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There are five main special senses in the human body These include sight, hearing, taste, smell, and touch. These senses can provide us with vital information that is needed to tell us about our external environment. These special senses, involving neurons, have structures which are located at their dendrites, which are specialized and are also sensitive to pressure, chemicals, and light. This essay will explore two of these senses sight and touch providing an overview of the structures and processes involved.
By reacting to light the human eye allows us to adapt to vision. The structures within the eye permits us to perceive movement, color differences and light. The main structures of the eye include the cornea, retina, iris, pupil, lens, optic nerve. The cornea protects the eye whilst allowing light to pass through the eye, it also bends the light rays making focusing on the retina easier. The retina contains rods and cones known as light-sensitive receptors. It forms an image when light rays are sent from the lens, which are then converted to electrical signals and sent to the brain. The iris made up of two layers of muscle, these muscles are able to adjust the size of the pupil, allowing light to enter and a retinal image to form. The inner layer of circular muscles contracts in bright light conditions, and the outer layer of radial muscles contract in dim light conditions. This is to ensure the correct amount of light is passed through the eye. Different amounts of pigment melanin are the outcome of different colored irises. The pupil is enhanced in dim light which allows light in, and in reverse constricts in bright light decreasing the amount of light entering. The lens is a clear capsule found behind the iris. Like the cornea, the lens bends light which forms an image on the retina. The lens is held in place by fibers which aid in the change to the lens shape. Finally, the optic nerve is fibers which connect the retina to the brain. The retina cells convert sight into an electrical impulse, while the optic nerve sends signals to the visual cortex of the brain. The image that is received initially appears upside down, but the brain can portray the image in the correct way (Sight, 2011). The light sensitive receptors found in the retina which are commonly known as the rods and cones, are involved in how we see color. Rods allow us to see in black and white whereas cones allow us to see color. Rods require low light for this, and cones require bright light. The eye also consists of two different types of fluid. The aqueous humor in the anterior chamber and the vitreous humor in the interior of the eye. Glaucoma is caused by the build-up of the fluid in the anterior chamber which is the main cause of blindness.
The sense of touch is thought to be one of the first senses that the body develops. Hot, cold, pressure, pain, touch, and fine touch are different types of touch receptors that are distributed unevenly around the human body that we react to on an everyday basis. The touch special sense does not have any one specific specialized organ that relates to it, but is in fact a somatic sense that uses a variety of receptors in the skin all over the body. These signals from the receptors in the skin are then combined with feedback from the muscles and tendons as we move around our daily lives, which communicate these with the brain. For example, if the human hand is exposed to an object that is extremely hot, the feedback from the muscles and tendons communicates this with the brain, which instantly tells the hand to remove itself from this situation in order to protect the body from any harm. The sense of touch can be referred to as active or haptic touch. This relates to touch that involves movement. Most cases involve the engagement of kinesthesis, awareness of movement, and proprioception, awareness of bodily position. Movement can be voluntary or exploratory of any sensory surfaces involved in touch, more often the hands. It can also be referred to reactions generated by objects moving towards a stationary body (Stanford Encyclopaedia of Philosophy, 2015).
To conclude, this essay has given an overview of the structures and processes involved in two of the special senses, sight and touch. The structure of the eye can be quite complicated, and even something as small as a build-up of a liquid can result in an individual losing their sense of sight. On the contrary, despite the fact that touch has no specific specialized organ, it is as important as sight. It is clear to see that we rely on our senses daily to provide us with the vital information that we need from our external environment.
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