ch 11

• only on axons
• make up white matter
• dev during late fetal period thru 1st yr

schwann cells

oligodendrocytes

several dendrites - one axon

most neurons in CNS

1 dendrite - one axon

1 process (axon)

sensory root of spinal nerves

• sensory
• motoir
• association

inherent ability to generate and conduct electrical impulses

exists when a barrier prevents movement of opposite charges toward each other

all cells have slightly different charges

a form of potential energy measured in volts (or millivolts-mV)

a difference in charge between two points

movement of charged particles

possessed by the membrane as it restricts the movement of charges

• cant diffuse across cell membranes
• must pass through channels
• channels are located at particular sites on membrane
• ion channels are selective

• leakage, non-gated
• always open

allows Na in

allows K out

high concentration of K inside and high concentration of Na outside cell

• *may be open (activated)
• * closed but able to open
• * closed but unable to open (inactivated)

open when the appropriate chemical (neurotransmitter) binds

open in response and close in response to changes in membrane potential

• around -70 mV
• varies from -40mV to 90mV

• passage of ions through leakage channels
• * permeability of membrane for K leaking out 75X greater than Na leaking in
• * activity of Na-K pump

• membrane proteins that actively transport ions
• (3) Na exported
• (2) K imported
• stabilizes the resting potential

produced by changes in membrane permiability to any ion

graded potentials (incoming over short distances)

• long distance signals of axons
• same as nerve impulses

reduction in membrane potential (becomes less negative)

membrane potential increases (becomes more negative)

• short lived, localized changes in membrane potential;
• triggered by stimuli in neurons' environment that cause gated channels to open

• dissipates quickly
• die out w/ increasing distance from site of origin

• nerve impulse
• incolves 3 consecutive but overlapping changes in membrane potential

voltage gated channels closed;only leakage channels open

activation gate: closed at rest, open w/ depolarization

inactivation gate: blocks channel once opened

*huge increase in permiability to Na (about 1000x more permeable to resting)

*axon membrane depolarized, Na rushes in, more depolarization

*becomes self-generating when it reaches a critical level threshold (-55mV to -50mV)

more Na enters, greater depolarization, opens more Na channels

overshoots to +30mV

• decreased Na permeability (inactivation gates closing)
• increased K permeability (k channels open; it leaves cell)

*decrease of Na going in; Increase of K going out= repolarization= internal negativity restored

K permeability continues fro a bit (more than needed to restore resting state; excess K efflux = afterhyperpolarization)

• * Na channels are resting
• * electrical condition back to resting; but not ion distribution
• * ion distribution restores quickly by Na-K pumps after repolarization

transmission of action potential; begins at one end and is conducted to axon terminal (domino effect)

usually depolarization of 15 to 20 mV from resting required to generate an ap

neuron cannot respond to another stimulus (from opening of Na channels to their resetting)

follows absolute; exceptionaly strong stimulus could reopen Na channels

(most Na channels reset; some K channels still open; repolarization occuring)

• axon diameter
• degree of myelinzation

depolarization the entire length of the axon

30x faster

concentration of Na channels @ nodes

• large diameter heavily myelinated
• 150 m/sec

• lightly myelinated intermmediate diameter
• 15 m/sec

• smallest diameter
• 1 m/sec

functions between neurons sites of information transfer

conducts impulses towards synapse sender

• conducts impulses away from synapse
• reciever

• uncommon
• connected by protein channels to adjacent neurons
• ions flow directly from one to another
• rapid synchronized communication

release and reception of neurotransmitters; 2 parts

axon terminal- lots of synaptic vessicles that contain neurotransmitters

receptors that bind to neurotransmitters

• 1. calcium channels open at presynaptic axon terminal
• 2. neurotransmitter released
• 3. neurotransmitter binds to synaptic receptors
• 4. ion channels open in post synaptic membrane
• 5. neurotransmitter effects are terminated

• degrade NT enzymatically in cleft
• reuptake NT and store or degrade
• diffusion away from synapse

• neurotransmitters bind to receptors and open ion channels
• * mediate graded potentials
• * either excitatory or inhibitory

fast timing of bursts of NT release by one or more presynaptic neurons

large number of neuron terminals from one neurons simultaneously stimulate a postsynaptic neuron

best known, action varies with type of receptor

norepinephrine, dopamine, seratonin, histamine

ATP, adenosine

GABA, glutamate, glycine

endorphines, substance P, somatostatin

nitric oxide, carbon monoxide

inhibits ACH release, paralyzing voluntary muscle

prevents ACh binding to receptors, paralyzes muscle, arrow poision

prevent ach breakdown by ache, prolonged muscle spasm

decreased rate of ACH release, acts as CNS depressant