Biology · Coordination and Control

Diffusion of sodium ions (Na⁺) across the postsynaptic membrane causes it to depolarize. When an excitatory neurotransmitter binds to a receptor, it opens ion channels, allowing positively charged ions like sodium ions to rush into the cell. This influx of positive charge makes the inside of the cell less negative, which is known as depolarization and can lead to an action potential. 

At the synaptic terminal, Ca²⁺ ions enter the neuron when an action potential arrives. This influx of Ca²⁺ triggers vesicles containing neurotransmitters to fuse with the presynaptic membrane and release their contents into the synaptic cleft, facilitating communication between neurons.

Chloride ions play a role in inhibiting neuron firing. When Cl⁻ ions enter the neuron, they make the inside more negatively charged (hyperpolarization), which counteracts depolarization and decreases the likelihood of an action potential. This inhibitory effect is crucial for balancing excitation in the nervous system.

During the repolarization phase of the action potential, K⁺ ions flow out of the neuron, helping to restore the negative resting membrane potential after depolarization. This outflow of K⁺ is crucial for resetting the neuron to be ready for the next impulse.

Diffusion of sodium ions (Na⁺) across the postsynaptic membrane causes it to depolarize. When an excitatory neurotransmitter binds to a receptor, it opens ion channels, allowing positively charged ions like sodium ions to rush into the cell. This influx of positive charge makes the inside of the cell less negative, which is known as depolarization and can lead to an action potential.