Human Anatomy and Physiology Chapter 15 Fall 2020 PDF

Human Anatomy and Physiology Eleventh Edition Chapter 15 The Special Senses Slides have been modified and edited by C. Youngson PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Pre-...

Human Anatomy and Physiology Eleventh Edition Chapter 15 The Special Senses Slides have been modified and edited by C. Youngson PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Pre-lecture questions 1. Which parts of the ear are important for sensing linear acceleration (forward and back, up and down), rotational acceleration (spinning) and sound? 2. Explain what happens to the photoreceptor in the dark and in the light? What is happening in the optic nerve in the dark and in the light? 2 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Special Senses • The sense of touch is one of the general senses, mediated by general receptors • Special senses of body include: – Vision – Taste – Smell – Hearing – Equilibrium Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Eye • Small sphere; only one-sixth of surface visible • Most of eye enclosed and protected by fat cushion and bony orbit • Consists of accessory structures and the eyeball Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Lacrimal Apparatus Figure 15.2 The lacrimal apparatus. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball • Wall of eyeball contains three layers 1. Fibrous layer 2. Vascular layer 3. Inner layer Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball 1. Fibrous layer – Outermost layer; dense avascular connective tissue – Two regions: § Sclera – Opaque posterior region – Protects and shapes eyeball – Anchors extrinsic eye muscles § Cornea – Transparent anterior one-sixth of fibrous layer • Forms clear window that lets light enter and bends light as it enters eye – Epithelium covers both surfaces • Outer surface protects from abrasions – Numerous pain receptors contribute to blinking and tearing reflexes Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball 2. Vascular layer – Three regions: choroid, ciliary body, and iris § Choroid region: Supplies blood to all layers of eyeball – Brown pigment absorbs light to prevent scattering of light, which would cause visual confusion § Ciliary body: Anteriorly, choroid becomes ciliary body – Consists of smooth muscle bundles, ciliary muscles, that control shape of lens – Capillaries of ciliary processes secrete fluid for anterior segment of eyeball § Iris: Colored part of eye that lies between cornea and lens – Pupil: central opening that regulates amount of light entering eye • Close vision and bright light cause sphincter pupillae (circular muscles) to contract and pupils to constrict; parasympathetic control • Distant vision and dim light cause dilator pupillae (radial muscles) to contract and pupils to dilate; sympathetic control Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Pupil Constriction and Dilation Figure 15.5 Pupil constriction and dilation. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball 3. Inner layer (retina) – Retina originates as an outpocketing of brain – Contains: § Millions of photoreceptor cells that transduce light energy § Neurons § Glial cells – Delicate two-layered membrane § Outer pigmented layer § Inner neural layer Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball • Inner layer – Pigmented layer of the retina – Absorbs light and prevents its scattering – Neural layer of the retina § Composed of three main types of neurons – Photoreceptors, bipolar cells, ganglion cells § Signals spread from photoreceptors to bipolar cells to ganglion cells § Ganglion cell axons exit eye as optic nerve (Optic disc) – Site where optic nerve leaves eye § Retina has quarter-billion photoreceptors that are one of two types: – Rods – Cones Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Rods and Cones – Rods § Dim light, peripheral vision receptors § More numerous and more sensitive to light than cones § No color vision or sharp images § Numbers greatest at periphery – Cones § Vision receptors for bright light § High-resolution color vision § Macula lutea area at posterior pole lateral to blind spot – Contains mostly cones § Fovea centralis: tiny pit in center of macula lutea that contains all cones, so is region with best visual acuity Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Part of the Posterior Wall (Fundus) of the Right Eye as Seen With an Ophthalmoscope Figure 15.7 Part of the posterior wall (fundus) of the right eye as seen with an ophthalmoscope. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Clinical – Homeostatic Imbalance • Retinal detachment: condition where pigmented and neural layers separate (detach), allowing jellylike vitreous humor to seep between them • Can lead to permanent blindness • Usually happens when retina is torn during traumatic blow to head or sudden stopping of head during movement (example: bungee jumping) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball • Internal chambers and fluids – The lens and ciliary zonule separate eye into two segments 1. Posterior segment 2. Anterior segment Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Lens – Biconvex, transparent, flexible, and avascular – Changes shape to precisely focus light on retina Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Clinical – Homeostatic Imbalance • Clouding of lens – Consequence of aging, diabetes mellitus, heavy smoking, frequent exposure to intense sunlight – Crystallin proteins clump – Lens can be replaced surgically with artificial lens Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Overview: Visible Light • Wavelength and color – Light: packets of energy (photons or quanta) that travel in wavelike fashion at high speeds – When visible light passes through spectrum, it is broken up into bands of colors (rainbow) § Red wavelengths are longest and have lowest energy, and violet are shortest and have most energy – Color that eye perceives is a reflection of that wavelength § Grass is green because it absorbs all colors except green § White reflects all colors, and black absorbs all colors Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Overview: Refraction • Refraction and lenses – Refraction: bending of light rays § Due to change in speed of light when it passes from one transparent medium to another and path of light is at an oblique angle – Example: from liquid to air § Lenses of eyes can also refract light because they are curved on both sides – Convex: thicker in center than at edges – Concave: thicker at edges than in center Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Light is Focused by a Convex Lens Figure 15.12 Light is focused by a convex lens. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Focusing Light on the Retina • Pathway of light entering eye: cornea, aqueous humor, lens, vitreous humor, entire neural layer of retina, and finally photoreceptors • Light is refracted three times along path: (1) entering cornea, (2) entering lens, and (3) leaving lens • Majority of refractory power is in cornea; however, it is constant and cannot change focus • Lens is able to adjust its curvature to allow for fine focusing – Can focus for distant vision and for close vision Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Focusing Light on the Retina: distant vision • Focusing for distant vision – Eyes are best adapted for distant vision – Far point of vision: distance beyond which no change in lens shape is needed for focusing § 20 feet for emmetropic (normal) eye § Cornea and lens focus light precisely on retina at this distance – Ciliary muscles are completely relaxed in distance vision, which causes a pull on ciliary zonule; as a result, lenses are stretched flat Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Focusing Light on the Retina: close vision – Light from close objects (<6 m) diverges as approaches eye – Requires eye to make active adjustments using three simultaneous processes: § Accommodation of the lenses – Changing lens shape to increase refraction – Near point of vision • Closest point on which the eye can focus – Presbyopia: loss of accommodation over age 50 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Clinical – Homeostatic Imbalance • Problems associated with refraction related to eyeball shape: – Myopia (nearsightedness) § Eyeball is too long, so focal point is in front of retina § Corrected with a concave lens – Hyperopia (farsightedness) § Eyeball is too short, so focal point is behind retina § Corrected with a convex lens – Astigmatism § Unequal curvatures in different parts of cornea or lens § Corrected with cylindrically ground lenses or laser procedures Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Functional Anatomy of Photoreceptors • Photoreceptors (rods and cones) are modified neurons that resemble upsidedown epithelial cells • Consists of cell body, synaptic terminal, and two segments: – Outer segment: light-receiving region § Contains visual pigments (photopigments) that change shape as they absorb light – Inner segment of each joins cell body § Inner segment is connected via cilium to outer segment and to cell body via outer fiber Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Comparing Rod and Cone Vision • Rods are very sensitive to light, making them best suited for night vision and peripheral vision – Contain a single pigment, so vision is perceived in gray tones only – Pathways converge, causing fuzzy, indistinct images § As many as 100 rods may converge into one ganglion • Cones have low sensitivity, so require bright light for activation – React more quickly than rods – Have one of three pigments, which allow for vividly colored sight – Nonconverging pathways result in detailed, high-resolution vision § Some cones have their own ganglion cell, so brain can put together accurate, high-acuity resolution images Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 15.1 Comparison of Rods and Cones Table 15.1 Comparison of Rods and Cones Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Visual Pigments • Retinal: key light-absorbing molecule that combines with one of four proteins (opsins) to form visual pigments – Synthesized from vitamin A – Four opsins are rhodopsin (found in rods only), and three found in cones: green, blue, red (depending on wavelength of light they absorb) – Cone wavelengths do overlap, so same wavelength may trigger more than one cone, enabling us to see variety of hues of colors § Example: yellow light stimulates red and green cones, but if more red are triggered, we see orange – Retinal isomers are different 3-D forms § Retinal is in a bent form in dark, but when pigment absorbs light, it straightens out – Bent form called 11-cis-retinal – Straight form called all-trans-retinal § Conversion of bent to straight initiates reactions that lead to electrical impulses along optic nerve Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Photoreceptors of the Retina Figure 15.15b Photoreceptors of the retina. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Phototransduction • Phototransduction: process by which pigment captures photon of light energy, which is converted into a graded receptor potential • Capturing light – Deep purple pigment of rods is rhodopsin § Arranged in rod’s outer segment § Three steps of rhodopsin formation and breakdown: – Pigment synthesis, pigment bleaching, and pigment regeneration – Similar process in cones, but different types of opsins and cones require more intense light Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Phototransduction • Capturing light (cont.) – Pigment synthesis § Opsin and 11-cis retinal combine to form rhodopsin in dark – Pigment bleaching § When rhodopsin absorbs light, 11-cis isomer of retinal changes to all-trans isomer § Retinal and opsin separate (rhodopsin breakdown) – Pigment regeneration § All-trans retinal converted back to 11-cis isomer § Rhodopsin is regenerated in outer segments Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Phototransduction • Light transduction reactions – Light-activated rhodopsin activates G protein transducin – Transducin activates PDE, which breaks down cyclic GMP (cGMP) – In dark, cGMP holds cation channels of outer segment open § Na+ and Ca2+ enter and depolarize cell – In light cGMP breaks down, channels close, cell hyperpolarizes § Hyperpolarization is signal for vision! Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Information Processing in the Retina: in the light • Photoreceptors and bipolar cells generate only graded potentials (EPSPs and IPSPs), not APs • When light hyperpolarizes photoreceptor cells, they stop releasing inhibitory neurotransmitter glutamate to biopolar cells • Bipolar cells (no longer inhibited) depolarize, release neurotransmitter onto ganglion cells • Ganglion cells generate APs transmitted in optic nerve to brain Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved In the dark: Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Light and Dark Adaptation • Rhodopsin is so sensitive that bleaching occurs even in starlight – In bright light, bleaching occurs so fast that rods are virtually nonfunctional • Cones respond to bright light • So, activation of rods and cones depends on: – Light adaptation – Dark adaptation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Light and Dark Adaptation • Light adaptation – When moving from darkness into bright light we see glare because: § Both rods and cones are strongly stimulated § Large amounts of pigments are broken down instantaneously, producing glare § Pupils constrict • Dark adaptation – When moving from bright light into darkness, we see blackness because: § Cones stop functioning in low-intensity light § Bright light bleached rod pigments, so they are still turned off § Pupils dilate § Rhodopsin accumulates in dark, so retinal sensitivity starts to increase Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Clinical – Homeostatic Imbalance • Nyctalopia (night blindness): condition in which rod function is seriously hampered – Ability to drive safely at night is impaired • Due to rod degeneration, commonly caused by prolonged vitamin A deficiency – If administered early, vitamin A supplements restore function • Can also be caused by retinitis pigmentosa – Degenerative retinal diseases that destroy rods – Tips of rods are not replaced when they slough off Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Visual Pathway to the Brain and Visual Fields, Inferior View Figure 15.19 Visual pathway to the brain and visual fields, inferior view. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Smell: Olfactory Receptors Olfactory neurons are unusual bipolar neurons Bundles of axons of olfactory receptor cells gather to form olfactory nerve (cranial nerve I) Olfactory neurons, unlike other neurons, have stem cells that give rise to new neurons every 30–60 days Figure 15.20a Olfactory receptors. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Physiology of Smell • In order to smell substance, it must be volatile – Must be in gaseous state – Odorant must also be able to dissolve in olfactory epithelium fluid • Activation of olfactory sensory neurons – Dissolved odorants bind to receptor proteins in olfactory cilium membranes § Open cation channels, generating receptor potential § At threshold, AP is conducted to first relay station in olfactory bulb Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Taste: Taste Buds on the Tongue Figure 15.22a Location and structure of taste buds on the tongue. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Basic Taste Sensations • There are five basic taste sensations 1. Sweet—sugars, saccharin, alcohol, some amino acids, some lead salts 2. Sour—hydrogen ions in solution 3. Salty—metal ions (inorganic salts); sodium chloride tastes saltiest 4. Bitter—alkaloids such as quinine and nicotine, caffeine, and nonalkaloids such as aspirin 5. Umami—amino acids glutamate and aspartate; example: beef (meat) or cheese taste, and monosodium glutamate Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Physiology of Taste • To be able to taste a chemical, it must: – Be dissolved in saliva – Diffuse into taste pore – Contact gustatory hairs • Activation of taste receptors – Binding of food chemical (tastant) depolarizes cell membrane of gustatory epithelial cell membrane, causing release of neurotransmitter § Neurotransmitter binds to dendrite of sensory neuron and initiates a generator potential that lead to action potentials – Different gustatory cells have different thresholds for activation § Bitter receptors are most sensitive – All adapt in 3–5 seconds, with complete adaptation in 1–5 minutes Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Physiology of Taste • Taste transduction – Gustatory epithelial cell depolarization caused by: § Salty taste is due to Na+ influx that directly causes depolarization § Sour taste is due to H+ acting intracellularly by opening channels that allow other cations to enter § Unique receptors for sweet, bitter, and umami, but all are coupled to G protein gustducin – Activation causes release of stored Ca2+ that opens cation channels, causing depolarization and release of neurotransmitter ATP Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Gustatory Pathway Figure 15.23 The gustatory pathway. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Hearing and Balance and Equilibrium: Structure of the Ear Figure 15.24a Structure of the ear. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Three Auditory Ossicles and Associated Skeletal Muscles Figure 15.25 The three auditory ossicles and associated skeletal muscles. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Clinical – Homeostatic Imbalance • Otitis media – Middle ear inflammation – Commonly seen in children with sore throat § Especially those with shorter, more horizontal pharyngotympanic tubes – Most frequent cause of hearing loss in children – Acute infectious forms cause eardrum to bulge outward and become inflamed § Most cases respond to antibiotics Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Internal Ear • Also referred to as the labyrinth (maze) • Located in temporal bone behind eye socket • Two major divisions: – Bony labyrinth: system of tortuous channels and cavities that worm through the bone – Divided into three regions: vestibule, semicircular canals, and cochlea § Filled with perilymph fluid; similar to CSF – Membranous labyrinth; series of membranous sacs and ducts contained in bony labyrinth; filled with potassium-rich endolymph Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Internal Ear • Vestibule – Central egg-shaped cavity of bony labyrinth – Contains two membranous sacs § Saccule is continuous with cochlear duct § Utricle is continuous with semicircular canals – Sacs house equilibrium receptor regions (maculae) that respond to gravity and changes in position of head • Semicircular canals – Three canals oriented in three planes of space: anterior, lateral, and posterior § Anterior and posterior are at right angles to each other, whereas the lateral canal is horizontal – Membranous semicircular ducts line each canal and communicate with utricle – Ampulla: enlarged area of ducts of each canal that houses equilibrium receptor region called the crista ampullaris § Receptors respond to angular (rotational) movements of the head Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Internal Ear • Cochlea – A small spiral, conical, bony chamber, size of a split pea § Contains cochlear duct, which houses spiral organ (organ of Corti) and ends at cochlear apex Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Hearing • Hearing is the reception of an air sound wave that is converted to a fluid wave that ultimately stimulates mechanosensitive cochlear hair cells that send impulses to the brain for interpretation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Properties of Sound • Sound can be described by two physical properties: frequency and amplitude – Frequency § Number of waves that pass given point in a given time § Pure tone has repeating crests and troughs § Wavelength – Distance between two consecutive crests – Shorter wavelength = higher frequency of sound – Wavelength is consistent for a particular sound – Frequency (cont.) § Frequency range of human hearing is 20–20,000 hertz (Hz = waves per second), but most sensitive between 1500 and 4000 Hz – Pitch: perception of different frequencies • Higher the frequency, higher the pitch – Quality: characteristic of sounds • Most sounds are mixtures of different frequencies • Tone: one frequency (ex: tuning fork) • Sound quality provides richness and complexity of sounds (music) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Frequency and Amplitude of Sound Waves Figure 15.29a Frequency and amplitude of sound waves. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Transmission of Sound to Internal Ear • Pathway of sound – Tympanic membrane: sound waves enter external acoustic meatus and strike tympanic membrane, causing it to vibrate § The higher the intensity, the more vibration – Auditory ossicles: transfer vibration of eardrum to oval window § Tympanic membrane is about 20´ larger than oval window, so vibration transferred to oval window is amplified about 20´ – Scala vestibuli: stapes rocks back and forth on oval window with each vibration, causing wave motions in perilymph § Wave ends at round window, causing it to bulge outward into middle ear cavity – Helicotrema path: waves with frequencies below threshold of hearing travel through helicotrema and scali tympani to round window – Basilar membrane path: sounds in hearing range go through cochlear duct, vibrating basilar membrane at specific location, according to frequency of sound Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Pathway of Sound Waves Figure 15.30 Pathway of sound waves. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Resonance of the Basilar Membrane • Resonance: movement of different areas of basilar membrane in response to a particular frequency • Basilar membrane changes along its length: – Fibers near oval window are short and stiff § Resonate with high-frequency waves – Fibers near cochlear apex are longer, floppier § Resonate with lower-frequency waves • So basilar membrane mechanically processes sound even before signals reach receptors Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Sound Transduction • Excitation of inner hair cells – Stereocilia project into K+-rich endolymph, with longest hairs enmeshed in gel-like tectorial membrane – Bending of stereocilia toward tallest ones pull on tip links, causing K+ and Ca2+ ion channels in shorter stereocilia to open § K+ and Ca2+ flow into cell, causing receptor potential that can lead to release of neurotransmitter (glutamate) – Can trigger AP in afferent neurons of cochlear nerve – Bending of stereocilia toward shorter ones causes tip links to relax § Ion channels close, leading to repolarization (and even hyperpolarization) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Auditory Pathway and Processing • Perception of pitch: impulses from hair cells in different positions along basilar membrane are interpreted by brain as specific pitches • Detection of loudness is determined by brain as an increase in the number of action potentials (frequency) that result when hair cells experience larger deflections Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Balance and Equilibrium • Equilibrium is response to various movements of head that rely on input from inner ear, eyes, and stretch receptors • Vestibular apparatus: equilibrium receptors in semicircular canals and vestibule Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Maculae • Anatomy of a macula – Each is a flat epithelium patch containing hair cells with supporting cells – Hair cells have stereocilia and special “true stereocilium” called kinocilium § Located next to tallest stereocilia – Stereocilia are embedded in otolith membrane, jelly-like mass studded with otoliths (tiny CaCO3 stones) § Otoliths increase membrane’s weight and increase its inertia (resistance to changes in motion) Anatomy of a macula Utricle maculae are horizontal with vertical hairs Respond to change along a horizontal plane, such as tilting head Forward/backward movements stimulate utricle Saccule maculae are vertical with horizontal hairs Respond to change along a vertical plane Up/down movements stimulate saccule (Example: acceleration of an elevator) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Maculae •The Activating receptors of a macula Maculae – Hair cells releaseof neurotransmitter continuously • Activating receptors a macula § Acceleration/deceleration causes a change in – Hair cells release neurotransmitter continuously of neurotransmitter released § amount Acceleration/deceleration causes a change in – Leads to change in AP released frequency to brain amount of neurotransmitter – Leads to change in AP frequency to brain • Activating receptors of a macula (cont.) – Bending of hairs in kinocilia: • Activating receptors of direction a maculaof(cont.) § Depolarizes hair cells of kinocilia: – Bending of hairs in direction § Increases amount of neurotransmitter release Depolarizes hair cells § Increases More impulses travel up vestibular nerve to brain amount of neurotransmitter release – Bending hairs away from § Moreofimpulses travel upkinocilia: vestibular nerve to brain § Hyperpolarizes receptors – Bending of hairs away from kinocilia: Less neurotransmitter released § Hyperpolarizes receptors Reduces rate of impulse generation § Less neurotransmitter released – Thus brain is informed of changing position of head § Reduces rate of impulse generation – Thus brain is informed of changing position of head Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Semicircular Canals • Receptor for rotational acceleration is crista ampullaris (crista) – Small elevation in ampulla of each semicircular canal • Cristae are excited by angular acceleration and deceleration of head – Semicircular canals are located in all three planes of space, so cristae can pick up on all rotational movements of head • Anatomy of a crista ampullaris – Each crista has supporting cells and hair cells that extend into gel-like mass called ampullary cupula – Dendrites of vestibular nerve fibers encircle base of hair cells • Activating receptors of crista ampullaris – Cristae respond to changes in velocity of rotational movements of head – Inertia in ampullary cupula causes endolymph in semicircular ducts to move in direction opposite body’s rotation, causing hair cells to bend Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Cristae Ampullares • Activating receptors of crista ampullaris – Bending hairs in cristae causes depolarization § Rapid impulses reach brain at faster rate – Bending of hairs in opposite direction causes hyperpolarizations § Fewer impulses reach brain – Thus brain is informed of head rotations Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Cristae Ampullares • Vestibular nystagmus – Semicircular canal impulses are linked to reflex movements of eyes – Nystagmus is strange eye movements during and immediately after rotation § Often accompanied by vertigo – As rotation begins, eyes drift in direction opposite to rotation; then CNS compensation causes rapid jump toward direction of rotation – As rotation ends, eyes continue in direction of spin, then jerk rapidly in opposite direction Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Equilibrium Pathway to the Brain • Equilibrium information goes to reflex centers in brain stem – Allows fast, reflexive responses to imbalance so we don’t fall down • Impulses from activated vestibular receptors travel to either vestibular nuclei in brain stem or to cerebellum Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Clinical – Homeostatic Imbalance • Motion sickness: sensory inputs are mismatched – Visual input differs from equilibrium input – Conflicting information causes motion sickness – Warning signs are excess salivation, pallor, rapid deep breathing, profuse sweating – Treatment with antimotion drugs that depress vestibular input, such as meclizine and scopolamine Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Independent Readings Glaucoma pg 563 Colour Blindness pg 569 Clinical Case Study 42-Year-Old Make with Recurring Vertigo pg 600 68 Copyright © 2019, 2016, 2013 Pearson Education, Inc. 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