Chapter 10 Somatic Senses

If you enter a room and smell a strong odor, but the odor soon seems to fade away, you have experienced sensory adaptation. Receptors stimulated by changes in temperature are called thermoreceptors The process by which the brain causes a sensation to seem to come from the stimulated receptors is called projection.

Pain receptors are generally stimulated by factors that can cause tissue damage. Meninges on the surface of the brain and blood vessels within the brain are the structures that contain pain receptors. Pain that feels like it is coming from a part other than the part being stimulated is called referred pain Referred pain occurs when the brain projects the sensation from some part of the body other than the part being stimulated.

Pain sensations arising from visceral organs may be cased by the stretching of tissues. The olfactory receptors are examples of chemoreceptors. Olfactory receptor cells are best described as neurons. The interference with vision and the feeling of numbness in the limbs experienced by a person with a migraine is probably caused by cerebral blood deficiency.

Anosmia is a condition in which there is a loss of smell. Taste receptors are modified epithelial cells. Three of the primary taste sensations is sweet, salty, and bitter. Nerve impulses from taste receptors can travel in the facial, glossopharyngeal, and vagus nerve. The auditory ossicles are located within the middle ear. The stapes transmits vibrations to the inner ear through the oval window. The auditory tube connects the middle ear with the throat.

Blowing the nose improperly may cause an infection within the auditory tube to spread the middle ear. The hearing receptors are contained within the organ of Corti. The range of human hearing is about 20-200,000 vibrations per second. The auditory nerve pathways carry impulses to the auditory cortices in the temporal lobes. Torn tympanic membrane would cause a form of conductive deafness. The utricle and saccule contain the sensory receptors associated with the sense of static equilibrium. The sensory receptors associated with the semicircular canals are located in swellings called ampullae

Tears contain an enzyme that functions to reduce the chances of developing an eye infection. The fine conjunctiva lines the inner surface of the eyelid and covers the anterior surface of the eye. The transplant, anterior portion of the eye’s outer tunic is called the cornea. Lights passes through the eye in the following parts. Cornea Aqueous humor Lens Vitreous humor Lack of donor tissue is the reason that so many people are in need of treatment to fail to undergo cornea transplantations.

Worldwide, blindness is most commonly caused by changes in the cornea. The lens of the eye thickens when the ciliary muscles contract. Treatment for cataract usually involves removal of the lens. The adjustments of the thickness of the lens to make close vision possible is called accomodation. The inner part of the inner tunic of the eye is the retina. The disorder called glaucoma is usually caused by excessive accumulation of aqueous humor. When the radial muscles of the iris contract, the diameter of the pupil increases. The fovea centralis is the region of sharpest vision within the retina.

Floaters that cast shadows on the visual receptors are usually located within the vitreous humor. Rod cells contain the pigment rhodopsin. Rods are more sensitive to light than cones, but cones are important for color vision. Night blindness is most commonly caused by an improper diet. The sets of color receptors within the retina are sensitive to lights that are red, green, and blue.