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Senses

Senses. General senses of touch Temperature Pressure Pain. Special Senses. Smell Taste Sight Hearing Equilibrium. Eye and Vision. 70% of all sensory receptors are in the eyes Each eye has over a million nerve fibers Protection for the eye

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Senses

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  1. Senses General senses of touch Temperature Pressure Pain

  2. Special Senses • Smell • Taste • Sight • Hearing • Equilibrium

  3. Eye and Vision • 70% of all sensory receptors are in the eyes • Each eye has over a million nerve fibers • Protection for the eye • Most of the eye is enclosed in a bony orbit • A cushion of fat surrounds most of the eye • Eyelids and eyelashes • lubricates the eye • Conjunctiva (part of eye that is affected by pink eye or conjuctivitis) • Membrane that lines the eyelids • Connects to the surface of the eye • Secretes mucus to lubricate eye

  4. Lacrimal Apparatus • Functions: • Protects, moistens, and lubricates the eye • Empties into the nasal cavity • Properties of lacrimal fluid • Dilute salt solution (tears) • Contains antibodies and lysosomes Extrinsic eye Muscles • 6 muscles attach to outer surface of eye • Produces eye movement

  5. Layers of the eyeball • Fibrous layer • Outside layer • Vascular layer • Middle layer • Sensory layer • Inside layer

  6. Fibrous Layer • Sclera • White connective tissue layer • Seen anteriorly as the “white of the eye” • Cornea • Transparent, central anterior portion • Allows for light to pass through • Repairs itself easily • The only human tissue that can be transplanted without fear of rejection

  7. Vascular Layer • Choroid is a blood-rich nutritive layer in the posterior of the eye • Pigment prevents light from scattering • Modified anteriorly into 2 structures • Ciliary body-smooth muscle attached to lens • Iris-regulates amount of light entering eye • Pigmented layer that give eye color • Pupil- rounded opening in the iris

  8. Sensory Layer • Retina contains 2 layers • Outer pigmented layer • Inner neural layer • Contains receptor cells (rods, cones) • Signals pass from photoreceptors via a 2-neuron chain • Signals leave the retina toward the brain through the optic nerve • Optic disc (blind spot) where optic nerve leaves eyeball • Cannot see images focused on the optic disc

  9. Neurons of the Retina • Rods • Most are found towards the edges of the retina • Allow dim light vision and peripheral vision • All perception is in gray tones • Cones • Three types of cones • Different cones are sensitive to different wavelengths • Color blindness is the result of the lack of one cone type • No photoreceptor cells are at the optic disc or blind spot

  10. Lens • Biconvex crystal-like structure • Held in place by a suspensory ligament attached to the ciliary body • Cataracts result when the lens becomes hard and opaque with age • Vision becomes hazy and distorted • Eventually causes blindness in affected eye

  11. Aqueous humor • Found in anterior segment • Watery fluid found between lens and cornea • Similar to blood plasma • Helps maintain intraocular pressure • Provides nutrients for the lens and cornea • Reabsorbed into venous blood through the scleral venous sinus or canal of Schlemm

  12. Vitreous Humor • Gel-like substance posterior to the lens • Prevents the eye from collapsing • Helps maintain intraocular pressure

  13. Conditions of the Eye • Emmetropia- eye focuses images correctly on the retina • Myopia-nearsighted • Eyeball is too long, distant objects appear blurry, light from objects fails to reach the retina and are focused in front of it • Hyperopia-farsighted • Eyeball is too short, near objects are blurry, distant objects are focused behind the retina • Astigmatism-images are blurry, light focuses as lines, not points due to unequal curves of the cornea or lens

  14. Imbalances of the eye • Night blindness • Inhibited rod function that hinders the ability to see at night • Color blindness • Genetic condition that result in the inability to see certain colors • Cataracts • Lens becomes hard and opaque • Glaucoma • Increasing pressure within the eye • Hemianopia • Loss of the same side of the visual field of both eyes, damage to visual cortex on only 1 side.

  15. Eye

  16. Ear • Controls 2 senses • Hearing • Equilibrium • Ear is divided into 3 areas • External (outer) ear-Hearing • Middle Ear-hearing • Inner Ear-hearing and balance

  17. Ear • Opening from the auditory canal is covered by a tympanic membrane (eardrum) • There are 3 bones (ossicles)in the middle ear: • Vibrations from eardrum move the malleus -> incus->stapes • Worksheet Label the parts of the ear

  18. Anatomy of the Ear

  19. Taste • There are 4 sensations of taste • Sweet (sugars) • Sour ( acids ) • Bitter ( alkaloids ) • Salty ( metal ions ) • Impulses are governed by several cranial nerves because taste buds are found in different areas • Facial nerve • Glossopharyngeal nerve • Vagus nerve

  20. Developmental Aspects of Special Senses • Formed early in embryonic development • Eyes are outgrowths of the brain • All special senses are functional at birth

  21. Developmental Problems • Cross eyes- results from unequal pulls by the external eye muscles in babies • Ophthalmianeonatoroum- conjunctivitis resulting from mother having gonorrhea, baby’s eyelids are swollen and pus is produced.

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