The Nervous SystemThe Nervous System

Chapter 7Chapter 7

Functions of Nervous systemFunctions of Nervous system

Sensory input:Sensory input: Nervous Nervous system receives information system receives information from environment (inside and from environment (inside and outside of the body)outside of the body)

Integration:Integration: It analyses the It analyses the information and responds to information and responds to the information. How?the information. How?

Motor output:Motor output: By activating By activating muscles or glandsmuscles or glands

Structure and Function of Nervous TissueStructure and Function of Nervous Tissue

Consists of two major Consists of two major types of cells:types of cells:

Neuron:Neuron: nerves cells nerves cells involved in generating involved in generating and conducting nerve and conducting nerve impulses impulses

Glial cells:Glial cells: nourish, nourish, support and protect support and protect nerve cellsnerve cells

Neurons or Nerve CellsNeurons or Nerve CellsConsists of 3 parts:Consists of 3 parts:

Cell body: Cell body:

Metabolic center of the bodyMetabolic center of the body

contains nucleus and nucleoluscontains nucleus and nucleolus

cytoplasm filled with rough ER cytoplasm filled with rough ER (Nissl bodies), Golgi, and other (Nissl bodies), Golgi, and other organelles.organelles.

Primary site for neurotransmitter Primary site for neurotransmitter synthesissynthesis

Neurofibrils:Neurofibrils: provide shape, provide shape, made of Intermediate filamentsmade of Intermediate filaments

Dendrites:Dendrites: cytoplasmic extension cytoplasmic extension

extend from cell bodyextend from cell body

Conduct nerve impulse Conduct nerve impulse towards cell bodytowards cell body

They are generally They are generally branchedbranched

Neurons or Nerve CellsNeurons or Nerve Cells

Axon:Axon: arise from cell body arise from cell body Each neuron contains Each neuron contains

single axonsingle axon The place where axon The place where axon

originates from the cell originates from the cell body is called body is called axon axon hillockhillock

Cytoplasm is called Cytoplasm is called axoplasm,axoplasm, cell cell membrane is called membrane is called axolemma. axolemma.

Neurons or Nerve CellsNeurons or Nerve Cells

AxonAxon

Axons end in Axons end in axonal axonal terminalsterminals

Axonal terminals contain Axonal terminals contain vesicles with vesicles with neurotransmittersneurotransmitters

Axonal terminals are Axonal terminals are separated from the next separated from the next neuron by a gapneuron by a gap Synaptic cleft—Synaptic cleft— gap gap

between adjacent neuronsbetween adjacent neurons Synapse—Synapse— junction junction

between nervesbetween nerves

Axon:Axon:

Conduct nerve impulses Conduct nerve impulses away from cell body away from cell body towards another neuron towards another neuron or muscleor muscle

Axon can be Axon can be myelinatedmyelinated or or nonmyelinated nonmyelinated

Myelination (Myelin Myelination (Myelin sheath) helps in sheath) helps in conducting action conducting action potential at a faster ratepotential at a faster rate

Neurons or Nerve CellsNeurons or Nerve Cells

Classification of NeuronsClassification of Neurons Nerve cells are classified into different types based on Nerve cells are classified into different types based on

structure or functionstructure or function Structural Classification:Structural Classification: Nerve fiber arising from cell body Nerve fiber arising from cell body

differentiates into differentiates into axon and dendriteaxon and dendrite

Unipolar:Unipolar: cell body gives off two branches from the same cell body gives off two branches from the same point, one axon and second dendrite like structurepoint, one axon and second dendrite like structure

ClassificationClassification

Bipolar:Bipolar: Neurons with one dendrite and one axon Neurons with one dendrite and one axon

Multipolar:Multipolar: Contains many dendrites and one axon . Contains many dendrites and one axon .

Functional ClassificationFunctional Classification Sensory or afferent neurons:Sensory or afferent neurons: send impulses from organs to central send impulses from organs to central

nervous system(CNS).Generally nervous system(CNS).Generally unipolarunipolar

Interneuron:Interneuron: receive impulse from sensory neuron and relays it to receive impulse from sensory neuron and relays it to motor neuron within CNS. Present within the brain or spinal cord. motor neuron within CNS. Present within the brain or spinal cord. Generally Generally multipolarmultipolar

Motor or efferent neurons:Motor or efferent neurons: send impulses from CNS to organs. send impulses from CNS to organs.Generally Generally multipolarmultipolar

ClassificationClassification

Different types of CNS glia cells: Different types of CNS glia cells:

AstrocytesAstrocytes

Ependymal cells Ependymal cells

MicrogliaMicroglia

OligodendrocytesOligodendrocytes

Schwann cellsSchwann cells

Neuroglia or Glia CellsNeuroglia or Glia Cells

Neuroglia or Glia CellsNeuroglia or Glia CellsAstrocytes:Astrocytes: regulate chemical regulate chemical

composition of brain fluid.composition of brain fluid. Helps in forming blood brain barrier.Helps in forming blood brain barrier.

Connect nerve cell to capillariesConnect nerve cell to capillaries

Ependymal cells:Ependymal cells: lines the cavities of lines the cavities of brain and spinal cord andbrain and spinal cord and

circulate cerebrospinal fluid around circulate cerebrospinal fluid around CNSCNS

Microglia:Microglia: macrophages of CNS and macrophages of CNS and Dispose of debris, dead cells and Dispose of debris, dead cells and

bacteriabacteria

Neuroglia or Glia CellsNeuroglia or Glia Cells Oligodendrocytes:Oligodendrocytes: form myelin sheath around axon of form myelin sheath around axon of

neuron neuron in in CNSCNS

Schwann cellsSchwann cells form myelin sheath form myelin sheath In In PNSPNS

On the axon, schwann cells are separated, by gaps called On the axon, schwann cells are separated, by gaps called nodes of ranviernodes of ranvier

Help in nerve cell conductionHelp in nerve cell conduction

Resting neuronsResting neurons maintain a maintain a difference in electrical charge difference in electrical charge across their cell membranes. across their cell membranes.

TheThe inside inside of the resting of the resting neuron is neuron is negatively chargednegatively charged, , the outside is positively the outside is positively charged. charged.

Due to unequal distribution of Due to unequal distribution of NaNa++ and K and K++ and other charged and other charged moleculesmolecules

Nerve Impulse TransmissionNerve Impulse Transmission

The The sodium-potassium sodium-potassium pumpspumps(membrane proteins) (membrane proteins) actively transport sodium actively transport sodium out of the cell and out of the cell and potassium in.potassium in.

Three NaThree Na++ are pumped out are pumped out for every two Kfor every two K++ pumped in. pumped in.

The cell has more NaThe cell has more Na++ on on the outside and more Kthe outside and more K++ on on the inside. the inside.

Thus outside is positive and Thus outside is positive and inside is negative.inside is negative.

The Neuron Membrane at Rest :The Neuron Membrane at Rest :

Resting membrane potential contains -70 millivolts inside the cell membraneResting membrane potential contains -70 millivolts inside the cell membrane

On nerve stimulation,On nerve stimulation, i.e,inside is positive and outside is negative i.e,inside is positive and outside is negative

Due to opening of Na-K pump and Due to opening of Na-K pump and

allows Naallows Na++ to pass freely into the cells. to pass freely into the cells. Resulting in Resulting in depolarizationdepolarization . . The membrane potential is now >+40mV.The membrane potential is now >+40mV. This phenomenon is called This phenomenon is called action potentialaction potential..

The Stimulated Neuron (action potential)

This action potential moves along the cell like a wave. This action potential moves along the cell like a wave. Speed impulse flow is directly proportional to diameter Speed impulse flow is directly proportional to diameter

of the nerve cell of the nerve cell The membrane restores the resting potential very The membrane restores the resting potential very

quickly (in less than 7 milliseconds). quickly (in less than 7 milliseconds). This is called This is called repolarizationrepolarization

Neuron to Neuron Communication: The Neuron to Neuron Communication: The SynapseSynapse

Synaptic cleft –Synaptic cleft – gap gap between adjacent between adjacent neuronsneurons

Synapse –Synapse – junction junction between nerves or between nerves or between nerve and a between nerve and a musclemuscle

Into the synaptic cleft Into the synaptic cleft chemical messengers chemical messengers called neurotransmitterscalled neurotransmitters are released are released

Neuron to Neuron Communication: The Neuron to Neuron Communication: The SynapseSynapse

neurotransmitters are neurotransmitters are synthesized in the cell synthesized in the cell body and body and

Transported through axon Transported through axon into axon terminalsinto axon terminals

Different typesDifferent types

Acetyl choline : Acetyl choline : neuromuscular junctionneuromuscular junction

Norpeinephrine, Norpeinephrine, dopamine, serotonindopamine, serotonin

Synapse between Synapse between an axon terminal an axon terminal of a nerve cell and of a nerve cell and a muscle is known a muscle is known asas

neuromuscular neuromuscular junctionjunction

SynapsesSynapses

Rules for stimulation of nerve impulsesRules for stimulation of nerve impulses

Neuron require a Neuron require a threshold threshold activation potentialactivation potential to be to be stimulated.stimulated.

If the activation potential is If the activation potential is below threshold, it will not below threshold, it will not be stimulated.be stimulated.

This requirement is called This requirement is called all and none law all and none law

How are impulses processedHow are impulses processed

They produce their effect on the They produce their effect on the peripheral nervous systemperipheral nervous system

Ultimately resulting in performance of a Ultimately resulting in performance of a specific function by the bodyspecific function by the body

The Reflex ArcThe Reflex Arc Reflex –Reflex – rapid, predictable, and involuntary rapid, predictable, and involuntary

responses to stimuliresponses to stimuli

Reflex arc –Reflex arc – direct route from a direct route from a sensory neuron,sensory neuron, to an ito an interneuronnterneuron, to an , to an effectoreffector

  Reflex ArcReflex Arc   A complete pathway A complete pathway

through the nervous system through the nervous system from stimulus to responsefrom stimulus to response

Following parts represent Following parts represent the typical reflex arcthe typical reflex arc

Receptor:Receptor: The end of the The end of the dendrite or some specialized dendrite or some specialized receptor cell as in a special receptor cell as in a special sense organ(skin) that sense organ(skin) that detects the stimulusdetects the stimulus

Sensory neuron (or afferent neuron):Sensory neuron (or afferent neuron): A cell that transmits impulse A cell that transmits impulse from receptor towards CNS.from receptor towards CNS.

  Central neuron( interneuron or associated neuron):Central neuron( interneuron or associated neuron): A cell or cells A cell or cells in the CNS carry impulses to and from the brain within the brain or to in the CNS carry impulses to and from the brain within the brain or to different regions of the spinal cord.different regions of the spinal cord.  

Reflex ArcReflex Arc

Motor neuron (or Motor neuron (or efferent neuron):efferent neuron): A A cell that carries cell that carries impulses away from impulses away from CNSCNS

Effector:Effector: A muscle or a A muscle or a gland outside the CNS gland outside the CNS that carries out a that carries out a responseresponse

Reflex ArcReflex Arc

Reflexes are involuntary Reflexes are involuntary actions involving actions involving

a. skeletal musclea. skeletal muscle b. spinal cord andb. spinal cord and c. brain stem c. brain stem

e.g. e.g. withdrawal reflex (withdrawal withdrawal reflex (withdrawal

from painful stimulus) and from painful stimulus) and

knee jerk reflex(patellar knee jerk reflex(patellar REFLEX), results in quadriceps REFLEX), results in quadriceps to contract and leg to extend)to contract and leg to extend)

Reflex ArcReflex Arc

Simple Reflex ArcSimple Reflex Arc

Organization of the Nervous SystemOrganization of the Nervous System

Central Nervous System (CNS)Central Nervous System (CNS) CNS develops from the CNS develops from the

embryonic neural tubeembryonic neural tube

The neural tube becomes The neural tube becomes the brain and spinal cordthe brain and spinal cord

The opening of the neural The opening of the neural tube becomes the tube becomes the ventriclesventricles

Four chambers within Four chambers within the brainthe brain

Filled with Filled with cerebrospinal fluidcerebrospinal fluid

Nervous tissue is organized into brain and Nervous tissue is organized into brain and spinal cord asspinal cord as

Gray matterGray matter:: collection of neuron collection of neuron cell bodies , dendrites cell bodies , dendrites and axon terminals or and axon terminals or bundles of bundles of unmyelinated axons unmyelinated axons and ganglia.and ganglia.

White matterWhite matter:: Bundles of axons of Bundles of axons of several neurons, several neurons, which are wrapped in which are wrapped in myelin sheath.myelin sheath.

CENTRAL NERVOUS SYSTEMCENTRAL NERVOUS SYSTEM

Site for initiating Site for initiating responses and integrating responses and integrating mental process (emotions mental process (emotions and intelligence)and intelligence)

Constitutes spinal cord Constitutes spinal cord and brain.and brain.

Protected by three Protected by three connective tissue connective tissue covering called covering called meninges.meninges.

Outer layer is the Outer layer is the duramaterduramater . .

It is made of dense white It is made of dense white fibrous connective tissue and fibrous connective tissue and blood vesselsblood vessels

It continues along the spinal It continues along the spinal cord and ends in a called cord and ends in a called epidural spaceepidural space..

This space is not seen in This space is not seen in brainbrain

In spinal cord it is also made In spinal cord it is also made of adipose connective tissue of adipose connective tissue to protect spinal cordto protect spinal cord

Middle layer is arachnoid Middle layer is arachnoid matermater

It is made of connective It is made of connective tissue rich in collagen tissue rich in collagen fibers. fibers.

The space between The space between arachnoid and third layer arachnoid and third layer pia mater is known as pia mater is known as subarachnoid space. subarachnoid space.

It is filled with cerebrospinal It is filled with cerebrospinal fluid.fluid.

It is not supplied with It is not supplied with nerves or blood vesselsnerves or blood vessels

c. c. Inner layer is Pia Inner layer is Pia matermater

It is made of thin It is made of thin connective tissue layer connective tissue layer

It is in direct contact It is in direct contact with the brain with the brain

It is supplied with blood It is supplied with blood vessels and nervesvessels and nerves

Cerebrospinal Fluid (CSF)Cerebrospinal Fluid (CSF)

Similar to blood plasma Similar to blood plasma compositioncomposition

Forms a watery cushion Forms a watery cushion to protect the brainto protect the brain

Circulated in arachnoid Circulated in arachnoid space, ventricles, and space, ventricles, and central canal of the spinal central canal of the spinal cordcord

Central Nervous systemCentral Nervous system

BrainBrain

Spinal CordSpinal Cord

BrainBrain is the largest organ of is the largest organ of nervous system. nervous system.

12 pairs of cranial nerves 12 pairs of cranial nerves arise from brainarise from brain

It is enclosed in skull. It is enclosed in skull.

Brain is subdivided intoBrain is subdivided into Cerebrum (cerebral Cerebrum (cerebral

hemispheres)hemispheres) CerebellumCerebellum DiencephalonDiencephalon Brain stemBrain stem

BrainBrain

CerebrumCerebrum: or cerebral hemispheres: or cerebral hemispheres has two large cerebral has two large cerebral

hemispheres connected hemispheres connected by nerves fibers calledby nerves fibers called

Corpus callosum.Corpus callosum.

Surface of cerebrum Surface of cerebrum has ridgeshas ridges or or gyrigyri

Gyri are separated by Gyri are separated by grooves calledgrooves called sulcussulcus

Deep grooves separate Deep grooves separate cerebrum into 4 distinct lobes.cerebrum into 4 distinct lobes.

Frontal lobeFrontal lobe: motor : motor function of muscles, function of muscles, speech and intellectual speech and intellectual processes.processes.

Parietal lobeParietal lobe:: sensations sensations and speech.and speech.

Occipital lobeOccipital lobe:: vision vision

Temporal lobeTemporal lobe:: sensory sensory areas of smell, auditory, areas of smell, auditory, memory, language memory, language comprehensioncomprehension

Basal nuclei:Basal nuclei: grey grey matter surrounded matter surrounded by white matter in by white matter in the cerebral cortex.the cerebral cortex.

Its function is not Its function is not understoodunderstood

May have a role in May have a role in voluntary functionsvoluntary functions

Limbic system: below the cerebral cortexLimbic system: below the cerebral cortex Parts of cerebrum, thalamus and Parts of cerebrum, thalamus and

hypothalamushypothalamus

Relates conscious and subconscious Relates conscious and subconscious aspects of brainaspects of brain

Results in relating an action and Results in relating an action and sensory stimulus to pain, pleasure, sensory stimulus to pain, pleasure, anger etcanger etc

Thus helping in survivalThus helping in survival

Gives raise to feelings of emotions Gives raise to feelings of emotions such as pleasure, pain, anxietysuch as pleasure, pain, anxiety

cerebellumcerebellum Posterior to brain stem Posterior to brain stem Separated from brain stem by Separated from brain stem by

forth ventricleforth ventricle

Divided into two hemispheres Divided into two hemispheres connected mediallyconnected medially

Each hemispere is made of grey Each hemispere is made of grey matter superficially and white matter superficially and white matter interiorly matter interiorly

Important for Muscle coordination Important for Muscle coordination received from cerebral cortex inreceived from cerebral cortex in

Skeletal muscle contraction Skeletal muscle contraction muscle tone and posturemuscle tone and posture

Damage to cerebellum causes Damage to cerebellum causes tremors and problem with tremors and problem with equilibrium, postureequilibrium, posture

DiencephalonDiencephalon: has hypothalamus and thalamus : has hypothalamus and thalamus surrounding third ventricle and made of grey mattersurrounding third ventricle and made of grey matter

Present below cerebrum and above midbrainPresent below cerebrum and above midbrain

It is divided into It is divided into

HypothalamusHypothalamus

ThalamusThalamus

HypothalamusHypothalamus: It is : It is combination of nervous combination of nervous and endocrine organsand endocrine organs

Forms the floor of third Forms the floor of third ventricleventricle

Controls involuntary Controls involuntary functions likefunctions like

maintenance of maintenance of homeostasis, homeostasis,

regulation of sleep,regulation of sleep, temperature, temperature, BP, etcBP, etc

ThalamusThalamus: above the : above the midbrain midbrain

Forms the lateral walls Forms the lateral walls of the third ventricleof the third ventricle

central relay station central relay station from spinal cord, from spinal cord, brainstem, and brainstem, and cerebellum to cerebral cerebellum to cerebral cortex.cortex.

Besides hypothalamus Besides hypothalamus and thalamusand thalamus,,

diencephalon harborsdiencephalon harbors

pineal body,pineal body,

pituitary glandpituitary gland

d. Brain Stemd. Brain Stem: Medulla, pons and : Medulla, pons and

midbrain.midbrain.

Mid brainMid brain

superior to pons.superior to pons.

coordinating the visual coordinating the visual and auditory activitiesand auditory activities

Tactile( general touch) Tactile( general touch) response.response.

It helps in the movement It helps in the movement of head and neck to of head and neck to

eye and hearing eye and hearing responsesresponses

PonsPons Made of axons Made of axons

transporting from transporting from cerebellum and rest of the cerebellum and rest of the brain and spinal cordbrain and spinal cord

relays information from relays information from spinal cord and medulla to spinal cord and medulla to cerebral cortexcerebral cortex

regulates respiratory regulates respiratory movements rate, visual movements rate, visual and auditory functionsand auditory functions

Medulla Medulla oblongataoblongata

MedullaMedulla: Lies superior to spinal : Lies superior to spinal cord and inferior to pons. cord and inferior to pons.

It is the vital center for regulation It is the vital center for regulation of autonomous activities such asof autonomous activities such as

Heartbeat ( cardiac center), Heartbeat ( cardiac center), breathing, ( respiratory center)breathing, ( respiratory center) vasoconstriction (vasomotor vasoconstriction (vasomotor

center) and others such ascenter) and others such as reflex centers for vomiting, reflex centers for vomiting,

coughing, sneezing hiccups, coughing, sneezing hiccups, swallow.swallow.

Relay center between cerebral Relay center between cerebral cortex and spinal cordcortex and spinal cord

4 ventricles4 ventricles 2 Lateral : cerebral 2 Lateral : cerebral

hemisphereshemispheres Third ventricle- Third ventricle-

diencephalondiencephalon Fourth ventricle: base of Fourth ventricle: base of

cerebellum connects to cerebellum connects to central canal of spinal central canal of spinal cordcord

Cerebrospinal fluid:Cerebrospinal fluid: Surrounds brain and spinal cord and protects them from Surrounds brain and spinal cord and protects them from

mechanical shockmechanical shock

produced by ependymal cells of lateral ventricles,third and fourth produced by ependymal cells of lateral ventricles,third and fourth ventricles.ventricles.

CSF exchanges its nutrients and excretory material with the CSF exchanges its nutrients and excretory material with the blood vessels of brain called blood vessels of brain called dural sinusesdural sinuses..

Spinal CordSpinal Cord:: It is enclosed in the vertebral It is enclosed in the vertebral

columncolumn

Spinal cord continues from the Spinal cord continues from the medulla oblongota medulla oblongota

To the second lumbar vertebraTo the second lumbar vertebra Connecting link between organs Connecting link between organs

and brain with the help ofand brain with the help of 31 pairs of spinal nerves arise 31 pairs of spinal nerves arise

from spinal cord to various from spinal cord to various organs.organs.

Made ofMade of gray matter surrounding central gray matter surrounding central

canal in the form of butter flycanal in the form of butter fly

white matter surrounding the grey white matter surrounding the grey matter.matter.

Gray matterGray matter.made of dendrites, cellbodies .made of dendrites, cellbodies and unmylinated axons of interneuronsand unmylinated axons of interneurons

Grey matter looks like Grey matter looks like butterfly. It is divided butterfly. It is divided intointo

Dorsal hornDorsal horn : sensory : sensory nerve fibers from nerve fibers from sensory organs endsensory organs end

ventral hornventral horn: from : from which motor fibers which motor fibers arise to skeletal arise to skeletal musclesmuscles

White matter: surrounds grey matter or butterflyWhite matter: surrounds grey matter or butterfly has axons wrapped in myelinated has axons wrapped in myelinated

sheath.sheath.

form columns in the tracts( nerves) in form columns in the tracts( nerves) in the spinal cordthe spinal cord

Ascending tractsAscending tracts: carry information : carry information from spinal cord to brainfrom spinal cord to brain

Descending tractsDescending tracts: carry information : carry information from brain to spinal cordfrom brain to spinal cord

Spinal CordSpinal Cord: : enclosed in vertebral column.enclosed in vertebral column.

It has two It has two main main functions.functions.

Communation Communation centercenter

Reflex centerReflex center

Spinal cord provides Spinal cord provides means means of communicationsof communications

between brain and various between brain and various organs with the help of organs with the help of spinal nervesspinal nerves

conduction of conduction of sensory sensory impulsesimpulses upward upward

through ascending tractsthrough ascending tracts to the brainto the brain

conduction of conduction of motor motor impulsesimpulses from brain down from brain down

through descending tracts to through descending tracts to the efferent neurons the efferent neurons

that supply muscles or glandsthat supply muscles or glands

It is the It is the center for center for reflex actionsreflex actions

automatic, involuntary automatic, involuntary responses to changes responses to changes

occurring inside or occurring inside or outside the body. E.g.outside the body. E.g.

Withdrawal reflexWithdrawal reflex

Blood Brain BarrierBlood Brain Barrier

Includes the least permeable Includes the least permeable capillaries of the bodycapillaries of the body

Excludes many potentially Excludes many potentially harmful substancesharmful substances

Useless against some Useless against some substancessubstances Fats and fat soluble Fats and fat soluble

moleculesmolecules Respiratory gasesRespiratory gases AlcoholAlcohol NicotineNicotine AnesthesiaAnesthesia

Traumatic Brain InjuriesTraumatic Brain Injuries

ConcussionConcussion Slight brain injurySlight brain injury No permanent brain damageNo permanent brain damage

ContusionContusion Nervous tissue destruction occursNervous tissue destruction occurs Nervous tissue does not regenerateNervous tissue does not regenerate

Cerebral edemaCerebral edema Swelling from the inflammatory responseSwelling from the inflammatory response May compress and kill brain tissueMay compress and kill brain tissue

Cerebrovascular Accident (CVA)Cerebrovascular Accident (CVA)

Commonly called a strokeCommonly called a stroke

The result of a ruptured The result of a ruptured blood vessel supplying a blood vessel supplying a region of the brainregion of the brain

Brain tissue supplied with Brain tissue supplied with oxygen from that blood oxygen from that blood source diessource dies

Loss of some functions or Loss of some functions or death may resultdeath may result

Alzheimer’s DiseaseAlzheimer’s Disease Progressive degenerative Progressive degenerative

brain diseasebrain disease

Mostly seen in the elderly, but Mostly seen in the elderly, but may begin in middle agemay begin in middle age

Structural changes in the brain Structural changes in the brain include abnormal protein include abnormal protein deposits and twisted fibers deposits and twisted fibers within neuronswithin neurons

Victims experience Victims experience memory loss, irritability, memory loss, irritability,

confusion and confusion and ultimately, hallucinations ultimately, hallucinations

and deathand death

Peripheral nervous system (PNS)

Peripheral nervous system (PNS)Part of the nervous system outside the CNS

Consists of cranial nerves and spinal nerves

Carries messages to and from the spinal cord and brain

Two Functional DivisionsSensory (afferent) division

Carry impulses from sensory receptors located in skin, skeletal muscles, joints, visceral organs to the brain

Motor (efferent) division Transmits impulses from the CNS to effector

organs, such as muscles, glands

Peripheral Nervous System (PNS)

Motor division has two main parts:Somatic nervous system

Conscious control of skeletal musclesAutonomic nervous system (ANS)

Regulates smooth muscle, cardiac muscle, and glands

Two divisions of ANS:SympatheticParasympathetic

Motor Division

Peripheral Nervous System (PNS) PNS consists of nerves (bundles of axons) extend from brain and

spinal cord

And ganglia (neuronal cell bodies) outside the CNS

These nerves can be:

Sensory nerves: carry impulses to the brain or spinal cord

Motor nerves: carry impulses to muscles or glands, away from CNS

Mixed nerves: combination of both sensory and motor nerves

Transverse section of a nerve

Nerves consists of axons (some myelinated some not) are surrounded by delicate connective tissue called endoneurium

Groups of nerve fibers are bound into bundles or fascicles by heavier connective tissue layer called perineurium

Finally, all the fascicles are bound together by third layer of connective tissue, epineurium

Cranial nerves There are 12 pairs of nerves originating from the brain and

serve head and neck

Only the pair of vagus nerves extend to thoracic and abdominal cavities

I and II arise from cerebral hemispheres

All others arise from brain stem

I, II and VIII ( sensory nerves)

Rest are mixed motor nerves

Cranial nerves from cerebrum

I (olfactory) nerve: Sensory for smell Convey information from

nose to base of frontal lobe and temporal lobe of cerebral hemispheres

II (optic) nerves: Sensory for vision Convey information from

eye to occipital lobes of cerebral hemispheres

Cranial nerves arising from midbrain III (occulomotor) nerve: Is a combination of

somatic motor and autonomic motor nerves

They regulate the amount of light entering eye and also focusing lens

IV (trochlear) nerve: controls the movement of

eye muscle Smallest nerve

Cranial nerves arising from pons V( trigeminal) nerve: largest nerve Three branches: Mandibulary: ( motor), motor fibers to

chewing muscles Maxillary: (sensory) , conveys

impulses from upper teeth, upper lip

Ophthalmic: Sensory Convey impulses from

scalp, eye and nose

Cranial nerves arising from Pons VI abducens: Motor fiber to eye muscle Arising at the site of pons Important for eye movement

VII (facial): Activates the muscles of

facial expressions and carries sensory impulses from the taste bud

VIII (vestibulocochlear): Purely sensory Transmit impulses for

hearing and balance

Cranial nerves arising from Medulla

IX (glassopharyngeal): Is important for taste and swallowing Supplies motor fibers to tongue

and pharynx

X (vagus): Fibers carry sensory impulses

from and motor impulses to larynx, pharynx, thoracic and abdominal viscera

Regulate digestive and heart activity

Cranial nerves arising from Medulla XI (accessory): Important for

mastication, Supplies nerves to

tongue, soft palate, pharynx etc and muscles of neck

XII (hypoglossal): Is important for tongue

function such as speaking, chewing, swallowing

Cranial NervesCranial Nerves

Spinal nerves There are 31 pairs of spinal nerves each numbered

according to the level of the spinal cord from where it arises

Each spinal nerve is a mixed nerve consisting of sensory and motor nerve      

Each nerve is attached to the spinal cord by two roots

Dorsal root (sensory) arising from dorsal horn (posterior)  

   

  

Spinal nervesSpinal nerves

ventral root (motor) arising from ventral horn (anterior) It is mainly made of axons from motor neurons Their cell bodies are located in the gray matter of the spinal

cord

Spinal nervesSpinal nerves

 Each spinal nerve continues a short distance from the spinal cord and emerges from the intervertebral foramina

branches out further to different organs

Spinal nervesSpinal nerves

Each spinal nerve has two roots

Dorsal root Ventral root Each root has several

branches Each branch is called Ramus Each rami can be

dorsal( sensory) or ventral( motor)

Spinal nervesSpinal nerves

  The spinal nerves arising

from the respective region of the spinal cord:

a. 8 cervical (C1-C8),  b. 12 thoracic (T1-T12),

  c. 5 lumbar (L1-L5),   d. 5 sacral (S1-S5), and   e. 1coccygeal(Co).

Spinal nervesSpinal nerves

 

Cauda equina  :

5 lumbar (L1-L5), 5 sacral (S1-S5), and1coccygeal(Co).

together taper out forming Cauda equina

Spinal nervesSpinal nerves

Except thoracic region,

Spinal nerves form a network called plexuses.

These networks distribute branches to the parts of the body

There are 3 different plexuses  

Plexuses Plexuses

Cervical plexusFormed by C1-C4. Serve to Muscles

and skin of neck and shoulder

Brachial plexus

Formed by C5-T1

They are musculocutaneous nerve

Radial nerve

Median nerve

Ulnar nerve

Supply arm, forearm and hand

Phrenic nerve : C3-C5

Supplies diaphragm

PlexusesPlexuses

Lumbosacral plexus formed by T12-S5

Important nerves arising from them are

Femoral nerve:

muscles and skin of thighs and legs

Sciatic nerve:

muscles and skin of thigh legs and feet

T2-T11 : intercoastal nerves Thoracic spinal nerves serves

to muscles of respiration,

and upper abdomen And receive information

from thorax and abdomen

Autonomous nervous system (ANS) Motor subdivision of the PNS

Consists only of motor nerves

Also known as the Involuntary nervous system Regulates activities of cardiac and smooth

muscles and glands

Two subdivisions Sympathetic division Parasympathetic division

PNS: Differences Between Somatic

and Autonomic Nervous Systems Nerves

Somatic: one motor neuron

Autonomic: preganglionic and postganglionic nerves

Effector organs Somatic: skeletal

muscle Autonomic: smooth

muscle, cardiac muscle, and glands

PNS: Differences Between Somatic

and Autonomic Nervous Systems

NeurotransmittersSomatic: always use acetylcholineAutonomic: use acetylcholine, epinephrine, or

norepinephrine

PNS: Anatomy of the Sympathetic Division Originates from T1 through L2

Ganglia are at the sympathetic trunk (near the spinal cord)

Short pre-ganglionic neuron synapses with long post-ganglionic neuron and transmit impulse from CNS to the effector

Norepinephrine and epinephrine are neurotransmitters to the effector organs

PNS: Anatomy of the Parasympathetic Division

Originates from the brain stem and S1 through S4

Always uses acetylcholine as a neurotransmitter

PNS: Autonomic Functioning

Sympathetic — “fight or flight”Response to unusual stimulusTakes over to increase activities

Exercise, excitement, emergency, and embarrassment

Sympathetic nervous system increases heart rate, blood pressure, blood glucose levels

PNS: Autonomic Functioning

Parasympathetic—“housekeeping” activitesConserves energyMaintains daily necessary body functions

digestion, defecation, and diuresis (urination)

Development Aspects of the Nervous System

The nervous system is formed during the first month of embryonic development

Any maternal infection can have extremely harmful effects

The hypothalamus is one of the last areas of the brain to develop

No more neurons are formed after birth, but growth and maturation continues for several years

The brain reaches maximum weight in young adult