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Anatomy & Physiology I Lecture 14 Chapter 15: The Special Senses: A Brief Overview The Senses • Special sensory receptors – Distinct, localized receptor cells in head • • • • • Vision Taste Smell Hearing Equilibrium Figure 15.1a The eye and accessory structures. Eyebrow Eyelid Eyelashes Site where conjunctiva merges with cornea Palpebral fissure Iris Eyelid Pupil Sclera (covered by conjunctiva) Surface anatomy of the right eye © 2013 Pearson Education, Inc. Figure 15.1b The eye and accessory structures. Levator palpebrae superioris muscle Orbicularis oculi muscle Eyebrow Tarsal plate Palpebral conjunctiva Tarsal glands Cornea Palpebral fissure Eyelashes Bulbar conjunctiva Conjunctival sac Orbicularis oculi muscle Lateral view; some structures shown in sagittal section © 2013 Pearson Education, Inc. Conjunctiva • Transparent mucous membrane – Produces a lubricating mucous secretion – Palpebral conjunctiva lines eyelids – Bulbar conjunctiva covers white of eyes Structure of the Eyeball • Wall of eyeball contains three layers – Fibrous – Vascular – Inner • Internal cavity filled with fluids called humors Figure 15.4a Internal structure of the eye (sagittal section). Ora serrata Ciliary body Sclera Ciliary zonule (suspensory ligament) Choroid Cornea Iris Pupil Anterior pole Anterior segment (contains aqueous humor) Lens Scleral venous sinus Posterior segment (contains vitreous humor) Retina Macula lutea Fovea centralis Posterior pole Optic nerve Central artery and vein of the retina Optic disc (blind spot) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball. © 2013 Pearson Education, Inc. Fibrous Layer • Outermost layer; dense avascular connective tissue • Two regions: – Sclera – Cornea Fibrous Layer • Sclera – Opaque posterior region – Protects, shapes eyeball; anchors extrinsic eye muscles • Cornea – Bends light as it enters eye – Sodium pumps of corneal endothelium on inner face help maintain clarity of cornea – Numerous pain receptors contribute to blinking and tearing reflexes Vascular Layer • Middle pigmented layer • Three regions: – Choroid – Ciliary body – Iris Vascular Layer • Choroid region – Supplies blood to all layers of eyeball – Brown pigment absorbs light to prevent light scattering and visual confusion Vascular Layer • Ciliary body – Ring of tissue surrounding lens – Smooth muscle bundles (ciliary muscles) control lens shape Vascular Layer • Iris – Colored part of eye – Pupil—central opening that regulates amount of light entering eye Figure 15.5 Pupil constriction and dilation, anterior view. Sympathetic + Parasympathetic + Sphincter pupillae muscle contracts: Pupil size decreases. © 2013 Pearson Education, Inc. Iris (two muscles) • Sphincter pupillae • Dilator pupillae Dilator pupillae muscle contracts: Pupil size increases. Inner Layer (Retina) • Delicate two-layered membrane: • Outer Pigmented layer – Absorbs light and prevents its scattering • Inner Neural layer – Transparent – Composed of three main types of neurons: • Photoreceptors, bipolar cells, ganglion cells Figure 15.6a Microscopic anatomy of the retina. Neural layer of retina Pigmented layer of retina Choroid Pathway of light Sclera Optic disc Central artery and vein of retina Optic nerve Posterior aspect of the eyeball © 2013 Pearson Education, Inc. Figure 15.6b Microscopic anatomy of the retina. Ganglion cells Axons of ganglion cells Bipolar cells Photoreceptors • Rod • Cone Amacrine cell Horizontal cell Pathway of signal output Pathway of light Pigmented layer of retina Cells of the neural layer of the retina © 2013 Pearson Education, Inc. Photoreceptors • Rods – Dim light, peripheral vision receptors – More numerous, more sensitive to light than cones – No color vision or sharp images • Cones – Vision receptors for bright light – High-resolution color vision Light And Optics • Eyes respond to visible light – Small portion of electromagnetic spectrum – Wavelengths of 400-700 nm • Light – Packets of energy (photons or quanta) that travel in wavelike fashion at high speeds – Color of light objects reflect determines color eye perceives Figure 15.10 The electromagnetic spectrum and photoreceptor sensitivities. 10–5 nm 10–3 Gamma rays 103 nm 1 nm X rays UV nm 106 Infrared (109 nm =) nm 1m 103 m Micro- Radio waves waves Light absorption (percent of maximum) Visible light Blue cones (420 nm) Green Red Rods cones cones (500 nm) (530 nm) (560 nm) 100 50 0 400 © 2013 Pearson Education, Inc. 450 500 550 600 Wavelength (nm) 650 700 Refraction • Bending of light rays – Due to change in speed when light passes from one transparent medium to another – Occurs when light meets surface of different medium at an oblique angle • Curved lens can refract light Figure 15.12 Light is focused by a convex lens. Point sources Focal points Focusing of two points of light. The image is inverted—upside down and reversed. © 2013 Pearson Education, Inc. Vision and Distance • Eyes best adapted for distant vision • Far point of vision – Distance beyond which no change in lens shape needed for focusing – Cornea and lens focus light precisely on retina – Ciliary muscles relaxed Figure 15.13a Focusing for distant and close vision. Sympathetic activation Nearly parallel rays from distant object Lens Ciliary zonule Ciliary muscle Inverted image Lens flattens for distant vision. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens. © 2013 Pearson Education, Inc. Focusing and Short Distance • Light from close objects (<6 m) diverges as approaches eye – Requires eye to make active adjustments using three simultaneous processes – Accommodation of lenses – Constriction of pupils – Convergence of eyeballs Figure 15.13b Focusing for distant and close vision. Parasympathetic activation Divergent rays Inverted from close object image Lens bulges for close vision. Parasympathetic input contracts the ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge. © 2013 Pearson Education, Inc. Functional Anatomy Of Photoreceptors • Rods and cones – Modified neurons – Contain visual pigments (photopigments) – Molecules change shape as absorb light – Process light as action potentials to reach the optic nerve Rods • Functional characteristics – Very sensitive to light – Best suited for night vision and peripheral vision – Contain single pigment – Perceived input in gray tones only Cones • Functional characteristics – Need bright light for activation (have low sensitivity) – React more quickly – Have one of three pigments for colored view – Detailed, high-resolution vision • Color blindness–lack of one or more cone pigments Chemistry Of Visual Pigments • Retinal – Light-absorbing molecule that combines with one of four proteins (opsins) to form visual pigments – Synthesized from vitamin A • Retinal isomers – 11-cis-retinal (bent form) – All-trans-retinal (straight form) Rhodopsin Pigment • Deep purple pigment of rods • 11-cis-retinal + opsin = rhodopsin Figure 15.15a Photoreceptors of the retina. Process of bipolar cell Synaptic terminals Rod cell body Inner fibers Rod cell body Nuclei Cone cell body Mitochondria The outer segments of rods and cones are embedded in the pigmented layer of the retina. © 2013 Pearson Education, Inc. Pigmented layer Inner Outer segment segment Outer fiber Melanin granules Connecting cilia Apical microvillus Discs containing visual pigments Discs being phagocytized Pigment cell nucleus Basal lamina (border with choroid) Figure 15.15b Photoreceptors of the retina. Rod discs Visual pigment consists of • Retinal • Opsin Rhodopsin, the visual pigment in rods, is embedded in the membrane that forms © 2013 Pearson Education, Inc. discs in the outer segment. Phototransduction • Light converts 11-cis retinal to All-trans-retinal – Activates a G protein signal transduction pathway – Activates Phosphodiesterase to convert cGMP to GMP – Loss of GMP closes Na/Ca channels from ions entering cell resulting in hyperpolarization • Similar process of both rods and cones Figure 15.16 The formation and breakdown of rhodopsin. 11-cis-retinal 2H+ 1 Pigment synthesis: Oxidation 11-cis-retinal, derived from vitamin A, is Vitamin A 11-cis-retinal Rhodopsin combined with opsin to form rhodopsin. Reduction 2H+ 3 Pigment regeneration: Enzymes slowly convert all-trans-retinal to its 11cis form in cells of the pigmented layer; requires ATP. Dark Light 2 Pigment bleaching: Light absorption by rhodopsin triggers a rapid series of steps in which retinal changes shape (11-cis to alltrans) and eventually releases from opsin. Opsin and All-transretinal O © 2013 Pearson Education, Inc. All-trans-retinal Figure 15.17 Events of phototransduction. Slide 1 Recall from Chapter 3 that G protein signaling mechanisms are like a molecular relay race. 2nd Light Receptor G protein Enzyme messenger (1st messenger) 1 Retinal absorbs light and changes shape. Visual pigment activates. Phosphodiesterase (PDE) Visual pigment All-trans-retinal Light cGMP-gated cation channel open in dark 11-cis-retinal Transducin (a G protein) 2 Visual pigment activates transducin (G protein). © 2013 Pearson Education, Inc. 3 Transducin activates phosphodiesteras e (PDE). 4 PDE converts cGMP into GMP, causing cGMP levels to fall. cGMP-gated cation channel closed in light 5 As cGMP levels fall, cGMP-gated cation channels close, resulting in hyperpolarization. Figure 15.18 Signal transmission in the retina (1 of 2). Slide 1 In the dark 1 cGMP-gated channels open, allowing cation influx. Photoreceptor depolarizes. Na+ Ca2+ 2 Voltage-gated Ca2+ channels open in synaptic terminals. Photoreceptor cell (rod) −40 mV 3 Neurotransmitter is released continuously. Ca2+ 4 Neurotransmitter causes IPSPs in bipolar cell. Hyperpolarization results. 5 Hyperpolarization closes voltage-gated Ca2+ channels, inhibiting neurotransmitter release. Bipolar Cell 6 No EPSPs occur in ganglion cell. 7 No action potentials occur along the optic nerve. © 2013 Pearson Education, Inc. Ganglion cell Figure 15.18 Signal transmission in the retina. (2 of 2). Below, we look at a tiny column of retina. The outer segment of the rod, closest to the back of the eye and farthest from the incoming light, is at the top. In the light 1 cGMP-gated channels close, so cation influx stops. Photoreceptor hyperpolarizes. Light Light Photoreceptor cell (rod) −70 mV 2 Voltage-gated Ca2+ channels close in synaptic terminals. 3 No neurotransmitter is released. 4 Lack of IPSPs in bipolar cell results in depolarization. 5 Depolarization opens voltage-gated Ca2+ channels; neurotransmitter is released. Bipolar Cell Ca2+ Ganglion cell © 2013 Pearson Education, Inc. 6 EPSPs occur in ganglion cell. 7 Action potentials propagate along the optic nerve. Slide 1 Adapting to Bright Light • Move from darkness into bright light – Both rods and cones strongly stimulated – Pupils constrict to lessen entering light – Large amounts of pigments broken down instantaneously, producing glare Adapting to Darkness • Move from bright light into darkness – Cones stop functioning in low-intensity light – Rod pigments bleached; system turned off – Rhodopsin accumulates in dark – Pupils dilate to allow more light in – Increased light allows for improved vision in dark settings Visual Processing • Thalamus – Process for depth perception, cone input emphasized, contrast sharpened • Primary visual cortex (striate cortex) – Neurons respond to dark and bright edges, and object orientation – Provide form, color, motion inputs to visual association areas Depth Perception • Both eyes view same image from slightly different angles • Three-dimensional results from cortical fusion of slightly different images • Requires input from both eyes Figure 15.19 Visual pathway to the brain and visual fields, inferior view. Both eyes Fixation point Right eye Suprachiasmatic nucleus Pretectal nucleus Lateral geniculate nucleus of thalamus Superior colliculus Left eye Optic nerve Optic chiasma Optic tract Lateral geniculate nucleus Superior colliculus (sectioned) Uncrossed (ipsilateral) fiber Crossed (contralateral) fiber Optic radiation Occipital lobe (primary visual cortex) The visual fields of the two eyes overlap considerably. Note that fibers from the lateral portion of each retinal field do not cross at the optic chiasma. © 2013 Pearson Education, Inc. Corpus callosum Photograph of human brain, with the right side dissected to reveal internal structures. The Sense of Smell • Olfactory epithelium in roof of nasal cavity – Contains olfactory sensory neurons – Bundles of nonmyelinated axons of olfactory receptor cells form olfactory nerve (CN I) Olfactory Receptors • Humans can distinguish ~10,000 odors – ~400 "smell" genes active only in nose – Each encodes unique receptor protein – Protein responds to one or more odors – Each odor binds to several different receptors Smell Transduction • • • • Odorant binds to receptor activates G protein G protein activation cAMP synthesis cAMP activates Na+ and Ca2+ channels ion influx depolarizes cell Figure 15.21 Olfactory transduction process. Slide 1 1 Odorant binds to its receptor. Odorant Adenylate cyclase G protein (Golf) cAMP cAMP Open cAMP-gated cation channel Receptor GDP 2 Receptor activates G protein (Golf). © 2013 Pearson Education, Inc. 3 G protein activates adenylate cyclase. 4 Adenylate cyclase converts ATP to cAMP. 5 cAMP opens a cation channel, allowing Na+ and Ca2+ influx and causing depolarization. Taste Senses • Receptor organs are taste buds – Most of 10,000 taste buds on tongue papillae • There are five basic taste sensations – Sweet—sugars, saccharin, alcohol, some amino acids, some lead salts – Sour—hydrogen ions in solution – Salty—metal ions (inorganic salts) – Bitter—alkaloids such as quinine and nicotine; aspirin – Umami—amino acids glutamate and aspartate Activating Taste Receptors • Binding of food chemical depolarizes taste cell membrane – neurotransmitter release – Initiates a generator potential that elicits an action potential • Different thresholds for activation – Bitter receptors most sensitive Tasteduction • Gustatory epithelial cell depolarization caused by – Salty taste due to Na+ influx (directly causes depolarization) – Sour taste due to H+ (by opening cation channels) – Unique receptors for sweet, bitter, and umami coupled to G protein activation • neurotransmitter ATP release Role of Taste • Triggers reflexes involved in digestion • Increase secretion of saliva into mouth • Increase secretion of gastric juice into stomach • May initiate protective reactions – Gagging – Reflexive vomiting Figure 15.23 The gustatory pathway. Gustatory cortex (in insula) Thalamic nucleus (ventral posteromedial Pons nucleus) Solitary nucleus in medulla oblongata Facial nerve (VII) Glossopharyngeal nerve (IX) © 2013 Pearson Education, Inc. Vagus nerve (X) Influences on Taste • Taste is 80% smell • Thermoreceptors, mechanoreceptors, nociceptors in mouth also influence tastes – Temperature The Ear: Hearing and Balance • Three major areas of ear – External (outer) ear – hearing only – Middle ear (tympanic cavity) – hearing only – Internal (inner) ear – hearing and equilibrium Figure 15.24a Structure of the ear. Middle Internal ear External ear (labyrinth) ear Auricle (pinna) Helix Lobule External acoustic Tympanic Pharyngotympanic meatus membrane (auditory) tube The three regions of the ear © 2013 Pearson Education, Inc. External Ear • External ear – Funnels sound waves into auditory canal • External acoustic meatus (auditory canal) – Transmits sound waves to eardrum • Tympanic membrane (eardrum) – Boundary between external and middle ears – Connective tissue membrane that vibrates in response to sound – Transfers sound energy to bones of middle ear Middle Ear (Tympanic Cavity) • A small, air-filled, mucosa-lined cavity in temporal bone • Flanked laterally by eardrum • Flanked medially by bony wall containing oval (vestibular) and round (cochlear) windows Figure 15.24b Structure of the ear. Oval window (deep to stapes) Entrance to mastoid antrum in the epitympanic recess Malleus (hammer) Incus Auditory (anvil) ossicles Stapes (stirrup) Tympanic membrane Semicircular canals Vestibule Vestibular nerve Cochlear nerve Cochlea Round window Middle and internal ear © 2013 Pearson Education, Inc. Pharyngotympanic (auditory) tube Ear Ossicles • Three small bones in tympanic cavity: the malleus, incus, and stapes – Suspended by ligaments and joined by synovial joints – Transmit vibratory motion of eardrum to oval window Internal Ear • Two primary divisions – Semicircular canals – Cochlea Semicircular Canals • Three canals (anterior, lateral, and posterior) that each define ⅔ circle – Lie in three planes of space (x, y and z) – Receptors respond to angular (rotational) movements of the head – Work in tandem with eyes and muscles for coordination, balance, positioning, and movement The Cochlea • A spiral, conical, bony chamber • Transmits sound waves via hair cells to the cochlear branch of CN VIII Figure 15.27a Anatomy of the cochlea. Helicotrema at apex Modiolus Cochlear nerve, division of the vestibulocochlear nerve (VIII) Spiral ganglion Osseous spiral lamina Vestibular membrane Cochlear duct (scala media) © 2013 Pearson Education, Inc. Properties of Sound • Sound is – Pressure disturbance (alternating areas of high and low pressure) produced by vibrating object • Sound wave – Moves outward in all directions – Illustrated as an S-shaped curve or sine wave Figure 15.28 Sound: Source and propagation. Area of high pressure (compressed molecules) Air pressure Wavelength Area of low pressure (rarefaction) Crest Trough Distance Amplitude A struck tuning fork alternately compresses and rarefies the air molecules around it, creating alternate zones of high and low pressure. © 2013 Pearson Education, Inc. Sound waves radiate outward in all directions. Figure 15.29 Frequency and amplitude of sound waves. Pressure High frequency (short wavelength) = high pitch Low frequency (long wavelength) = low pitch 0.01 0.02 Time (s) 0.03 Frequency is perceived as pitch. Pressure High amplitude = loud Low amplitude = soft 0.01 0.02 Time (s) 0.03 © 2013 Pearson Education, Inc. Amplitude (size or intensity) is perceived as loudness. Transmission of Sound • Sound waves vibrate tympanic membrane • Ossicles vibrate and amplify pressure within internal ear • Cochlear fluid set into wave motion • Wave vibration activates action potential Figure 15.30a Pathway of sound waves and resonance of the basilar membrane. Slide 1 Auditory ossicles Malleus Incus Stapes Cochlear nerve Oval window Scala vestibuli Helicotrema 4a Scala tympani Cochlear duct 2 3 4b Basilar membrane 1 Tympanic membrane Round window Route of sound waves through the ear 1 Sound waves 2 Auditory ossicles 3 Pressure waves created by the stapes vibrate the tympanic vibrate. Pressure is pushing on the oval amplified. membrane. window move through fluid in the scala © 2013 Pearson Education, Inc. vestibuli. 4a Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells. 4b Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells. Figure 15.32 The auditory pathway. Medial geniculate nucleus of thalamus Primary auditory cortex in temporal lobe Inferior colliculus Lateral lemniscus Superior olivary nucleus (ponsmedulla junction) Midbrain Cochlear nuclei Vibrations Medulla Vestibulocochlear nerve Vibrations Spiral ganglion of cochlear nerve Bipolar cell Spiral organ © 2013 Pearson Education, Inc. Auditory Processing • Pitch – impulses from specific hair cells in different positions along membrane • Loudness – by increased numbers of action potentials that result when hair cells experience larger deflections • Localization of sound – relative intensity and timing of sound waves reaching both ears End • No lab • Student Presentations