Types of cells in the nervous system
There are two types of cells in the nervous system. One type of cells are called neurons, the other type of cells are called glia. Studies have found that there are about 86 billion neurons in the human brain. In comparison, there are about 200 million neurons in the rat brain.
Dendrites and axons
The sizes and shapes of neurons can be very different, from 10 mm (micrometers) to 50 mm. A neuron is composed of dendrites and an axon. Dendrites get information from stimuli or input from other neurons or receptors. Membranes on the dendrites have small channels controlling the traffic of ions across the membrane. Chemical or physical stimuli can influence the ion channels and cause voltage changes across the membrane.
Stimulation of the dendrites make the neuron produces an electronic signal. The signal is transmitted by the axon and brought to other neurons or cells by the axon. Axons can carry away information and have many terminals.
Membrane potentials and communications among neurons
To keep the balanced chemical environment in the cells, neurons can pump ions and molecules across the membranes. The electrical potential caused by the voltage difference as a result of this pumping is named the membrane potential. A ‘spike’ is also called an action potential, which is a short and big jump in the membrane potential upon the stimulation on a neuron. Action potentials on the surface of a neuron can cause chain reactions and transmit down to the axon and across the whole cell, enabling the communication among the neurons in the nervous system.
Axons, neurotransmitters, and action potentials
Axons have terminal branches with boutons on them. Upon action potentials, the boutons can release neurotransmitters, the signaling molecules that have receptors on the membrane of the target cells. Neurotransmitters are molecules that can signal neurons. The receptors of neurotransmitters can locate on the dendrites of neurons and membranes of the glial cells, muscle cells, and gland cells. The binding of the neurotransmitters and their corresponding receptors can lead to changes including the opening of ion channels.