Gated Ion Channels A. Voltage-gated Na + channels 5. generation of AP dependent only on Na + repolarization is required before another AP can occur K + efflux

Gated Ion Channels A. Voltage-gated Na + channels 6. positive feedback in upslope a. countered by reduced emf for Na + as V m approaches E Na b. Na + channels close very quickly after opening (independent of V m )

Gated Ion Channels B. Voltage-gated K + channels 1. slower response to voltage changes than Na + channels 2. g K increases at peak of AP

Gated Ion Channels B. Voltage-gated K + channels 3. high g K during falling phase decreases as V m returns to normal channels close as repolarization progresses

Gated Ion Channels B. Voltage-gated K + channels 4. hastens repolarization for generation of more action potentials

Does [Ion] Change During AP? A. Relatively few ions needed to alter V m B. Large axons show negligible change in Na + and K + concentrations after an AP.

Potential Transmission A. Electrotonic 1. graded 2. receptor (generator) potentials

Potential Transmission a.  stimulus, then  ∆ V m b. electrical signal spreads from source of stimulus c. problem: no voltage-gated channels here d. signal decay “passive electrotonic transmission”

Potential Transmission A. Electrotonic 3. good for only short distances 4. might reach axon hillock - that’s where voltage-gated channels are - where action potentials may be triggered

Potential Transmission B. Action potential 1. propagation without decrement 2. to axon terminal

Synaptic Transmission

A. Presynaptic neuron 1. neurotransmitter (usually) 2. synaptic cleft

Synaptic Transmission B. Postsynaptic neuron 1. bind neurotransmitter 2. postsynaptic potential (∆ V m ) 3. may trigger action potential on postsynaptic effector

Synaptic Transmission C. Alternation of graded and action potentials

Intraneuron Transmission A. All neurons have electrotonic conduction (passive) B. Cable properties 1. determine conduction down the axon process 2. some cytoplasmic resistance to longitudinal flow 3. high resistance of membrane to current “but membrane is leaky”

Intraneuron Transmission C. Nonspiking neurons 1. no APs 2. local-circuit neurons 3. still release neurotransmitter 4. vertebrate CNS, retina, insect CNS 5. are very short with increased R m

Intraneuron Transmission A. All neurons have electrotonic conduction (passive) B. Cable properties 1. determine conduction down the axon process 2. some cytoplasmic resistance to longitudinal flow 3. high resistance of membrane to current “but membrane is leaky”

Intraneuron Transmission C. Nonspiking neurons 1. no APs 2. local-circuit neurons 3. still release neurotransmitter 4. vertebrate CNS, retina, insect CNS 5. are very short with increased R m

Intraneuron Transmission D. Propagation of action potentials 1. ∆ V m much larger than threshold - safety factor

Intraneuron Transmission D. Propagation of action potentials 2. spreads to nearby areas - depends on cable properties - inactive membrane depolarized by electrotonically conducted current

Intraneuron Transmission D. Propagation of action potentials - K + efflux behind region of Na + influx

Intraneuron Transmission D. Propagation of action potentials 3. unidirectional a. refractory period b. K + channels still open

Intraneuron Transmission D. Propagation of action potentials 4. speed a. relates to axon diameter and presence of myelin b.  axon diameter,  speed of conduction

Intraneuron Transmission E. Saltatory conduction 1. myelination a.  R m,  C m b. the more layering, the greater the resistance between ICF and ECF

Intraneuron Transmission E. Saltatory conduction c. charge flows more easily down the axon than across the membrane

Intraneuron Transmission E. Saltatory conduction 2. nodes of Ranvier a. internodes (beneath Schwann cells or oligodendrocytes) b. nodes are only exit for current c. only location along axon where APs are generated