The human brain consists of about 150 billion nerve cells (also called neurons), which are connected.
Neurons or nerve cells are the information carrier of the nervous system. The neurons consist of a cell body and two types of fiber: dendrites and axons. The dendrites have many branches that receive stimulation from other neurons. On the contrary, the axons are quite long and conduct nerve impulses to other neurons or muscles or glands. The axons are covered with a white fatty covering called the myelin sheath. Myelin sheath increases the speed of the nerve impulses that are transferred through the axon.
Nerve impulses are impulses of very short duration that move along the axon.
Synapses and their function
The connections between the axon tips of a neuron and dendrites or cell bodies of other neurons are called synapses. The neurons are separated by a narrow gap called the synaptic cleft. Many small bulbs, called boutons, are found at the end of the axons. Inside the boutons lies small bodies, or vesicles, that contain the neurotransmitters. These chemicals (neurotransmitters) are released from the vesicles into the synaptic cleft and combines with the specialized receptors molecules in the receptor region of the receiving cell.
The neurotransmitter either increases the tendency to fire nerve impulses – excitation or decrease this tendency – inhibition.