E S L PUL IMT I A S

THE NATURE OF NERVE IMPULSE • Nerve impulses are caused by the movement of

RESTING POTENTIAL Organic negative protein - Gives overall To prevent diffusion • When neuron

ACTION POTENTIAL – UP SWING • aka Depolarization • Nerves stimulated by electric shock

ACTION POTENTIAL - DOWNSWING • aka Repolarization • Restores negative potential - K+ gates

$RECOVERY PHASE • Aka refractory period • Na+ and K+ gates unable to open$

ALL OR NOTHING LAW The “All or Nothing” Law states that if the threshold

$Repolarization Depolarization ACTION POTENTIAL GRAPH Refractory Hyperpolarization$

SPEED OF CONDUCTION Action potential occurs at one small section of a neuron at

MYELINATED AXON Action potential moves up to 200 m/sec In myelinated neurons action potential

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E S L PUL IMT I A S EN U O T O V P R ON E N TI A C

THE NATURE OF NERVE IMPULSE • Nerve impulses are caused by the movement of electrically charged ions. **sodium, potassium** • These messages are caused by a potential or a difference between the inside and outside of the membrane of the neuron

RESTING POTENTIAL Organic negative protein - Gives overall To prevent diffusion • When neuron is at rest • More Na+ ions outside • More K+ ions inside Uses ATP for active transport to maintain concentration difference

ACTION POTENTIAL – UP SWING • aka Depolarization • Nerves stimulated by electric shock p. H • Membrane becomes permeable to Na+ ions Na+ gates open and Na+ diffuses in

ACTION POTENTIAL - DOWNSWING • aka Repolarization • Restores negative potential - K+ gates open (membrane becomes permeable) - K+ diffuses out Na+ Gates close

$RECOVERY PHASE • Aka refractory period • Na+ and K+ gates unable to open$

RECOVERY PHASE • Aka refractory period • Na+ and K+ gates unable to open ensures action potential doesn’t move backwards • As soon as action potential has moved to next portion of neuron, previous portion undergoes refractory period. (Draw Picture from board) • This process requires 1/1000 sec.

ALL OR NOTHING LAW The “All or Nothing” Law states that if the threshold is reached an impulse is carried, but if the threshold is not reached then there will be no impulse. It doesn’t matter how strong the stimulus. The same impulse is sent regardless of strength. The sensitivity to mild or severe pain depends on the number of neurons stimulated as well as the frequency of their stimulation.

$Repolarization Depolarization ACTION POTENTIAL GRAPH Refractory Hyperpolarization$

Repolarization Depolarization ACTION POTENTIAL GRAPH Refractory Hyperpolarization

SPEED OF CONDUCTION Action potential occurs at one small section of a neuron at a time Non myelinated neuron - Usually occurs in invertebrates/small animals - Action potential moves slowly (0. 5 m/sec)

MYELINATED AXON Action potential moves up to 200 m/sec In myelinated neurons action potential concentrated at nodes of Ranvier = saltatory conduction. Action potential jumps from node to node Causes “flip-flop” flow of charge Animation

ACTION POTENTIAL REVIEW Animation