Study Guide For Senses
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Eye In the human eye, the nerve cells are located in a single layer called the retina, located along the back wall of the eye. Light rays enter the eye through a curved, transparent structure called the cornea, and then pass through the pupil, an opening in the eyeball. The iris regulates the size of the pupil. Next, the lens focuses the light on the retina, which contains two types of light-sensitive cells, rod cells and cone cells, which detect light. Cone cells, which detect color, are concentrated in the central portion of the retina, while rod cells, which permit vision in dim light, are concentrated at the edge of the retina. A light-sensitive pigment called rhodopsin functions in the detection of light. From the eye, a series of impulses is generated for transmission to the brain.
The optic nerve carries these impulses. The region of keenest vision, the fovea, is located at the center of the retina. When vision is poor, light is not focusing on the fovea, and corrective lenses are prescribed. Ear The ear is the organ of hearing in humans. The outer ear funnels vibrations to the eardrum, or tympanic membrane, which transmits the vibrations to three inner ear bones: the malleus (hammer), the incus (anvil), and the stapes (stirrup).
These bones transmit the vibrations to the inner ear where the receptor of hearing, the cochlea, is located. The cochlea is a snail-like series of coiled tubes within the skull. As the ear bones vibrate, they push and pull a membrane at one end of the cochlea, causing fluid within the tubules to vibrate.
The vibrations are detected by sensitive hair cells, and nerve impulses are generated. The auditory nerve carries the impulses to the brain for interpretation. Taste and smell Specialized receptor cells called chemoreceptors transmit taste and smell. Chemoreceptors of the human tongue distinguish four different tastes: sweet, sour, salty, and bitter. In the human nose, chemoreceptors detect a variety of scents, including minty, floral, musky, putrid, and pungent.
In both taste and smell, chemoreceptors are stimulated by molecules and ions that reach the tongue and nose. Liquid materials affect the chemoreceptors in the taste buds of the tongue, while gaseous molecules affect the chemoreceptors in the upper reaches of the nose.
The olfactory nerve carries nerve impulses from the nose to the brain for interpretation. Other senses The other senses of the body include receptors for touch, pain, temperature, and balance. Touch and pain receptors, called Pacinian corpuscles, are located in the skin, muscles, and tendons. The sense of balance is centered in the semicircular canals of the inner ear. Visceral senses include stretch receptors in the muscles, as well as carbon dioxide receptors in the arteries.
The sensory division of the peripheral nervous system (PNS) includes several sense organs—the eyes, ears, mouth, nose, and skin. Each sense organ has special cells, called sensory receptors, that respond to a particular type of stimulus.
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For example, the nose has sensory receptors that respond to chemicals, which we perceive as odors. Sensory receptors send nerve impulses to sensory nerves, which carry the nerve impulses to the central nervous system. The brain then interprets the nerve impulses to form a response. Sight is the ability to sense light, and the eye is the organ that senses light. Light first passes through the cornea of the eye, which is a clear outer layer that protects the eye (see Figure 1.42). Light enters the eye through an opening called the pupil.
The light then passes through the lens, which focuses it on the retina at the back of the eye. The retina contains light receptor cells. These cells send nerve impulses to the optic nerve, which carries the impulses to the brain. The brain interprets the impulses and “tells” us what we are seeing. Spirit airlines flight attendant manual.
Hearing is the ability to sense sound waves, and the ear is the organ that senses sound. Sound waves enter the auditory canal and travel to the eardrum (see Figure 1.43).
They strike the eardrum and make it vibrate. The vibrations then travel through several other structures inside the ear and reach the cochlea. The cochlea is a coiled tube filled with liquid. The liquid moves in response to the vibrations, causing tiny hair cells lining the cochlea to bend. In response, the hair cells send nerve impulses to the auditory nerve, which carries the impulses to the brain. The brain interprets the impulses and “tells” us what we are hearing.
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The ears are also responsible for the sense of balance. Balance is the ability to sense and maintain body position. The semicircular canals inside the ear (see Figure 1.43) contain fluid that moves when the head changes position. Tiny hairs lining the semicircular canals sense movement of the fluid. In response, they send nerve impulses to the vestibular nerve, which carries the impulses to the brain.
Study Guide Senses
The brain interprets the impulses and sends messages to the peripheral nervous system. This system maintains the body’s balance by triggering contractions of skeletal muscles as needed.