A sensory neuron is a nervous system cell that is involved in the transportation of sensory neural impulses from receptors or sensory organs throughout the body. These neural impulses are sent to the brain and translated into an understandable form so that the organism can react to the stimuli. Such understandable forms include sensations of pain, heat, texture, and visual input. The proper reception of such stimuli is crucial to the survival of most organisms, as it keeps them informed of the world around them and allows them to respond accordingly.
A neuron is a cell that is specialized to carry neural information throughout the body; as such, it differs greatly from most cells. Structures known as dendrites are at one end of the nerve cell; these receive signals from other neurons or sources of sensory information. They are connected to the cell body, which contains the nucleus and other essential organelles that sustain the cell. The axon extends outward from the cell body toward wherever it needs to carry its sensory information; the longest axons in human cells can sometimes exceed 3.2 feet (1 meter) in length. The axon terminates at the axon terminal, which passes on the neural information to where it is needed.
A sensory neuron generally transmits its information toward the central nervous system, which is primarily contained in the brain and in parts of the spine. Sensory input, then, is received by the dendrites of the nerve cell and sent through the axon until it either reaches another and passes the signal off or it reaches its destination. Other kinds of cells have limited involvement in this process, making neurons the primary functional part of the nervous system.
There are three primary types of neurons: afferent, efferent, and interneurons. Those that transmit sensory information are afferent neurons, meaning that they take information from sensory organs or tissues and communicate it to the brain. Efferent neurons carry impulses from the central nervous system to other parts of the body and most notably include motor neurons. Interneurons simply connect other neurons, allowing them to reach their destinations in the most effective way possible.
Sensory neurons do not always send their information to the brain, though they typically do in complex organisms, such as humans. In a simple organism lacking a complex central nervous system, they may simply send their information directly to a motor neuron. This allows for a rapid reaction without intensive processing of stimuli.