{ nervous system. sensory input sensory receptors collect info integration interpretation of...
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Nervous SystemNervous System
Sensory inputSensory inputSensory Sensory receptorsreceptors
Collect infoCollect info IntegrationIntegration
Interpretation Interpretation of stimuliof stimuli
Occurs in CNS (brain & spinal Occurs in CNS (brain & spinal cord)cord)
Nervous System OverviewNervous System Overview
Motor OutputMotor Output Conduction of signal from CNS to Conduction of signal from CNS to
effector cellseffector cells Carry out response to stimuliCarry out response to stimuli Muscles & glandsMuscles & glands
Signal conducted by Signal conducted by nervesnerves
CNSCNS PNS (outside of CNS)PNS (outside of CNS)
Nervous System Nervous System OverviewOverview
Nervous System Nervous System OverviewOverview
Nerve CircuitNerve CircuitSimplest: automatic (reflex arc)Simplest: automatic (reflex arc)
Sensory neuronSensory neuron interneuron interneuron of spinal cord of spinal cord motor neuron motor neuron effector cell effector cell
Nervous System Nervous System OverviewOverview
Ganglion: cluster of nerve cell Ganglion: cluster of nerve cell bodies with similar functions in bodies with similar functions in PNSPNSCluster within brain: nucleiCluster within brain: nuclei
Supporting cells :gliaSupporting cells :glia““Glue” neurons Glue” neurons togethertogether
Helps embryonic Helps embryonic development of CNSdevelopment of CNS
Nervous System Nervous System OverviewOverview
Astrocytes: provide support for Astrocytes: provide support for neurons, induce tight junction neurons, induce tight junction formation for cells lining formation for cells lining capillaries of braincapillaries of brainBlood-brain barrierBlood-brain barrier
Restricts passage Restricts passage of substances into of substances into brainbrain
Nervous System Nervous System OverviewOverview
Oligodendrocytes (in CNS) Oligodendrocytes (in CNS) [Schwann cells in PNS][Schwann cells in PNS]Form insulating lipid sheath Form insulating lipid sheath around neuron axonaround neuron axon
Increase Increase speed ofspeed of nerve nerve impulseimpulse
Deterioration Deterioration of: MSof: MS
Nervous System Nervous System OverviewOverview
Nerve signals: changes in voltage across Nerve signals: changes in voltage across plasma membrane of nerve cellsplasma membrane of nerve cellsCaused by ion movementCaused by ion movementMore anions inside; more cations More anions inside; more cations outsideoutsideMembrane now electrically polarizedMembrane now electrically polarized -50 to –100 mV in resting state -50 to –100 mV in resting state (unstimulated)(unstimulated)
Membrane PotentialMembrane Potential
Inside: cations are mostly K+, some Na+ Inside: cations are mostly K+, some Na+ (anions are proteins, a.a., sulfate, P, Cl-)(anions are proteins, a.a., sulfate, P, Cl-)
Outside: cations are mostly Na+, some K+ Outside: cations are mostly Na+, some K+ (anions are mostly Cl-)(anions are mostly Cl-)
Ions only pass through selective protein Ions only pass through selective protein channelschannels
Most cells more permeable to K+ than Na+Most cells more permeable to K+ than Na+ Internal anions too large to crossInternal anions too large to cross
Membrane PotentialMembrane Potential
Tendency for K+ to diffuse out, Na+ inTendency for K+ to diffuse out, Na+ inThrough channels that are always Through channels that are always open (ungated)open (ungated)
Sodium-potassium pump uses ATP to Sodium-potassium pump uses ATP to bring K+ in & Na+ outbring K+ in & Na+ outMaintains ionic gradient – keep Maintains ionic gradient – keep potentialpotential
Membrane PotentialMembrane Potential
Cells that generate changes in Cells that generate changes in potential – excitable cellspotential – excitable cellsWhen unexcited: resting potentialWhen unexcited: resting potentialWhen stimulated, gated ion When stimulated, gated ion channels open - allow specific ion channels open - allow specific ion throughthrough
Membrane PotentialMembrane Potential
Some stimuli trigger hyperpolarization Some stimuli trigger hyperpolarization – inc in voltage across membrane (K+ – inc in voltage across membrane (K+ out out cell more negative) cell more negative)
Some trigger depolarization (Na+ in Some trigger depolarization (Na+ in cell less negative) cell less negative)
Strong enough stimuli trigger action Strong enough stimuli trigger action potential (nerve impulse)potential (nerve impulse)
Membrane PotentialMembrane Potential
All or nothingAll or nothing
Few millisecondsFew milliseconds
In between stimuli: refractory periodIn between stimuli: refractory period
More intense stimuli – repeated action potentials with More intense stimuli – repeated action potentials with
refractory period in betweenrefractory period in between
Action potential at one point of axon triggers next action Action potential at one point of axon triggers next action
potentialpotential
Action PotentialAction Potential
Speed of action potential influenced by:Speed of action potential influenced by:
Diameter of axon (larger = faster)Diameter of axon (larger = faster)
Myelination of axonMyelination of axon
Action potential only occurs at nodes (between Action potential only occurs at nodes (between
Schwann cells)Schwann cells)
Appears to “jump” – saltatory conductionAppears to “jump” – saltatory conduction
Action PotentialAction Potential
Cell junctions between neurons, receptors, effectorsCell junctions between neurons, receptors, effectors
Two typesTwo types
Electrical synapsesElectrical synapses
Action potential spreads directly from cell to Action potential spreads directly from cell to
cellcell
Cells connected by gap junctionsCells connected by gap junctions
SynapsesSynapses
Chemical synapsesChemical synapses
Gap (synaptic cleft) separates cellsGap (synaptic cleft) separates cells
Action potential cannot be directly Action potential cannot be directly
transmittedtransmitted
Conversion of electrical signal to chemical Conversion of electrical signal to chemical
signal that bridges gapsignal that bridges gap
Action potential at end of neuron releases Action potential at end of neuron releases
CaCa2+2+ into neuron into neuron
SynapsesSynapses
This causes synaptic vesicles to This causes synaptic vesicles to release chemicals release chemicals (neurotransmitters) into synaptic (neurotransmitters) into synaptic cleftcleft
Receptors on next neuron receive Receptors on next neuron receive chemicals – opens ion channels – chemicals – opens ion channels – allows K+, Na+, Cl- across – impulse allows K+, Na+, Cl- across – impulse continuescontinues
SynapsesSynapses
Figure 48.1Figure 48.1
NeurotransmittersNeurotransmitters
Nervous System DiversityNervous System Diversity
Vertebrate Nervous Vertebrate Nervous SystemSystem
