Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 12 Lecture PowerPoint Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Type Institution Name Here Type Course Number Here: Type Course Name Here Chapter 12 Type Professor Name Here Type Academic Rank Here Type Department Name Here 2 Hole’s Human Anatomy and Physiology Twelfth Edition Shier w Butler w Lewis Chapter 12 Nervous System III: Senses Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3 12.1: Introduction • General senses • Receptors that are widely distributed throughout the body • Skin, various organs and joints • Special senses • Specialized receptors confined to structures in the head • Eyes, ears, nose and mouth 4 12.2: Receptors, Sensation, and Perception • Sensory receptors • Specialized cells or multicellular structures that collect information from the environment • Stimulate neurons to send impulses along sensory (afferent) fibers to the brain • Sensation • A feeling that occurs when brain becomes aware of sensory impulse • Perception • A person’s view of the stimulus; the way the brain interprets the information 5 Pathways From Sensation to Perception (Example of an Apple) 6 Receptor Types • Chemoreceptors • Respond to changes in chemical concentrations • Pain receptors (nociceptors) • Respond to chemicals released during tissue damage • Thermoreceptors • Respond to changes in temperature • Mechanoreceptors • Respond to mechanical forces (touch, stretch, pressure) • Photoreceptors • Respond to light 7 Sensory Impulses • Stimulation of receptor causes local change in its receptor potential • A graded electrical current is generated that reflects intensity of stimulation • If receptor is part of a neuron, the membrane potential may generate an action potential • If receptor is not part of a neuron, the receptor potential must be transferred to a neuron to trigger an action potential • Peripheral nerves transmit impulses to CNS where they are analyzed and interpreted in the brain 8 Sensations and Perception • Projection • Process in which the brain projects the sensation back to the apparent source • It allows a person to pinpoint the region of stimulation 9 Sensory Adaptation • Ability to ignore unimportant stimuli • Involves a decreased response to a particular stimulus from the receptors (peripheral adaptation) or along the CNS pathways leading to the cerebral cortex (central adaptation) • Sensory impulses become less frequent and may cease • Stronger stimulus is required to trigger impulses 10 12.3: General Senses • Senses associated with skin, muscles, joints and viscera • Three (3) groups: • Exteroceptive senses (exteroceptors) • Senses associated with body surface such as touch, pressure, temperature, and pain • Visceroceptive senses (interoceptors) • Senses associated with changes in the viscera such as blood pressure stretching blood vessels and ingestion of a meal • Proprioceptive senses • Senses associated with changes in muscles and tendons 11 such as at joints Touch and Pressure Senses Free nerve endings • Common in epithelial tissues • Simplest receptors • Sense itching Tactile (Meissners) corpuscles • Abundant in hairless portions of skin and lips • Detect fine touch; distinguish between two points on the skin Lamellated (Pacinian) corpuscles • Common in deeper subcutaneous tissues, tendons and ligaments • Detect heavy pressure and vibrations 12 Touch and Pressure Receptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Free nerve endings Section of skin Epithelial cells Epidermis (a) Sensory (afferent) nerve fiber Epithelial cells Dermis Tactile (Meissners) corpuscle (touch receptor) (b) Sensory (afferent) nerve fiber Lamellated (Pacinian) corpuscle (pressure receptor) Connective tissue cells (c) © Ed Reschke Sensory (afferent) nerve fiber 13 Temperature Senses • Warm receptors • Sensitive to temperatures above 25oC (77o F) • Unresponsive to temperature above 45oC (113oF) • Cold receptors • Sensitive to temperatures between 10oC (50oF) and 20oC (68oF) • Pain receptors • Respond to temperatures below 10oC • Respond to temperatures above 45oC 14 Sense of Pain • Free nerve endings • Widely distributed • Nervous tissue of brain lacks pain receptors • Stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature • Adapt very little, if at all 15 Visceral Pain • Pain receptors are the only receptors in viscera whose stimulation produces sensations • Pain receptors respond differently to stimulation • Pain receptors are not well localized • Pain receptors may feel as if coming from some other part of the body • Known as referred pain… 16 Referred Pain • May occur due to sensory impulses from two regions following a common nerve pathway to brain Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Liver and gallbladder Lung and diaphragm Liver and gallbladder Heart Stomach Pancreas Small intestine Ovary (female) Appendix Colon Kidney Ureter Urinary bladder 17 Pain Nerve Pathways • Acute pain fibers • Chronic pain fibers • A-delta fibers • C fibers • Thin, myelinated • Thin, unmyelinated • Conduct impulses rapidly • Conduct impulses more • Associated with sharp pain slowly • Well localized • Associated with dull, aching pain • Difficult to pinpoint • Blocked by narcotics (controlled substances) • CCC (Chronic, C fibers, Controlled substances) 18 Regulation of Pain Impulses • Thalamus • Allows person to be aware of pain • Cerebral cortex • Judges intensity of pain • Locates source of pain • Produces emotional and motor responses to pain • Pain inhibiting substances: • Enkephalins • Serotonin • Endorphins 19 12.1 Clinical Application Treating Pain 20 Proprioception • Mechanoreceptors • Send information to spinal cord and CNS about body position and length, and tension of muscles • Main kinds of proprioceptors: • Pacinian corpuscles – in joints • Muscle spindles – in skeletal muscles* • Golgi tendon organs – in tendons* *considered to be stretch receptors 21 Stretch Receptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sensory (afferent) nerve fiber Sensory nerve endings Golgi tendon organ Sensory (afferent) nerve fiber Tendon Intrafusal fiber Skeletal muscle fiber Muscle spindle Skeletal muscle fiber Connective tissue sheath (a) (b) 22 Visceral Senses • Receptors in internal organs • Convey information that includes the sense of fullness after eating a meal as well as the discomfort of intestinal gas and the pain that signals a heart attack 23 Summary of Receptors of the General Senses 24 12.4: Special Senses • Sensory receptors are within large, complex sensory organs in the head • Smell in olfactory organs • Taste in taste buds • Hearing and equilibrium in ears • Sight in eyes 25 Sense of Smell • Olfactory receptors • Chemoreceptors • Respond to chemicals dissolved in liquids • Olfactory organs • Contain olfactory receptors and supporting epithelial cells • Cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum 26 Olfactory Receptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nerve fibers within the olfactory bulb Olfactory Olfactory tract bulb Cribriform plate Olfactory area of nasal cavity Superior nasal concha Nasal cavity Cilia (a) Olfactory Columnar Cribriform receptor cells epithelial cells plate (b) 27 Olfactory Nerve Pathways • Once olfactory receptors are stimulated, nerve impulses travel through • Olfactory nerves olfactory bulbs olfactory tracts limbic system (for emotions) and olfactory cortex (for interpretation) 28 Olfactory Stimulation • Olfactory organs located high in the nasal cavity above the usual pathway of inhaled air • Olfactory receptors undergo sensory adaptation rapidly • Sense of smell drops by 50% within a second after stimulation • Olfactory code • Hypothesis • Odor that is stimulated by a distinct set of receptor cells and its associated receptor proteins 29 12.2 Clinical Application Mixed-Up Senses: Synesthesia 30 Sense of Taste • Taste buds • Organs of taste • Located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx • Taste receptors • Chemoreceptors • Taste cells – modified epithelial cells that function as receptors • Taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells 31 Taste Receptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Papillae Taste buds Epithelium of tongue (a) Taste cell Taste hair Supporting cell Taste pore (b) Connective tissue Sensory (afferent) nerve fibers 32 Taste Sensations • Four primary taste sensations • Sweet – stimulated by carbohydrates • Sour – stimulated by acids • Salty – stimulated by salts • Bitter – stimulated by many organic compounds • Spicy foods activate pain receptors 33 Taste Nerve Pathways • Sensory impulses from taste receptors travel along: • Cranial nerves VII, IX, and X to… • Medulla oblongata to… • Thalamus to… • Gustatory cortex (for interpretation) 34 12.3 Clinical Application Smell and Taste Disorders 35 Sense of Hearing • Ear • Organ of hearing • Three (3) sections: • External ear • Middle ear • Inner ear 36 External Ear • Auricle • Collects sounds waves • External auditory meatus • Lined with ceruminous glands • Carries sound to tympanic membrane • Terminates with tympanic membrane • Tympanic membrane • Vibrates in response to sound waves Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Auricle Semicircular canals Incus Stapes Malleus Cochlea Vestibulocochlear nerve Oval window (under stapes) Round window Tympanic cavity Tympanic membrane External acoustic meatus Auditory tube Pharynx 37 Middle Ear • Tympanic cavity • Air-filled space in Auricle temporal bone • Auditory ossicles • Vibrate in response to tympanic membrane • Malleus, incus and stapes • Hammer, anvil and stirrup • Oval window • Opening in wall of tympanic cavity • Stapes vibrates against it to move fluids in inner ear Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Semicircular canals Incus Stapes Malleus Cochlea Vestibulocochlear nerve Oval window (under stapes) Round window Tympanic cavity Tympanic membrane External acoustic meatus Auditory tube Pharynx 38 Auditory Tube • Also known as the Auricle Eustachian tube • Connects middle ear to throat • Helps maintain equal pressure on both sides of tympanic membrane • Usually closed by valvelike flaps in throat Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Semicircular canals Incus Stapes Malleus Cochlea Vestibulocochlear nerve Oval window (under stapes) Round window Tympanic cavity Tympanic membrane External acoustic meatus Auditory tube Pharynx 39 Inner Ear Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Complex system of labyrinths • Osseous labyrinth • Bony canal in temporal bone • Filled with perilymph • Membranous labyrinth • Tube within osseous labyrinth • Filled with endolymph Bony labyrinth Perilymph Membranous labyrinth Endolymph Bony labyrinth (contains perilymph) Membranous labyrinth (contains endolymph) Semicircular canals Utricle Vestibular nerve Saccule Cochlear nerve Scala vestibuli (cut) Scala tympani (cut) Cochlear duct (cut) containing endolymph Ampullae (a) OvalVestibuleRoundMaculae window window Cochlea 40 Inner Ear • Three (3) parts of labyrinths: • Cochlea • Functions in hearing Bony labyrinth • Semicircular canals (contains perilymph) Membranous labyrinth • Functions in (contains endolymph) equilibrium Semicircular canals • Vestibule • Functions in equilibrium Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bony labyrinth Perilymph Membranous labyrinth Endolymph Utricle Vestibular nerve Saccule Cochlear nerve Scala vestibuli (cut) Scala tympani (cut) Cochlear duct (cut) containing endolymph Ampullae (a) OvalVestibuleRoundMaculae window window Cochlea 41 Cochlea • Scala vestibuli • Upper compartment Stapes vibrating in oval window • Leads from oval Scala vestibuli filled with perilymph window to apex of Vestibular spiral membrane • Part of bony labyrinth Basilar membrane • Scala tympani Scala tympani with • Lower compartment filled perilymph • Extends from apex of Round window the cochlea to round window • Part of bony labyrinth Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Helicotrema Membranous labyrinth Cochlear duct filled with endolymph 42 Cochlea Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Cochlear duct • Portion of membranous labyrinth in cochlea • Vestibular membrane • Separates cochlear duct from scala vestibuli • Basilar membrane • Separates cochlear duct from scala tympani Scala vestibuli (contains perilymph) Vestibular membrane Branch of cochlear nerve Cochlear duct (contains endolymph) Spiral organ (organ of Corti) Basilar membrane Scala tympani (contains perilymph) (a) 43 12.4 Clinical Application Getting a Cochlear Implant 44 Organ of Corti Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Group of hearing receptor cells (hair cells) • On upper surface of basilar membrane • Different frequencies of vibration move different parts of basilar membrane • Particular sound frequencies cause hairs of receptor cells to bend • Nerve impulse generated Scala vestibuli (contains perilymph) Vestibular membrane Cochlear duct (contains endolymph) Branch of cochlear nerve Spiral organ (organ of Corti) Basilar membrane Scala tympani (contains perilymph) (a) Tectorial membrane Hair cells Basilar membrane (b) Branch of cochlear nerve Nerve fibers Supporting cells 45 Organ of Corti Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cochlear duct Tectorial membrane Scala tympani Hair cells Basilar membrane (a) (b) a: © John D. Cunningham/Visuals Unlimited; b: © Fred Hossler/Visuals Unlimited 46 Auditory Nerve Pathways Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Auditory cortex (temporal lobe) Thalamus Medial geniculate body of thalamus Midbrain Pons Superior olivary nucleus Medulla oblongata Cochlear nuclei Vestibulocochlear nerve 47 12.5 Clinical Application Hearing Loss 48 Summary of the Generation of Sensory Impulses from the Ear 49 Sense of Equilibrium • Static equilibrium • Vestibule • Senses position of head when body is not moving • Dynamic Equilibrium • Semicircular canals • Senses rotation and movement of head and body 50 Vestibule • Utricle • Communicates with saccule and membranous portion of semicircular Ampullae of semicircular canals canals • Saccule • Communicates with cochlear duct • Macula • Hair cells of utricle and saccule Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vestibulocochlear nerve Cochlea Utricle Cochlear duct Maculae Saccule Vestibule 51 Macula Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Responds to changes in head position • Bending of hairs results in generation of nerve impulse Hairs of hair cells bend Gelatinous material sags Otoliths Macula of utricle Hair cells Sensory (afferent) nerve fiber Gravitational force Supporting cells 52 (a) Head upright (b) Head bent forward Semicircular Canals • Three (3) canals at right angles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Ampulla • Swelling of membranous Vestibulocochlear labyrinth that communicates Ampullae of nerve semicircular Cochlea Utricle with the vestibule canals Cochlear • Crista ampullaris duct • Sensory organ of ampulla • Hair cells and supporting cells • Rapid turns of head or body stimulate hair cells Maculae Saccule Vestibule 53 Crista Ampullaris Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endolymph Semicircular canal Cupula Crista ampullaris (a) Head in still position Ampulla Crista ampullaris Hairs Hair cell Supporting cells Sensory (afferent) nerve fibers (b) Head rotating (c) 54 Sense of Sight • Visual accessory organs • Eyelids • Lacrimal apparatus • Extrinsic eye muscles 55 Eyelid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Palpebra • Composed of four (4) layers: • Skin • Muscle • Connective tissue • Conjunctiva • Orbicularis oculi – closes eyelid • Levator palpebrae superioris – opens eyelid • Tarsal glands – secrete oil onto eyelashes • Conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball Tendon of levator palpebrae superioris Superior rectus Orbicularis oculi Eyelid Tarsal glands Eyelash Cornea Conjunctiva Inferior rectus 56 Lacrimal Apparatus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Lacrimal gland • Lateral to eye • Secretes tears Lacrimal gland • Canaliculi • Collect tears Superior and inferior canaliculi • Lacrimal sac Lacrimal sac • Collects from canaliculi Nasolacrimal • Nasolacrimal duct duct • Collects from lacrimal sac • Empties tears into nasal cavity 57 Extrinsic Eye Muscles • Superior rectus • Rotates eye up and medially Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Medial Superior Superior rectus rectus oblique • Inferior rectus • Rotates eye down and medially • Medial rectus • Rotates eye medially Lateral rectus (cut) Inferior rectus Inferior oblique 58 Extrinsic Eye Muscles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Lateral rectus • Rotates eye laterally Medial Superior Superior rectus rectus oblique • Superior oblique • Rotates eye down and laterally • Inferior oblique • Rotates eye up and laterally Lateral rectus (cut) Inferior rectus Inferior oblique 59 Structure of the Eye • Hollow • Spherical • Wall has three (3) layers: • Outer fibrous tunic • Middle vascular tunic • Inner nervous tunic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ciliary body Suspensory ligaments Iris Lens Pupil Lateral rectus Retina Choroid coat Sclera Vitreous humor Fovea centralis Cornea Aqueous humor Anterior cavity Anterior chamber Posterior chamber Optic nerve Optic disc Posterior cavity Medial rectus 60 Outer Tunic • Cornea • Anterior portion • Transparent • Light transmission • Light refraction • Sclera • Posterior portion • Opaque • Protection Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ciliary body Suspensory ligaments Iris Lens Pupil Lateral rectus Retina Choroid coat Sclera Vitreous humor Fovea centralis Cornea Aqueous humor Anterior cavity Anterior chamber Posterior chamber Optic nerve Optic disc Posterior cavity Medial rectus 61 Middle Tunic • Iris • Anterior portion • Pigmented • Controls light intensity Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ciliary body Suspensory ligaments • Ciliary body Iris Lens • Anterior portion Pupil • Pigmented Cornea Aqueous • Holds lens humor • Moves lens for Anterior Anterior chamber cavity focusing Posterior chamber • Choroid coat • Provides blood supply • Pigments absorb extra light Lateral rectus Retina Choroid coat Sclera Vitreous humor Fovea centralis Optic nerve Optic disc Posterior cavity Medial rectus 62 Anterior Portion of Eye • Filled with aqueous humor Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cornea Anterior chamber Iris Posterior chamber Suspensory ligaments Ciliary process Ciliary muscles Ciliary body Conjunctiva Vitreous humor Lens Sclera 63 Lens Transparent, Biconvex , Lies behind iris, Composed of lens fibers, Elastic, Held in place by suspensory ligaments of ciliary body Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cornea Anterior chamber Iris Posterior chamber Suspensory ligaments Ciliary process Ciliary muscles Ciliary body Conjunctiva Vitreous humor Lens Sclera 64 Ciliary Body • Forms internal ring around the front of the eye • Ciliary processes – radiating folds • Ciliary muscles – contract and relax to move lens Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ciliary processes of ciliary body Suspensory ligaments Lens Retina Choroid coat Sclera 65 Accommodation • Changing of lens shape to view objects Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ciliary muscle fibers contracted Suspensory ligaments relaxed Lens thick (a) Ciliary muscle fibers relaxed Suspensory ligaments taut Lens thin 66 (b) Iris • Composed of connective tissue and smooth muscle • Pupil is hole in iris • Dim light stimulates radial muscles and pupil dilates • Bright light stimulates circular muscles and pupil constricts Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sympathetic motor nerve fiber In dim light Radially arranged Smooth muscle fibers of the iris Circularly arranged smooth muscle fibers of the iris Parasympathetic ganglion Pupil In normal light Parasympathetic motor nerve fiber In bright light 67 Aqueous Humor • Fluid in anterior cavity of eye • Secreted by epithelium on inner surface of the ciliary body • Provides nutrients • Maintains shape of anterior portion of eye • Leaves cavity through Canal of Schlemm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cornea Aqueous humor Iris Scleral venous sinus (canal of Schlemm) Sclera Anterior chamber Lens Ciliary Ciliary process body Ciliary muscles Vitreous humor Posterior chamber 68 Inner Tunic • Retina • Contains visual receptors • Continuous with optic nerve • Ends just behind margin of the ciliary body • Composed of several layers • Macula lutea – yellowish spot in retina • Fovea centralis – center of macula lutea; produces sharpest vision • Optic disc – blind spot; contains no visual receptors • Vitreous humor – thick gel that holds retina flat against choroid coat 69 Posterior Cavity • Contains vitreous humor – thick gel that holds retina flat against choroid coat Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lateral rectus Ciliary body Suspensory ligaments Retina Choroid coat Sclera Vitreous humor Iris Lens Fovea centralis Pupil Cornea Aqueous humor Anterior cavity Anterior chamber Posterior chamber Optic nerve Optic disc Posterior cavity Medial rectus 70 Major Groups of Retinal Neurons • Receptor cells, bipolar cells, and ganglion cells - provide pathway for impulses triggered by photoreceptors to reach the optic nerve • Horizontal cells and amacrine cells – modify impulses Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sclera Pigmented choroid coat Retinal pigment epithelium Rod Cone Receptor cells Horizontal cell Retina Bipolar neuron Amacrine cell Layer of connecting neurons Ganglion cell Nerve fibers Impulses to optic nerve Vitreous humor 71 Light waves Layers of the Eye 72 Light Refraction • Refraction • Bending of light • Occurs when light waves pass at an oblique angle into mediums of different densities Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Perpendicular line Air Light wave Glass Refracted light wave 73 Types of Lenses • Convex lenses cause light waves to converge • Concave lenses cause light waves to diverge Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Light wave Air Convex surface Concave surface Glass Converging light waves (a) Diverging light waves (b) 74 Focusing On Retina • As light enters eye, it is refracted by: • Convex surface of cornea • Convex surface of lens • Image focused on retina is upside down and reversed from left to right Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Light waves Image Retina Object Cornea 75 Visual Receptors • Rods • Cones • Long, thin projections • Short, blunt projections • Contain light sensitive • Contain light sensitive pigment called rhodopsin pigments called erythrolabe, • Hundred times more sensitive chlorolabe, and cyanolabe to light than cones • Provide vision in bright • Provide vision in dim light light • Produce colorless vision • Produce sharp images • Produce outlines of objects • Produce color vision 76 Rods and Cones Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Retinal pigment epithelium Cones Rods Single sensory (afferent) nerve fiber (a) Many sensory (afferent) nerve fibers (b) Rod Cone 77 (c) c: © Frank S. Werblin, PhD. 12.6 Clinical Application Refraction Disorders • Concave lens corrects nearsightedness • Convex lens corrects farsightedness Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lens Cornea Light waves Point of focus Uncorrected point of focus Light waves (a) Eye too long (myopia) Point of focus Concave lens (a) Corrected point of focus Light waves Retina Uncorrected point of focus (b) Normal eye Point of focus Light waves Convex lens (c) Eye too short (hyperopia) (b) Corrected point of focus 78 Visual Pigments • Rhodopsin • Light-sensitive pigment in rods • Decomposes in presence of light • Triggers a complex series of reactions that initiate nerve impulses • Impulses travel along optic nerve • Pigments on cones • Each set contains different lightsensitive pigment • Each set is sensitive to different wavelengths • Color perceived depends on which sets of cones are stimulated • Erythrolabe – responds to red • Chlorolabe – responds to green • Cyanolabe – responds to blue 79 Rod Cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Discs of membrane within cell Mitochondria Nucleus Synaptic ending 80 Stereoscopic Vision • Provides perception of distance and depth • Results from formation of two slightly different retinal images Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Light waves Left eye Right eye 81 Visual Nerve Pathway Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Eye Optic nerve Fibers from nasal (medial) half of each retina crossing over Optic chiasma Optic tract Lateral geniculate body of thalamus Optic radiations 82 Visual cortex of occipital lobe 12.5: Lifespan Changes • Age related hearing loss due to: • Damage of hair cells in organ of Corti • Degeneration of nerve pathways to the brain • Tinnitus • Age-related visual problems include: • Dry eyes • Floaters (crystals in vitreous humor) • Loss of elasticity of lens • Glaucoma • Cataracts • Macular degeneration 83 Important Points in Chapter 12: Outcomes to be Assessed 12.1: Introduction Explain the difference between general senses and special senses. 12.2: Receptors, Sensation, and Perception Name the five types of receptors and state the function of each. Explain how receptors stimulate sensory impulses. Explain how a sensation is produced. 12.3: General Senses Distinguish between general and special senses. Describe the differences among receptors associated with the senses of touch, pressure, temperature, and pain. Describe how the sensation of pain is produced. 84 Important Points in Chapter 12: Outcomes to be Assessed Explain the importance of stretch receptors in muscles and tendons. 12.4: Special Senses Explain the relationship between the senses of smell and taste. Name the parts of the ear and the function of each part. Distinguish between static and dynamic equilibrium. Name the parts of the eye and the function of each part. Explain how the eye refracts light. Explain how the brain perceives depth and distance. Draw a diagram of the visual nerve pathways. 85 Quiz 12 Complete Quiz 12 now! Read Chapter 13. 86