THE NERVOUS SYSTEMTHE NERVOUS SYSTEM

HEADINGHEADING

VOCABULARYVOCABULARY

IMPORTANT INFOIMPORTANT INFO

Major Structures of the Nervous Major Structures of the Nervous SystemSystem

Brain, cranial nerves, spinal cord, spinal nerves, Brain, cranial nerves, spinal cord, spinal nerves, ganglia, enteric plexuses and sensory receptorsganglia, enteric plexuses and sensory receptors

Nervous System DivisionsNervous System Divisions

Central nervous systemCentral nervous system ((CNSCNS) ) consists of the consists of the brainbrain and and

spinal cordspinal cord Peripheral nervous systemPeripheral nervous system

((PNSPNS)) consists of consists of cranialcranial and and spinal nervesspinal nerves that that

contain both sensory and motor fiberscontain both sensory and motor fibers connects CNS to muscles, glands & all connects CNS to muscles, glands & all

sensory receptorssensory receptors

Subdivisions of the PNSSubdivisions of the PNS

SomaticSomatic ( (voluntaryvoluntary) nervous system (SNS)) nervous system (SNS) neurons from cutaneous and special sensory neurons from cutaneous and special sensory

receptors to the CNSreceptors to the CNS motor neurons to skeletal muscle tissuemotor neurons to skeletal muscle tissue

AutonomicAutonomic ( (involuntaryinvoluntary) nervous systems) nervous systems sensory neurons from visceral organs to CNSsensory neurons from visceral organs to CNS motor neurons to smooth & cardiacmotor neurons to smooth & cardiac muscle and muscle and

glandsglands sympathetic division (speeds up heart rate)sympathetic division (speeds up heart rate) parasympathetic division (slow down heart rate)parasympathetic division (slow down heart rate)

EntericEnteric nervous system (ENS) nervous system (ENS) involuntary sensory & motorinvoluntary sensory & motor neurons control GI tract neurons control GI tract neurons neurons function independentlyfunction independently of ANS & CNS of ANS & CNS

NeuronsNeurons Functional unit of nervous systemFunctional unit of nervous system Have capacity to produce Have capacity to produce action action

potentialspotentials electrical excitabilityelectrical excitability

Cell bodyCell body single nucleus with prominent single nucleus with prominent

nucleolusnucleolus Nissl bodiesNissl bodies (chromatophilic (chromatophilic

substance) substance) rough ER & free ribosomes rough ER & free ribosomes

for protein synthesisfor protein synthesis NeurofilamentsNeurofilaments give cell shape give cell shape

and supportand support MicrotubulesMicrotubules move material move material

inside cellinside cell Cell processes = dendrites & Cell processes = dendrites &

axonsaxons

The basic unit of the The basic unit of the nervous nervous system = system = neuron?neuron?

DendritesDendrites receive stimulireceive stimuli

Nerve cell bodyNerve cell body

@ nucleus @ nucleus transmits the transmits the stimulistimuli

AxonAxon transmits transmits the impulse to the impulse to another another dendritedendrite

Nucleus with Nucleolus

Parts of a NeuronParts of a Neuron

Axons or Dendrites

Cell body

Neuroglial cells

DendritesDendrites

Conducts impulses Conducts impulses towardstowards cell bodycell body

Typically short, highly Typically short, highly branched & branched & unmyelinatedunmyelinated

Surfaces specialized Surfaces specialized for contact with other for contact with other neuronsneurons

Contains neurofibrils Contains neurofibrils & Nissl bodies& Nissl bodies

AxonsAxons

Conduct impulses Conduct impulses away away from cell bodyfrom cell body

Long, thin cylindrical Long, thin cylindrical process of cell process of cell

Impulses arise from initial Impulses arise from initial segment (trigger zone)segment (trigger zone)

Side branches Side branches (collaterals) end in fine (collaterals) end in fine processes called axon processes called axon terminalsterminals

Swollen tips called Swollen tips called synaptic end bulbs synaptic end bulbs contain vesicles filled contain vesicles filled with neurotransmitterswith neurotransmitters

Synaptic boutons

Functional Classification of Functional Classification of NeuronsNeurons

Sensory (Afferent) Sensory (Afferent) neuronsneurons transport sensory transport sensory

information from skin, information from skin, muscles, joints, sense muscles, joints, sense organs & viscera to CNSorgans & viscera to CNS

Motor (Efferent) neuronsMotor (Efferent) neurons send motor nerve impulses send motor nerve impulses

to muscles & glandsto muscles & glands Interneurons Interneurons

(Association) neurons(Association) neurons connect sensory to motor connect sensory to motor

neuronsneurons 90% of neurons in the body90% of neurons in the body

What is a synapse ?What is a synapse ?

Junction of two Junction of two neuronsneurons

NeurotransmittNeurotransmittererconvert the convert the electrical electrical impulse into a impulse into a chemical chemical messagemessage

Axon ending: terminal Axon ending: terminal budbud

Transfers the Transfers the electricaelectrical l nerve impulsenerve impulse

By chemical By chemical neuron-neuron-transmitterstransmitters

From one From one neuron to the neuron to the nextnext

The Action Potential: SummarizedThe Action Potential: Summarized

Chemical Chemical SynapsesSynapses

Action potential reaches end Action potential reaches end bulb and voltage-gated Ca+ bulb and voltage-gated Ca+ 2 channels open2 channels open

Ca+2 flows inward triggering Ca+2 flows inward triggering release of neurotransmitterrelease of neurotransmitter

Neurotransmitter crosses Neurotransmitter crosses synaptic cleft & binding to synaptic cleft & binding to receptors receptors the more neurotransmitter the more neurotransmitter

released the greater the released the greater the change in potential of the change in potential of the postsynaptic cellpostsynaptic cell

Synaptic delay is 0.5 msecSynaptic delay is 0.5 msec One-way information transferOne-way information transfer

The Central Nervous The Central Nervous System:System:

1) 1) Spinal CordSpinal Cord2) 2) BrainBrain medullamedulla for for breathingbreathing cerebellum cerebellum for for balancebalance cerebrumcerebrum for for higher higher

thinkingthinking bwbw

Spinal Cord ProtectionSpinal Cord Protection

•By the vertebral column, meninges, cerebrospinal fluid, and vertebral ligaments.

External Anatomy of Spinal External Anatomy of Spinal CordCord

Flattened cylinderFlattened cylinder 16-18 Inches long & 16-18 Inches long &

3/4 inch diameter3/4 inch diameter In adult ends at L2In adult ends at L2 In newborn ends at L4In newborn ends at L4 Growth of cord stops Growth of cord stops

at age 5at age 5 Cervical enlargementCervical enlargement

upper limbsupper limbs Lumbar enlargementLumbar enlargement

lower limbslower limbs

Spinal Cord & Spinal Spinal Cord & Spinal NervesNerves

Spinal nerves begin as rootsSpinal nerves begin as roots Dorsal or posterior root is incoming sensory fibersDorsal or posterior root is incoming sensory fibers

dorsal root ganglion (swelling) = cell bodies of sensory dorsal root ganglion (swelling) = cell bodies of sensory nervesnerves

Ventral or anterior root is outgoing motor fibersVentral or anterior root is outgoing motor fibers

Spinal NervesSpinal Nerves

31 Pairs of spinal nerves31 Pairs of spinal nerves Named & numbered by Named & numbered by

the cord level of their the cord level of their originorigin 8 pairs of cervical nerves8 pairs of cervical nerves

(C1 to C8) (C1 to C8) 12 pairs of thoracic nerves12 pairs of thoracic nerves

(T1 to T12)(T1 to T12) 5 pairs of lumbar nerves5 pairs of lumbar nerves

(L1 to L5) (L1 to L5) 5 pairs of sacral nerves5 pairs of sacral nerves

(S1 to S5) (S1 to S5) 1 pair of coccygeal nerves1 pair of coccygeal nerves

Mixed sensory & motor Mixed sensory & motor nervesnerves

The Brain and Cranial NervesThe Brain and Cranial Nerves

almost almost 3 lb.3 lb. Brain functions in sensations, memory, emotions, Brain functions in sensations, memory, emotions,

decision making, behaviordecision making, behavior

Principal Parts of the Principal Parts of the BrainBrain

CerebrumCerebrum DiencephalonDiencephalon

thalamus & thalamus & hypothalamushypothalamus

CerebellumCerebellum BrainstemBrainstem

medulla, pons & medulla, pons & midbrainmidbrain

Medulla Medulla OblongataOblongata

Continuation of spinal cordContinuation of spinal cord Ascending sensory tractsAscending sensory tracts Descending motor tractsDescending motor tracts Nuclei of 5 cranial nervesNuclei of 5 cranial nerves Cardiovascular centerCardiovascular center

force & rate of heart beatforce & rate of heart beat diameter of blood vesselsdiameter of blood vessels

Respiratory centerRespiratory center medullary rhythmicity area sets basic rhythm of medullary rhythmicity area sets basic rhythm of

breathingbreathing Information in & out of cerebellumInformation in & out of cerebellum Reflex centersReflex centers for coughing, sneezing, swallowing for coughing, sneezing, swallowing

etcetc

PonsPons

One inch longOne inch long White fiber tracts White fiber tracts

ascend and ascend and descenddescend

Pneumotaxic & Pneumotaxic & apneustic areas apneustic areas help help control control breathingbreathing

Middle cerebellar Middle cerebellar peduncles carry peduncles carry sensory info to sensory info to the cerebellumthe cerebellum

Cranial nerves 5-7Cranial nerves 5-7

MidbrainMidbrain One inch in One inch in

lengthlength Extends from Extends from

pons to pons to diencephalondiencephalon

Cerebral Cerebral aqueduct aqueduct connects 3rd connects 3rd ventricle ventricle above to 4th above to 4th ventricle ventricle belowbelow

CerebellumCerebellum

2 cerebellar hemispheres and 2 cerebellar hemispheres and VermisVermis ( (central areacentral area)) FunctionFunction

correct voluntary muscle contraction and posture based correct voluntary muscle contraction and posture based on sensory data from body about actual movementson sensory data from body about actual movements

sense of equilibriumsense of equilibrium

ThalamusThalamus

1 inch long mass of 1 inch long mass of gray matergray mater in each half of brain in each half of brain (connected across 3rd ventricle by intermediate mass)(connected across 3rd ventricle by intermediate mass)

Relay stationRelay station for sensory information on way to cortex for sensory information on way to cortex Crude perception of some sensationsCrude perception of some sensations

HypothalamusHypothalamus

Dozen or so nuclei in Dozen or so nuclei in 4 major regions4 major regions mammillary bodies are relay station for olfactory reflexes;mammillary bodies are relay station for olfactory reflexes;

infundibulum suspends the pituitary glandinfundibulum suspends the pituitary gland Major regulator of homeostasisMajor regulator of homeostasis

receives somatic and visceral input, taste, smell & hearing receives somatic and visceral input, taste, smell & hearing information; monitors osmotic pressure, temperature of bloodinformation; monitors osmotic pressure, temperature of blood

Functions of HypothalamusFunctions of Hypothalamus Controls and integrates activities of ANS which Controls and integrates activities of ANS which

regulates smooth, cardiac regulates smooth, cardiac muscle and glandsmuscle and glands

Synthesizes regulatory Synthesizes regulatory hormones that control the hormones that control the anterior pituitaryanterior pituitary

Contains cell bodies of axons Contains cell bodies of axons that end in posterior pituitary that end in posterior pituitary where they secrete hormoneswhere they secrete hormones

Regulates rage, aggression, pain, pleasure & arousalRegulates rage, aggression, pain, pleasure & arousal Feeding, thirst & satiety centersFeeding, thirst & satiety centers Controls body temperatureControls body temperature Regulates daily patterns of sleepRegulates daily patterns of sleep

EpithalamuEpithalamuss

Pineal GlandPineal Gland endocrine gland endocrine gland

the size of small the size of small peapea

secretes secretes melatonin during melatonin during darknessdarkness

promotes promotes sleepiness & sets sleepiness & sets biological clockbiological clock

Habenular NucleiHabenular Nuclei emotional emotional

responses to responses to odorsodors

CerebrumCerebrum (Cerebral (Cerebral

Hemispheres)Hemispheres)

Cerebral cortex is Cerebral cortex is gray mattergray matteroverlying white matteroverlying white matter 2-4 mm thick containing 2-4 mm thick containing billionsbillions

of cellsof cells grew so quickly formed foldsgrew so quickly formed folds

((GyriGyri) and grooves () and grooves (Sulci or FissuresSulci or Fissures)) Longitudinal fissure separates left & right Longitudinal fissure separates left & right

cerebral hemispherescerebral hemispheres Corpus CallosumCorpus Callosum is band of white matter is band of white matter

connecting left and right cerebral hemispheresconnecting left and right cerebral hemispheres Each hemisphere is subdivided into Each hemisphere is subdivided into 4 lobes4 lobes

Right versus left Right versus left CerebrumCerebrum

Limbic SystemLimbic System

Emotional brain-Emotional brain--intense pleasure & intense -intense pleasure & intense painpain

Strong emotions increase efficiency of memoryStrong emotions increase efficiency of memory

2 Types of Nervous 2 Types of Nervous Responses?Responses?

A. A. VoluntaryVoluntary the brain &the brain & spinal cordspinal cord

B. B. Involuntary Involuntary or or

Autonomic System Autonomic System SympatheticSympathetic ParasympatheticParasympathetic

Somatic Sensory PathwaysSomatic Sensory Pathways

First-order neuronFirst-order neuron conduct impulses to conduct impulses to brainstem or spinal cordbrainstem or spinal cord either spinal or cranial nerves either spinal or cranial nerves

Second-order neuronsSecond-order neurons conducts impulses conducts impulses from spinal cord or brainstem to thalamus--from spinal cord or brainstem to thalamus--cross over to opposite side before reaching cross over to opposite side before reaching thalamusthalamus

Third-order neuronThird-order neuron conducts impulses from conducts impulses from thalamus to primary somatosensory cortex thalamus to primary somatosensory cortex (postcentral gyrus of parietal lobe)(postcentral gyrus of parietal lobe)

Somatic Motor PathwaysSomatic Motor Pathways Control of body movementControl of body movement

motor portions of cerebral cortexmotor portions of cerebral cortex initiate & control precise movementsinitiate & control precise movements

Basal GangliaBasal Ganglia help establish muscle tone & integrate help establish muscle tone & integrate semivoluntary automatic movementssemivoluntary automatic movements

CerebellumCerebellum helps make movements smooth & helps helps make movements smooth & helps maintain posture & balancemaintain posture & balance

Somatic motor pathwaysSomatic motor pathways direct pathway direct pathway

from cerebral from cerebral cortex to spinal cortex to spinal cord & out to cord & out to musclesmuscles

indirect pathway indirect pathway includes synapsesincludes synapses in basal ganglia, in basal ganglia, thalamus, reticular thalamus, reticular formation & formation & cerebellumcerebellum

The Autonomic Nervous The Autonomic Nervous SystemSystem

Regulate activity of Regulate activity of smooth muscle, cardiac smooth muscle, cardiac muscle & certain glandsmuscle & certain glands

Structures involvedStructures involved general visceral general visceral afferent afferent

neurons (Sensory)neurons (Sensory) general visceral general visceral efferent efferent

neurons (Motor)neurons (Motor) integration center within integration center within

the brainthe brain Receives input from Receives input from

limbic system and other limbic system and other regions of the cerebrumregions of the cerebrum

The Autonomic Nervous The Autonomic Nervous SystemSystem

Autonomic versus Somatic NSAutonomic versus Somatic NS

Somatic NSSomatic NS consciously consciously

perceived perceived sensationssensations

excitation of excitation of skeletal muscleskeletal muscle

one neuronone neuron connects CNS to connects CNS to organorgan

•Autonomic NSAutonomic NS–unconsciously unconsciously perceived visceral perceived visceral sensations sensations –involuntary inhibition or involuntary inhibition or

excitation of smooth excitation of smooth muscle, cardiac muscle muscle, cardiac muscle or glandular secretion or glandular secretion–2 neurons 2 neurons needed to needed to connect CNS to organ connect CNS to organ–PreganglionicPreganglionic and and PostganglionicPostganglionic neurons neurons

Autonomic versus Somatic Autonomic versus Somatic NSNS

Notice that the ANS pathway is a 2 neuron Notice that the ANS pathway is a 2 neuron pathway while the Somatic NS only contains one pathway while the Somatic NS only contains one neuron.neuron.

Divisions of the ANSDivisions of the ANS 2 major divisions2 major divisions

ParasympatheticParasympathetic SympatheticSympathetic

Dual innervation Dual innervation (2 nerve supplies)(2 nerve supplies) 1 speeds up 1 speeds up

organorgan 1 slows down 1 slows down

organorgan SympatheticSympathetic NS NS

increasesincreases heart heart raterate

ParasympathetiParasympathetic c NS NS decreasesdecreases heart rateheart rate

Sympathetic ResponsesSympathetic Responses Dominance by the sympathetic system is Dominance by the sympathetic system is

caused by physical or emotional stress – caused by physical or emotional stress – ““E situations”: E situations”: emergency, embarrassment, emergency, embarrassment,

excitement, exerciseexcitement, exercise Alarm Reaction = Alarm Reaction = Flight or Fight ResponseFlight or Fight Response

dilation of pupils, increase of heart rate, force dilation of pupils, increase of heart rate, force of contraction & BPof contraction & BP

decrease in blood flow to nonessential organsdecrease in blood flow to nonessential organs increase in blood flow to skeletal & cardiac increase in blood flow to skeletal & cardiac

musclemuscle airways dilate & respiratory rate increasesairways dilate & respiratory rate increases blood glucose level increaseblood glucose level increase

Long lasting due to lingering of NE in Long lasting due to lingering of NE in synaptic gap and release of synaptic gap and release of norepinephrine by the adrenal glandnorepinephrine by the adrenal gland

Parasympathetic Parasympathetic ResponsesResponses

Enhance “REnhance “Rest-and-Digestest-and-Digest” activities” activities Mechanisms that help Mechanisms that help conserveconserve and and restorerestore

body energy during times of restbody energy during times of rest Normally dominate over sympathetic impulsesNormally dominate over sympathetic impulses SLUDD Type ResponsesSLUDD Type Responses = = salivation, salivation,

lacrimation, urination, digestion & defecation lacrimation, urination, digestion & defecation and 3 “decreases”--- decreased HR, diameter of and 3 “decreases”--- decreased HR, diameter of airways and diameter of pupilairways and diameter of pupil

Paradoxical FearParadoxical Fear when there is no escape route when there is no escape route or no way to winor no way to win causes massive activation of parasympathetic divisioncauses massive activation of parasympathetic division loss of control over urination and defecationloss of control over urination and defecation

Control of Autonomic Control of Autonomic NSNS

Not aware of autonomic responses because Not aware of autonomic responses because control center is in lower regions of the braincontrol center is in lower regions of the brain

Hypothalamus is major control centerHypothalamus is major control center InputInput: emotions and visceral sensory information : emotions and visceral sensory information

smell, taste, temperature, osmolarity of blood, smell, taste, temperature, osmolarity of blood, etcetc

OutputOutput: to nuclei in brainstem and spinal cord: to nuclei in brainstem and spinal cord posterior & lateral portions control sympathetic NSposterior & lateral portions control sympathetic NS

increase heart rate, inhibition GI tract, increase increase heart rate, inhibition GI tract, increase temperaturetemperature

anterior & medial portions control anterior & medial portions control parasympathetic NSparasympathetic NS decrease in heart rate, lower blood pressure, decrease in heart rate, lower blood pressure,

increased GI tract secretion and mobilityincreased GI tract secretion and mobility