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The Nervous SystemThe Nervous System

Millions of interconnected neurons form the nervous Millions of interconnected neurons form the nervous systemsystem

Human nervous system two major parts: central Human nervous system two major parts: central nervous system and peripheral nervous systemnervous system and peripheral nervous system

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Nervous System OrganizationNervous System Organization

BrainBrain Spinal cordSpinal cord

Central Nervous SystemCentral Nervous System

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Nervous System OrganizationNervous System Organization

All neurons outside the All neurons outside the CNSCNS– 31 pairs spinal nerves31 pairs spinal nerves

– 12 pairs of cranial 12 pairs of cranial nervesnerves

Peripheral Nervous System

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The Brain - 3 Major AreasThe Brain - 3 Major Areas

Cerebrum (telencephalon, diencephalon,)Cerebrum (telencephalon, diencephalon,) CerebellumCerebellum Brainstem (midbrain, pons, medulla Brainstem (midbrain, pons, medulla

oblongata)oblongata)

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CerebrumCerebrum

Composed of Telencephalon (Cerebral Composed of Telencephalon (Cerebral Cortex) and DiencephalonCortex) and Diencephalon

Cerebral Cortex is gray matter because Cerebral Cortex is gray matter because nerve fibers lack white myelin coatingnerve fibers lack white myelin coating

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Cerebral Cortex - 4 Major Cerebral Cortex - 4 Major LobesLobes

ParietalParietal FrontalFrontal TemporalTemporal OccipitalOccipital

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Functions of the Cerebral Functions of the Cerebral CortexCortex

Intellectual processes: thought, intelligence.Intellectual processes: thought, intelligence. Processes sensory information and integrates with past Processes sensory information and integrates with past

experience to produce appropriate motor response.experience to produce appropriate motor response.

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Diencephalon - 2 Major PartsDiencephalon - 2 Major Parts

ThalamusThalamus– Relays stimuli received from all sensory neurons to cortex Relays stimuli received from all sensory neurons to cortex

for interpretationfor interpretation

– Relays signals from the cerebral cortex to the proper area Relays signals from the cerebral cortex to the proper area for further processingfor further processing

HypothalamusHypothalamus– Monitors many parametersMonitors many parameters

temperature, blood glucose levels, various hormone levelstemperature, blood glucose levels, various hormone levels

– Helps maintain homeostasisHelps maintain homeostasis

– Signals the pituitary via releasing factorsSignals the pituitary via releasing factors

– Signals the lower neural centersSignals the lower neural centers

DiencephalonDiencephalon

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CerebellumCerebellum

Located behind the Located behind the brainstembrainstem

Helps monitor and Helps monitor and regulate movementregulate movement

Integrates postural Integrates postural adjustments, adjustments, maintenance of maintenance of equilibrium, perception equilibrium, perception of speed, and other of speed, and other reflexes related to fine reflexes related to fine tuning of movement.tuning of movement.

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BrainstemBrainstem

Composed of midbrain, pons, and medulla Composed of midbrain, pons, and medulla oblongataoblongata

Maintains vegetative functioningMaintains vegetative functioning– Where is respiratory control center?Where is respiratory control center?– Where is cardiovascular control center?Where is cardiovascular control center?

ReflexesReflexes

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Brain StemBrain Stem

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Spinal CordSpinal Cord

Contains both gray and white matterContains both gray and white matter Gray matter is H-shape in core of cordGray matter is H-shape in core of cord

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Gray MatterGray Matter

Regions of brain and spinal cord made up Regions of brain and spinal cord made up primarily of cell bodies and dendrites of primarily of cell bodies and dendrites of nerve cellsnerve cells

Interneurons in spinal cordInterneurons in spinal cord– small nerves which do not leave the spinal cordsmall nerves which do not leave the spinal cord

Terminal portion of axons Terminal portion of axons

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White MatterWhite Matter

Contains tracts or pathways made up of Contains tracts or pathways made up of bundles of myelinated nervesbundles of myelinated nerves

Carry ascending and descending signalsCarry ascending and descending signals– Ascending nerve tract from sensory receptors Ascending nerve tract from sensory receptors

through dorsal root, up cord to thalamus, to through dorsal root, up cord to thalamus, to cerebral cortexcerebral cortex

– Pyramidal tract transmits impulses downward Pyramidal tract transmits impulses downward eventually excites motoneurons control muscles.eventually excites motoneurons control muscles.

– Extrapyramidal originate in brain stem descend Extrapyramidal originate in brain stem descend to control posture.to control posture.

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Descending Nerve TractsDescending Nerve Tracts

Ascending: dorsalAscending: dorsalDescending: lateral, ventro-Descending: lateral, ventro-medial tractsmedial tracts

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Peripheral Nervous SystemPeripheral Nervous System

Thirty-one pairs of Thirty-one pairs of spinal nerves & 12 pairs spinal nerves & 12 pairs of cranial nerves.of cranial nerves.

Each spinal nerve is a Each spinal nerve is a mixed nerve containing:mixed nerve containing:– Somatic afferentSomatic afferent

– Visceral afferentVisceral afferent

– Somatic efferentSomatic efferent

– Visceral efferentVisceral efferent Which is a motor fiber?Which is a motor fiber?

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Somatic Nervous SystemSomatic Nervous System

Somatic afferent Somatic afferent (sensory): carry (sensory): carry sensations from periphery sensations from periphery to spinal cord. Includes to spinal cord. Includes exteroceptive (pain, exteroceptive (pain, temperature, touch) & temperature, touch) & proprioceptive.proprioceptive.

Somatic efferent (motor): Somatic efferent (motor): communicate from spinal communicate from spinal cord to skeletal muscles.cord to skeletal muscles.

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Autonomic Nervous System Autonomic Nervous System SubdivisionsSubdivisions

SympatheticSympathetic– responsible for increasing activity in most responsible for increasing activity in most

systems (except GI)systems (except GI)– adrenergic fibers release epinephrineadrenergic fibers release epinephrine

ParasympatheticParasympathetic– responsible for slowing activity in most systems responsible for slowing activity in most systems

(except GI)(except GI)– cholinergic fibers release acetylcholinecholinergic fibers release acetylcholine

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Autonomic ReflexAutonomic Reflex

Monosynaptic reflex Monosynaptic reflex arcarc

Knee jerk responseKnee jerk response

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Complex ReflexesComplex Reflexes

Involve multiple Involve multiple synapsessynapses

Crossed extensor reflex Crossed extensor reflex

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Motor UnitMotor Unit A single motor neuron and all of the muscle fibers which it A single motor neuron and all of the muscle fibers which it

innervates. Represents functional unit of movement.innervates. Represents functional unit of movement. Ratio of muscle fibers to nerve relates to muscle’s movement Ratio of muscle fibers to nerve relates to muscle’s movement

function.function.

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NeuronsNeurons

Two basic typesTwo basic types1.1. MotorMotor

2.2. SensorySensory Three basic partsThree basic parts

1.1. Axons Axons

2.2. DendritesDendrites

3.3. Soma or Cell BodiesSoma or Cell Bodies

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Sensory NervesSensory Nerves

Enter the spinal cord on Enter the spinal cord on the dorsal sidethe dorsal side

Cell bodies lie outside Cell bodies lie outside the spinal cord in the spinal cord in Dorsal Root GangliaDorsal Root Ganglia

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Motor NervesMotor Nerves

Exit the spinal cord on the ventral sideExit the spinal cord on the ventral side Cell bodies lie within grey matter of spinal Cell bodies lie within grey matter of spinal

cordcord Somatic Somatic

– innervates skeletal muscleinnervates skeletal muscle Autonomic (visceral)Autonomic (visceral)

– innervates organs / smooth muscleinnervates organs / smooth muscle

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Neuron Part: AxonsNeuron Part: Axons

Carry impulses away from the cell bodyCarry impulses away from the cell body

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MyelinMyelin

Schwann cells Schwann cells wrapped around the wrapped around the axon of some axon of some neuronsneurons

– appear as multiple lipid-protein layersappear as multiple lipid-protein layers– are actually a continuous cellare actually a continuous cell– increase the speed of action potential conductionincrease the speed of action potential conduction

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Nodes of RanvierNodes of Ranvier

Gaps between Schwann CellsGaps between Schwann Cells– impulse jumps from node to nodeimpulse jumps from node to node– saltatory conductionsaltatory conduction

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Neuron Parts:Neuron Parts: Dendrites and Cell body Dendrites and Cell body

Dendrite: receives stimuli and carry it to the Dendrite: receives stimuli and carry it to the cell bodycell body

Cell body: site of cellular activityCell body: site of cellular activity

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SynapseSynapse

Junction between the dendrites of one neuron Junction between the dendrites of one neuron and the axon of a second neuronand the axon of a second neuron

Nerves communicate by releasing chemical Nerves communicate by releasing chemical messenger at synapsemessenger at synapse

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SynapseSynapse

Important neurotransmitters:MonoaminesNeuropeptidesNitric oxide

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Motor Nerves - SizeMotor Nerves - Size

Alpha motor nervesAlpha motor nerves– Larger fibersLarger fibers– Conduct impulses fasterConduct impulses faster– Innervate regular muscle fibersInnervate regular muscle fibers

Gamma Motor nervesGamma Motor nerves– smaller fiberssmaller fibers– conduct impulses more slowlyconduct impulses more slowly– Innervate proprioceptors such as muscle spindlesInnervate proprioceptors such as muscle spindles

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Nerve Properties Nerve Properties Related to FunctionRelated to Function

IrritabilityIrritability– able to respond to stimuliable to respond to stimuli

ConductivityConductivity– able to transmit electrical potential along the axonable to transmit electrical potential along the axon

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Resting Membrane PotentialResting Membrane Potential

Difference in charge between the inside and Difference in charge between the inside and outside of the celloutside of the cell– sodium in greater concentration outsidesodium in greater concentration outside– potassium in greater concentration insidepotassium in greater concentration inside– anions in greater concentration insideanions in greater concentration inside– membrane permeability greater for potassium membrane permeability greater for potassium

than sodiumthan sodium– NaNa+ + / K/ K++ pump moves sodium out, potassium in pump moves sodium out, potassium in

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Generating Action PotentialsGenerating Action Potentials

Voltage gated ion channels Voltage gated ion channels – sodium channels open --- sodium rushes insodium channels open --- sodium rushes in– sodium channels close --- stops inward flow of sodium channels close --- stops inward flow of

sodiumsodium– potassium channels open --- potassium rushes outpotassium channels open --- potassium rushes out

Net effect - Depolarization then Net effect - Depolarization then RepolarizationRepolarization– electrical flow created by ionic flow, not electron electrical flow created by ionic flow, not electron

flowflow

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NaNa+ + / K / K ++ Pump Pump

Membrane bound proteinsMembrane bound proteins Utilizes ATPUtilizes ATP Maintains resting membrane potentialMaintains resting membrane potential Establishes sodium & potassium Establishes sodium & potassium

concentration gradientsconcentration gradients

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Neuromuscular JunctionNeuromuscular Junction

Motor neuron cell body and dendrites in gray Motor neuron cell body and dendrites in gray matter of spinal cordmatter of spinal cord

Axons extend to muscleAxons extend to muscle Axon’s terminal end contains a synaptic knobAxon’s terminal end contains a synaptic knob Synaptic knob has synaptic vesicles Synaptic knob has synaptic vesicles

containing acetylcholinecontaining acetylcholine

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Neuromuscular Neuromuscular JunctionJunction

Axon leaves spinal Axon leaves spinal cord.cord.

Extends to skeletal Extends to skeletal muscle.muscle.

Terminal branches Terminal branches end in synaptic end in synaptic knob.knob.

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Motor End PlateMotor End Plate

Area beneath the terminal branches of the Area beneath the terminal branches of the axonsaxons

Contains acetylcholine receptor complexesContains acetylcholine receptor complexes Acetylcholine binding opens the receptor Acetylcholine binding opens the receptor

complexcomplex Cholinesterase degrades acetylcholine into Cholinesterase degrades acetylcholine into

acetate and cholineacetate and choline

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Tension Generating Tension Generating CharacteristicsCharacteristics

All or None LawAll or None Law– when a neuron reaches threshold it generates an when a neuron reaches threshold it generates an

action potential which is conducted the length of action potential which is conducted the length of the axon without any voltage changethe axon without any voltage change

– when the nerve fires, all the muscle fibers it when the nerve fires, all the muscle fibers it innervates contractinnervates contract

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Summation of Local Graded Summation of Local Graded PotentialsPotentials

Temporal SummationTemporal Summation– additive effect of additive effect of

successive stimuli from successive stimuli from an axon an axon

Spatial SummationSpatial Summation– additive effect of additive effect of

stimuli from various stimuli from various axonsaxons

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Gradation of ForceGradation of Force

Force of muscle varies Force of muscle varies from slight to maximal:from slight to maximal:– Increase number of Increase number of

motor units recruitedmotor units recruited

– Increase frequency of Increase frequency of motor unit discharge.motor unit discharge.

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ProprioceptorsProprioceptors

Muscle SpindlesMuscle Spindles Golgi Tendon OrgansGolgi Tendon Organs Pacinian CorpusclesPacinian Corpuscles Ruffini EndingsRuffini Endings

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Muscle SpindlesMuscle Spindles

Encapsulated fibers Encapsulated fibers within the muscle bellywithin the muscle belly

Monitor changes in Monitor changes in muscle lengthmuscle length

Monitor the rate of Monitor the rate of change in muscle change in muscle lengthlength

Respond by causing Respond by causing muscle contractionmuscle contraction

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Golgi Tendon OrgansGolgi Tendon Organs

Encapsulated receptors Encapsulated receptors Located at the Located at the

musculotendinous musculotendinous junctionjunction

Monitor tension within Monitor tension within the tendonthe tendon

Respond by causing the Respond by causing the muscle to relaxmuscle to relax

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Pacinian Corpuscles & Pacinian Corpuscles & Ruffini EndingsRuffini Endings

Encapsulated receptors Encapsulated receptors Located near joints, in muscle, tendon, and bone Located near joints, in muscle, tendon, and bone