Sensory system: Structure and function

The sensory system is a part of the nervous system, and it can be split into two divisions: the general senses and the special senses.

Both divisions gather information about your surroundings and what’s happening inside your body. The sensation you experience, also called a stimulus, is captured by sensory receptors, which receive the stimulus and convert them into nerve impulses that travel all the way through sensory nerves to the brain for interpretation.

Alright, the general senses include touch, pressure, position, and pain. There are receptors for these distributed all over the body.

Now for touch, tactile receptors pick up sensory information when something comes in contact with your skin, like when you’re petting a dog.

Some parts of your body, like the tips of the fingers, are more sensitive to touch because they have more tactile receptors than other areas, like your back.

Now, in addition to touch, some tactile receptors sense pressure on the skin. This is why we feel uncomfortable after sitting in a certain position for a long time and need to change our position to another one.

Clients like those with spinal cord injuries might have problems with this sensation, so they stay in the same position, which causes prolonged compression of blood vessels in their skin and a decrease in blood flow to that area. This causes their skin to break down and form pressure ulcers.

The next general sense is the sense of position. When you’re sitting on your couch, you know your legs are straight or crossed without looking at them.

This is because position receptors found in joints, muscles, and tendons inform your brain about the position of different parts of the body relative to each other.

Also, these receptors inform your brain about how much your muscles are contracting or stretching and help prevent injury when you’re doing something like lifting heavy weights at the gym.

Now, the last general sense is pain. Pain receptors can be found on the surface of skin or within internal organs and tissues of the body.

Pain can sometimes be well-localized; for example, when you get an injection, you can tell exactly where you feel the pain. However, sometimes the pain may be felt at another location far away from the cause.

This is known as referred pain. Examples of referred pain include a client with a heart attack: They can have pain that travels to the jaw, neck, or arm. A client with gallbladder disease will often have pain that appears in the right shoulder or back.

Alright, let’s switch gears and talk about the special senses. They are called “special senses” because they rely on specialized sensory organs. These senses are taste, smell, sight, hearing, and balance.

Alright, let’s start with taste. When you eat food or drink a beverage, your saliva acts as a solvent for different chemicals coming from what you ingested.

These dissolved chemicals then stimulate taste buds, which cover the surface of the tongue. Each taste bud may contain up to one hundred chemoreceptors, which are specialized types of cells that sense chemicals, and convert these chemical signals into electrical signals, which travel through sensory nerves to the brain.

There are five different tastes: sweet; salty; sour; bitter; and umami, which is savory. Interestingly, these tastes are sensed at specific areas of the tongue more than others.

Sweet is sensed more at the tip of the tongue, salty is sensed more at the front sides, whereas sour things are sensed at the back sides.

Bitter is sensed more at the back of the tongue and lastly, umami is sensed on the entire taste-bud containing surface of the tongue.

Alright, next is smell. Similar to taste, chemicals from odors are dissolved in a solvent. In this case, it’s the mucus secreted by the nasal cavity.

Now, these chemicals then stimulate smell chemoreceptors, which are present on the roof of the nasal cavity, and get converted into electrical signals that go to the brain.

Okay, so both smell and taste rely on chemoreceptors. Unfortunately, the number of taste and smell chemoreceptors decrease with age.

This makes it harder for older clients to taste and smell food, which decreases their appetite and puts them at risk of poor nutrition.

Also, a client with a decreased sense of smell can’t smell the odor of a gas leak or smoke of a fire, which predisposes them to danger.

Alright, moving to the next special sense, which is sight. The organ responsible for it is, that’s right, the eyes. The eye itself is shaped like a sphere that sits within the orbit, or eye socket.

The eye consists of three layers: the outermost fibrous layer, the uvea, and the retina. The outer fibrous layer contains two main structures: the cornea and the sclera.