chapter 15.txt

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chapter 15.txt
2011-04-27 23:22:03

chapter 15
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  1. The ear
    • * Has two functions:
    • o Hearing
    • o Equilibrium
    • * Divided into three major parts:
    • o Outer
    • o Middle
    • o Inner
  2. The outer ear
    • * Function in hearin only
    • * Pinna (auricle)
    • o Helps direct sound
    • * External auditory canal
    • o Narrow canal in the temporal bone
    • o Contain ceruminous glands that secrete wax
    • * Tyempanic membrane (ear drum)
    • o Thin membrane that vibrates in response to sound
  3. The eye
    • * Contains visual receptors
    • * Provides vision
    • * Contains accessory organs
    • o Eyelids
    • o Lacrimal apparatus
    • o Extrinsic muscles
  4. Acessory organs
    • * Extrinsic eye muscles move the eye
    • o Superior rectus (oculomotoror nerve)
    • o Inferior rectus (oculomotoror nerve)
    • o Medial rectus (oculomotoror nerve)
    • o Latera rectus (abducen nerve)
    • o Superior oblique (trochlear nerve)
    • o Inferior oblique (oculomotor nerve)
  5. How does hearing occur
    • * Vibration of air molecules go through the pinna, passinf through the external auditory canal
    • * The air then vibrates the tympanic membrane which causes the three ossicles to vibrate
    • * The ossicles cause the oval window to vibrate
    • * The oval window cause the perilymph inside the scala vestibul to move
    • * The perilymph in the scala tympani moves as well
    • * This cause the tectorial and basilar membranes to vibrate
    • * The hair cells are active and fire axons of the auditory nerve
    • * The auditory nerve sends the signal to the brain
  6. Outer fiberous layer
    • * Made of two major parts: sclera and cornea
    • o Sclera:
    • * Makes up the posterior 5/6th of the eye
    • * Made of connective tissue to protect the eye
    • * Serves as an attachment for eye muscles
    • * The optic nerve passes through the sclera
    • o Cornea:
    • * Anterior 1/6th of the eye
    • * Made of conenctive tissue and a thin layer of epithelium
    • * Help in focusing the entering light ray
  7. Structure of the eye
    • o The eye has three distinct layers
    • o Outer -fiberous layer
    • o Middle -coroid layer
    • o Inner-nervous layer
  8. Middle ear
    • o air filled space in the temporal bone
    • o contains the ossicles (malleus, incus, stapes)
    • o Transmits vibration between outer and inner ear
    • o The ossicles connect to the oval window
    • o Amplifies the force of vibrations
    • o Contains auditory tube that equalizes pressure with the outside
  9. The cochlea
    • o The cochlea is divided into three chambers
    • * Scala vestibul
    • * Scala media
    • * Scala tympani
  10. Inner ear
    • o Function in hearing and balance
    • o Has two part of labyrinth: osseous and membranous
    • o The membraneous labyrinth is surrounded by osseous labyrinth
    • o The labyrinth includes three parts :
    • o Semicircular canals, the cochlea, and the vestibule
    • o Semicircular canals function in providing the sense of equalibrium
    • o Cochlea provides a sense of hearing
  11. Accessory organs
    • o The lacrimal gland secretes tears
    • o The tears are collected in the superior and inferior canaliculi and then to the lacrimal sac
    • o Tears then go to the nasolacrimal duct which empty in to the nasal cavity
    • * Tears lubricates the surface of the eye and contains the enzyme lysozyme which reduces the risk of eye infection
  12. Sense of equilibrium
    • * Static equilibrium occurs in the vesibule which is located between the cochlea and the semicircular canal
    • * Hair cells synapses on axons of the vestibular nerve
    • * The otolith (calcium stones) sit on top of the hair cell
    • * When the head bends, the otolith
  13. Inner nervous layer
    • * Consists of the retina
    • * Contains visual receptors cells known as photorecteptors
    • * Has many layers
    • * Macula lutea [has high concentration of photorecptor] and the fovea centralis [has highest amount of photoreceptor] produces the sharpest vision
    • * Contain the optic disc (Blind spot-lacks photoreceptor) where the optic nerve, arteries, and veins pass through
    • * The space bordered by the lens, retina, and ciliary body is called the posterior cavity that is filled with a fluid called vitreous humor [thick gel-like substance]
  14. Middle vascular layer
    • * Includes three parts: choroid coart, cilliary body, iris
    • * Choroid coat
    • o Located in the posterior 5/6th of the eye
    • o Has many blood vessels that nourish surrounding tissue
    • o Produce melanin to absorb excess light
    • * Cilliary body
    • o Forms a ring around the front of the eye
    • o Contain the ciliary process (folds) and ciliary muscles
    • o Suspensory ligaments hold the lens in place
    • o Suspensoy ligament and ciliary muscles enables the lens to adjust shape to focus the image
    • o Epithelial cells secrete aqueous humor
    • * Iris
    • o Made of connective tissue and smooth muscle fibers
    • o Is the colord portion of the eye
    • o Located between the cornes and the lens
    • o Forms anterior chamber between the iris and cornea
    • o Forms posterior chamber between iris and lens
    • o Central circular opening called pupil
    • o Smooth muscles control the size of the pupil
  15. Organ of corti
    • * Contains the hearing receptors known as hair cells
    • * Hair cells sit on the basilar membrane
    • * Hair cells are located bellow the tectorial membrane
    • * Hair cells synapses with axon of the cochlear nerve
  16. Visual receptors: rod and cones
    • * Rods
    • o Provide b/w vision
    • o More sensitive to light
    • o Provided vision in dim light
    • * Cones
    • o Provides color visiom
    • o Less sensitive to light
    • o Provides visions in bright light
    • o Cone provide sharp image
    • o Constitute the fovea centralis
  17. Visual pathways images
    • * Optice nerve
    • * Eye
    • * Thalamus
    • * Optic tract
    • * Visual cortex of the occipital lobe
  18. Visual Pathways
    • * The retina sends input to the optic nerve
    • * The optic nerve sends the signal to the thalamus
    • * The thalamus sends the signal to the visual cortex of the occipital nerve
  19. Accommodation
    • * When the ciliary muscles are relaxed
    • o The suspensory ligament are contracted
    • o As a result, the lens thin and flat to focus distant objects
    • * When the ciliary muscles are contracted
    • o The suspensory ligaments are relaxed
    • o As a result, the lens thick to focus close objects
    • [in bright light-pupil constricts]
    • [in dim light- pupil dialates]