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THE SPECIAL SENSES 4th year m29/11/2021dent Structure and function of the eyes– vision & tears Intended movement Learning Structure and function of the ears– hearing Outcomes Structure and function of the nose– smell & breathing Structure and function of the mouth– tasteThe Cranial Nerves The cranial nerves are a set of 12 paired nerves that arise directly from the brain. The first two nerves (olfactory and optic) arise from the cerebrum, whereas the remaining ten emerge from the brain stem. Learn this ... you will thank Company yourself later! Strategy # 1To Remember EYE EARS Optic nerve (CN2) Balance and hearing (CN 8) Eye movement (CN 3, 4, 6) NOSE MOUTH Smell (CN 1) Taste (CN 5, 7 and 9) Tongue muscle (CN 12)The Eye LR6(SO4)3 is a simple mnemonic representing the innervation of the extraocular muscles. Through which structure is the light passed in the eye? Light passes through the CORNEA, in between the IRIS called PUPIL, where it is focused by the lens onto the back of the eye at the RETINA, where impulses are transmitted via the OPTIC NERVE to the brain. In the brain, some of impulses transmitted via the OPTIC NERVE passes through the OPTIC CHIASM and continues via the OPTIC TRACT to the OPTIC RADIATION and finally interpreted at the OCCIPITAL LOBE of the brain. From where are tears secreted and to where do they drain? Tear is secreted in the LACRIMAL GLAND, moved across the eyes from LATERAL to MEDIAL to remove debris and eventually drained into the SUPERIOR and INFERIOR LACRIMAL CANAL into the NSAOLACRIMAL DUCT to inferior nasal meatus (NASAL CAVITY). Sinuses Small, air-filled cavities in the bone around the nasal cavity. Lined with ciliated ps-stratified epithelium and goblet cells. Produce Important: eye falls into the maxillary sinuses during a bl-out fracture Functions: reduce skull weight, allow mucus circulation and improve sound resonanceThe Ear• The auricle/ pinna directs sound waves into the external auditory canal. • When sound waves strike the tympanic membrane, the alternating waves of high and low pressure in the air cause the tympanic membrane to vibrate back and forth. Slowly = low-frequency (low-pitched) sounds and rapidly = high-frequency (high-pitched) sounds. • The tympanic membrane connects to the malleus, which vibrates along with the tympanic membrane. This vibration is transmitted from the malleus to the incus and then to the stapes. • As the stapes moves back and forth, its oval-shaped footplate, which is attached via a ligament to the circumference of the oval window, vibrates in the oval window. The vibrations at the oval window are about 20 times more vigorous than the tympanic membrane because the auditory ossicles amplify them. • The movement of the stapes at the oval window sets up fluid pressure waves in the perilymph of the cochlea. • As the oval window bulges inward, it pushes on the perilymph of the scala vestibuli. Pressure waves are transmitted from the scala vestibuli to the scala tympani and eventually to the round window, causing it to bulge outward into the middle ear. • The pressure waves travel through the perilymph of the scala vestibuli, then the vestibular membrane, and then move into the endolymph inside the cochlear duct. • The pressure waves in the endolymph cause the basilar membrane to vibrate, which moves the hair cells of the spiral organ against the tectorial membrane. This leads to bending of the stereocilia and ultimately to the generation of nerve impulses in first-order neurones in cochlear nerve fibres. Sound waves of various frequencies cause certain regions of the basilar membrane to vibrate more intensely than other regions. Each segment of the basilar membrane is “tuned” for a particular pitch. Because the membrane is narrower and stiffer at the base of the cochlea (closer to the oval window), high-frequency (high- pitched) sounds induce maximal vibrations in this region. Toward the apex of the cochlea, the basilar membrane is wider and more flexible; low-frequency (low-pitched) sounds cause maximal vibration of the basilar membrane there. The Nose How does the nose help with breathing? Air entering the nasal cavity is: • Warmed (to body temperature) • Humidified (to prevent drying of the mucosa) • Filtered (dusts) This is possible because nasal cavity is: • Richly supplied by blood (to warm the incoming air as blood transmit heat) • Mucous provides moisture (from goblet cells) • Mucous and hairs trap particles The Mouth Where is taste detected? By the taste receptors papillae on the tongue. What nerves are involved in taste? Anterior 2/3 of tongue • Taste: Facial nerve (chorda tympani) CN VII • General sensation (pain): Trigeminal Nerve (lingual nerve) CNV3 Posterior 1/3 of tongue • Both taste and general sensation: Glossopharyngeal nerve CN IX What other nerve is involved? • Hypoglossal nerve in motor control of most tongue muscles. •Some say marry money, but my brother Mneumonics says big brains matter more •S – sensory •M- motor •B- both •Ooh, ooh, ooh to touch and feel very good velvet. Such heaven! •LR6 SO4THANK YOU Questions?