BMS 100 - Chapter 10 Outline
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Sense of Hearing (p. 256)
  1. outer ear - includes auricle and external auditory canal
  2. tympanic membrane (eardrum)
    1. partition between the external ear and the middle ear
    2. sound waves cause tympanic membrane to vibrate
  3. middle ear & middle ear cavity
    1. auditory ossicles ("ear bones")
      1. "hammer" - attached to inside of eardrum
      2. "anvil" - between hammer and...
      3. "stirrup" - partially inserted into oval window of internal ear
    2. functions of ossicles
      1. conduct vibrations to inner ear (creates "waves" in fluid in inner ear)
      2. area of eardrum > area of oval window, therefore the pressure of incoming vibrations is increased by ossicles
    3. stapedius and tensor tympani muscles
      1. attached to hammer and to stirrup
      2. loud sounds cause these muscles to contract ("stapedius reflex")
      3. muscle tension holds ossicles tighter
      4. reduces movements of bones / decreases energy imparted to inner ear (protects inner ear)
    4. auditory (Eustachian) tube
      1. connects middle ear cavity to pharynx (throat)
      2. for equalization of air pressure between atmosphere and middle ear cavity (e.g., between inner and outer surfaces of eardrum)
  4. inner ear
    1. is a complex system of tubes and chambers – the "labyrinths"
    2. cochlea - contains spiral organ with hair cells (receptors)
      • receptors produce electrical signals (nerve impulses) when stimulated
      • receptors are connected to sensory neurons, which conduct electrical signals to the CNS
    3. hair cells of spiral organ
      • waves in inner ear fluid cause membranes to vibrate
      • hair cells are "tucked in" between two vibrating membranes in spiral organ
      • hair cells generate electrical impulses when stretched, compressed, twisted, etc.
      • AP's enter cranial nerve VIII for conduction to brain
    4. different frequencies (pitches) of vibrations stimulate different sets of hair cells
  5. Click Here for a Hearing Animation.
Sense of Equilibrium (p. 261)
  1. semicircular canals, etc. - location of hair cells (receptors) for sense of equilibrium
  2. these hair cells are either attached to a dense membrane or immersed in a fluid
  3. if head is tilted, rotated, accelerated, etc., hair cells are "bent" and they send signals to the CNS
  4. signals are perceived as change in position or motion of head (sense of equilibrium)
Chapter 10 Questions at OLC - 1, 14, 15, 16, 18, 23, 24, 25, 27, 28, 35, 36, 37, 39

General notes about the eyeball:
  • the eyeball consists of three major layers
  • for clear vision, light rays must be focused on the retina (innermost layer)
  • cavities (spaces) within the eyeball are slightly pressurized by fluid (helps maintain shape of the eyeball)
    1. outer layer (fibrous layer)
      1. sclera - "white" of the eye (tough, protective)
      2. cornea - transparent anterior portion; the cornea refracts (bends) light waves toward retina
    2. middle layer
      1. inner wall contains pigments that keep the inside of the eye dark
      2. iris
        1. contains pigments that block entry of excessive light energy
        2. pupil - hole in center of iris (for passage of light)
        3. "pupillary constrictor" & "pupillary dilator" = muscles in iris
      3. lens
        1. posterior to ("behind") pupil
        2. is transparent and elastic
        3. the lens is held in place by the suspensory ligaments
        4. the suspensory ligaments are attached to the "ring-shaped" ciliary muscle
      4. accommodation (cm = ciliary muscle / sl = suspensory ligaments)
        1. for far vision: cm relaxes > sl become tighter > lens becomes "taller and thinner" (bends light less)
        2. for near vision: cm contracts > sl become looser > lens becomes "thicker and fatter" (bends light more)
    3. inner layer
      1. photoreceptors: rods and cones
      2. rods and cones are actually dendrites that produce electrical signals when stimulated by light
      3. rods
        1. sensitive to dim light
        2. abundant in peripheral (outer) part of retina - provide "peripheral vision"
        3. many rods may "share" one sensory neuron (relatively imprecise)
      4. cones provide visual acuity ("sharp vision") and color vision
        1. color vision comes from three sets of cones ("RGB")
          • different sensitivities to wavelengths allow brain to perceive different colors
        2. central fovea
          • in center of retina
          • high concentration of cones (no rods)
          • cones do not share sensory neurons with other cones (able to send detailed data)
          • provides "central vision" (opposite of peripheral vision)
    4. Visual nerve pathways
      1. optic nerves - include axons that originated in the retina
      2. in the optic chiasma, fibers in medial ("inner") halves of each optic nerve "cross over" to the opposite side
      3. most fibers pass to the occipital lobes (after some processing in the thalamus)
    5. For a Real Player video clip, click "Animation" after clicking here.
    Chapter 10 Questions at OLC - 1, 14, 15, 16, 18, 23, 24, 25, 27, 28, 35, 36, 37, 39
    Spring 2011