Physiology of synapses :
The human brain is made up of approximately 86 billion neurons ,the neuron consists of a cell body, axons, and dendrites.
-There are two types of synapses found in your body:
electrical and chemical.
*The process of synaptic transmission at a chemical synapse between two neurons follows these steps:
1- An action potential, propagating along the axon of a presynaptic neuron, arrives at the axon terminal.
2- The depolarization of the axolemma (the plasma membrane of the axon) at the axon terminal opens Ca2+ channels and Ca2+ diffuses into the axon terminal.
3-Ca2+ bind with calmodulin, the ubiquitous intracellular calcium receptor, causing the synaptic vesicles to migrate to and fuse with the presynaptic membrane.
4-The neurotransmitter is released into the synaptic cleft by the process of exocytosis.
5-The neurotransmitter diffuses across the synaptic cleft and binds with receptors on the postsynaptic membrane.
6-Binding of the neurotransmitters to the postsynaptic receptors causes a response in the postsynaptic cell.
-Postsynaptic potentials develop in the postsynaptic cell’s membrane when neurotransmitter binding to receptors leads to the opening of ion channels.
1- excitatory postsynaptic potential (EPSP) occurs if the membrane is depolarized by the ion movement.
*Opening of sodium- or calcium channels leads to depolarization of the membrane.
2- inhibitory postsynaptic potential (IPSP) is generated.
the membrane becomes hyperpolarized when the ions move.
*Opening of potassium- or chloride channels leads to hyperpolarization of the membrane.