lecture 7 - local potentials & action potentials Flashcards
What are local potentials?
Graded local changes in membrane potentials caused by the opening/closing of ion channels
What causes local potentials?
External stimulus causes the opening/opening of ion channels
What are the 2 types of local potentials?
Excitatory, Inhibitory
What is an excitatory local potential?
Local change in membrane potential that leads to active, regenerative responses in the membrane
What is inhibitory local potential?
One which leads to reduced responses or decreased neuronal activity by repolarising the membrane
Why are local potentials considered graded?
Because stimuli can generate different sized changes in local potential - the large the stimulus the more channels open and the greater the depolarisation
How does the degree of depolarisation of a local potential change with distance from the origin?
Decrease in depolarisation due to outward leak of negative charge
Why do graded potentials outlast the stimulus?
The spread passively with a delayed rise and fall with the opening of ion channels
What feature of graded potentials allows for input integration?
Temporal and spatial summation
Why are graded potentials not good for carrying information long distances?
They get smaller as they spread and cannot regenerate
What do ion pumps maintain in a neuron?
Electrochemical gradients
At a neuron, what are inputs processed as?
Graded potentials
At a neuron, what are signals transmitted as?
Action potentials
Where are action potentials generated?
Axon hillock
What is the difference from resting membrane potential that must be reached for threshold for an action potential?
approx. 10mV above resting membrane potential (~-60mV)
What channels are involved in action potential generation and propogation?
Voltage gated Na+ channels, K+ channels
What happens when the axon hillock reaches threshold?
Opening of voltage gated Na+ channels leading to a rapid depolarisation
What channels are responsible for the repolarisation after an action potential?
K+ channels
What is the name for the period in which it is impossible for another action potential to occur?
Absolute refractory period
What is an absolute refractory period?
A period when the axon is repolarising where it is impossible for an action potential to occur
What is a relative refractory period?
Period when another action potenial can occur, but only with a greater depolarisation - threshold is greater
Why does the membrane hyperpolarise during the repolarisation stage of an action potential?
K+ channels are open and Na+ channels are inactivated so the membrane becomes more permeable to K+ and the membrane potential becomes more negative
