In: Anatomy and Physiology
Part 1: Create a hand drawn diagram of action potential in a neuron leading to synaptic vesicle release at the neuromuscular junction, and include the following terms: Action Potential, Depolarization, Repolarization, Sodium, Potassium, Voltage-Gated Sodium Channel, Threshold Refractory Period, Voltage-gated Potassium Channel, Hyperpolarization, Resting Membrane Potential, Sodium/Potassium Pump, Vesicle, Acetylcholine, Calcium
ACTION POTENTIAL IN A NERVE
The neuron cell membrane is partially permeable to sodium ions which causes the sodium to leak into the neuron at resting state. This is prevented by the activity of the Na-K pump which pumps sodium out of the cell and potassium into the cell. This creates a negative resting potential (-70 mV) called the resting membrane potential.
To fire an action potential, the nerve is stimulated so that the potential become more towards the positive side. The minimum potential difference that must be reached to fire an action potential is called the Threshold potential (-55 mV)
During depolarisation phase of the ac tion potential, the voltage gated Na channels open causing inward flow of sodium ions. This causes the memrane potential to rise towards the positive side. During the repolarisation phase, the volatge gated K channels open, leding to pottasium efflux out of the cell. So the cell experiences a decrease of voltage. After repolarization, the cell's membrane potential becomes more negative before it reaches resting membrane potential. This is called hyperpolarisation.
Refractory period is the time during which another stimulus given to the neuron will not lead to a second action potential. There are two types of refractory periods - the absolute refractory period, corresponding to the depolarization and repolarization, and the relative refractory period, which corresponding to the hyperpolarization.
NEUROMUSCULAR JUNCTION
When this action potential reaches the nerve terminal, the calcium channels at the axon terminal open, causing Ca influx. This causes the release of neurotransmitter Acetyl choline stored in the vesicles. The acetyl choline binds to the receptor on the muscles, causing influx of sodium ions leading to an action potential in the muscle leading to muscle contraction .