Exam 10: The Human Body

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The senses and how information taken in is carried to the brain are as follows:
• Skin sensors - Your skin is able to sense a variety of stimuli, including touch, pressure, pain, heat, and cold; whenever a receptor is stimulated, an impulse (nerve message) begins traveling along the nerve to which the receptor is connected and eventually arrives at the central nervous system.
• Taste - There are specialized nerve receptors on the tongue; the areas containing these receptors are called taste buds; taste is actually a combination of taste and smell, for when you chew food, vapors from it reach your nose
• Smell - The principal nerve that carries information about smell to the brain is the olfactory nerve; branches of this nerve are contained in a cavity in your nasal passage; vapor from the food you eat enters your nasal cavity, is dissolved in a liquid, and stimulates the endings of the olfactory nerve
• Hearing - The ear is the principal organ through which sound waves enter the body; sound waves enter the opening in your external ear and travel through a tube called the auditory canal; this canal ends at a membrane called the eardrum; the sound waves stimulate the eardrum, causing it to vibrate; on the other side of the eardrum, a group of tiny bones - the hammer, the anvil, and the stirrup - transmit energy in the form of vibrations from the eardrum to the cochlea and the semicircular canals, located in the inner ear; these organs relay the vibrations to the sensitive receptors at the end of the auditory nerve, which send signals to the brain that is interpreted as sound
• Sight - Eyes receive information in the form of light from the external world; light passes through a transparent covering called the cornea and enters the pupil, a small opening at the front of the eyeball; directly behind the pupil is the lens, which focuses sight; between the lens and the cornea is a watery liquid known as the aqueous humor; within the eyeball is a thicker, transparent substance called the vitreous humor; the structures at the front of the eyeball all serve to focus light on the retina, the rear portion of the eyeball containing light receptors; receptors are of two types: cones and rods; focused light rays, or images, that reach the retina stimulate the receptors, which in turn transmit information about them to the brain via the optic nerve; in interpreting these messages, the brain gives the sense of sight