The nervous system receives information (or stimulus) from outside and inside the body. Millions of tiny nerve cells, called sensory receptors, sense the stimuli. This is called sensory input and its signal is transmitted along nerve cells to the brain. The brain interprets the stimuli and reacts. The reaction can be the brain signaling the muscles to move, increasing the heart rate, breathing or releasing hormones. The brain also stores experiences in memory, so your responses to stimuli can be more effective over time with more experience. For example, when you learn to ride a bike, your body has to learn to balance, pedal and steer. You might feel anxious and shaky at first. If you fall, it may hurt. These are all sensory inputs. Yet, over time, your body and brain will remember which positions and movements work. Eventually, you will be able to jump on the bike and ride with confidence.
Sensory input can be received in different ways. It can be electromagnetic, mechanical, or chemical stimuli. Electromagnetic or photoreceptors respond to light energy detected by the eyes. Mechanical or mechanoreceptors are stimulated by touch, pressure, vibrations, stretch and sound. Chemical or chemoreceptors respond to smells, tastes or changes in blood chemistry. There are also thermoreceptors that are sensitive to temperature changes and nociceptors that feel pain. All the sensory receptors can function as nociceptors for pain if the stimulus is applied too excessively, e.g. scorching heat, blistering cold, sudden bright light, or extreme pressure.
Most sensory input comes from the simple receptors found in the skin, mucous membranes, muscles, and other tissues that monitor general sensory information, such as: touch, pressure, stretch, movement, and position. The more complex receptors are called the special senses and are associated with vision, hearing, smell and taste. These receptors are considered sense organs because they include other structures besides sensory cells to collect their sensory input. For example, hearing involves the transmission of sound along nerve cells in the inner ear to the brain, but the sensory organ, which makes hearing possible, includes the ear canal, eardrum, the tiny bones of the middle ear, the oval window into the inner ear, and the cochlea.
The nervous system controls how all the body systems work in a huge communication network with messages coming in and going out every second. It keeps track of everything going on in the body and with the help of the endocrine system makes it run smoothly and in balance – it maintains homeostasis. Messages coming and going through the nervous system are communicated via electrical signals that are very quick and specific.
The nervous system has three jobs, which overlap to keep the body running smoothly.
1) It receives information (or stimulus) from outside and inside the body. Millions of tiny nerve cells – called sensory receptors, sense the stimuli. The stimulus is the sensory input. Your brain is getting sensory input from all kinds of body sensors all the time. You will know when you are hot, cold, hungry, thirsty, sleepy or sore. You can tell when you are lying down, standing up, falling, or get stung by a wasp. Your brain gets the stimulus and tells you what it is. It also stores the information in memory so you can retrieve it the next time you feel it.
2) It decides what to do with all that sensory input. This is called integration, because it integrates or brings together the stimulus with what you are going to do about it.
3) It triggers action. This is the motor response or motor output. Your muscles (or glands) respond to orders.
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Amsel, Sheri. "Information Processing - Reading (6-8 Grade NGSS)" Exploring Nature Educational Resource ©2005-2021. June 22, 2021
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