7/24/2018. Special Senses. Special sensory receptors. Vision - 70% of body's sensory receptors in eye Taste Smell Hearing Equilibrium.

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1 Special Senses Special sensory receptors Distinct, localized receptor cells in head Vision - 70% of body's sensory receptors in eye Taste Smell Hearing Equilibrium Sense of Vision Ora serrata Ciliary body Ciliary zonule (suspensory ligament) Cornea Iris Pupil Anterior pole Anterior segment (contains aqueous humor) Sclera Choroid Retina Macula lutea Fovea centralis Posterior pole Optic nerve Lens Scleral venous sinus Posterior segment (contains vitreous humor) 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. Inner Layer: Retina Delicate two-layered membrane Outer Pigmented layer Absorbs light and prevents its scattering Phagocytize photoreceptor cell fragments Stores vitamin A Inner Neural layer Transparent 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 1

2 Pigmented layer Outer segment Inner segment 7/24/2018 Figure 15.6c Microscopic anatomy of the retina. Nuclei of ganglion cells Outer segments of rods and cones Choroid Axons of ganglion cells Nuclei of Nuclei of bipolar rods and cells cones Photomicrograph of retina Pigmented layer of retina Figure 15.15a Photoreceptors of the retina. Process of bipolar cell Inner fibers Rod cell body Cone cell body Outer fiber Synaptic terminals Rod cell body Nuclei Mitochondria Connecting cilia Apical microvillus The outer segments of rods and cones are embedded in the pigmented layer of the retina. Melanin granules Discs containing visual pigments Discs being phagocytized Pigment cell nucleus Basal lamina (border with choroid) 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) and all-trans-retinal (straight form) Bent form straight form when pigment absorbs light Conversion of bent to straight initiates reactions electrical impulses along optic nerve 2

3 Figure Signal transmission in the retina (1 of 2). Slide 1 In the dark 1 cgmp-gated channels open, allowing cation influx. Photoreceptor depolarizes. 2 Voltage-gated Ca 2+ channels open in synaptic terminals. 3 Neurotransmitter is released continuously. 4 Neurotransmitter causes IPSPs in bipolar cell. Hyperpolarization results. 5 Hyperpolarization closes voltage-gated Ca 2+ channels, inhibiting neurotransmitter release. 6 No EPSPs occur in ganglion cell. 7 No action potentials occur along the optic nerve. 40 mv Ca 2+ Na + Ca 2+ Photoreceptor cell (rod) Bipolar Cell Ganglion cell Figure Signal transmission in the retina. (2 of 2). Slide 1 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 Light Photoreceptor cell (rod) Bipolar Cell Ganglion cell Light 70 mv Ca 2+ 1 cgmp-gated channels close, so cation influx stops. Photoreceptor hyperpolarizes. 2 Voltage-gated Ca 2+ 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 Ca 2+ channels; neurotransmitter is released. 6 EPSPs occur in ganglion cell. 7 Action potentials propagate along the optic nerve. Figure 15.15b Photoreceptors of the retina. 11-cis-retinal Rod discs 2H + Oxidation Vitamin A 11-cis-retinal Reduction 2H + Rhodopsin Dark Light Visual pigment consists of Retinal Opsin Opsin and All-transretinal Rhodopsin, the visual pigment in rods, is embedded in the membrane that forms discs in the outer segment. All-trans-retinal 3

4 Figure Events of phototransduction. Slide 6 Recall from Chapter 3 that G protein signaling mechanisms are like a molecular relay race. 1 Retinal absorbs light and changes shape. Visual pigment activates. Light Receptor G protein Enzyme 2nd (1st messenger messenger) Visual pigment Light All-trans-retinal Phosphodiesterase (PDE) 11-cis-retinal Transducin (a G protein) cgmp-gated cation cgmp-gated channel cation open in channel dark closed in light 2 Visual pigment 3 Transducin activates activates transducin phosphodiesteras (G protein). e (PDE). 4 PDE converts 5 As cgmp levels fall, cgmp into GMP, cgmp-gated cation causing cgmp channels close, resulting levels to fall. in hyperpolarization. Olfactory Epithelium and the Sense of Smell Olfactory epithelium 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 Bundles of nonmyelinated axons of olfactory receptor cells form olfactory nerve (cranial nerve I) Figure 15.20a Olfactory receptors. Olfactory epithelium Olfactory tract Olfactory bulb Nasal conchae Route of inhaled air 4

5 Figure 15.20b Olfactory receptors. Olfactory tract Olfactory gland Olfactory epithelium Mucus Mitral cell (output cell) Glomeruli Olfactory bulb Cribriform plate of ethmoid bone Filaments of olfactory nerve Lamina propria connective tissue Olfactory axon Olfactory stem cell Olfactory sensory neuron Supporting cell Dendrite Olfactory cilia Route of inhaled air containing odor molecules Figure Olfactory transduction process. Slide 1 1 Odorant binds to its receptor. Odorant Adenylate cyclase G protein (G olf) Receptor camp camp Open camp-gated cation channel GDP 2 Receptor activates G protein (G olf). 3 G protein activates adenylate cyclase. 4 Adenylate cyclase converts ATP to camp. 5 camp opens a cation channel, allowing Na + and Ca 2+ influx and causing depolarization. Taste Buds and the Sense of Taste Receptor organs are taste buds Most of 10,000 taste buds on tongue papillae On tops of fungiform papillae On side walls of foliate and vallate papillae Few on soft palate, cheeks, pharynx, epiglottis 5

6 Figure 15.22a Location and structure of taste buds on the tongue. Epiglottis Foliate papillae Fungiform papillae Taste buds are associated with fungiform, foliate, and vallate papillae. Palatine tonsil Lingual tonsil To taste, chemicals must Be dissolved in saliva Diffuse into taste pore Contact gustatory hairs Figure 15.22c Location and structure of taste buds on the tongue. Connective tissue Taste fibers of cranial nerve Gustatory hair Basal epithelial cells Gustatory epithelial cells Taste pore Stratified squamous epithelium of tongue Enlarged view of a taste bud (210x). 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) 4. Bitter alkaloids such as quinine and nicotine; aspirin 5. Umami amino acids glutamate and aspartate 6

7 Basic Taste Sensations Possible sixth taste Growing evidence humans can taste longchain fatty acids from lipids Perhaps explain liking of fatty foods Taste likes/dislikes have homeostatic value Guide intake of beneficial and potentially harmful substances The Ear: Hearing and Balance Three major areas of ear 1. External (outer) ear hearing only 2. Middle ear (tympanic cavity) hearing only 3. Internal (inner) ear hearing and equilibrium Receptors for hearing and balance respond to separate stimuli Are activated independently Hearing External ear terminates at tympanic membrane Thin membrane of two layers of epithelium with connective tissue between Includes auricle (pinna) and external auditory (acoustic) canal (meatus) Hairs and cerumen Middle ear Air-filled space containing auditory ossicles: malleus, incus, stapes Separated from the inner air by the oval and round windows Oval window: Foot of the stapes rests here and is held in place by ligament Two passages for air Auditory or eustachian tube Passage to mastoid air cells in mastoid process 7

8 Transmission of Sound to the Internal Ear Sound waves vibrate tympanic membrane Ossicles vibrate and amplify pressure at oval window Cochlear fluid set into wave motion Pressure waves move through perilymph of scala vestibuli 8

9 Transmission of Sound to the Internal Ear Waves with frequencies below threshold of hearing travel through helicotrema and scali tympani to round window Sounds in hearing range go through cochlear duct, vibrating basilar membrane at specific location, according to frequency of sound HIGH frequency sound detected here LOW frequency sound detected here Figure 15.27c Anatomy of the cochlea. Tectorial membrane Hairs (stereocilia) Outer hair cells Inner hair cell Afferent nerve fibers Supporting cells Fibers of cochlear nerve Basilar membrane 9

10 Excitation of Hair Cells in the Spiral Organ Stereocilia Protrude into endolymph Longest enmeshed in gel-like tectorial membrane Sound bends these toward kinocilium Opens mechanically gated ion channels Inward K + and Ca 2+ current causes graded potential and release of neurotransmitter glutamate Cochlear fibers transmit impulses to brain Generating Signals Equilibrium and Orientation Vestibular apparatus Equilibrium receptors in semicircular canals and vestibule Vestibular receptors monitor static equilibrium Semicircular canal receptors monitor dynamic equilibrium 10

11 Vestibule Central egg-shaped cavity of bony labyrinth Contains two membranous sacs 1. Saccule is continuous with cochlear duct 2. Utricle is continuous with semicircular canals These sacs House equilibrium receptor regions (maculae) Respond to gravity and changes in position of head Figure Structure of a macula. Macula of utricle Macula of saccule Kinocilium Stereocilia Otoliths Otolith membrane Hair bundle Vestibular nerve fibers Hair cells Supporting cells Activating Maculae Receptors Hair cells release neurotransmitter continuously Movement modifies amount they release Bending of hairs in direction of kinocilia Depolarizes hair cells Increases amount of neurotransmitter release More impulses travel up vestibular nerve to brain 11

12 Activating Maculae Receptors Bending away from kinocilium Hyperpolarizes receptors Less neurotransmitter released Reduces rate of impulse generation Thus brain informed of changing position of head Figure The effect of gravitational pull on a macula receptor cell in the utricle. Otolith membrane Kinocilium Stereocilia Receptor potential Depolarization Hyperpolarization Nerve impulses generated When hairs bend toward in vestibular fiber the kinocilium, the hair cell depolarizes, exciting the nerve fiber, which generates more frequent action potentials. When hairs bend away from the kinocilium, the hair cell hyperpolarizes, inhibiting the nerve fiber, and decreasing the action potential frequency. Optional Slides The following slides may be used in lecture or May be helpful in your preparation for testing, for your reference 12

13 Figure 15.6a Microscopic anatomy of the retina. Neural layer of retina Pathway of light Optic disc Pigmented layer of retina Choroid Sclera Central artery and vein of retina Optic nerve Posterior aspect of the eyeball Functional Anatomy Of Photoreceptors Rods and cones Modified neurons Receptive regions called outer segments Contain visual pigments (photopigments) Molecules change shape as absorb light Inner segment of each joins cell body Rods Functional characteristics Very sensitive to light Best suited for night vision and peripheral vision (most common in peripheral retina) Non-color vision; Contain single pigment Perceived input in gray tones only Pathways converge, causing fuzzy, indistinct images Low acuity 20 rods for every cone in retina 13

14 Cones Functional characteristics Need bright light for activation (have low sensitivity) React more quickly Have one of three pigments for colored view Nonconverging pathways result in detailed, highresolution vision Most common in central retina Color blindness lack of one or more cone pigments Phototransduction: Capturing Light Deep purple pigment of rods rhodopsin 11-cis-retinal + opsin rhodopsin Pigment synthesis Rhodopsin forms and accumulates in dark Pigment bleaching When rhodopsin absorbs light, retinal changes to all-trans isomer Retinal and opsin separate (rhodopsin breakdown) Pigment regeneration All-trans retinal converted to 11-cis isomer Rhodopsin regenerated in outer segments Information Processing In The Retina Photoreceptors and bipolar cells only generate graded potentials (EPSPs and IPSPs) When light hyperpolarizes photoreceptor cells Stop releasing inhibitory neurotransmitter glutamate Bipolar cells (no longer inhibited) depolarize, release neurotransmitter onto ganglion cells Ganglion cells generate APs transmitted in optic nerve to brain 14

15 Figure 15.6b Microscopic anatomy of the retina. Ganglion cells Bipolar cells Axons of ganglion 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 Physiology of Smell Gaseous odorant must dissolve in fluid of olfactory epithelium Activation of olfactory sensory neurons Dissolved odorants bind to receptor proteins in olfactory cilium membranes Smell Transduction Odorant binds to receptor activates G protein G protein activation camp (second messenger) synthesis camp Na + and Ca 2+ channels opening Na + influx depolarization and impulse transmission Ca 2+ influx olfactory adaptation Decreased response to sustained stimulus 15

16 Activation of Taste Receptors Binding of food chemical (tastant) depolarizes taste cell membrane neurotransmitter release Initiates a generator potential that elicits an action potential Different thresholds for activation Bitter receptors most sensitive All adapt in 3-5 seconds; complete adaptation in 1-5 minutes Taste Transduction 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 gustducin Stored Ca 2+ release opens cation channels depolarization neurotransmitter ATP release Semicircular Canals Three canals (anterior, lateral, and posterior) that each define ⅔ circle Lie in three planes of space Membranous semicircular ducts line each canal and communicate with utricle Ampulla of each canal houses equilibrium receptor region called the crista ampullaris Receptors respond to angular (rotational) movements of the head 16

17 Figure 15.35a b Location, structure, and function of a crista ampullaris in the internal ear. Ampullary cupula Crista ampullaris Endolymph Membranous labyrinth Crista ampullaris Fibers of v estibular nerve Hair bundle (kinocilium plus stereocilia) Hair cell Supporting cell Anatomy of a crista ampullaris in a semicircular canal Scanning electron micrograph of a crista ampullaris (200x) Section of Cupula ampulla, filled with endolymph Fibers of v estibular nerv e Flow of endolymph At rest, the cupula stands upright. During rotational acceleration, As rotational mov ement slows, endolymph mov es inside the endolymph keeps mov ing in the semicircular canals in the direction direction of rotation. Endolymph flow opposite the rotation (it lags behind due bends the cupula in the opposite to inertia). Endolymph flow bends the direction from acceleration and cupula and excites the hair cells. inhibits the hair cells. Movement of the ampullary cupula during rotational acceleration and deceleration The Crista Ampullares (Crista) Sensory receptor for rotational acceleration One in ampulla of each semicircular canal Major stimuli are rotational movements 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 17