The Nervous System Section 35-4: The Senses

The Senses Sensory Receptors: neurons that react to specific stimuli such as light or sound by sending impulses to other neurons and eventually to the central nervous system. Sense organs: Eyes (Sense of Vision) Ears (Sense of Hearing and Equilibrium) Nose (Sense of Smell aka Olfactory) Mouth (Sense of Taste aka Gustatory) Skin (Sense of Touch)

Sensory Receptors 5 general categories: Pain Receptors Throughout body except the brain. Responds to tissue damage. Thermoreceptors Located in skin, body core, and hypothalamus. Responds to changes in temperatures Mechanoreceptors Found in skin, skeletal muscles, and inner ears. Responds to movement and pressure Chemoreceptors Found in nose and tongue Responds to chemical changes Photoreceptors Found in the eyes Responds to light

Vision: Parts of the Eye Pupil Small opening where light enters Size adjusted by the iris Lens Structure that adjusts the focus Retina Inner layer of the eye containing photoreceptors Rods Photoreceptors that are sensitive to light Detects black and white Cones Photoreceptors that detect color Concentrated in the fovea Fovea Area on the retina where vision is sharpest

Vision Light enters the eye through the pupil and focused at the fovea of the retina Photoreceptors (rods and cones) receive the light Impulses are sent to the brain where they are interpreted as visual images

Ear Has two functions Hearing Balance

Hearing Sound vibrations enter the outer ear through the auditory canal Vibrations cause the eardrum to vibrate Vibrations are picked up by the middle ear bones – hammer, anvil, and stirrup Vibrations transmitted to the cochlea found in the inner ear Cochlea contains receptors, hair cells, that receive these vibrations Impulses are sent to the brain where the vibrations are translated as sound

Balance (Equilibrium) Found in the inner ears above the cochlea Semicircular Canals Monitor the position of your body in relation to gravity Contain hair cells Movement of hair cells when you move your body sends impulses to the brain to determine motion and position (cerebellum) and maintain balance

Smell and Taste Detects chemicals Chemoreceptors Chemoreceptors for the tongue are called Taste Buds

Touch and Related Senses Skin Contains receptors that respond to temperature, touch, and pain Not all parts are equally sensitive Greatest density found in fingers, toes, and face

Exit Slip 35-4 Section Assessment #1-5 Page 909 For #5, feel free to perform the demonstration in class 