nervous The Nervous System The Nervous System Millions of interconnected neurons Millions of interconnected neurons form the nervous system form the nervous system Human nervous system two major parts: Human nervous system two major parts: central nervous system and peripheral central nervous system and peripheral nervous system nervous system
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Nervous The Nervous System Millions of interconnected neurons form the nervous system Millions of interconnected neurons form the nervous system Human.
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nervous
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
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
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
– 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.
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
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
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
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
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
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.