UNIT 20 - SPECIAL SENSES PDF

BIOL1410 Lecture Notes – Fall 2024 Unit 20: Special Senses UNIT 20: Special Senses A) Special Senses: Eye — 3 layered sphere filled with fluid — structural features: 1) Fibrous Tu...

BIOL1410 Lecture Notes – Fall 2024 Unit 20: Special Senses UNIT 20: Special Senses A) Special Senses: Eye — 3 layered sphere filled with fluid — structural features: 1) Fibrous Tunic: — parts: a) sclera (white) — avascular connective tissue (CT) b) cornea (transparent) — avascular CT c) conjunctiva — covers anterior sclera — vascular mucous membrane o when vessels dilate = bloodshot eyes 2) Vascular Tunic — parts: a) choroid (posterior) — contains melanin — highly vascular b) ciliary body (anterior) — ciliary muscle and ciliary processes – focus the lens c) iris — coloured part of eye d) pupil — hole in iris 3) Nervous (Sensory) Tunic = Retina: — parts: a) outer pigmented layer b) inner neural layer — 3 layers of neurons: i. Photoreceptors (2 types) 1 Rods – black and white 2 Cones - colour ii. Bipolar Cells iii. Ganglion Cells — axons from optic nerve (= Cranial Nerve II) c) fovea centralis — where light is focused — = area of greatest visual acuity — no rods, just cones d) optic disc — blind spot where blood vessels + optic nerve exit eye — no rods or cones 4) Lens — avascular, transparent 1  BIOL1410 Lecture Notes – Fall 2024 Unit 20: Special Senses — cataracts = clouding of lens 5) Anterior Segment — anterior to lens — contains aqueous humor o fluid similar to plasma 6) Posterior Segment — posterior to lens — contains vitreous humor o gel-like B) Special Senses: Ear — structural features: 1) External Ear — conducts sound — parts: a) auricle (pinna) — elastic cartilage, covered with skin b) external auditory canal (meatus) c) tympanic membrane (eardrum) 2) Middle Ear — conducts sound — parts: a) Eustachian tube — also called pharyngotympanic tube b) ear ossicles i. malleus — secured to tympanic membrane ii. incus iii. stapes — transmits sound to inner ear via oval window 3) Inner Ear (Labyrinth) — conducts sound — parts: a) bony labyrinth — tunnels in temporal bone o contain perilymph — parts: i. semicircular canals — equilibrium ii. vestibule — equilibrium iii. cochlea — hearing b) membranous labyrinth — surrounded and protected by bony labyrinth — contains endolymph — parts: i. semicircular duct 2  BIOL1410 Lecture Notes – Fall 2024 Unit 20: Special Senses — inside canals ii. utricle and saccule — inside vestibule iii. cochlear duct — inside cochlea 4) Cochlea — coiled — each coil has 3 channels: a) scala vestibuli — upper; perilymph b) scala tympani — lower; perilymph c) cochlear duct — middle; endolymph — membranes: a) vestibular membrane — between cochlear duct + scala vestibuli b) basilar membrane — between cochlear duct + scala tympani c) tectorial membrane — covers hair cells (= receptor cells) 5) Receptors in Inner Ear — called hair cells that synapse with neurons o send impulses to brain via cranial nerve VIII — hairs are cilia that extend into endolymph o tips of cilia embedded in tectorial membrane (stability) 3