Neurons are nerve cells, making up the functional core of the peripheral and central nervous systems. The function of neurons is to carry electrical signals, where they carry them to and from depends on the location of the neuron in the nervous system.
Basic neuron structure
The basic structure of a neuron consists of a cell body (also known as the soma) and processes reaching out from the cell body. The cell body contains the nucleus and organelles, including the mitochondria, which produces energy, and the Golgi and endoplasmic reticulum, which package proteins. The processes are the dendrites and axon. How many dendrites a neuron has (from 0 to many) depends on the type of neuron (bipolar, pseudounipolar, multipolar). The dendrites receive chemical signals from the axon of another neuron, conveying the information to the soma. The axon reaches out away from the cell body, carrying signals to the synapse with another neuron. Axons are activated by membrane potentials, at the axon hillock in larger neurons. The end of the axon branches into terminal buttons to convey these messages by releasing chemical signals (neurotransmitters). Most neurons have one axon, though neurons lacking dendrites (the dorsal root ganglia) have two axons.
Central nervous system function
The central nervous system consists of the brain and spinal cord. The brain contains an often estimated hundred billion neurons communicating via neurotransmitters. Neurons in different parts of the brain control various functions in the body, from involuntary responses like heart rate and breathing to voluntary motor reactions.
Signals travel from the brain through nerve fibers in the spinal cord. The white matter of the spinal cord contain axons traveling away from the brain, down the spinal column to branch out to the various areas of the body, as well as axons traveling from the various areas of the body to communicate with the brain. The grey matter of the spinal cord contains nerve cell bodies for motor nerve fibers.
Peripheral nervous system function
The peripheral nerve cells are divided into afferent (sensory) and efferent (motor) neurons. The cell bodies of the afferent nerve fibers are located in the dorsal root ganglion, allowing the axons to travel up the spinal cord. Nerve endings (technically dendrites) act as receptors in the skin and mucosa, transmitting sensory information to the central nervous system. Motor neurons provide responses to the muscles and glands from the central nervous system.
A third type of peripheral neuron, interneurons, communicate between the sensory and motor neurons, allowing full integration of the signals between the various neurons in the body.