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 The Senses Introduction • General senses • Receptors are widely distributed throughout the body • Skin, various organs and joints • Touch, pain, temperature, pressure, ect. • Special senses • Specialized receptors confined to structures in the head • Vision, Taste, Smell, Hearing 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 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 3 Receptor Types • Chemoreceptors • Respond to changes in chemical concentrations (smell, taste, pH) • Pain receptors (nociceptors) • Respond to tissue damage • Thermoreceptors • Respond to changes in temperature • Mechanoreceptors • Respond to mechanical forces • Stretch receptors, proprioceptors, baroreceptors • Photoreceptors • Respond to light 5 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 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 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 such as at joints 8 Touch and Pressure Senses Free nerve endings • Common in epithelial tissues • Simplest receptors • Sense itching Tactile (Meissner’s) 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 9 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 nerve fiber Epithelial cells Dermis Tactile (Meissner’s) corpuscle (touch receptor) (b) Sensory nerve fiber Lamellated (Pacinian) corpuscle (pressure receptor) Connective tissue cells Sensory nerve fiber (c) b, c: © Ed Reschke 10 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 11 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 12 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… 13 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 Appendix Ovary (female) Colon Kidney Ureter Urinary bladder 14 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 15 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 16 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 17 Stretch Receptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sensory nerve fiber Sensory nerve endings Golgi tendon organ Sensory nerve fiber Tendon Intrafusal fiber Skeletal muscle fiber Muscle spindle Skeletal muscle fiber Connective tissue sheath (a) (b) 1818 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 19 Summary of Receptors of the General Senses End of Section 1, chapter 12 section 2, chapter 12 Smell, Taste, and Hearing • 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 21 Sense of Smell • Olfactory receptors • Bipolar Chemoreceptors • Respond to chemicals (called odorants) dissolved in liquids • Olfactory organs • Olfactory epithelium - contain olfactory receptors and supporting epithelial cells • Cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum 22 Olfactory Receptors Figure 12.5 Olfactory receptors. (a) columnar epithelial cells support olfactory receptor cells, which have cilia at their distal ends. The olfactory receptors pass through olfactory foramina in the cribriform plate and synapse with the olfactory bulb in the brain. (b) Olfactory epithelium cover the upper nasal cavity and superior nasal conchae. Olfactory Nerve Pathways • Once olfactory receptors are stimulated, nerve impulses travel through • •Olfactory nerves olfactory bulbs olfactory tracts limbic system (for emotions) & olfactory cortex (for interpretation) The limbic system, which is involved with emotions and memory is strongly effected by smell. 24 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 25 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 26 Taste Receptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Papillae Taste buds Epithelium of tongue Taste cell (a) Taste hair Supporting cell Taste pore Connective tissue Sensory nerve fibers 27 (b) 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 28 Taste Nerve Pathways • Sensory impulses from taste receptors travel along: • Cranial nerves to… • Medulla oblongata to… • Thalamus to… • Gustatory cortex (for interpretation) 29 Sense of Hearing • Ear • Organ of hearing • Three (3) sections: • External ear • Middle ear • Inner ear 30 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 Auricle 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 31 Middle Ear Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Tympanic cavity • Air-filled space in 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 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 32 Auditory Tube Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Also known as the Eustachian tube • Connects middle ear to throat • Helps maintain equal pressure on both sides of tympanic membrane • Usually closed by valvelike flaps in throat 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 33 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 Saccule Vestibular nerve Cochlear nerve Scala vestibuli (cut) Scala tympani (cut) Cochlear duct (cut) containing endolymph Ampullae Oval Vestibule Round Maculae window window Cochlea (a) 34 Inner Ear • Three (3) parts of labyrinths: • Cochlea • Functions in hearing • Semicircular canals • Functions in equilibrium • Vestibule • Functions in equilibrium Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bony labyrinth Perilymph Membranous labyrinth Endolymph Bony labyrinth (contains perilymph) Membranous labyrinth (contains endolymph) Semicircular canals Utricle Saccule Vestibular nerve Cochlear nerve Scala vestibuli (cut) Scala tympani (cut) Cochlear duct (cut) containing endolymph Ampullae Oval Vestibule Round Maculae window window Cochlea (a) 35 Cochlea • Scala vestibuli • Upper compartment • Leads from oval window to apex of spiral • Part of bony labyrinth • Scala tympani • Lower compartment • Extends from apex of the cochlea to round window • Part of bony labyrinth Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stapes vibrating in oval window Helicotrema Scala vestibuli filled with perilymph Vestibular membrane Basilar membrane Scala tympani filled with perilymph Round window Membranous labyrinth Cochlear duct filled with endolymph 36 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) 37 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) Spiral organ (organ of Corti) Branch of cochlear nerve Basilar membrane Scala tympani (contains perilymph) (a) Tectorial membrane Hair cells (b) Branch of cochlear nerve Nerve fibers Supporting cells Basilar membrane 38 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 39 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 Cochlear nuclei Superior olivary nucleus Medulla oblongata Vestibulocochlear nerve 40 Summary of the Generation of Sensory Impulses from the Ear 41 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 42 Vestibule • Utricle • Communicates with saccule and membranous portion of semicircular 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. Ampullae of semicircular canals Vestibulocochlear nerve Cochlea Utricle Cochlear duct Maculae Saccule Vestibule 43 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 nerve fiber Gravitational force Supporting cells (a) Head upright (b) Head bent forward 44 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 nerve Ampullae of Cochlea semicircular Utricle with the vestibule canals Cochlear duct • Crista ampullaris • Sensory organ of ampulla • Hair cells and supporting cells • Rapid turns of head or body stimulate hair cells Maculae Saccule Vestibule 45 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 nerve fibers (b) Head rotating (c) End of section 2, chapter 12 46 ivyanatomy.com section 3, chapter 12 vision Sense of Sight • Visual accessory organs • Eyelids • Lacrimal apparatus • Extrinsic eye muscles 48 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 49 Lacrimal Apparatus • 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 50 Extrinsic Eye Muscles • Superior rectus • Rotates eye up and medially Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Medial Superior rectus rectus Superior oblique • Inferior rectus • Rotates eye down and medially • Medial rectus • Rotates eye medially Lateral rectus (cut) Inferior rectus Inferior oblique 51 Extrinsic Eye Muscles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Lateral rectus • Rotates eye laterally Medial Superior rectus rectus Superior oblique • Superior oblique • Rotates eye down and laterally • Inferior oblique • Rotates eye up and laterally Lateral rectus (cut) Inferior rectus Inferior oblique 52 Structure of the Eye The eye has three distinct layers “tunics” 1. Fibrous tunic 2. Vascular tunic 3. Nervous tunic Outer Tunic • Cornea • Anterior 1/6th of eye • “window of the eye” • Transparent • Light transmission • Sclera • Posterior portion • Opaque • Protection Middle Tunic • Choroid coat • Provides blood supply • Pigments absorb extra light • Iris “rainbow” • Anterior portion • Pigmented • Controls light intensity • Ciliary body • Anterior portion • Pigmented • Suspensory ligaments holds lens • Ciliary muscles moves lens for focusing Anterior Portion of Eye • Filled with aqueous humor Lens • The lens is an elastic, biconvex, and transparent structure largely composed of epithelial cells, called lens fibers. •The lens lies behind the iris and is held in place by suspensory ligaments of ciliary body 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 58 (b) 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 Anterior chamber Iris Scleral venous sinus (canal of Schlemm) Lens Sclera Ciliary process Ciliary body Ciliary muscles Vitreous humor Posterior chamber 59 Ciliary Body • Forms internal ring around the front of the eye • Ciliary processes – radiating folds • Ciliary muscles – contract and relax to move lens Figure 12.28 Lens and ciliary body viewed from behind. 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 Inner Tunic • Retina • Contains visual receptors • Continuous with optic nerve • Fovea centralis – center of macula lutea; produces sharpest vision •Macula lutea – yellowish spot in retina • Optic disc – blind spot; contains no visual receptors • Vitreous humor – thick gel that holds retina flat against choroid coat 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 Retina Ciliary body Suspensory ligaments 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 63 Layers of the Eye 64 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 65 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) 66 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 67 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 Figure 12. Notice that photoreceptors (rods and cones) are the posterior most cells in this circuit. Light waves stimulate the photoreceptors, which send impulses forward to horizontal cells and ganglion cells before leaving the eye through the optic disc. Visual Receptors • Rods • Long, thin projections • Contain light sensitive pigment called rhodopsin • Hundred times more sensitive to light than cones • Provide vision in dim light • Produce outlines of objects • Cones • Short, blunt projections • Provide vision in bright light • Produce sharp images • Produce color vision • Pigments include: • Erythrolabe – responds to red • Chlorolabe – responds to green • Cyanolabe – responds to blue Color perceived depends on which sets of cones are stimulated Figure 12.38 Rods and cones. (a) Several rods converge onto a single sensory nerve fiber to the brain (b) separate sensory nerve fibers transmits impulses from the cones to the brain. (c) Scanning electron micrograph of rods and cones. 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 Point of focus Uncorrected point of focus Cornea Light waves 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 71 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 72 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 73 Visual Nerve Pathways Axons from ganglion cells in retina leave the eyes to form the optic nerves. Some of the fibers decussate at the optic chiasm. • Fibers from the nasal (medial) half of retina cross over • Fibers from temporal half (lateral) of retina do not cross over Most fibers of the optic tract continue to the lateral geniculate nucleus of the thalamus, which relays impulses towards the visual cortex. Figure 12.41 The visual pathway includes the optic nerve, optic chiasma, optic tract, and optic radiations. End of Chapter 12