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Lecture 14

Week/Lecture 14: The Special Senses.pdf

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BIOL 171

The Special Senses Sensation stimuli are converted to nerve impulses by specialized receptors senses are categorized as general or special The Special Senses smell, taste, vision, hearing, equilibrium housed in complex sensory organs (all in the head) Chemical Senses smell and taste project to cerebral cortex and limbic system (evoke emotional responses / memory) Olfactory Sense dissolved odorants bind to receptors —> nerve impulses in CN 1 rapid adaptation 50% in 1 sec complete in 1 min Epithelium found near cribiform plate 10-100 million receptors Membrane olfactory receptor (bipolar neuron that only lives 1 month) basal cell takes over + acts as stem cell —> receptor olfactory gland produces mucus others: olfactory bulb, cribiform plate, supporting cells odorant binds to olfactory receptor; changes polarization of membrane (depolarization); AP travels to olfactory bulb through cribiform plate; info is sent to olfactory nerve, to brain Gustatory Sense dissolved substances (tastant) bind to taste buds on tongue, soft palate, larynx five classes of stimuli bitter sweet salty sour umami papillae bulges, folds on surface of tongue taste buds are found on sides of vallate and fungiform papillae taste bud gustatory hair projects from each receptor cell sends AP after tastant travels down groove and binds each receptor cell sensitive to more than one of the 5 tastes gustatory receptor cells convert taste into neural impulses basal cells differentiate into gustatory receptor cells grow back after 10 days if injured (burned) Physiology of Taste dissolved substances bind to gustatory hairs —> nerve impulse in CN V11 (anterior ⅔ tongue), IX (post ⅓ tongue) and X (palate, epiglottis) complete adaptation in 1-5 mins (don't eat one food for a few minutes—mix it up!) most senses of taste are actually stimulation of our olfactory receptors (70-75% of taste) taste is also heavily dependent on temperature and texture (taste may be exactly the same, but smell, temp and texture "change" taste) The Eye External/Accessory Structures conjunctiva: mucosa [mucous membrane] lining lids, covering front of eye eyelid (palpebra): protects and lubricates tarsal glands: oily secretion keeps lids from sticking together Tears: produced in lacrimal glands (lateral side) and secreted from lacrimal ducts (each produces ~1 ml. tears/day) contain bactericidal enzyme (lysozyme) spread across eye by blinking (washes away dust, bacteria) pathway: lacrimal gland (exocrine)—lacrimal ducts—lacrimal canal— nasolacrimal duct—nasal cavity lacrimal: tears Extrinsic Structures six muscles superior rectus superior oblique inferior oblique lateral rectus medial rectus inferior rectus rectus: straight muscle oblique: slanting muscle finest, most precise movement in body wall of the eye 3 layers: fibrous tunic (outermost layer) cornea: transparent; covers anterior 1/6 of eye sclera: tough fibrous layer; white, covers all but anterior portion [cornea]; maintains shape, protects contents vascular tunic (middle layer) choroid: vascular, pigmented (black) layer; supplies blood to eye structures ciliary body: ciliary processes (folds on ciliary body secrete aqueous humor) and ciliary muscle (smooth muscle attached to suspensory ligaments to alter shape of lens) suspensory ligaments: holds lens iris: anterior extension of choroid; visible through cornea as pigmented ring; 2 layer of muscle regulates pupil size under control of ANS; colour regulated by melanin (more=darker) muscles: circular muscle fibres constrict pupil in bright light (innervated by parasympathetic NS) radial muscle fibres dilate pupil in dim light (innervated by sympathetic NS) lens: classified as part of vascular tunic, though it itself is avascular; focuses light on retina; held in place by suspensory ligaments nervous tunic retina: lines posterior ¾ of eyeball; contains photoreceptors (rods: dark; concentrated at periphery, cones: colour; concentrated at fovea) fovea centralis: max. visual acuity; all cones optic disc: blood vessels, optic nerve forms and leaves eye; no photoreceptors (blind spot) optic nerve: carries only sensory information to brain cells: bipolar + ganglion cells light passes around bipolar/ganglion cells to photoreceptors. Nerve impulse then runs back through B/G cells to optic nerve to brain neurotransmitters cones: 3 types each more sensitive to particular wavelength (red, blue, green) due to the presence of different photopigments (rhodopsins) when msgs are received from 2 types simultaneously, intermediate colours (purple, orange) are produced if all 3 are stimulated we see white colour blindness: lacking at least 1 type of cone; brain learns to interpret new visual stimuli Cavities of the Eyeball Anterior: (anterior to lens) 2 chambers fil
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