Human Anatomy and Physiology Eleventh Edition - Chapter 15 Part A - Special Senses PDF

Human Anatomy and Physiology Eleventh Edition Chapter 15 Part A The Special Senses PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College...

Human Anatomy and Physiology Eleventh Edition Chapter 15 Part A The Special Senses PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College 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 (covered in Chapter 13) Special senses of body include: – Vision – Taste – Smell – Hearing – Equilibrium Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Special Senses All use special sensory receptors, which are distinct receptor cells localized in head region – Not like modified nerves of general receptors Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.1 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 Accessory Structures of the Eye Accessory structures protect the eye and aid eye function Structures include: – Eyebrows – Eyelids – Conjunctiva – Lacrimal apparatus – Extrinsic eye muscles Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Accessory Structures of the Eye Conjunctiva – Transparent mucous membrane that produces a lubricating mucous secretion – Palpebral conjunctiva: membrane that lines underside of eyelids – Bulbar conjunctiva: membrane that covers white of eyes (not cornea) ▪ Small blood vessels found in this membrane; seen easily in “bloodshot” eyes – Conjunctival sac: space between palpebral and bulbar conjunctiva ▪ Area where contact lens rests Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Accessory Structures of the Eye Lacrimal apparatus – Consists of lacrimal gland and ducts that drain into nasal cavity – Lacrimal gland is located in orbit above lateral end of eye and secretes lacrimal secretion (tears), a dilute saline solution containing mucus, antibodies, and antibacterial lysozyme – Blinking spreads tears toward medial commissure, where they enter paired lacrimal canaliculi via lacrimal puncta Lacrimal apparatus – Tears then drain into lacrimal sac and nasolacrimal duct, which empties into nasal cavity 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 Clinical – Homeostatic Imbalance 15.2 Conjunctivitis: inflammation of the conjunctiva resulting in reddened, irritated eyes Pinkeye: conjunctival infection caused by bacteria or viruses – Highly contagious Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball Wall of eyeball contains three layers – Fibrous layer – Vascular layer – Inner layer Internal cavity filled with fluids called humors Lens separates internal cavity into anterior and posterior segments Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Internal Structure of the Eye (Sagittal Section) bolded structures only Ora serrata Ciliary body Sclera Ciliary zonule Choroid (suspensory ligament) Retina Cornea Macula lutea Iris Fovea centralis Pupil Optic nerve Anterior segment (contains aqueous humor) Lens Scleral venous sinus Central artery and vein of the retina Posterior segment Optic disc (contains vitreous humor) (blind spot) (a) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball. Figure 15.4a Internal structure of the eye (sagittal section). Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball ▪ 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 Inner layer, corneal endothelium, contains sodium pumps that help maintain clarity of cornea – Numerous pain receptors contribute to blinking and tearing reflexes Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball ▪ Ciliary body – Anteriorly, choroid becomes ciliary body – Thickened ring of tissue surrounding lens – Consists of smooth muscle bundles, ciliary muscles, that control shape of lens – Ciliary zonule (suspensory ligament) extends from ciliary processes to lens Holds lens in position Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball ▪ Iris – Colored part of eye that lies between cornea and lens, continuous with ciliary body – 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 Changes in emotional state—pupils dilate when subject matter is appealing or requires problem-solving skills 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 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 Microscopic Anatomy of the Retina Figure 15.6a Microscopic anatomy of the retina. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball Inner layer (retina) (cont.) – Pigmented layer of the retina ▪ Single-cell-thick lining next to choroid ▪ Extends anteriorly, covering ciliary body and iris ▪ Functions: – Absorbs light and prevents its scattering Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball Inner layer (retina) (cont.) – Neural layer of the retina ▪ Transparent layer that runs anteriorly to margin of ciliary body – Anterior end has serrated edges called ora serrata ▪ 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 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Structure of the Eyeball Inner layer (retina) (cont.) – Neural layer of the retina (cont.) ▪ Optic disc – Site where optic nerve leaves eye – Lacks photoreceptors, so referred to as blind spot ▪ Retina has quarter-billion photoreceptors that are one of two types: – Rods – Cones Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball Inner layer (retina) (cont.) – 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 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball Inner layer (retina) (cont.) – 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 – Eye movement allows us to focus in on object so that fovea can pick it up Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Microscopic Anatomy of the Retina Fovea Figure 15.6b Microscopic anatomy of the retina. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Clinical – Homeostatic Imbalance 15.5 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) Symptom described by victims as “curtain being drawn across the eye” and/or sootlike spots or light flashes Treatment: reattachment of retina with laser surgery Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball Lens – Biconvex, transparent, flexible, and avascular – Changes shape to precisely focus light on retina – Two regions: ▪ Lens epithelium: anterior region of cuboidal cells that differentiate into lens fiber cells ▪ Lens fibers: form bulk of lens and are filled with transparent protein crystallin – Lens fibers are continually added, so lens becomes more dense, convex, and less elastic with age Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Human Anatomy and Physiology Eleventh Edition Chapter 15 Part B The Special Senses PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.2 Focusing and Light Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Overview: Light and Optics Wavelength and color – Electromagnetic radiation: all energy waves, from long radio waves to short X rays; visible light occupies a small portion in the middle of the spectrum ▪ Light has wavelengths between 400 and 700 nm – Eyes respond only to visible light Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Visible light The Electromagnetic Spectrum and Photoreceptor Blue Green Red Sensitivities cones Rods cones cones Light absorption (percent of maximum) (420 nm) (500 nm) (530 nm) (560 nm) 100 50 Figure 15.10b The 0 electromagnetic spectrum and 400 450 500 550 600 650 700 photoreceptor sensitivities. Wavelength (nm) (b) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Overview: Light and Optics 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 Overview: Light and Optics Refraction and lenses (cont.) – Convex lenses bend light passing through it, so that rays converge at focal point ▪ Image formed at focal point is upside-down and reversed from left to right 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 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Focusing Light on the Retina 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 for Distant and Close Vision Figure 15.13b Focusing for distant and close vision. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Focusing for Distant and Close Vision Figure 15.13c Focusing for distant and close vision. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.3 Phototransduction Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Functional Anatomy of Photoreceptors More photopigment Less Photoreceptors (rods and cones) are photopigment modified neurons that resemble upside- down 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 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Photoreceptors of the Retina Figure 15.15a Photoreceptors of the retina. 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 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Comparing Rod and Cone Vision 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 Clinical – Homeostatic Imbalance 15.9 Color blindness: lack of one or more cone pigments Inherited as an X-linked condition, so more common in males – As many as 8–10% of males have some form The most common type is red-green, in which either red cones or green cones are absent – Depending on which cone is missing, red can appear green, or vice versa 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 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Visual Pigments – 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 Isomerization of retinal Inactive state, binds to opsin Activated, released from opsin 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 The Formation and Breakdown of Rhodopsin Figure 15.16 The formation and breakdown of rhodopsin. 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 Events of Phototransduction Figure 15.17 Events of phototransduction. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Information Processing in the Retina 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 Signal Transmission in the Retina Figure 15.18-1 Signal transmission in the retina. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Human Anatomy and Physiology Eleventh Edition Chapter 15 Part C The Special Senses PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Part 2 – The Chemical Senses: Smell and Taste Smell (olfaction) and taste (gustation): complementary senses that let us know whether a substance should be savored or avoided Chemoreceptors are used by these systems – Chemicals must be dissolved in aqueous solution to be picked up by chemoreceptors ▪ Smell receptors are excited by chemicals dissolved in nasal fluids ▪ Taste receptors respond to chemicals dissolved in saliva Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.5 Sense of Smell Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Location and Structure of Olfactory Receptors Olfactory epithelium: organ of smell – Located in in roof of nasal cavity – Covers superior nasal conchae – Contains olfactory sensory neurons ▪ Bipolar neurons with radiating olfactory cilia ▪ Supporting cells surround and cushion olfactory receptor cells – Olfactory stem cells lie at base of epithelium Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Location and Structure of Olfactory Receptors Olfactory neurons are unusual bipolar neurons – Thin apical dendrites terminate in knob – Long, largely nonmotile cilia, olfactory cilia, radiate from knob ▪ Covered by mucus (solvent for odorants) Bundles of nonmyelinated axons of olfactory receptor cells gather in fascicles that make up filaments of olfactory nerve (cranial nerve I) Olfactory neurons, unlike other neurons, have stem cells that give rise to new neurons every 30–60 days Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Specificity of Olfactory Receptors Smells may contain 100s of different odorants Humans have ~400 “smell” genes active in nose – Each encodes a unique receptor protein ▪ Protein responds to one or more odors – Each odor binds to several different receptors – Each receptor cell has only one type of receptor protein Pain and temperature receptors are also in nasal cavities – Respond to irritants, such as ammonia, or can “smell” hot or cold (chili peppers, menthol) 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 Physiology of Smell Smell transduction – Odorant binds to receptor, activating a G protein ▪ Referred to as Golf – G protein activation causes cAMP (second messenger) synthesis – cAMP opens Na+ and Ca2+ channels – Na+ influx causes depolarization and impulse transmission Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Physiology of Smell Smell transduction (cont.) – Ca2+ influx causes decreased response to a sustained stimulus, referred to as olfactory adaptation ▪ People can’t smell a certain odor after being exposed to it for a while ▪ Eg. Sitting in a smelly room for a long time Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  The Olfactory Pathway Filaments of olfactory nerves synapse with mitral cells located in overlying olfactory bulb – Mitral cells are second-order neurons that form olfactory tract Synapse occurs in structures called glomeruli Axons from neurons with same receptor type converge on given type of glomerulus Mitral cells amplify, refine, and relay signals Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.6 Sense of Taste Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Location and Structure of Taste Buds Taste buds: sensory organs for taste – Most of 10,000 taste buds are located on tongue in papillae, peglike projections of tongue mucosa ▪ Fungiform papillae: mushroom-shaped structures, each with only 1-5 taste buds; scattered across tongue ▪ Foliate papillae: on side walls of tongue, more numerous in childhood ▪ Vallate papillae: largest papillae with 8– 12 taste buds each, forming “V” at back of tongue – Few on soft palate, cheeks, pharynx, epiglottis Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Location and Structure of Taste Buds Each taste bud consists of 50–100 flask-shaped epithelial cells of two types: – Gustatory epithelial cells: taste receptor cells have microvilli called gustatory hairs that project into taste pores, bathed in saliva ▪ Gustatory hairs are the sensitive areas – receptor membranes ▪ Sensory dendrites coiled around gustatory epithelial cells send taste signals to brain – Basal epithelial cells: dynamic stem cells that divide every 7–10 days 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 ie. acids 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 Basic Taste Sensations Possible sixth taste – Growing evidence humans can taste long-chain fatty acids from lipids – Perhaps explain liking of fatty foods Taste likes/dislikes have homeostatic value – Guide intake of beneficial and potentially harmful substances – Dislike for sourness and bitterness is a protective way of warning us if something is spoiled or poisonous 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 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Physiology of Taste 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 Part 3 – The Ear: Hearing and Balance Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.7 Structure of the Ear The ear has three major areas: – External (outer) ear: hearing only – Middle ear (tympanic cavity): hearing only – Internal (inner) ear: hearing and equilibrium Receptors for hearing and balance respond to separate stimuli and are activated independently Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved External Ear The external (outer) ear consists of two parts: – Auricle (pinna): shell-shaped structure surrounding ear canal that functions to funnel sound waves into auditory canal ▪ Helix: cartilaginous rim ▪ Lobule: fleshy earlobe – External acoustic meatus (auditory canal) ▪ Short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous (earwax) glands ▪ Transmits sound waves to eardrum Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved External Ear Tympanic membrane (eardrum) – Boundary between external and middle ears – Thin, translucent connective tissue membrane – Vibrates in response to sound – Transfers sound energy to bones of middle ear Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Middle Ear (Tympanic Cavity) A small, air-filled, mucosa-lined cavity in temporal bone – Flanked laterally by eardrum and medially by bony wall containing oval and round membranous windows Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Middle Ear (Tympanic Cavity) Auditory ossicles: three small bones in tympanic cavity, named for their shape: – Malleus: the “hammer” is secured to eardrum – Incus: the “anvil” – Stapes: the “stirrup” base fits into oval window ▪ Synovial joints allow malleus to articulate with incus, which articulates with stapes ▪ Suspended by ligaments; transmit vibratory motion of eardrum to oval window ▪ Tensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to hearing receptors 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 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 Membranous Labyrinth of the Internal Ear Figure 15.26 Membranous labyrinth of the internal ear. 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 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Internal Ear 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 ▪ Extends from vestibule ▪ Coils around bony pillar (modiolus) ▪ 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 Internal Ear Cochlea (cont.) Cavity of cochlea divided into three chambers: – Scala vestibule (vestibular duct): abuts oval window, contains perilymph (Na+ rich) – Scala media (cochlear duct): contains endolymph (K+ rich) – Scala tympani (tympanic duct): terminates at round window; contains perilymph Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Internal Ear Cochlea (cont.) Scalae tympani and vestibuli are continuous with each other at helicotrema (apex) Vestibular membrane: “roof” of cochlear duct that separates scala media from scala vestibuli Helicotrema (apex) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Internal Ear Cochlea (cont.) Stria vascularis: external wall of cochlear duct composed of mucosa that secretes endolymph “Floor” of cochlear duct composed of: – Bony spiral lamina – Basilar membrane, which supports spiral organ Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Internal Ear Cochlea (cont.) Spiral organ contains cochlear hair cells functionally arranged in one row of inner hair cells and three rows of outer hair cells – Hair cells are sandwiched between tectorial and basilar membranes The cochlear branch of nerve VIII runs from spiral organ to brain Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Anatomy of the Cochlea Figure 15.27a Anatomy of the cochlea. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 15.2 Summary of the Internal Ear Table 15.2 Summary of the Internal Ear. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Human Anatomy and Physiology Eleventh Edition Chapter 15 Part D The Special Senses PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Hearing Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15.8 Sound Detection 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 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 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Transmission of Sound to Internal Ear – 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 Sound Transduction Excitation of inner hair cells – Movement of basilar membrane deflects hairs of inner hair cells ▪ Cochlear hair cells have microvilli that contain many stereocilia (hairs) that bend at their base ▪ Longest hair cells are connected to shortest hair cells via tip links – Tip links, when pulled on, open ion channels they are connected to – Stereocilia project into K+-rich endolymph, with longest hairs enmeshed in gel-like tectorial membrane Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Sound Transduction Excitation of inner hair cells – 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 Bending of Stereocilia Opens or Closes Mechanically Gated Ion Channels in Hair Cells Figure 15.32 Pivoting of stereocilia (hairs) opens or closes mechanically gated ion channels in hair cells. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved