Neuroscience Exploring the Brain Chapter 4

Bursting, accommodating, single spiking
frequency and patterns

Threshold potential = - 45mV
Rising phase - depolarization
Overshoot - positive inside
Falling phase - repolarization
Undershoot - after hyperpolarization

Greater depolarization, more and faster AP firing
no increase in AP amplitude

Influx of Na+
efflux of K+

At Vm huge driving force of Na+
Rising phase - inward of Na+
Falling phase - outward of K+

Four homologous domains 1-4
1 continuous polypeptide with 6 transmembrane a-helices
1pore loop/domain
1 voltage sensor/domain (S4)
each pore loop contributes to 1/4th of selectivity filter
1 activation gate/domain
1 inactivation loop/domain

Open when threshhold is reached, open with little delay, open for 1msec and inactivate, cannot be opened until Vm returns to rest

Time period between channel inactivation and time it takes for the Vm to repolarize and Na+ channels to deinactivate takes 1.5msec

Both open in response to depolarization, Na+ open fast .2msec, K+ open slower 1msec
Na+ undergo voltage dependent inaction, K+ does not
Takes 1-2msec to return to activatable state

Puffer fish
Bind to Na+ channel and block its pore
Block Na+ conductance

Cocaine
Lidocaine - bind inside sodium channel pore reduce Na+ influx, only inhibit when channel are open

Sensory nerve ending, and axon hillock

Orthodromic - AP travels down axon to terminal
antidromic - backward propagation of AP

Diameter constricted packed with NFs and MTs
voltage-gated na+ channels in axon membrane at nodes
K+ located adjacent to nodes under myelin sheath
Saltatory conduction