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The ear
- * Has two functions:
- o Hearing
- o Equilibrium
- * Divided into three major parts:
- o Outer
- o Middle
- o Inner
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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
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The eye
- * Contains visual receptors
- * Provides vision
- * Contains accessory organs
- o Eyelids
- o Lacrimal apparatus
- o Extrinsic muscles
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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)
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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
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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
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Structure of the eye
- o The eye has three distinct layers
- o Outer -fiberous layer
- o Middle -coroid layer
- o Inner-nervous layer
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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
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The cochlea
- o The cochlea is divided into three chambers
- * Scala vestibul
- * Scala media
- * Scala tympani
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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
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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
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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
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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]
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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
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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
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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
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Visual pathways images
- * Optice nerve
- * Eye
- * Thalamus
- * Optic tract
- * Visual cortex of the occipital lobe
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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
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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]
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