Neurons are the basic unit of the nervous system. All cells of the nervous system are comprised of neurons. The nervous system can be divided into two parts: the central nervous system
and the peripheral nervous system
. The central nervous system consists of the brain
and spinal cord, while the peripheral nervous system consists of sensory and motor nervous cells that run throughout the rest of the body. Neurons are responsible for sending, receiving, and interpreting information from all parts of the body.
Parts Of A Neuron
A neuron consists of two major parts:
- Cell Body
Neurons contain the same cellular components as other body cells. The central cell body is the largest part of a neuron and contains the neuron's nucleus, associated cytoplasm, and other cell structures. The cell body produces proteins needed for the construction of other parts of the neuron.
- Nerve Processes
Nerve processes are "finger-like" projections from the cell body that are able to conduct and transmit signals. There are two types:
Axons - typically carry signals away from the cell body. They are long nerve processes that may branch out to convey signals to various areas. Some axons are wrapped in an insulating coat of glial cells called oligodendrocytes and Schwann cells. These cells form the myelin sheath which indirectly assists in the conduction of impulses as myelinated nerves can conduct impulses quicker than unmyelinated ones. Axons end at junctions known as synapses.
Dendrites - typically carry signals toward the cell body. Dendrites are usually more numerous, shorter and more branched than axons. They have many synapses in order to receive signal messages from nearby neurons.
Neurons: Nerve Impulse
Axons and dendrites are bundled together into what are called nerves. These nerves send signals between the brain, spinal cord, and other body organs via nerve impulses. Nerve impulses are received at the neuronal dendrites and are carried along the axon to the terminal branches. These branches end at a junction called a synapse. It is at the synapse where chemical or electrical impulses must cross the gap and be carried to the dendrites of adjacent cells. At electrical synapses, ions and other molecules pass through gap junctions allowing for the passive transmission of electrical signals from one cell to the other. At chemical synapses, chemical signals called neurotransmitters are released which cross the gap junction to stimulate the next neuron.
Neurons are classified as either motor, sensory, or interneurons. Motor neurons
carry information from the central nervous system to organs
, glands, and muscles
. Sensory neurons
send information to the central nervous system from internal organs or from external stimuli. Interneurons
relay signals between motor and sensory neurons.