Sensory Neuron
A sensory neuron is a neuron which collects or responds to sensory information in the periphery of an organism, and sends the information (itself or through associated neurons) toward the central nervous system (spinal cord and brain). Motor neurons (which are responsible for carrying impulses to direct movement) carry nerve impulses from the brain (the central nervous system) to the muscles (the peripheral nervous system). These neurons are considered to be efferent. Conversely, sensory neurons are considered to be afferent. That is, information in the form of a nervous impulse flows from the peripheral nervous system (eyes, ears, skin, nose, mouth) to the central nervous system.
Sensory neurons may themselves serve as the sensory receptor, or they may be closely associated with the actual receptor.
Sensory neurons are unique in that they are extremely specific. That is, they pick up on a very narrow type of sensation, and are essentially oblivious to any other type of sensation. Therefore, a sensory neuron may be particularly suited to transmit information about sight. More specifically, that neuron may only respond to sight which involves specific wavelengths of light; that is, specific colors.
Sensory neurons have particular thresholds which must be met in order for impulses to be transmitted. Sensory information which does not meet the minimum threshold for a neuron's sensitivity will not be transmitted. In order to account for variations in intensity of sensation, sensory neurons may recruit other neurons in the area to transmit impulses simultaneously.
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