what does action potential allow for?
signalling within neuronal cells
what do neuronal cells release as a result of an action potential?
neurotransmitters
neurotransmitters have specific effects on what kind of cells?
their receiving cells
describe the development and propagation of an action potential
- membrane potential quickly rises to about +40 mV (depolarization)
- it then falls slowly to about -75 mV (Hyperpolarization)
- it stabilizes again at the resting potential (-60mV)
what happens when a region of the nerve cells is depolarized past the threshold level?
some of the sodium channels open- the flow of sodium through the channels increases membrane depolarization nearby
What happens when you increase depolarization?
- opens more channels causing more sodium to flow
- Hodgkin cycle (positive feedback loop)
what happens when tetrodotoxin inhibits it?
prevents the opening of sodium channels
what are the steps of action potential‘s?
- voltage gated channels are closed
- Neuron may be receiving positive signals from other neurons
- The threshold level is reached
- sodium channel is opened and the sodium rushes in which increases the membrane potential
- The sodium channel closes then the potassium channel opens (stays open for a while)
- potassium rushes out which decreases the membrane potential
- leak channels help reestablish the resting membrane potential (-60mV)
what is an absolute refractory period?
- cannot trigger another action potential
- sodium channels are inactivated by inactivating particle
- cannot be opened by depolarization
what is a relative refractory period?
- difficult to trigger another action potential
- membrane is hyperpolarized
- potassium channels are still open
- to get another action potential need to open sodium channels again and reach the threshold level which is difficult because potassium channels are still open
what are the steps of passive depolarization?
- The membrane is completely polarized (start)
- when an action potential is initiated a region of the membrane depolarizes as a result the adjacent regions become depolarized
- when the adjacent region is depolarized to its threshold an action potential starts there
- Repolarization occurs due to the outward flow of potassium ions. the depolarization spreads forward triggering an action potential
- depolarization spreads forward repeating the process
- signal only moves left to right
what is saltatory propagation?
when action potential’s jump from one node to the next
what is electrical synapse?
One neuron (presynaptic) is connected to a second neuron (post synaptic) via gap junctions
- ions move directly between cells
- axon of one neuron is directly connected to the dendrite of another
what is chemical synapses?
- presynaptic and postsynaptic neuron‘s are not directly connected
- The two cell membranes are separated by a small space called the synaptic cleft
where are neurotransmitters stored?
in synaptic bouton’s in the presynaptic neuron
-released due to the arrival of an action potential
what happens once neurotransmitters diffuse across the cleft?
- bind to receptors in the plasma membrane of the postsynaptic cell
- they are converted into electric signals and either stimulate or inhibit an action potential in the receiving cell
