A. The human cerebral cortex is divided into three main areas: sensory, motor and associated areas (Association Cortex, 2016). Sensory areas belong to the peripheral nervous system. They extend from the spinal cord to the receptor cells located in all parts of the body. The primary function of sensory area to carry impulses from the receptor cells to the brain for interpretation. These impulses can be those of sensations like touch, pain, smell, taste and sight. The motor area or the primary motor cortex is located in the interior part of the brain at the central sulcus. Its pyramidal cells are connected to the medulla oblongata and the spinal cord. The motor nerves control motor activities of the body. They carry nervous impulses from the brain to the muscle to affect movement. Motor neurons also control activity of various kinds of cells such as epithelial cells, smooth muscle cells, mucous glands etc. The associated areas of the cerebral cortex occupy the largest surface of the cortex (Association Cortex, 2016). They work in association with primary sensory area and motor area to interpret sensations in the brain.
In the cortex region, the sensory area helps to interpret and recognize a sensation, the motor area helps to act on this sensation and the association area makes association with these sensations, stimuli and their effecting activity. In the cerebral cortex, the gyrus region consists of motor area while the sulcus region consists of sensory area. The sensory area stretches onto both the gyrus and the sulcus (Medical Art Library, 2016). The sensory area is made of sensory nerves which carry impulses to the brain. The motor area is composed of motor nerves which carry impulses from the brain to the muscles. The associated area is responsible for interpreting these sensations and stimuli. They also control complicated actions like recognition of objects, memory, thinking etc.
B. Refractive errors are errors caused by the inability of the eye to focus objects on the retina clearly, due to which the objects appear blurred and dim. The inability may be due to the change in shape of cornea, size and shape of the eyeball or aging. (NIH, 2010).The four main kinds of refractive errors are:
a. Myopia – Myopia or nearsightedness is a condition in which light falls in front of the retina instead of on the retina. This causes inability to see far objects clearly.
b. Hyperopia – Hyperopia or farsightedness is characterized by light falling beyond the retina due to which near objects may not be seen clearly.
c. Astigmatism – This happens due to uneven focusing of light on the retina because of which images appear blurred or stretched.
d. Presbyopia – It is a condition caused by aging due to which the eye is unable to focus on objects clearly due to the lens which cannot change shape easily as before.
Inner Ear:
The inner ear consists of the following four main parts:
a. Cochlea: It structure resembles a snail shell and is filled with a fluid called perilymph. This fluid is separated by membranes which have microscopic hair. Sound vibrations entering the cochlea put these hair fibers into motion (The Inner Ear, 2016).
b. The auditory nerve: These are bundles of nerve fibers connecting the cochlea to the brain. Sound vibrations through the cochlea; get transmitted through the auditory nerve which sends the impulses through the brain.
c. The vestibular: It consists of three ring-shaped passages placed at three different plans. They are filled with fluid and lined by hair fibers which are set in motion on sound reception. These impulses are then sent to the brain. The vestibular also controls the equilibrium of the body by keeping track of body movements and maintaining balance of the body (The Inner Ear, 2016).
References
Association Cortex. (2016). Indiana University. Retrieved from Indiana University.Edu:
http://www.indiana.edu/~p1013447/dictionary/assn_cor.htm
Hear It.(2016). The Inner Ear. Retrieved from Hear It.Org
http://www.hear-it.org/The-inner-ear-1.htm
Medical Art Library. (2016). Cerebral Cortex: Functional Areas. Retrieved from
Medical Art Library.com:
http://www.medicalartlibrary.com/cerebral-cortex.html
National Eye Institute. (2010). Facts About Refraction Errors. Retrieved from
NIH.Gov:
http://www.nei.nih.gov/health/errors/errors.htm
