ANPS - Action Potential

chemically gated channel

-gated channels that must be activated by a binding protein that binds to the receptors -located at the receptive region of a nerve cell.

threshold

-minimum voltage change required to open a voltage gated channel, membrane becomes more positive -when reached, voltage gated channels open and allow ions to diffuse into the cell.

node of Ranvier (neurofibril node in text book)

-nodes along the axon that are unmyelinated -action potential jumps from node to node

repolarization

-occurs due to closure of voltage gated sodium channels and opening of voltage gated potassium channels and K moves out of the cell and then close -reversing polarity from positive to negative

saltatory conduction

-occurs in myelinated axons -action potential only propagated at nodes of rangier -myelinated regions have limited number of voltage gated channels and well insulated to they prevent ion movement -nodes of ranvier have large number of voltage gated channels

continuous conduction

-occurs in unmyelinated axons -sequential opening of voltage gated Na and K channels along the entire length of axon

depolarization

-occurs when threshold is reached, and voltage gated sodium channels open and Na enters rapidly into the cell, go to inactive state and then closed state -reversing the polarity from negative to positive

relative refractory period

-period during which its more difficult to get another action potential but it can be done -hyperpolarization region

absolute refractory period

-period during which you cannot get another action potential -ensures Action potential does not travel backwards -depolarization and repolarization region

Draw an action potential and label the following: resting membrane potential, threshold, depolarizing phase, repolarizing phase, absolute refractory period, relative refractory period. During what phase is Na+ permeability the greatest? During what phase is K+ permeability the greatest?

...

What is the difference between a chemically gated channel and a voltage-gated channel in terms of how they function?

chemically gates - receptive (dendrites and cell body) -Both types of channels are normally closed. Chemically gated channels open in response to binding of a neurotransmitter. Voltage-gated channels open in response to changes in electrical charge (potential) across the plasma membrane.

action potential

dynamic change in membrane potential -generated in the axon hillock -due to opening of voltages gated Na and K channels -temporary reversal of polarity across the membrane -maintains intensity until it reaches the synaptic terminal

How does conduction of an action potential in an unmyelinated axon and myelinated axon differ?

Conduction along a myelinated neuron (saltatory conduction) is significantly faster than in an unmyelinated neuron because an action potential is generated only in unmyelinated nodes.

How does depolarization and repolarization occur in the conductive segment of a neuron?

Depolarization occurs when the threshold voltage of −55 mV is reached; voltage-gated Na+ channels open and Na+ rapidly enters the cell, reversing the polarity from negative to positive. Repolarization occurs due to closure of the voltage-gated Na+ channels and opening of voltage-gated K+ channels. K+ moves out of the cell and polarity is reversed from positive to negative.

voltage gated channel

- normally closed -open in response to changes in electrical charge across a membrane -allow specific type of ion to diffuse -volage gated Na, K, and Ca channels -go from closed channel, to open/activated, to inactive channel, back to closed -initial segment, conductive segment, and transmissive segment of nerve cell

Which functional segment of a neuron contains chemically gated channels? Which functional segments contain voltage-gated channels?

The receptive segment of a neuron (dendrites and cell body) contain chemically gated ion channels. The initial (axon hillock), conductive (axon and telodendria) and transmissive segment (synaptic knobs) contain only voltage-gated channels

What is the significance of the threshold membrane potential in the initial segment of a neuron?

The threshold membrane potential is the voltage difference that must be achieved in order to generate an action potential within the initial segment of a neuron. Typically this is at −55 mV, +15 mV above the resting membrane potential. If the ratio of IPSPs and EPSPs reaches the threshold membrane potential, only then will an action potential be generated and propagated along the neuron.