The Nervous System:The Nervous System:Neural TissueNeural Tissue

Coordination of activities:Coordination of activities:Nervous SystemNervous System

Nervous System:Nervous System:– Swift, brief, temporarySwift, brief, temporary

Functions: (motor & sensory)Functions: (motor & sensory)– Provide sensationProvide sensation– Integrate infoIntegrate info– Coordinate voluntary & involuntary Coordinate voluntary & involuntary

activitiesactivities– Regulate & control systemsRegulate & control systems

Nervous System OverviewNervous System Overview 2 Anatomical Divisions2 Anatomical Divisions

1.1. CentralCentral Nervous System (CNS) Nervous System (CNS)1.1. Brain and spinal cordBrain and spinal cord

2.2. PeripheralPeripheral Nervous System (PNS) Nervous System (PNS)1.1. SomaticSomatic Nervous System (SNS) Nervous System (SNS)2.2. AutonomicAutonomic Nervous System (ANS) Nervous System (ANS)

1.1.SympatheticSympathetic N. S.- “flight or fight” N. S.- “flight or fight”2.2.ParasympatheticParasympathetic N. S.- “rest & repose” N. S.- “rest & repose”3.3. http://itc.gsw.edu/faculty/gfisk/anim/index.html http://itc.gsw.edu/faculty/gfisk/anim/index.html

2 Functional Divisions (based on function)2 Functional Divisions (based on function)1.1. AfferentAfferent: Sensory (muscles/ glands: Sensory (muscles/ glands CNS) CNS)2.2. EfferentEfferent: Motor (CNS: Motor (CNS muscles/ glands muscles/ glands

Cellular Organization in Neural Cellular Organization in Neural TissueTissue

1.1. NeuronsNeurons: (=Nerve cells): (=Nerve cells) Soma (cell body)Soma (cell body) DendritesDendrites Axon & Nodes of Ranvier/ InternodesAxon & Nodes of Ranvier/ Internodes Synaptic terminals (knobs)Synaptic terminals (knobs)

2.2. Neuroglia= Glial CellsNeuroglia= Glial Cells• Protects neurons Protects neurons • Provides support Provides support • PhagocytesPhagocytes

Neuron DiagramNeuron Diagram

Neuron Functional Neuron Functional ClassificationsClassifications

1.1. Sensory NeuronsSensory Neurons= Afferent fibers= Afferent fibers TOTO CNS from ext & int environment CNS from ext & int environment Cell bodies in Cell bodies in peripheral gangliaperipheral ganglia neuronsneurons

from from sensory receptorssensory receptors spinal cord spinal cord Types:Types:

1.1. Somatic Sensory NeuronsSomatic Sensory Neurons: ext environment: ext environment

2.2. ExteroceptorsExteroceptors: sight, smell, hear, touch: sight, smell, hear, touch

3.3. ProprioceptorsProprioceptors: position joints & muscles: position joints & muscles

4.4. Visceral Sensory NeuronsVisceral Sensory Neurons= Interoceptors: = Interoceptors: internal envmt like visceral systems & internal envmt like visceral systems & taste, deep pressure, paintaste, deep pressure, pain

Neuron Functional Neuron Functional ClassificationClassification

2.2. Motor NeuronsMotor Neurons: Efferent fibers: Efferent fibers FromFrom CNS to effectors (muscles/ glands) CNS to effectors (muscles/ glands) Stimulates or modifies activity of peripheral Stimulates or modifies activity of peripheral

tissues, organs, organ systemstissues, organs, organ systems Types:Types:

1.1. Somatic Motor NeuronsSomatic Motor Neurons: : Voluntary skeletal muscleVoluntary skeletal muscle Spinal cordSpinal cord neuromuscular junction neuromuscular junction

2.2. Visceral Motor NeuronsVisceral Motor Neurons (of ANS) (of ANS) Involuntary peripheral effectorsInvoluntary peripheral effectors Spinal Cord (preganglionic fibers)Spinal Cord (preganglionic fibers)

peripheral ganglion (PNS cell bodies)peripheral ganglion (PNS cell bodies) postganglionic fiberspostganglionic fibers effectors effectors

Neuron Functional Neuron Functional ClassificationClassification

3.3. Interneurons= Association NeuronsInterneurons= Association Neurons– b/w sensory & motor neuronsb/w sensory & motor neurons– Located entirely in brain & spinal cordLocated entirely in brain & spinal cord– Function:Function:

Analysis of sensory inputsAnalysis of sensory inputs Coordination of motor outputsCoordination of motor outputs

– Classified as excitatory or inhibitoryClassified as excitatory or inhibitory

Nervous System:Functional Nervous System:Functional Classification OrganizationClassification Organization

Neuron CommunicationNeuron Communication SynapseSynapse

– Space between synaptic knob & next cellSpace between synaptic knob & next cell Neurons communicate with:Neurons communicate with:

1.1. Other neurons Other neurons

2.2. Other Cells: Other Cells:

1.1. Neuromuscular JunctionNeuromuscular Junction

2.2. Neuroglandular JunctionNeuroglandular Junction NeurotransmittersNeurotransmitters

– Chemical messenger at synapseChemical messenger at synapse

Resting Membrane Potential Resting Membrane Potential Intracellular FluidsIntracellular Fluids: High in [K+]: High in [K+] Extracellular FluidsExtracellular Fluids: High in [Na+]: High in [Na+] Na+/K+ exchange pumpNa+/K+ exchange pump

– Pump 2K+ in and 3 Na+ outPump 2K+ in and 3 Na+ out– Resting potential: -70mV Resting potential: -70mV

Ion ChannelsIon Channels::1.1. Passive channelsPassive channels: always open & “leaky”: always open & “leaky”2.2. Active or Gated ChannelsActive or Gated Channels::

1.1. Chemically regulatedChemically regulated: neurotransmitter: neurotransmitter2.2. Voltage regulatedVoltage regulated: voltage changes: voltage changes3.3. Mechanically regulatedMechanically regulated: physical stim : physical stim

(Merkel’s discs)(Merkel’s discs)

Neuron Electrical Signal: Action Neuron Electrical Signal: Action PotentialPotential

Action Potential:Action Potential:– Electrical signalElectrical signal– Stimulated by neurotransmitter, voltage Stimulated by neurotransmitter, voltage

change, or physical stimuluschange, or physical stimulus Rules to occur:Rules to occur:

1.1. Depolarization to Depolarization to thresholdthreshold (-60 to -55mV) (-60 to -55mV)

2.2. Occurs in axons & muscle fibers (down T-Occurs in axons & muscle fibers (down T-tubules)tubules)

3.3. All action potentials generated are identical All action potentials generated are identical (gun)(gun)

4.4. All-or-None Response (toll booth) All-or-None Response (toll booth)

Action Potential Generation: StepsAction Potential Generation: Steps1.1. Activate voltage-gated Na+ channelsActivate voltage-gated Na+ channelsdepolarizationdepolarization

Increase membrane potential: Na+ inIncrease membrane potential: Na+ in

2.2. Inactivate Voltage-gated Na+ channels:Inactivate Voltage-gated Na+ channels: +30mV+30mV close & close & can’tcan’t be opened be opened

3.3. Activate Voltage-Gated K+ channelsActivate Voltage-Gated K+ channels repolarizationrepolarization Decrease membrane potential (-70mV): K+ outDecrease membrane potential (-70mV): K+ out

4.4. Return to resting membrane potential: -70mVReturn to resting membrane potential: -70mV Voltage-gated Na+ channels closed, can open.Voltage-gated Na+ channels closed, can open. Voltage-gated K+ channels closing with delay of Voltage-gated K+ channels closing with delay of

1msec 1msec hyperpolarizationhyperpolarization (below -70mV) (below -70mV) After 1msecAfter 1msec normal resting potential (-70mV) normal resting potential (-70mV)

5.5. Action Potential travels to next portion of membraneAction Potential travels to next portion of membrane

Action Potential: Steps & GraphAction Potential: Steps & Graph

Refractory Periods of Action Refractory Periods of Action PotentialsPotentials

1.1. Absolute refractory periodAbsolute refractory period: Repolarization: Repolarization Membrane Membrane CAN’TCAN’T respond to stim respond to stim From opening voltage-gated Na+ channelsFrom opening voltage-gated Na+ channels end end

of action potentialof action potential Action potential: Action potential: one one direction away from soma.direction away from soma.

2.2. Relative refractory periodRelative refractory period: Hyperpolarization: Hyperpolarization Only Only LARGERLARGER stimulus can initiate axn potential stimulus can initiate axn potential From when voltage-gated Na+ channels are From when voltage-gated Na+ channels are

restored to normal (closed but able to open) state, restored to normal (closed but able to open) state, but voltage-gated K+ channels still open.but voltage-gated K+ channels still open.

Refractory Period & Axn Pot MovementRefractory Period & Axn Pot Movement

Action Potential Conduction Action Potential Conduction VelocityVelocity

1.1. Myelin sheathMyelin sheath Continuous conductionContinuous conduction: segment by segment : segment by segment

UnmyelinatedUnmyelinated axons axons Saltatory ConductionSaltatory Conduction: leap from node to node: leap from node to node

MyelinatedMyelinated axons: ions can’t pass lipid nodes axons: ions can’t pass lipid nodes http://www.blackwellpublishing.com/matthews/http://www.blackwellpublishing.com/matthews/

actionp.html actionp.html

2.2. Axon DiameterAxon Diameter1.1. Type AType A: Largest, myelinated: Largest, myelinated fastest (300mph) fastest (300mph)

sk. mm. motor neurons, balance & L.T.sk. mm. motor neurons, balance & L.T.

2.2. Type BType B: Smaller, myelinated: Smaller, myelinated medium (40mph) medium (40mph)

3.3. Type CType C: Smallest, unmyelinated: Smallest, unmyelinated slowest (2mph) slowest (2mph) Both B & C carry pain, temp, to smooth mm & Both B & C carry pain, temp, to smooth mm &

glandsglands

Continuous v. Saltatory Continuous v. Saltatory ConductionConduction

Cocaine Effects on Cocaine Effects on DopamineDopamine

Other Factors on Rate of A.P.Other Factors on Rate of A.P.

1.1. HormonesHormones can promote facilitation or can promote facilitation or inhibitioninhibition

2.2. Presynaptic inhibitionPresynaptic inhibition: inhibits Ca: inhibits Ca2+2+ channelschannels decr postsynaptic stim (i.e. decr postsynaptic stim (i.e. GABA)GABA)

3.3. Presynaptic FacilitationPresynaptic Facilitation: keep Ca: keep Ca2+2+ channels openchannels open

4.4. [Na+, K+, Ca2+][Na+, K+, Ca2+] (dehydration or kidney (dehydration or kidney dz), dz), pHpH (basic (basic convulsions, acidic convulsions, acidic inhibition), inhibition), temptemp changes changes

Other Neurotransmitters: Excite & Other Neurotransmitters: Excite & InhibitInhibit

ATP Needs & ProductionATP Needs & Production

ATP needed for:ATP needed for:– Synthesis, release, & recycling NTSynthesis, release, & recycling NT– Movement of materialsMovement of materials– Recovery from a.p.: [ion]- Na+/ K+ pumpRecovery from a.p.: [ion]- Na+/ K+ pump

ATP Production:ATP Production:– Aerobic glycolysis (no glucose stores)Aerobic glycolysis (no glucose stores)– Need uninterrupted blood supply for O2 & Need uninterrupted blood supply for O2 &

glucoseglucose Stroke: Stroke:

– less than 1-2 hrsless than 1-2 hrs few weeks to recover few weeks to recover– longerlonger permanent permanent

Ach Drugs & Synaptic FunctionAch Drugs & Synaptic Function Drug EffectsDrug Effects::

1.1. Interferes w/ NT Interferes w/ NT synthesissynthesis

2.2. Alter rate of NT releaseAlter rate of NT release

3.3. Prevent NT inactivationPrevent NT inactivation

4.4. Prevent NT binding to Prevent NT binding to receptorsreceptors

CaffeineCaffeine lowers threshold lowers threshold at axon hillockat axon hillock more more sensitive to stim sensitive to stim (facilitation)(facilitation) “jumpy” “jumpy”

NicotineNicotine bind to receptor bind to receptor sites on postsynaptic sites on postsynaptic membrane & stimulate membrane & stimulate itit no enzymes to no enzymes to remove itremove it

ExamplesExamples

1.1. Botulinus toxinBotulinus toxin: blocks : blocks release Ach at presynaptic release Ach at presynaptic membranemembrane paralysis paralysis

2.2. Black Widow spiders Black Widow spiders venom venom : cause massive : cause massive release of Achrelease of Ach cramps/ cramps/ spasmsspasms

3.3. Anticholinesterase drugsAnticholinesterase drugs: : block breakdown Ach by block breakdown Ach by AchEAchE extreme contract extreme contract (ex: nerve gases, pst (ex: nerve gases, pst controls)controls)

4.4. AtropineAtropine: prevent Ach : prevent Ach binding to postsynaptic binding to postsynaptic neuronneuron paralysis (curare paralysis (curare plant extract) plant extract)

Drug Effects on Ach SynapsesDrug Effects on Ach Synapses