The Senses

Sensory receptors

detect all forms of energy, such as heat, light, pressure, and chemicals. The major classes of sensory receptors are photoreceptors, mechanoreceptors, chemoreceptors, pain receptors, and thermoreceptors.

nervous system detect stimuli?

Specialized neurons called sensory receptors detect sensory stimuli and convert them to electrical signals. These signals then can be interpreted by the brain. info sent to brain, which creates a motor response. also helps to maintain homeostatis.

Retina

a layer of specialized cells that lines the inner surface of the eye. contains two types of photoreceptors— rods and cones. Cones respond best to bright light and are stimulated by specific colors of light. The retina also contains many other neurons that process visual information. The axons of some of these cells make up the optic nerve. The optic nerve exits through the back of the eye, runs along the base of the brain to the thalamus, and later runs to the cortex for processing.

Other Senses and Touch!

-jessiewashere- Touch and other body-related senses are collectively referred to as somatosensation. Pain receptors respond to potentially harmful stimuli, such as intense heat or cold and tissue damage. These receptors are nerve endings located near the surface of the skin and elsewhere in the body. Many self-protective responses, such as reflexes, are started by pain receptors. Thermoreceptors Thermoreceptors are nerve endings that are located both in the skin and in the hypothalamus. These receptors detect changes in temperature and play an important role in homeostasis. They help keep the body temperature within its normal range. Mechanoreceptors Throughout the body, mechanoreceptors respond to physical stimuli—such as pressure and tension—that cause the bending of tissue. Many mechanoreceptors are found in the skin, and they are concentrated in very sensitive areas, including the face, hands, fingertips, and neck.

Taste and Smell

Chemoreceptors are sensory receptors that respond to chemicals. Taste buds. detect at least five basic chemical substances: sugars (sweet), acids (sour), alkaloids (bitter), salts (salty), and proteins (savory). Food molecules dissolved in saliva flow into the taste pores and bind to taste cells, which generate nerve impulses that are sent to the brain for interpretation. - Chemicals in the air stimulate olfactory receptors, chemoreceptors located deep in your nostrils. These sensory receptors produce nerve impulses that are sent to and interpreted by the brain. When you have a bad cold and your nose is stuffed up, your food may seem to have little taste. Your ability to taste food directly depends on your ability to smell it!

Balance

How do your ears help you maintain balance? The semicircular canals are another set of fluid-filled chambers in the inner ear that contain hair cells. Clusters of these hair cells respond to changes in head position relative to gravity. When your head moves, fluid in the semicircular canals also moves. Hair cells sense the strength and direction of the fluid's movement. The hair cells send electrical signals to the brain. These signals are then sent to the cerebellum along a branch of the auditory nerve. The brain processes these signals to determine the orientation and position of the head.

Processing Sensory Information

Most sense organs send signals through nerves of the PNS into the CNS. The thalamus then relays this information to specific regions of the cortex. Specialized regions of the cerebral cortex detect different sensory information.The parietal lobe of the cortex receives somatosensory ("body sense") stimuli. The amount of cortex devoted to a body part is proportional to the density of sensory receptors in that body part. For example, large areas of the somatosensory cortex are devoted to processing information from the hands. In the rear portion of the frontal lobe, immediately in front of the somatosensory cortex is the motor cortex. The motor cortex regulates the function of skeletal muscles. The frontal lobe also regulates intellectual function and aspects of our personality. Most visual processing occurs in the occipital lobe, located at the back of the head. The temporal lobe processes sound information.

Hearing

Sound waves enter the ear through the ear canal and strike the tympanic membrane, or eardrum. These vibrations cause the eardrum to vibrate. Behind the eardrum, three small bones of the middle ear act like a rattling chain. These bones are the hammer, the anvil, and the stirrup. They transfer the vibrations to the cochlea, a fluid-filled chamber within the inner ear. This chamber is coiled like a snail's shell. The cochlea contains hair cells. These hair cells rest on a membrane that vibrates when sound waves enter the cochlea. Various frequencies of sound waves cause the membrane to vibrate differently and thus stimulate the hair cells. When hair cells are stimulated, they generate action potentials in the axons of the auditory nerve. The impulses travel along the auditory nerve to the temporal lobe of the cerebral cortex. Here, the auditory information is processed.

Hearing and Balance

The human ear has two types of mechanoreceptors. One plays a role in hearing, and the other plays a role in balance. Both types of mechanoreceptors are hair cells that are in an enclosed space. These cells bend when the surrounding fluid moves. Figure 14 shows the structure of the ear.