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Chapter 35.4 The Senses

Chapter 35.4 The Senses. SENSORY RECEPTORS. Neurons that receive information from the environment Five categories: Pain receptors : respond to chemicals from damaged cells Thermoreceptors : detect variations in temperature

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Chapter 35.4 The Senses

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  1. Chapter 35.4 The Senses

  2. SENSORY RECEPTORS • Neurons that receive information from the environment • Five categories: • Pain receptors: respond to chemicals from damaged cells • Thermoreceptors: detect variations in temperature • Mechanoreceptors: sensitive to touch, pressure, muscle stretching, sound and motion • Chemoreceptors: sensitive to chemicals in the environment • Photoreceptors: sensitive to light

  3. VISION AND THE EYE • Structure of the eye: • Cornea: tough, transparent layer of cells; focuses light • Iris: colored part • Pupil: opening in the iris, adjusts in size to change light intensity • Lens: changes shape to focus light on the retina • Retina: layer of photoreceptors (light  nerve impulses) • Photoreceptors: • Rods: light sensitive; night vision • Cones: color vision (daytime); mostly contained in the fovea (sharpest vision) • Optic Nerve: sends impulses to the brain; no photoreceptors (blind spot)

  4. HEARING AND BALANCE Hearing • Sound waves (vibrations) travel through the auditory canal to the tympanum (ear drum) • Three tiny bones (hammer, anvil, stirrup) send vibrations to the oval window • Vibrations send waves through the fluid-filled cochlea • Hair cells in the cochlea pick up vibrations and transmit nerve impulses down the cochlear nerve to the brain Balance • Semicircular canals: three half-circle shaped canals above the cochlea; filled with fluid and lined with tiny hairs that help determine body motion and position

  5. SMELL AND TASTE • Chemoreceptors in the nose detect different “smells” (chemicals) and transmit impulses to the brain • The tongue is covered with taste buds that are chemoreceptors for the taste of food • Five tastes • Salty • Sweet • Sour • Bitter • Umami “savory”

  6. TOUCH AND RELATED SENSES • Touch receptors found in many locations, specifically on the skin. • Skin is the largest sense organ; senses touch, temperature and pain. • Touch receptors are distributed unevenly. Most receptors are found on fingers, toes and the face.

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