Receptor potential
occur in the primary afferent sensory neuron that experiences the stimulus
Synaptic potential
occur in postsynaptic neurons after the primary afferent neuron
Graded potential
local change in potential due to stimulus which increases in amplitude with increase in amplitude of stimulus
how do graded potentials spread?
They depolarize adjacent regions without membrane receptors by decrementally spreading positive charge
Length constant
Distance over which grade potential declines to 37% or 1/e of the original
Length constant increases with ___________ and decreases with ________
electrical resistance of the membrane ; electrical resistance of cytoplasm
Larger diameter axons have _______ length constants
Greater
The larger the area of axon the _________ the cytoplasmic resistance
smaller
The greater the length constant the ________ the decrement, the _______ the intracellular resistance and the ________the membrane resistance
slower; lower ; greater
Depolarizations that are all or none and show no decrement
Action potentials
Trigger zone aka
impulse initiation zone (IIZ)
describe IIZ
dense population of voltage sensitive Na+ channels which open when sufficient depolarization has been reached
IIZ or trigger zone in Multipolar neurons
Axon hillock ( btw cell body and first myelinating cell)
IIZ or trigger zone in pseudounipolar and bipolar neurons
near sensory nerve ending
What occurs during rising phase of Action potential
- opening of enough Na+ channels that exceeds K+ efflux
- neuron depolarizes
- more Na+ channels open
- Na+ moves down its electrochemical gradient into the cell
- delayed rectifying K+ channels are also induced but are very slow
What occurs during falling phase
- efflux of K+ causes repolarization
- often hyperpolarizes
- depolarization induced Na channel inactivation
General structure of superfamily of voltage gated ion (K+,Na+, Ca2+) channels
- 4 identical subunits
- each subunit has 6 membrane spanning domains
- charged voltage sensor in segment 4
- pore loop
What confers ion specificity to the voltage gated ion channel
Pore loop
Absolute refractory period
- all Na+ channels are inactivated
- 1ms
- no impulse can be generated
Relative refractory period
incomplete return of inactivated Na+ channels to normal closed state plus residual K+ currents
- lasts longer (several ms)
- new impulse can be generated if stimulus is large enough
Where are voltage gated Na+ channels found in myelinated neurons of PNS and CNS?
1) Nodes
2) Trigger zone (IIZ)
3) terminal
Where are voltage gated K+ channels found in myelinated neurons of PNS and CNS?
1) Paranodal
2) Juxtaparanodal
3) Terminal
Where are voltage gated Ca2+ channels found in myelinated neurons of PNS and CNS?
Terminal
Where do impulses occur in myelinated axons
at nodes of Ranvier
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