Gated Ion ChannelsA. Voltage-gated Na+ channels

5. generation of AP dependent only on Na+

repolarization is required before another AP can occurK+ efflux

Gated Ion ChannelsA. Voltage-gated Na+ channels

6. positive feedback in upslopea. countered by reduced emf for Na+ as Vm approaches ENa

b. Na+ channels close very quickly after opening (independent of Vm)

Gated Ion ChannelsB. Voltage-gated K+ channels

1. slower response to voltage changes than Na+ channels2. gK increases at peak of AP

Gated Ion ChannelsB. Voltage-gated K+ channels

3. high gK during falling phasedecreases as Vm returns to normalchannels close as repolarization progresses

Gated Ion ChannelsB. 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 Vm

B. Large axons show negligible change in Na+ and K+ concentrations after an AP.

Potential TransmissionA. Electrotonic

1. graded2. receptor (generator) potentials

Potential Transmissiona. stimulus, then ∆ Vm

b. electrical signal spreads from source of stimulusc. problem: no voltage-gated channels hered. signal decay“passive electrotonic transmission”

Potential TransmissionA. Electrotonic

3. good for only short distances4. might reach axon hillock

- that’s where voltage-gated channels are- where action potentials may be triggered

Potential TransmissionB. Action potential

1. propagation without decrement2. to axon terminal

Synaptic Transmission

Synaptic TransmissionA. Presynaptic neuron

1. neurotransmitter (usually)2. synaptic cleft

Synaptic TransmissionB. Postsynaptic neuron

1. bind neurotransmitter2. postsynaptic potential (∆ Vm)3. may trigger action potential on postsynaptic effector

Synaptic TransmissionC. Alternation of graded and action potentials

Intraneuron TransmissionA. All neurons have electrotonic conduction (passive)B. Cable properties

1. determine conduction down the axon process2. some cytoplasmic resistance to longitudinal flow3. high resistance of membrane to current

“but membrane is leaky”

Intraneuron TransmissionC. Nonspiking neurons

1. no APs2. local-circuit neurons3. still release neurotransmitter4. vertebrate CNS, retina, insect CNS5. are very short with increased Rm

Intraneuron TransmissionA. All neurons have electrotonic conduction (passive)B. Cable properties

1. determine conduction down the axon process2. some cytoplasmic resistance to longitudinal flow3. high resistance of membrane to current

“but membrane is leaky”

Intraneuron TransmissionC. Nonspiking neurons

1. no APs2. local-circuit neurons3. still release neurotransmitter4. vertebrate CNS, retina, insect CNS5. are very short with increased Rm

Intraneuron TransmissionD. Propagation of action potentials

1. ∆ Vm much larger than threshold- safety factor

Intraneuron TransmissionD. Propagation of action potentials

2. spreads to nearby areas- depends on cable properties- inactive membrane depolarized by electrotonically conducted current

Intraneuron TransmissionD. Propagation of action potentials

- K+ efflux behind region of Na+ influx

Intraneuron TransmissionD. Propagation of action potentials

3. unidirectionala. refractory periodb. K+ channels still open

Intraneuron TransmissionD. Propagation of action potentials

4. speeda. relates to axon diameter and presence of myelinb. axon diameter, speed of conduction

Intraneuron TransmissionE. Saltatory conduction

1. myelinationa. Rm , Cm

b. the more layering, the greater the resistance between ICF and ECF

Intraneuron TransmissionE. Saltatory conduction

c. charge flows more easily down the axon than across the membrane

Intraneuron TransmissionE. Saltatory conduction

2. nodes of Ranviera. internodes (beneath Schwann cells or oligodendrocytes)b. nodes are only exit for currentc. only location along axon where APs are generated