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
Feb 23, 2016
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