Special Senses (Week 14, 15) - Seeley's Anatomy & Physiology - PDF

Because learning changes everything. ® Chapter 15 The Special Senses Seeley’s ANATOMY & PHYSIOLOGY Thirteenth Edition Cinnamon VanPutte, Jennifer Regan, Andrew Russo © 2023 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom....

Because learning changes everything. ® Chapter 15 The Special Senses Seeley’s ANATOMY & PHYSIOLOGY Thirteenth Edition Cinnamon VanPutte, Jennifer Regan, Andrew Russo © 2023 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill, LLC.  Lecture Outline The special senses include olfaction, taste, vision, hearing, and balance. Access the text alternative for slide images. © McGraw Hill, LLC 2  15.1 Olfaction Olfaction: sense of smell. Olfactory epithelium found in superior nasal cavity in the olfactory region. 10 million olfactory neurons. Dendrites of olfactory neurons have enlarged ends called olfactory vesicles. Olfactory hairs are cilia of olfactory neuron embedded in mucus. Odorants dissolve in mucus. Odorants attach to receptors, cilia depolarize and initiate action potentials in olfactory neurons. One receptor may respond to more than one type of odor. Olfactory epithelium is replaced as it wears down. Olfactory neurons are replaced by basal cells every two months. © McGraw Hill, LLC 3  Olfactory Region, Epithelium, and Bulb Access the text alternative for slide images. © McGraw Hill, LLC 4  Action of Odorant Binding to Membrane Receptor of Olfactory Hair 1. Each odorant receptor molecule is associated with a G protein. 2. Binding of an odorant to the receptor molecule activates the G protein. 3. The G protein activates adenylate cyclase. 4. Adenylate cyclase is an enzyme that catalyzes the formation of cyclic AMP (cAMP) from ATP. 5. cAMP in these cells causes Na  and Ca2 channels to open. The influx of ions into the olfactory hairs results in depolarization and the production of action potentials in the olfactory neurons. Access the text alternative for slide images. © McGraw Hill, LLC 5  Olfactory Receptors Receptor molecules vary in structure to allow for about 1000 different odorant receptor molecules that react to odorants of different sizes, shapes, and functional groups. Use multiple intracellular pathways involving G proteins, adenylate cyclase, and ion channels. People can detect about 4000 different smells. Threshold for detecting odors is very low and adaptation occurs quickly. Replaced about every 2 months from basal cells in the olfactory epithelium © McGraw Hill, LLC 6  Neuronal Pathways for Olfaction Olfactory sensory pathway: olfactory neurons (bipolar) in the olfactory epithelium pass through cribriform plate to olfactory bulbs and synapse with tufted cells or mitral cells. These extend to the olfactory tract and synapse with association neurons. Association neurons also receive input from brain, so information can be modified before it reaches the brain. Information goes to olfactory cortex of the frontal lobe without going through thalamus (only major sense that does not go through thalamus). © McGraw Hill, LLC 7  Olfactory Cortex and Neuronal Pathways 1. Axons from the olfactory neurons, which form the olfactory nerves (cranial nerve I), project through numerous small foramina in the bony cribriform plate to the olfactory bulb. 2. Within the olfactory bulbs, the olfactory neurons synapse with secondary neurons, which relay olfactory information to the brain through the olfactory tracts. Olfactory bulb neurons also receive input from nerve cell processes entering the olfactory bulb from the brain, enhancing adaptation that occurs along this first part of the olfactory pathway. Access the text alternative for slide images. © McGraw Hill, LLC 8  Olfactory Processing Majority of neurons in the olfactory tracts project to the central olfactory cortex areas in the temporal and frontal lobes where they are processed to allow us to perceive odors. Includes the piriform cortex, amygdala, and orbitofrontal cortex Secondary olfactory areas involved with emotional and autonomic responses to smell. Includes the hypothalamus, hippocampus, and limbic system. © McGraw Hill, LLC 9  15.2 Taste Taste bud: supporting cells surrounding taste (gustatory) cells. Taste cells have microvilli (gustatory hairs) extending into taste pores. Types of papillae: Filiform. Filament-shaped. Most numerous. No taste buds. Vallate. Largest, least numerous. 8 to 12 in V along border between anterior and posterior parts of the tongue. Have taste buds. Foliate. Leaf-shaped. In folds on the sides of the tongue. Contain most sensitive taste buds. Decrease in number with age. Fungiform. Mushroom-shaped. Scattered irregularly over the superior surface of tongue. Look like small red dots interspersed among the filiform. Have taste buds. © McGraw Hill, LLC 10  Papillae Access the text alternative for slide images. © McGraw Hill, LLC 11  Histology of Taste Buds Consist of three major cells types: Taste cells Basal cells Supporting cells A taste bud has about 50 taste cells, each having several microvilli called taste hairs. Taste hairs extend from apex of the taste cell through a taste pore. Taste cells are replaced every 10 days. Access the text alternative for slide images. © McGraw Hill, LLC 12  Taste Types Sour. Most sensitive receptors on lateral aspects of the tongue. Salty. Most sensitive receptors on tip of tongue. Shares lowest sensitivity with sweet. Anything with Na+ causes depolarization plus other metal ions. Craved by humans. Bitter. Most sensitive receptors on posterior aspect. Highest sensitivity. Sensation produced by alkaloids, which are toxic. Sweet. Most sensitive receptors on tip of tongue. Shares lowest sensitivity with salty. Sugars, some carbohydrates, and some proteins (NutraSweet: aspartame). Craved by humans. © McGraw Hill, LLC 13  Taste Substances called testants, dissolve in saliva, enter the taste pores, then stimulate the taste cells. Texture and temperature affect the perception of taste. Very rapid adaptation, both at level of taste bud and within the CNS. Taste influenced by olfaction. Different tastes have different thresholds with bitter being the taste to which we are most sensitive. Many alkaloids (bitter) are poisonous. All taste buds can detect all five tastes but are usually more sensitive to one. © McGraw Hill, LLC 14  Pathways for the Sense of Taste 1. Axons of cranial nerves extend from the taste buds to the tractus solitarius of the medulla oblongata. 2. Fibers from this nucleus extend to the thalamus decussating at the level of the midbrain (not shown in figure). 3. Neurons from the thalamus project bilaterally to the taste areas of both hemispheres of the cerebrum. The taste areas are located in he insula, deep within the lateral fissure between the temporal and parietal lobes. Access the text alternative for slide images. © McGraw Hill, LLC 15  15.3 Visual System Includes the eyes, accessory structures, and optic nerves, tracts, and pathways. Accessory structures: Eyebrows: shade; inhibit sweat. Eyelids (palpebrae) with conjunctiva. Palpebral fissure: space between eyelids. Canthi: lateral and medial, eyelids meet. Medial canthus has caruncle with modified sweat and sebaceous glands. Five layers of tissues including a dense connective tissue tarsal plate that helps maintain shape of lid. Eyelashes: double/triple row of hairs Ciliary glands (modified sweat glands) empty into hair follicles. Meibomian glands at inner margins produce sebum. Conjunctiva: thin transparent mucous membrane. Palpebral conjunctiva: inner surface eyelids. Bulbar conjunctiva: anterior surface of eye except over pupil. © McGraw Hill, LLC 16  Accessory Structures of the Eye ©Eric A. Wise Access the text alternative for slide images. © McGraw Hill, LLC 17  Extrinsic Eye Muscles Six attached to each eye: Superior, inferior, medial, lateral rectus muscles. Superior and inferior oblique muscles. Access the text alternative for slide images. © McGraw Hill, LLC 18  Tunics and Structures of the Eyeball, Sagittal Section Access the text alternative for slide images. © McGraw Hill, LLC 19  Fibrous Tunic Sclera: white outer layer. Maintains shape, protects internal structures, provides muscle attachment point, continuous with cornea. Dense collagenous connective tissue with elastic fibers. Collagen fibers are large and opaque. Cornea: transparent window continuous anteriorly with sclera. Connective tissue matrix containing collagen, elastic fibers and proteoglycans. Layer of stratified squamous epithelium on the outer surface. Collagen fibers are small, thus transparent. More proteoglycans than sclera, low water content (water would scatter light). Avascular, transparent, allows light to enter eye; bends and refracts light. © McGraw Hill, LLC 20  Vascular Tunic Middle layer. Contains most of the blood vessels of the eye: branches off the internal carotid arteries. Contains melanin. Iris: colored part of the eye. Controls light entering the pupil. Smooth muscle determines size of pupil. Sphincter pupillae: parasympathetic (CN III); circular muscles Dilator pupillae: sympathetic; radial muscles Ciliary body: outer ciliary ring and inner ciliary processes. Ciliary muscles: control lens shape; smooth muscle. Ciliary processes attached to the lens by suspensory ligaments; produces aqueous humor that fills anterior chamber. Choroid: associated with sclera. Very thin, pigmented. © McGraw Hill, LLC 21  Lens, Cornea, Iris, and Ciliary Body Access the text alternative for slide images. © McGraw Hill, LLC 22  Retina 1 Two layers. Pigmented layer: outer, pigmented layer; pigmented simple cuboidal epithelium. Pigment of this layer and choroid help to separate sensory cells and reduce light scattering. Neural layer: inner layer of rod and cone cells sensitive to light and relay neurons. © McGraw Hill, LLC 23  Opthalmoscopic View of the Left Retina Lens focuses light on macula and fovea centralis. Macula: small yellow spot. Fovea centralis: area of greatest visual acuity; photoreceptor cells tightly (a) Steve Allen/Brand X Pictures/Getty Images packed. Optic disc: blind spot Area through which blood vessels enter eye, where nerve processes from neural layer meet and exit from eye. Access the text alternative for slide images. © McGraw Hill, LLC 24  Functions of the Eye 1. As light passes through the pupil of the iris, it is focused on the retina by the cornea, lens, and humors. 2. The light striking the retina is converted into action potentials. 3. The optic nerve conveys these action potentials to the brain. Access the text alternative for slide images. © McGraw Hill, LLC 25  Electromagnetic Spectrum Electromagnetic spectrum is the entire range of wavelengths or frequencies of electromagnetic radiation. Visible light: portion of electromagnetic spectrum detected by human eye (380 to 750 nm). Access the text alternative for slide images. © McGraw Hill, LLC 26  Structure and Function of the Retina Neural layer: three layers of neurons: photoreceptor cells, bipolar cells, and ganglionic cells. Cell bodies form nuclear layers separated by plexiform layers, where neurons of adjacent layers synapse with each other. Pigmented layer: single layer of cells; filled with melanin. With choroid, enhances visual acuity by isolating individual photoreceptors, reducing light scattering. © McGraw Hill, LLC 27  Retina 2 (b) Steve Gschmeissner/Science Source Access the text alternative for slide images. © McGraw Hill, LLC 28  Rods 1 Bipolar photoreceptor cells; black and white vision. Modified, dendritic, light-sensitive part is cylindrical; contains about 700 double-layered membranous discs that contain rhodopsin. Found over most of retina, but not in fovea. More sensitive to light than cones. Protein rhodopsin changes shape when struck by light; and eventually separates into its two components: opsin and retinal. Retinal can be converted to Vitamin A from which it was originally derived. In absence of light, opsin and retinal recombine to form rhodopsin. © McGraw Hill, LLC 29  Rods 2 Rods are unusual sensory cells: when not stimulated they are depolarized. Light causes them to hyperpolarize. Depolarization of rods causes depolarization of bipolar cells causing depolarization of ganglion cells. Light and dark adaptation: adjustment of eyes to changes in light. Happens because of changes in amount of available rhodopsin, pupil reflexes, and changes in level of photoreceptor function. © McGraw Hill, LLC 30  Sensory Receptor Cells of the Retina Access the text alternative for slide images. © McGraw Hill, LLC 31  Visual Pathways 2 4. Specifically, ganglion cell axons from the nasal retina (the medial portion of the retina) cross through the optic chiasm and project to the opposite side of the brain. Ganglion cell axons from the temporal retina (the lateral portion of the retina) pass through the optic nerves and project to the brain on the same side of the body without crossing. This results in both hemispheres receiving visual input from both eyes. 5. Beyond the optic chiasm, the route of the ganglionic axons is called the optic tract. Most of the optic tract axons terminate in the lateral geniculate nucleus of the thalamus. However, some axons do not terminate in the thalamus but separate from the optic tract to terminate in the superior colliculi, the center for visual reflexes. 6. Neurons of the lateral geniculate nucleus of the thalamus form the fibers of the optic radiations, which project to the visual cortex in the occipital lobe. Access the text alternative for slide images. © McGraw Hill, LLC 32  15.4 Hearing and Balance Divided into external, middle, and inner ear. External and middle: hearing. Internal: hearing and balance. External ear. Auricle or pinna: elastic cartilage covered with skin. External auditory canal: lined with hairs and ceruminous glands. Produce cerumen. Tympanic membrane. Thin membrane of two layers of epithelium with connective tissue between. Sound waves cause it to vibrate. Border between external and middle ear. © McGraw Hill, LLC 33  External, Middle, and Inner Ears Access the text alternative for slide images. © McGraw Hill, LLC 34  Auditory Structures and Their Functions Middle ear. Separated from the inner ear by the oval and round windows. Two passages for air. Auditory or eustachian tube: opens into pharynx, equalizes pressure. Passage to mastoid air cells in mastoid process. Ossicles: malleus, incus, stapes: transmit vibrations from eardrum to oval window. Oval window: connection between middle and inner ear. Foot of the stapes rests here and is held in place by annular ligament. © McGraw Hill, LLC 35  Inner Ear 1 Bony labyrinth: tunnels and chambers in the temporal bone. Cochlea: hearing. Vestibule: balance. Semicircular canals: balance. Membranous labyrinth: membranous tunnels and chambers suspended in the bony labyrinth. Fluids. Endolymph: in membranous labyrinth. Low K  , high Na  Perilymph: in spaces between membranous labyrinth and periosteum of bony labyrinth. High K  , low Na  © McGraw Hill, LLC 36  Inner Ear: Bony and Membranous Labyrinths Access the text alternative for slide images. © McGraw Hill, LLC 37  The Process of Hearing 1 External ear. Collects sound waves, conducts through external auditory canal. Middle ear. Tympanic membrane vibrates, ossicles vibrate, vibrations transferred to oval window. Tensor tympani and stapedius muscles reflexively dampen excessively loud sounds (sound attenuation reflex). © McGraw Hill, LLC 38  The Process of Hearing 2 Inner ear. Vibration of perilymph causes vestibular membrane to vibrate, which causes vibrations in endolymph. Basilar membrane displaced, detected by hair cells. Vibrations in scala tympani dissipated by movement of round window. © McGraw Hill, LLC 39  Effect of Sound Waves on Cochlear Structures 1 Access the text alternative for slide images. © McGraw Hill, LLC 40  Balance Static labyrinth: utricle and saccule of the vestibule. Evaluates position of head relative to gravity. Detects linear acceleration and deceleration (as in a car). Dynamic labyrinth: crista ampullaris of the semicircular canals. Evaluates movement of the head in three dimensional space. © McGraw Hill, LLC 41  Structure of the Utricular and Saccular Maculae (d) Susumu Nishinag/Science Source Access the text alternative for slide images. © McGraw Hill, LLC 42  Function of the Vestibule in Maintaining Balance (Top both) Trent Stephens Access the text alternative for slide images. © McGraw Hill, LLC 43  Dynamic Labyrinth Three semicircular canals filled with endolymph: transverse plane, coronal plane, sagittal plane. Base of each expanded into ampulla with sensory epithelium (crista ampullaris). Cupula suspended over crista hair cells. Acts as a float displaced by fluid movements within semicircular canals. Displacement of the cupula is most intense when the rate of head movement changes, thus this system detects changes in the rate of movement rather than movement alone. Access the text alternative for slide images. (d) Biophoto Associates/Science Source © McGraw Hill, LLC 44  Function of the Semicircular Canals (a) uniquely india/Getty Images Access the text alternative for slide images. © McGraw Hill, LLC 45  Effects of Aging on the Special Senses Slight loss in ability to detect odors. Decreased sense of taste. Lenses of eyes lose flexibility - presbyopia Development of cataracts, macular degeneration, glaucoma, diabetic retinopathy. Decline in visual acuity and color perception. Presbyacusis – age-related hearing loss Hair cells in the cochlea, utricle, saccule, and ampulla decrease. More falls due to instability and vertigo. © McGraw Hill, LLC 46  End of Main Content Because learning changes everything. ® www.mheducation.com © 2023 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill, LLC.