Nerve cells—also known as neurons—are the primary building blocks of the nervous system in humans and animals. On a fundamental level, a nerve cell functions by transmitting and receiving electrochemical messages. These messages can serve several purposes, including the transmission of sensory information to the central nervous system and the regulation and control of organs in the body. The function of a single nerve cell could be described as relatively straightforward, but when bundled together in groups, these cells can allow for complex processes like brain cognition.
Like most other cells in an organism, a nerve cell generally has both a nucleus and a cell body. Around the cell body, there are extensions called dendrites, which are specialized in receiving different kinds of stimuli depending on the location and purpose of the cell. Once the dendrites detect some form of stimuli, the cell body generates an electrical impulse called an action potential, which travels down a wire-like structure called an axon to its destination.
The three basic types of nerve cells are motor neurons, sensory neurons and interneurons. A motor neuron is a cell that transmits a signal to a muscle or gland. Sensory neurons receive information from sensory organs and transmit that information back to the central nervous system. Interneurons, which do most of the work in the brain and spinal cord, relay information between sensory and motor neurons. The speed of the electrical impulse that’s transmitted through a nerve cell can vary depending on a number of factors, but the average is about 200 mph (321.8688 kph), which is slower than electricity travels over a wire.
The average human brain has about 100 billion neurons and about 10 times as many glial support cells, which perform several vital functions that help the neurons work properly. One difference between neurons and other cells in the body is their lifespan. While most cells die and are replaced in relatively short cycles, research has shown that many neurons in the body aren’t replaced, and some will last for a person’s entire life. Over the course of a long lifespan, some neurons will gradually die off, but there are generally more than enough surviving neurons to compensate for any normal losses. Scientists have discovered that one part of the brain called the hippocampus has the capacity to regenerate lost neurons, but this does not appear to be possible anywhere else in the body.