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What are Sensory Nerves?
Sensory nerves are vessels of the peripheral nervous system that carry signals toward the brain in response to stimuli. Such stimuli may be environmental, as in changes in temperature; deliver cues about touch such as texture; involve an injury, as in feeling pain; or relate to the status of an internal organ. They are differentiated from motor nerves, the vessels that carry impulses from the brain to the muscles and tell them to move. Sensory nerves transmit what are known as afferent signals, which the brain receives and responds to accordingly.
Composed of chains of nerve cells called neurons, sensory nerves are a part of the peripheral nervous system. Extending from the spinal cord, a component of the central nervous system, to receptor cells throughout the body, they penetrate nearly all of the body’s tissues. They also tend to be paired with motor nerves, which are referred to as efferent because they transmit nerve impulses away from the central nervous system. For example, upon touching a hot stove, sensory receptors in the fingertips quickly send a message along the nerves to the brain telling the brain that this stimulus is both hot and painful. In response, the brain sends an impulse along the motor nerves that innervate the relevant muscles of the arm and hand, causing them to quickly contract and thereby retracting the hand.
Within the sensory nerves, nerve cells are bundled in fibers and end in receptors that can be classified according to their function. Nociceptors, for instance, are those that notify the brain of injury and produce a pain response, while photoreceptors respond to light, and mechanoreceptors respond to touch and pressure. In addition, olfactory receptors in the nose detect odors, while taste receptors on the tongue detect the flavors in food.
The sensory nerves transmit messages from these receptors via an electrical signal known as a nerve impulse. Nerve impulses are conducted toward the nerve roots, which is the place where the sensory nerves enter the spinal cord, and from the spinal cord to their respective center in the brain. The brain is then responsible for interpreting these messages, such as whether an unstable surface that is prodded with the foot is safe to walk upon. Once the stimuli is received by and interpreted in the brain, it determines the appropriate response. It then sends a message back down the spinal column, out through the motor nerves, and to the relevant muscles, telling them to move accordingly.
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![Sensory nerves are composed of chains of neurons.]()
By: Vector Art DesignSensory nerves are composed of chains of neurons. -
![Sensory nerves allow us to have a sense of balance.]()
By: Rob hyronsSensory nerves allow us to have a sense of balance. -
![Mechanoreceptors register changes in touch.]()
By: Svetlana FedoseevaMechanoreceptors register changes in touch. -
![Motor nerves carry impulses from the brain to the muscles and tell them to move.]()
By: abhijith3747Motor nerves carry impulses from the brain to the muscles and tell them to move. -
![Taste receptors on the tongue detect flavors in food.]()
By: yanmingzhangTaste receptors on the tongue detect flavors in food.
Discussion Comments
Thank heaven our motor nervous system and our sensory nervous system are programmed to work together. So if you start to wash your hands, not realizing that you turned on the hot water, the sensory nerves will send a message up to the brain very quickly and the brain signals the motor nerves to move that hand out of the hot water.
There are some people who don't feel the stimulus of hot or pain. So for some reason, there is a gap in the impulse and the brain doesn't receive the message. This condition can be very dangerous. I hope scientists are working on a way to fix this problem.
A number of babies are born with an extra strong sensitivity to touch. My friend's daughter, as a child, had a strong sensitivity to different textures of fabric and many objects. In addition, her sense of taste was very strong and her tongue could not tolerate food with certain textures and taste. She would also get upset in a noisy environment.
The messages that her sensory nerves sent to her brain interpreted the signal and the body responded in an exaggerated way.
She was taken to a therapist who was specially trained to help children to desensitize themselves to the strong stimuli that they feel through their sensory nerves. This helped quite a bit to tone things down.
I use my sensory nerves every time I go shopping for clothes. There are certain textures that I prefer and certain ones that I hate, and I touch the clothing to get a sense of its texture before I even bother trying it on.
I never buy silky clothing, because it will develop underarm stains very easily. If I touch a shirt and feel a silky texture, I will pass by it.
I love velvety suede, corduroy, and cotton. If I’m shopping for winter clothes, I use texture cues to determine how warm a certain garment will make me feel.
I realize the value of sensory nerves every time I go to the dentist and have to get a novocaine shot. Sections of my face become totally numb, and no matter what I do to those areas during that time, I cannot feel it.
After one dentist visit, I was so hungry that I decided to eat even with numb cheeks. Part of my tongue’s nerves had been deadened as well, which made it really difficult to maneuver the food around my mouth.
I bit my cheeks several times, but I didn’t know it until I tasted the blood. When the feeling returned to my sensory nerves, my cheeks really hurt.
My cousin has congenital insensitivity to pain. Her sensory nerves that should tell her when she is in pain don’t connect properly with the part of the brain that recognizes pain, so she is in constant danger.
Even though her sense of heat, touch, and sight are fine, her sense of pain is missing. As a child, she required constant supervision. She even broke her leg once without knowing it, and her parents only figured it out after they saw her walking strangely.
We may think the inability to sense pain is a good thing, but it is life threatening. You could never know if your appendix was about to rupture or if your hands were on fire. The sensory nerves’ ability to relay pain to the brain is a precious thing that preserves life.
Sometimes sensory nerves can become overly sensitive after a tragedy. The brain relates all stimuli associated with that bad event to the same stimuli in different situations, where an urgent response is not really necessary. This happened to me after my car wreck.
A white van pulled out in front of me, and there was nothing I could do but slam on the brakes, swerve, and hit it anyway. Since that day, every time I see a car waiting to pull out into the road, my immediate response is to brake, even though the car most likely will wait on me like it’s supposed to do. I even feel a rush of adrenaline in vehicle situations that would not even faze most people.
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