Answer to Question #94205 in Human Anatomy and Physiology for Olivia Eiesland

Question

describe an action potential from the moment dendrites receive a signal until the neuron releases neurotransmitters into the synaptic gap.

Answer 1

During an action potential a stimulus first causes sodium channels to open. Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron. This causes neurons to be more positive being sodium as a positively charged ion. Thus the membrane becomes depolarized. It takes longer for potassium channels to open. When they do open, potassium rushes out of the cell, reversing the depolarization. Also at about this time, sodium channels start to close. This causes the action potential to go back toward -70 mV (a repolarization). The action potential actually goes past -70 mV (a hyperpolarization) because the potassium channels stay open a bit too long. Gradually, the ion concentrations go back to resting levels and the cell returns to -70 mV. Thus action potential means disrupting the normal -70mv potential i.e the resting membrane potential of the cell.

When an action potential reaches the presynaptic terminal, it causes neurotransmitter to be released from the neuron into the synaptic cleft, a 20–40nm gap between the presynaptic axon terminal and the postsynaptic dendrite (often a spine). After travelling across the synaptic cleft, the transmitter will attach to neurotransmitter receptors on the postsynaptic side, and depending on the neurotransmitter released (which is dependent on the type of neuron releasing it), particular positive (e.g. Na+, K+, Ca+) or negative ions (e.g. Cl-) will travel through channels that span the membrane.