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Download Olfactory Receptors
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PowerPoint Lecture Outlines to accompany Hole’s Human Anatomy and Physiology Eleventh Edition Shier w Butler w Lewis Chapter 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Chapter 12 Nervous System III - Senses General Senses • receptors that are widely distributed throughout the body • skin, various organs and joints Special Senses • specialized receptors confied to structures in the head • eyes and ears 2 Senses 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 SENSORY RECEPTION • Sensory receptors convert stimulus energy to action potentials – Sensory receptors • Are specialized cells or neurons that detect stimuli 4 – Sensory transduction converts stimulus energy into receptor potentials • Which trigger action potentials that are transmitted to the brain Sugar molecule Taste pore Tongue Taste bud 1 Sugar molecule (stimulus) Membrane of sensory receptor cell 2 Sensory receptor cells Signal transduction pathway Ion channels Sensory receptor cell 3 Ion Sensory neuron Receptor potential 4 Neurotransmitter Sensory neuron mV Action potential No sugar Figure 29.2A 5 Action potentials Sugar present 5 – Action potential frequency • Reflects stimulus strength Sugar receptor “Sugar” interneuron “Salt” interneuron Salt receptor Brain Sensory neurons Taste bud No sugar Figure 29.2B Taste bud No salt Increasing sweetness Increasing saltiness 6 • Mechanoreceptors – Mechanoreceptors • Respond to mechanical energy such as touch, pressure, and sound “Hairs” of receptor cell Neurotransmitter at synapse More neurotransmitter Less neurotransmitter Sensory neuron Action potentials Action potentials 1 Receptor cell at rest Figure 29.3B 2 Fluid moving in one direction 3 Fluid moving in other direction 7 – Repeated stimulus • May lead to adaptation, a decrease in sensitivity 8 • Specialized sensory receptors detect five categories of stimuli – A section of human skin • Reveals many types of sensory receptors Light Heat touch Pain Cold Hair Light touch Epidermis Dermis Figure 29.3A Hair Nerve Connective movement tissue Strong pressure 9 Pathways From Sensation to Perception (Example of an Apple) 10 Receptor Types Chemoreceptors • respond to changes in chemical concentrations Pain receptors (Nociceptors) • respond to tissue damage Thermoreceptors • respond to changes in temperature Mechanoreceptors • respond to mechanical forces Photoreceptors • respond to light 11 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 12 Sensations Projection process in which the brain projects the sensation back to the apparent source it allows a person to pinpoint the region of stimulation 13 Sensory Adaptation • ability to ignore unimportant stimuli • involves a decreased response to a particular stimulus from the receptors (peripheral adaptations) 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 14 General Senses • senses associated with skin, muscles, joints, and viscera • three groups • exteroceptive senses – senses associated with body surface; touch, pressure, temperature, pain • visceroceptive senses – senses associated with changes in viscera; blood pressure stretching blood vessels, ingesting a meal • proprioceptive senses – senses associated with changes in muscles and tendons 15 Touch and Pressure Senses Free nerve endings • common in epithelial tissues • simplest receptors • sense itching Meissner’s corpuscles • abundant in hairless portions of skin; lips • detect fine touch; distinguish between two points on the skin Pacinian corpuscles • common in deeper subcutaneous tissues, tendons, and ligaments • detect heavy pressure and vibrations 16 Touch and Pressure Receptors 17 Temperature Senses Warm receptors • sensitive to temperatures above 25oC (77o F) • unresponsive to temperature above 45oC (113oF) Cold receptors • sensitive to temperature between 10oC (50oF) and 20oC (68oF) Pain receptors • respond to temperatures below 10oC • respond to temperatures above 45oC 18 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 19 Visceral Pain • pain receptors are the only receptors in viscera whose stimulation produces sensations • pain receptors respond differently to stimulation • not well localized • may feel as if coming from some other part of the body • known as referred pain 20 Referred Pain • may occur due to sensory impulses from two regions following a common nerve pathway to brain 21 Pain Nerve Pathways Acute pain fibers • A-delta fibers •thin, myelinated • conduct impulses rapidly • associated with sharp pain • well localized Chronic pain fibers • C fibers •thin, unmyelinated • conduct impulses more slowly • associated with dull, aching pain • difficult to pinpoint 22 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 23 Proprioceptors • mechanoreceptors • send information to spinal cord and CNS about body position and length and tension of muscles • Main kinds of proprioreceptors • Pacinian corpuscles – in joints • muscle spindles – in skeletal muscles* • Golgi tendon organs – in tendons* *stretch receptors 24 Stretch Receptors 25 Summary of Receptors of the General Senses 26 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 27 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 28 Olfactory Receptors 29 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) 30 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 31 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 32 Taste Receptors 33 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 34 Taste Nerve Pathways Sensory impulses from taste receptors travel along • cranial nerves to • medulla oblongata to • thalamus to • gustatory cortex (for interpretation) 35 Hearing Ear – organ of hearing Three Sections • External • Middle • Inner 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 37 Middle Ear • tympanic cavity • air-filled space in temporal bone • auditory ossicles • vibrate in response to tympanic membrane • malleus, incus, and stapes • oval window • opening in wall of tympanic cavity • stapes vibrates against it to move fluids in inner ear 38 Auditory Tube • eustachian tube • connects middle ear to throat • helps maintain equal pressure on both sides of tympanic membrane • usually closed by valve-like flaps in throat 39 Inner Ear • complex system of labyrinths • osseous labyrinth • bony canal in temporal bone • filled with perilymph • membranous labyrinth • tube within osseous labyrinth • filled with endolymph 40 Inner Ear Three Parts of Labyrinths • cochlea • functions in hearing • semicircular canals • functions in equilibrium • vestibule • functions in equilibrium 41 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 42 Cochlea Cochlear duct • portion of membranous labyrinth in cochlea Vestibular membrane • separates cochlear duct from scala vestibuli Basilar membrane • separates cochlear duct from scala tympani 43 Organ of Corti • 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 44 Organ of Corti 45 Auditory Nerve Pathways 46 Summary of the Generation of Sensory Impulses from the Ear 47 Equilibrium Static Equilibrium • vestibule • sense position of head when body is not moving Dynamic Equilibrium • semicircular canals • sense rotation and movement of head and body 48 Vestibule • Utricle • communicates with saccule and membranous portion of semicircular canals • Saccule • communicates with cochlear duct • Mucula • hair cells of utricle and saccule 49 Macula • responds to changes in head position • bending of hairs results in generation of nerve impulse 50 Semicircular Canals • three canals at right angles • ampulla • swelling of membranous labyrinth that communicates with the vestibule • crista ampullaris • sensory organ of ampulla • hair cells and supporting cells • rapid turns of head or body stimulate hair cells 51 Crista Ampullaris 52 Sight Visual Accessory Organs • eyelids • lacrimal apparatus • extrinsic eye muscles 53 Eyelid • palpebra • composed of four layers • skin • muscle • connective tissue • conjunctiva • orbicularis oculi - closes • levator palperbrae superioris – opens • tarsal glands – secrete oil onto eyelashes • conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball 54 Lacrimal Apparatus • lacrimal gland • lateral to eye • secretes tears • canaliculi • collect tears • lacrimal sac • collects from canaliculi • nasolacrimal duct • collects from lacrimal sac • empties tears into nasal cavity 55 Extrinsic Eye Muscles Superior rectus • rotates eye up and medially Inferior rectus • rotates eye down and medially Medial rectus • rotates eye medially 56 Extrinsic Eye Muscles Lateral rectus • rotates eye laterally Superior oblique • rotates eye down and laterally Inferior oblique • rotates eye up and laterally 57 58 Structure of the Eye • hollow • spherical • wall has 3 layers • outer fibrous tunic • middle vascular tunic • inner nervous tunic 59 Outer Tunic Cornea • anterior portion • transparent • light transmission • light refraction Sclera • posterior portion • opaque • protection 60 Middle Tunic Iris • anterior portion • pigmented • controls light intensity Ciliary body • anterior portion • pigmented • holds lens • moves lens for focusing Choroid coat • provides blood supply • pigments absorb extra light 61 62 Anterior Portion of Eye • filled with aqueous humor 63 Lens • transparent • biconvex • lies behind iris • largely composed of lens fibers • elastic • held in place by suspensory ligaments of ciliary body 64 Ciliary Body • forms internal ring around front of eye • ciliary processes – radiating folds • ciliary muscles – contract and relax to move lens 65 Accommodation • changing of lens shape to view objects 66 • To focus, a lens changes position or shape – Focusing • Involves changing the shape of the lens Choroid Ciliary muscle contracted Ligaments slacken Retina Light from a near object (diverging rays) Lens Near vision (accommodation) Ciliary muscle relaxed Ligaments pull on lens Light from a distant object (parallel rays) Figure 29.6 Distance vision 67 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 68 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 69 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 70 Posterior Cavity • contains vitreous humor – thick gel that holds retina flat against choroid coat 71 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 72 Layers of the Eye 73 Light Refraction Refraction • bending of light • occurs when light waves pass at an oblique angle into mediums of different densities 74 Types of Lenses Convex lenses cause light waves to converge Concave lenses cause light waves to diverge 75 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 76 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 colorless vision • produce outlines of objects Cones • short, blunt projections • contain light sensitive pigments called erythrolabe, chlorolabe, and cyanolabe • provide vision in bright light • produce sharp images • produce color vision 77 Rods and Cones 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 80 Stereoscopic Vision • provides perception of distance and depth • results from formation of two slightly different retinal images 81 Visual Nerve Pathway 82 Life-Span 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 Clinical Application Refraction Disorders • concave lens corrects nearsightedness • convex lens corrects farsightedness 84
