY ANOTHER IMPULSE !

• NA-K pump uses ATP• The above describes unmyelinated impulses –

Myeinated sheaths conducts impulses faster-__________________________________-leaps from node to node

• Conductivity can be impaired by sedatives and anesthetics by altering permeability

Salatory conduction

• Synapse Transmission-impulse does not traverse- synapse neurotransmitter do and they cause Na+ entry ,depolarization,etc.-brief transmission-electrochemical

• Reflexes-rapid and predictable and involuntary response to stimuli

• Somatic reflexes-stimulate skeletal muscles

• _____________________regulate smooth muscles,heart and glands

Autonomic reflexes

• _____________________________is a neural pathway and has at least 5 elements:____________________________________________________________________________________________________

Relex arcs

Sensory receptor,effector organ,sensory or motor neurons and synapse-CNS integration center

III. CNS

• Functional Anatomy of the Brain– Brain is ~ 3 lbs.– 4 regions-cerebral,diencephalons,brain

stem,cerebellum• Cerebral hemispheres

• Paired• Largest and most superior• ____________-elevated regions of tissue separated

by shallow _______• ______________________are less numerous

grooves and separate larger regions of brain

gyri sulci

fissures

• ______________-separates 2 hemispheres by deep fissure

• Other fissures or sulci divide into lobes,named for corresponding cranial bone

• 3 basic regions to ea hemisphere:_______________________

Longitudinal fissure

Superficial cortex of gray matter,internal white matter,and basal ganglia(Gray)

Cerebral Cortex:-includes speech,memory,logical and emotional response, consciousness , interpretation of

sensation,and voluntary movement

– ________________________-posterior to central sulcus-primary somatic sensory area-interprets impulses traveling from body sensory receptors(except for special senses)/allows you to perceive pain,coldness or light touch….as shown in 7-14,p.245…body is represented in an upside down manner in sensory area-such a spatial map is a ___________________-crossed pathways-left primary somatic sensory area receives impulse from right and vice verse

Primary somatic sensory area in parietal lobe

Sensory homunculus

– __________________________visual area in posterior

– ___________________________has auditory area and has olafactory area

– _________________________is primary motor area/the axons of these motor neurons make ________-major voluntary motor tract and it descends to cord-pathways again crossed

– _________is map on motor cortex

Occipital lobe Temporal lobe

Frontal lobe

Corticospinal or pyramidal tract

Motor homunculus

– ______________________at base of precentral gyrus-involved in speech-usually only in left hemisphere-damage here can cause inability to say words properly

– In anterior frontal lobes is believed to be intellectual reasoning and socially acceptable behavior region

– The main _____________________is located at junction of temporal,parietal,and occipital lobes-usually only in 1 hemisphere also

– __________________is involved w/word meanings– Cell bodies of neurons involved in cerebral

hemisphere are in outermost gray matter

Broca’s area

Speech area

Frontal lobes

Cerebral White Matter-deeper,remaining cerebrum-composed of fiber tracts carrying impulses to and from

or within cortex

• __________________________________-large fiber tract that connects cerebral hemispheres(an example of a commisure)-allows hemispheres to communicate with each other….Association fiber tracts connects areas w/in hemisphere and

projection fiber tract connects cerebrum

Corpus callosum

• _______________________________-islands of gray matter buried in white matter of cerebral hemispheres-help regulate voluntary motor activities by modifying instructions-esp. starting or stopping

• basal ganglia

Basal nuclei

• ______________________________- genetic disease, middle-age and leads to massive degeneration of basal nuclei and then cerebral cortex-includes jerky movements and an eventual vegetative state w/in 15 years fatal-overdrive in motor stimulation

• ______________-has basal nuclei problems-strikes in 50’s-60’s and comes from a degeneration of dopamine releasing neurons-dopamine deprived basal nuclei become overactive-tremors,head nodding etc.

Huntington’s disease or Chorea

Parkinson’s disease

*Diencephalon-interbrain-atop brain stem and enclosed by cerebral hemispheres

• ____________________________-encloses shallow 3rd ventricle of brain and is relay station for sensory impulses passing upward to sensory cortex-interpret sensation

• ____________________________________-is under the thalamus makes up floor of diencephalons-helps regulate body temp.,water balance and,metabolism-also centers for many drives and emotions-part of ___________________________-“emotional visceral brain”-thirst,appetite and sex drive

Thalamus hypothalamus Limbic System

• Contains pituitary gland and mammillary bodies that is involved in olafaction

• ___________________-roof of 3rd ventricle/contains ____________________-an endocrine organ,choroid plexus-form cerebrospinal fluid

epithalamusPineal body

____________________________________-about the size of a thumb in diameter and about 3’’ long…includes midbrain,pons and medulla oblongata/provides a pathway for ascending and

descending tracts and has small gray matter areas

» 1)____________________________-small/____________________________________ travels through midbrain and anteriorly midbrain has cerebral peduncles that convey ascending and descending impulses/dorsally are 4 rounded corpora quadrigemina-reflex centers for vision and hearing

Brain stemmidbrain

Cerebral aqueduct

» 2)___________________----rounded just below midbrain and has bridge of fiber tracts and involves in control of breathing

» 3)___________________________-most inferior part and merges into SC…fiber tract area and helps regulate visceral activity

pons Medulla oblongata

***Cerebellum-dorsally under occipital lobe and has 2 hemispheres-has outer cortex of gray matter and inner

cortex of white matter

» Provides timing factor for skeletal and controls muscle activity

• ________________________-cerebellum damage causing clumsiness and disorganization

ataxia

Protection of CNS

• A.__________-3 connective tissue membranes protecting CNS– 1)______________________-outermost layer and

leathery(“tough or hard mother”),double layered where surrounds brain

meningesDura mater

• _____________________-attached to inner surface of skull

• ___________________-Outermost covering of brain and continues as dura mater of spinal cord

• Dural layers fused except in 3 areas where they separate to enclose dural venous sinuses that collect _________________________.

Periosteal layer Meningeal layer

Venous blood

Inner dural membrane extends inward to form a fold that attaches brain to cranial cavity

______________________________-middle meningeal layer,weblike;spans

subarachnoid space to attach TO innermost membrane.

Arachnoid mater

– 3)_____________________________-innermost membrane(“gentle mother”)-clings tightly to surface of brain and spinal cord,following every fold

– Subarachnoid space is filled w/ cerebrospinal fluid and ______________________________protrude through dura mater

– Cerebrospinal fluid is absorbed into venous blood in dural sinuses through arachnoid villi

Projections of arachnoid membrane called arachnoid villi

Pia mater

• ______________________________-inflammation of meninges,serious threat to brain(bacterial or viral) because may spread to the nervous tissue of the CNS/spinal diagnostic taps derived from subarachnoid space

• ___________________________-brain inflammation

meningitis

encephalitis

Cerebrospinal Fluid(CSF)-somewhat watery and similar to blood plasma,but contains less protein and more

vitamin C and a different ion composition

• CSF continually formed from blood by choroids plexus(clusters of capillaries hanging from roof of each of brain’s ventricles)

• Forms a watery cushion to protect fragile nervous tissue

• Continually moves in brain,circulating from 2 _________________________into 3rd ventricle and then through cerebral aquaduct of midbrain into 4th ventricle….some of this continues down SC,but most circulates into subarachnoid space

Lateral ventricles

• CSF returns to blood in dural venous sinuses through _____________________________

• Normal means CSF forms and drains at a constant rate maintaining about ½ cup fluid.Any significant changes-like blood cells or general composition may mean ____________________

• Test w/ lumbar puncture• ________________________________--if

drainage of CSF is obstructed-maybe by tumor or born that way

Arachnoid villi

Sign of miningitisor certain brain pathologies such as tumor or MS

hydrocephalis

Blood-Brain Barrier

• Brain is very sensitive to pressure and chemical changes• Thus,the least permeable capillaries in body—almost

seamlessly bound by tight junctions all around-passing only water ,glucose and amino acids pass easily through—preventing _________________________

• Barrier useless against ____________________________(thus explains entrance of alcohol,nicotine and anesthetics

Preventing urea, toxins,proteins and many drugs from entering

Fats,respiratory gases and other fat-soluble molecules

Brain Dysfunctions• _______________________________-progressive

degenerative disease of brain resulting,eventually, in dementia;associated w/shortage of Ach and structural changes in brain;gyri shrink and brain atrophies

• _______________________-minor and not permanent brain damage

• __________________________-marked tissue destruction-severe forms always result in comas

Alzheimer’s disorder

concussion contusion

• ____________________________-after a blow to the head-bleed from ruptured vessels

• ________________________-swelling of brain from inflammatory response to injury

• ______________________________-3rd leading cause of death in US-when blood circulation is blocked and vital tissue dies

• ____________________one sided paralysis• _________________damage to left cerebrum and affects

speech• __________________-temporary restriction of blood flow

Intracranial hemorrhage

Cerebral edemaCerebrovascular accidents-CVA-ie.stroke

hemiplegia aphasiasTransient ischemic attack -TIA

SPINAL CORD-cylindrical and appx.17” long,glistening white;2 way conduction pathway to and from brain and

reflex center

• Extends from foramen magnum to _________________________________,ending below the ribs(thus L3 good for spinal tap)

• Protected by CSF and meningeal coverings• 31 prs spinal nerves-arise from cord and exit from vertebral

column to serve nearby area of body• ____________________collection of spinal nerves at end of

vertebral canal

1st or 2nd lumbar vertebra

Cauda equina

A)Gray matter of SC and spinal roots

– Looks like butterfly in crosssection– Contains dorsal horns(has interneurons) ,ventral

horns(contain cell bodies of motor somatic{voluntary} nervous sytem and surrounds central canal of SC ,containing CSF)

– Cell bodies of sensory neurons enter cord by dorsal root and are called ___________________________________-If severed ,sensation at that point is lost

– Ventral horn sends its axons out ______________________

– Dorsal and ventral roots fuse to form ________________________________

– ____________________________-damage to ventral root/affecting muscles served;muscles will atrophy

Dorsal root ganglion

Spinal nervesFlaccid paralysis

Ventral root of cord

B-White matter of SC• Myelinated fiber tracts-serving higher centers,some travel

brain to SC and some innervate one or the other side of the SC

• Dorsal,lateral and ventral columns-3 regions of white matter• Tracts conducting Sensory impulse to brain by

_________________or afferent tracts• Motor(efferent tracts) carry from

__________________________________• __________________________________-if SC is cut

crosswise or crushed-afferent stay intact and involuntary movement of those muscles results and sensation loss below cut-compare quadriplegic to paraplegic

sensoryBrain to skeletal muscles