Transcript The Senses
Lesson Overview The Senses SEC 31.4 The Senses Lesson Overview The Senses THINK ABOUT IT We live in a world of sensations. Our senses are our link to experiencing the outside world. The inputs we get from our senses are almost impossible to describe, and yet we use them every moment of the day. Lesson Overview The Senses Touch and Related Senses Because nearly all regions of the skin are sensitive to touch, your skin can be considered your largest sense organ. Lesson Overview The Senses Touch Human skin contains several types of sensory receptors. Stimulation of these receptors creates the sensation of touch. Not all parts of the body are equally sensitive to touch. The skin on your fingers has a higher density of touch receptors than the skin on your back. Lesson Overview The Senses Temperature Thermoreceptors are sensory cells that respond to heat and cold. They are found throughout the skin and in the hypothalamus, a part of the brain that senses blood temperature. Lesson Overview The Senses Pain Pain receptors are found throughout the body. Some receptors respond to physical injuries like cutting or tearing, while other receptors respond to chemicals released during infection or inflammation. The brain does not have pain receptors. Lesson Overview The Senses Smell and Taste Your senses of taste and smell involve the ability to detect chemicals. Chemical-sensing cells known as chemoreceptors in the nose and mouth are responsible for both of these senses. Lesson Overview The Senses Smell and Taste The sense organs that detect taste are the taste buds. Sensory cells in taste buds respond to salty, bitter, sweet, and sour foods. Recently, a fifth kind of taste sensation was identified, now called “umami,” from the Japanese word for savory. Lesson Overview The Senses Hearing and Balance The human ear has two sensory functions— hearing and detecting movement. Mechanoreceptors in the ear transmit impulses to the brain. The brain translates the impulses into sound and information about balance. Lesson Overview The Senses Hearing Sound is a result of vibrations moving through the air around us. Vibrations enter the ear through the auditory canal and cause the tympanum, or eardrum, to vibrate. Lesson Overview The Senses Hearing Three tiny bones - the hammer, anvil, and stirrup, transmit vibrations to a membrane called the oval window. Vibrations create pressure waves in the cochlea. Lesson Overview The Senses Hearing The cochlea is lined with tiny hair cells that move back and forth. This motion produces a nerve impulse that travels to the brain and is processed as sound. Lesson Overview The Senses Balance Three tiny canals within the inner ear, called semicircular canals, monitor the position of your body and help maintain balance, or equilibrium. Lesson Overview The Senses Sound Intensity Sound intensity, or loudness, is measured in units called decibels (dB). Loud noises can permanently damage the cochlea. Exposure to sounds above 80 dB for several hours can damage hearing. Exposure to sounds about 120 dB for a few seconds can damage hearing. Lesson Overview The Senses Sound levels for several sound sources are shown in the bar graph. Lesson Overview The Senses Structures of the Eye Light enters the eye through the cornea, a tough transparent layer of cells. The cornea focuses the light, which then passes through a chamber filled with a fluid called aqueous humor. Lesson Overview The Senses Structures of the Eye At the back of the chamber is the iris, or the colored part of the eye. In the middle of the iris is a small opening called the pupil. Lesson Overview The Senses Structures of the Eye Tiny muscles in the iris adjust the size of the pupil to regulate the amount of light that enters the eye. The pupil becomes larger in dim light. In bright light the pupil becomes smaller. Lesson Overview The Senses Structures of the Eye The lens is located behind the iris. It changes its shape to focus and see objects clearly. Behind the lens is a large chamber filled with a transparent, jellylike fluid called vitreous humor. Lesson Overview The Senses How You See The lens focuses light onto the retina, the inner layer of the eye. Photoreceptors in the retina convert light energy into nerve impulses that are carried to the brain. Lesson Overview The Senses How You See There are two types of photoreceptors: rods and cones. Rods are extremely sensitive to light. Cones producing color vision. Lesson Overview The Senses How You See The impulses produced by the rods and cones are carried by the optic nerve to the brain. The brain processes and interprets visual information.