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Special Senses. Equilibrium, Hearing, Vision. Ear. Three regions External ear Auricle External auditory meatus Tympanic membrane Middle ear Auditory ossicles Malleus, incus, stapes Inner ear Equilibrium and hearing. Auditory ossicles.
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Special Senses Equilibrium, Hearing, Vision
Ear • Three regions • External ear • Auricle • External auditory meatus • Tympanic membrane • Middle ear • Auditory ossicles • Malleus, incus, stapes • Inner ear • Equilibrium and hearing
Auditory ossicles • Malleus attaches to the inner surface of the tympanic membrane • Incus attaches between the malleus and the inner stapes • Stapes attaches to the oval window • Auditory ossicles conduct and amplify sound waves reaching the inner ear
Inner Ear • Equilibrium and hearing • Receptors found inside fluid filled tubes and chambers called the MEMBRANOUS LABYRINTH • The membranous labyrinth is filled with a fluid called endolymph – necessary for receptor function • The membranous labyrinth is surrounded by a bony shell called the BONY LABYRINTH • The bony labyrinth is filled with perilymph
Bony Labyrinth • Divided into the: • 1. vestibule • Contains the • Utricle – gravity and linear acceleration • Saccule – gravity and linear acceleration • 2. semicircular canals – rotation of head • 3. cochlea – hearing • 4. Vestibule and semicircular canals together are called the vestibular complex
Equilibrium (Balance) • Semicircular canals surround the semicircular ducts • Anterior, lateral, posterior semicircular ducts • The ducts respond to rotational movement of the head • Each duct contains an area called the ampulla which contains the sensory receptors • Sensory receptors are called HAIR CELLS. • Hair cells contain sterocilia and kinocilium which are embedded in a structure called the cupula • Simple answer for rotation: movement of the endolymph causes distortion on the hair cells and release neurotransmitter
Equilibrium • Semicircular ducts respond to one of three rotational planes • Lateral duct - horizontal rotation (NO) • Anterior duct - nodding (YES) • Posterior duct - tilting the head side to side
Utricle and Saccule • Gravity and linear acceleration • Hair cells of the utricle and saccule are clustered in the maculae • Bottom line on gravity and acceleration: • When the hair cells are distorted by the movement of the head the change in these receptors “tells” the CNS the head is no longer level!
Hearing • Cochlea • Divided into three chambers • Vestibular duct - perilymph • Cochlear duct- endolymph • Organ of Corti (spiral organ) • Tympanic duct – perilymph
Organ of Corti(Spiral organ) • Found in the cochlear duct • Contains hair cells for sound detection • Organ of Corti rest on the basilar membrane • Hair cells are in contact with overlying tectorial membrane • Pressure waves in the perilymph move the hair cells, and neurotransmitter is released
Production of auditory sensation • 1. Sound waves hit the ear drum • 2. Auditory ossicles move, stapes on the oval window causes pressure waves in the perilymph of the vestibular duct • 3. Pressure waves distort the basiliar membrane • 4. Movement of basiliar membrane cause distortion of hair cells in the Organ of Corti against the tectorial membrane • 5. Neurotransmitter release • 6. Information concerning the sound goes to the brain via the cochlear branch of cranial nerve VIII
Vision Structure of the Eye
Accessory Structures • 1. Eyelids – palpebrae • Inner surface of eyelid is the palpebral conjunctiva • 2. Eyelashes • 3. Tarsal glands • Inner margin of the eyelid • Lipid secretion, prevent eyelid sticking! • 4. Lacrimal apparatus • Produces tears – keeps eye surface clean and moist • Lysozyme
Eye • Two large chambers • Posterior cavity – vitreous humor • Anterior cavity – aqueous humor • Three layers or tunics • Fibrous tunic • Vascular tunic • Neural tunic
Fibrous tunic • Outermost layer • Consists of the sclera and the cornea • Sclera is the “white of the eye” • Fibrous connective tissue • Cornea is continuous with the sclera but is composed of stratified squamous epithelium • Cornea is avascular and transparent
Vascular tunic • Blood vessels for the eye • Regulation of the amount of light entering the eye • Secretion of aqueous humor • Controls shape of lens • Consists of • Iris • Ciliary body • Choroid
Iris • Seen through the cornea • Contains muscles that change the shape of the opening of the iris the pupil • May also contain pigment cells that give color to the eyes
Ciliary Body • Begins at the junction of the sclera and the cornea • Attachment of the iris • Most of the structure is the ciliary muscle • Suspensory ligament of the lens attach to the ciliary muscle at the ciliary processes • Hold the lens centered on the pupil
Choroid • Layer of blood vessels that delivers oxygen and nutrients to the retina
Neural tunic • Also called the retina • Consists of several layers • Pigment layer • Neural layer • Photoreceptors – rods and cones • Bipolar cells • Ganglion cells
Photoreceptors • Found in the outermost layer next to the pigment layer • Rods • Very light sensitive • Allow us to see in dim rooms or at night • 125 million rods in the retina • Cones • Color vision • Sharp vision but need more light • 6 million cones in the retina
Distribution of rods and cones • 125 million rods spread around the retina • 6 million cones on the posterior retina surface • Most cones are concentrated in an area called the macula lutea • Center of the macula lutea is the fovea centralis • Sight of the sharpest vision • When you look directly at an object this is where the image falls on the retina