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The Senses

The Senses. Chapter 35.4. Sensory Receptors. Sensory receptors react to specific stimuli Stimuli include light, sound, motion, chemicals, pressure, and changes in temperature. Sensory Receptors.

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The Senses

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  1. The Senses Chapter 35.4

  2. Sensory Receptors • Sensory receptors react to specific stimuli • Stimuli include light, sound, motion, chemicals, pressure, and changes in temperature

  3. Sensory Receptors • Each sensory receptor reacts to a specific stimulus by sending impulses to other neurons, and eventually to the central nervous system (CNS) Most sensory receptors are found in sense organs ex. eyes, inner ear, nose, mouth, and skin

  4. Categories of Sensory Receptors • There are five major categories of sensory receptors: 1. pain receptors 2. thermoreceptors 3. mechanoreceptors 4. chemoreceptors 5. photoreceptors

  5. Categories of Sensory Receptors • Pain receptors • Found all over the body EXCEPT in the brain • Respond to chemicals released by damaged cells • Thermoreceptors • Located in the skin, body core, and hypothalamus Detect variations in temperature • Mechanoreceptors • Found in the skin, skeletal muscles, and inner ear  Sensitive to touch, pressure, stretching of muscles, sound, and motion

  6. Categories of Sensory Receptors • Chemoreceptors • Located in the nose and taste buds Sensitive to chemicals in the external environment • Photoreceptors • Located in the eyes Sensitive to light

  7. Vision • Light enters through the cornea (a tough transparent layer of cells) cornea helps focus light • Light passes through a chamber filled with a liquid called aqueous humor • At the back of the chamber is the iris iris is the colored part of eye

  8. Vision • In the middle of the iris is the pupil (small opening)  Regulates the amount of light that enters the eye • Behind the iris is the lens  Changes shape to help adjust the eye’s focus to see near or distant objects • controlled by muscles

  9. Vision • Behind the lens is a chamber filled with vitreous humor (a transparent, jelly-like fluid) • Light is focused on retina • Photoreceptors found here • Converts light to nerve impulses which are then carried to the CNS

  10. The Retina • Two types of photoreceptors found on the retina: • Rods very sensitive to light but not to colors • Cones not as sensitive to light but responds to light of different colors, producing color vision

  11. Retina • Cones are concentrated in the fovea fovea = site of sharpest vision • A blind spot is a spot on the retina where no photoreceptors exist blind spot = where optic nerve passes through back of eye

  12. Vitreous humor Muscle Lens Fovea Aqueous humor Cornea Pupil Optic nerve Iris Blood vessels Ligaments Retina Choroid Sclera Figure 35-14 The Eye Section 35-4

  13. Question • If a tree falls in the woods and no one is there to hear, does it make a sound?

  14. Oval window Stirrup Anvil Semicircular canals Hammer Cochlear nerve Cochlea Bone Auditory canal Tympanum Round window Eustachian tube Figure 35-15 The Ear Section 35-4

  15. Hearing • Sound is vibrations in the air • The ear distinguishes the pitch and loudness of the vibrations • Vibrations enter the ear through the auditory canal • These vibrations hit the tympanum (eardrum)

  16. Hearing • The vibrations picked up by the tympanum are transferred to three bones hammer, anvil, stirrup • These are the smallest bones in the body • The stirrup transmits the vibrations to the oval window • When the oval window vibrates, it creates pressure waves in the cochlea

  17. Cochlea • The cochlea is fluid-filled and lined with tiny hairs • The pressure waves produced by the oval window push the hairs back and forth • This hair movement produces a nerve impulse that is transmitted through the cochlear nerve to the CNS

  18. Balance • Semicircular canals, and two tiny sacs behind them, monitor the position of your body, especially your head, in relation to gravity • Each canal and sac is filled with fluid and hair • As your head changes position, the fluid moves causing the hair to bend • The CNS receives a nerve impulse to determine body motion and position

  19. Smell and Taste • The senses of smell and taste are a result of chemoreceptors sending nerve impulses in response to chemicals in the environment • Smell  ability of chemoreceptors lining the nasal passageway to respond to chemicals • Taste ability of taste buds to detect chemicals • Taste buds are broken into categories: salty, bitter, sweet, and sour • The tongue’s sensitivity to each varies by region

  20. Touch • It is a unique sense in that the nerves are not found in one particular region of the body all regions of skin are sensitive to touch • It responds to temperature, pressure, and pain • Different body parts have different concentrations of nerves more touch receptors found on fingers, toes, and face

  21. Olfactory (smell) bulb Taste sensory area Olfactory nerve Thalamus Cerebral cortex Smell receptor Nasal cavity Smell sensory area Taste bud Taste pore Taste receptor Sensory nerve fibers The Senses of Smell and Taste Section 35-4

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