Copyright 2010, John Wiley & Sons, Inc. Chapter 12 Somatic Senses and Special Senses

Copyright 2010, John Wiley & Sons, Inc. Special Senses Smell (olfaction) Taste (gustation) Vision Balance Hearing

Copyright 2010, John Wiley & Sons, Inc. General Senses: Somatic and Visceral Somatic  Tactile: touch, pressure, vibration  Thermal (warm, cold)  Pain  Proprioception (joint, muscle position sense; movements of limbs, head) Visceral: internal organ conditions

Copyright 2010, John Wiley & Sons, Inc. Definition of Sensation Conscious or subconscious awareness of change in external or internal environment Requires 1.Stimulus 2.Sensory receptor 3.Neural pathway 4.Brain region for integration

Copyright 2010, John Wiley & Sons, Inc. Characteristics Perception: conscious awareness  Occurs in cerebral cortex Adaptation: decreased receptor response during prolonged stimulation  Decreased perception  Adaptation speed varies with receptor Rapid adaptation: pressure, touch, smell Slow adaptation: pain, body position, chemical levels in blood

Copyright 2010, John Wiley & Sons, Inc. Sensory Receptors: Structural Types Free nerve endings  Pain, thermal, tickle, itch, some touch receptors Encapsulated nerve endings  Touch pressure, and vibration Separate, specialized cells  Hair cells in inner ear  Photoreceptors in retina of eye

Copyright 2010, John Wiley & Sons, Inc. Sensory Receptors: Functional Types Mechanoreceptors  Cell deformation: stretching or bending  Touch, pressure, vibration Thermoreceptors: temperature Nociceptors: pain Photoreceptors: light Chemoreceptors: taste, smell Osmoreceptors  Osmotic pressure of body fluid

Copyright 2010, John Wiley & Sons, Inc. Somatic Senses Somatic receptors in skin, mucous membranes, muscles, tendons, and joints Distributed unevenly: dense concentration of receptors in very sensitive areas  Fingertips, lips, tip of tongue Include tactile, thermal, pain, proprioceptive

Copyright 2010, John Wiley & Sons, Inc. Tactile Sensations Touch, pressure, vibration  Encapsulated mechanoreceptors Itch and tickle  Free nerve endings

Copyright 2010, John Wiley & Sons, Inc. Touch Rapidly adapting receptors for touch  Meissner corpuscles  Hair root plexuses: detect hair movement Slowly adapting receptors for touch  Type I mechanoreceptors: Merkel discs or tactile discs Surface receptors: in epidermis  Type I mechanoreceptors: Ruffini corpuscles Deep in dermis and tendons

Copyright 2010, John Wiley & Sons, Inc. Pressure and Vibration Pressure  Pacinian (lamellated) corpuscles: layers like onion  Rapid adapting  Widely distributed: in dermis, subcutaneous, around joints, tendons, muscles, periosteum Vibration  Response to rapidly repetitive stimuli  Receptors: Meissner and pacinian

Copyright 2010, John Wiley & Sons, Inc. Structure and Location of Sensory Receptors

Copyright 2010, John Wiley & Sons, Inc. Itch and Tickle Itch: chemical stimulation of free nerve endings  Bradykinin from inflammation response Tickle: from free nerve endings and pacinian corpuscles  Tickle requires stimulus from outside of self  Effects of attempts to tickle oneself are blocked by signals to/from cerebellum

Copyright 2010, John Wiley & Sons, Inc. Thermal Sensations Two kinds of thermoreceptors  Cold receptors: 10˚– 40˚ C (50 – 105˚ F) Located in epidermis  Warm receptors: 32˚– 48˚ C (90 – 118˚ F) Located in dermis Both adapt rapidly but continue slow signals during prolonged stimulus Outside these ranges: nociceptors detect pain

Copyright 2010, John Wiley & Sons, Inc. Pain Sensations Nociceptors  Free nerve endings in every tissue except brain  Can respond to any excessive stimulus  Minimal adaptation Types of pain  Fast pain: acute, sharp pain Well localized  Slow pain: chronic, burning, aching, throbbing More diffuse (not localized) Referred pain is visceral pain displaced to surface

Copyright 2010, John Wiley & Sons, Inc. Distribution of Referred Pain

Copyright 2010, John Wiley & Sons, Inc. Proprioception (Kinesthesia) Awareness of  Body position, movements, weight of objects Sites of receptors  Muscles (muscle spindles)  Tendons (tendon organs)  Joint kinesthetic receptors (synovial joints)  Inner ear (hair cells): head position Tracts to  Somatosensory area of cerebral cortex and  Cerebellum Slight adaptation

Copyright 2010, John Wiley & Sons, Inc. Functional Areas of the Cerebrum

Copyright 2010, John Wiley & Sons, Inc. Special Senses Smell (olfaction) Taste (gustation) Vision Balance Hearing

Copyright 2010, John Wiley & Sons, Inc. Smell: Olfaction Site of olfactory receptors  In mucosa of superior region of nose Three types of olfactory cells  Olfactory receptors Consist of olfactory hairs with chemoreceptors These are first order neurons of olfactory pathway  Supporting cells Epithelial cells: support, protect  Basal cells: stem cells that produce new neurons (receptors) throughout life. Rare!

Copyright 2010, John Wiley & Sons, Inc. Smell: Olfaction

Copyright 2010, John Wiley & Sons, Inc. Stimulation of Receptors Genetic evidence: 100’s of primary odors exist Binding of chemical odorants stimulates receptor Recognition of 10,000 odors from combination of primary receptor input Rapid adaptation by 50% in 1 second

Copyright 2010, John Wiley & Sons, Inc. Olfactory Pathway First-order neurons  Olfactory receptors are neurons in nasal mucosa  Axons form olfactory nerves (cranial nerve I) Extend through cribriform plate into cranium to olfactory bulb Second-order neurons  Neuron cell bodies in olfactory bulb  Olfactory tract: axons extend from olfactory bulb to cerebral cortex (temporal lobe) Limbic system: emotional response to odors

Copyright 2010, John Wiley & Sons, Inc. Olfactory Receptors

Copyright 2010, John Wiley & Sons, Inc. Taste: Gustation Five primary tastes: salt, sweet, sour, bitter, and umami Perception of what is called “taste” includes olfactory input Receptors in 10,000 taste buds  Located on tongue, pharynx, epiglottis  In structures called papillae Vallate (posterior) Fungiform (all over) Filiform: touch receptors only

Copyright 2010, John Wiley & Sons, Inc. Taste: Gustation

Copyright 2010, John Wiley & Sons, Inc. Taste: Gustation

Copyright 2010, John Wiley & Sons, Inc. Structure of Taste Bud Contains 3 types of epithelial cells  Supporting cells that surround  Gustatory receptor cells Gustatory hair projects from receptor through taste pore  Basal cells Stem cells that produce supporting cells that develop into receptor cells (10-day life span)

Copyright 2010, John Wiley & Sons, Inc. Taste: Gustation

Copyright 2010, John Wiley & Sons, Inc. Stimulation of Taste Receptors Sequence of events  Tastant dissolves in saliva   Enters taste pore  contacts gustatory hair   Electrical signal produced   Causes gustatory cell to release neurotransmitter  That activates dendrites of first-order neurons Adaptation occurs within minutes Different tastes arise from activation of different groups of taste neurons

Copyright 2010, John Wiley & Sons, Inc. Gustatory Pathway Cranial nerves transmit impulses  Facial (CN VII) from anterior of tongue  Glossopharyngeal (CN IX) from posterior  Vagus (CN X) from pharynx, epiglottis To medulla oblongata   Thalamus  primary gustatory area of cerebral cortex   Limbic system or hypothalamus

Copyright 2010, John Wiley & Sons, Inc. Vision: Eyes Accessory structures  Eyebrows, eyelashes: protection  Eyelids: protection and lubrication (blinking)  Extrinsic muscles: move eyeball Superior rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, inferior oblique  Lacrimal apparatus: produces tears Lacrimal glands  lacrimal ducts  surface of upper eyelid  surface of eye  Lacrimal canals  lacrimal sac  nasolacrimal duct  nasal cavity

Copyright 2010, John Wiley & Sons, Inc. Vision: Eyes

Copyright 2010, John Wiley & Sons, Inc. Layers of Eyeball First layer: Fibrous tunic  Anteriorly: cornea (clear, colorless)  Posteriorly: sclera (“white of eye”) Second layer: Vascular tunic consists of  Choroid: lines most of internal surface of eye Contains blood vessels that nourish the eye  Ciliary body consists of Ciliary processes: secrete aqueous humor Ciliary muscles: changes lens shape for focusing  Iris: pigmented part of eye (blue, brown, green ) Smooth muscle that dilates or constricts pupil Pupil: hole for passage of light

Copyright 2010, John Wiley & Sons, Inc. Layers of Eyeball Third layer: Retina—composed of two layers  Neural layer: outgrowth of brain Photoreceptor layer: rods and cones Bipolar cell layer Ganglion cell layer: axons of neurons here form optic nerve (CN II) that exits eye at optic disc (“blind spot” since no rods/cones here)  Pigmented layer: helps absorb stray light Between choroid and neural layer

Copyright 2010, John Wiley & Sons, Inc. Pupil Response to Light

Copyright 2010, John Wiley & Sons, Inc. Layers of Eyeball

Copyright 2010, John Wiley & Sons, Inc. Photoreceptors: Rods and Cones Rods: black-and-white vision; 120 million Cones: color sensitive; 6 million cones  Three types: sensitive to blue, green or red light  Color vision results from combined input  Cones mostly in central fovea in center of macula lutea Point of highest visual acuity (sharpness) Visual pathway  Photoreceptor cells (rods or cones)   Bipolar layer   Ganglion cells; their axons form optic nerve

Copyright 2010, John Wiley & Sons, Inc. Photoreceptors: Rods and Cones

Copyright 2010, John Wiley & Sons, Inc. Interior of Eyeball Two cavities separated by the lens  Anterior cavity filled with aqueous humor Clear, colorless fluid secreted from capillaries in ciliary body Completely replaced every 90 min Establishes intraocular pressure, maintains eye shape; nourishes lens and cornea Drains into blood in scleral venous sinus (canal of Schlemm)  Vitreous chamber: filled with gel-like vitreous body (not replaced) Holds retina back against choroid

Copyright 2010, John Wiley & Sons, Inc. Physiology of Vision: Three Steps A.Formation of image on retina B.Stimulation of photoreceptors (rods and cones) C.Visual pathway: nerve impulses pass to cerebral cortex

Copyright 2010, John Wiley & Sons, Inc. A. Formation of Image on Retina: Four Steps 1.Refraction (bending) of light rays to focus them on retina 2.Accommodation: change of lens shape to focus for near (or far) vision 3.Constriction (narrowing) of pupil to control amount of light entering the eye 4.Convergence of eyeballs: for binocular vision

Copyright 2010, John Wiley & Sons, Inc. Step 1: Refraction of Light Definition: bending of light rays as they pass from medium of one density to another of different density 75% occurs at cornea; lens also helps focus light on retina Image is inverted but brain adjusts and interprets distance and size

Copyright 2010, John Wiley & Sons, Inc. Step 1: Refraction of Light

Copyright 2010, John Wiley & Sons, Inc. Step 1: Refraction of Light

Copyright 2010, John Wiley & Sons, Inc. Step 1: Refraction of Light

Copyright 2010, John Wiley & Sons, Inc. Step 2: Accommodation Lens adjusts shape for distance to allow image to focus on retina  For distant objects, ciliary muscle relaxes  flat lens  For closeup vision, ciliary muscle contracts  fat lens (rounder = more convex) Visual disorders  Myopia (nearsightedness): can see near but not far objects Eyeball is too long so lens cannot accommodate enough to focus images of distant objects onto retina

Copyright 2010, John Wiley & Sons, Inc. Step 2: Accommodation Visual disorders  Hyperopia (farsightedness): can see far but not near Eyeball is too short so lens cannot accommodate enough to focus images of near objects onto retina  Astigmatism: irregular curvature of cornea or lens  Presbyopia: aging change  loss of elasticity of lens  farsightedness  reading glasses  These disorders can be corrected with lenses or LASIK (laser-assisted in situ keratomileusis)

Copyright 2010, John Wiley & Sons, Inc. Step 2: Accommodation

Copyright 2010, John Wiley & Sons, Inc. Steps 3 and 4: Constriction and Convergence ■ Constriction of pupil  Autonomic (parasympathetic) reflex to prevent excessive light rays from entering eye  By contraction of circular muscles of iris ■ Convergence  Eyes rotate inward for binocular vision  By contraction of extrinsic eye muscles

Copyright 2010, John Wiley & Sons, Inc. B. Stimulation of Photoreceptors Photoreceptors: light  neural signal  In rods light is absorbed by a photopigment (rhodopsin) which splits into opsin + retinal and leads  receptor potential Vitamin A deficiency decreases rhodopsin production and leads to night blindness.  In cones light is absorbed by 3 opsins  receptor potential for color vision In colorblindness, red or green cones are missing.

Copyright 2010, John Wiley & Sons, Inc. C. Visual Pathway Rods or cones  bipolar cells  ganglion cells (their axons form optic nerve = CN II)  About 50% of these axons cross over to opposite side of brain in optic chiasm  Axons continue on into optic tract   Terminate/synapse in thalamus   Occipital lobes of cerebral cortex  Right brain sees left side of object  Left brain sees right side of object

Copyright 2010, John Wiley & Sons, Inc. Physiology of Vision: Three Steps

Copyright 2010, John Wiley & Sons, Inc. Hearing and Equilibrium: Ear Structure Outer ear: auricle, external auditory canal, and tympanic membrane (ear drum)  Canal contains hairs and ceruminous glands Middle ear: auditory tube (eustachian tube) and ossicles (bones)  Ossicles (malleus, incus, stapes: attached to oval window) Inner ear: bony labyrinth + membranous labyrinth filled with endolymph  Cochlea: sense organ of hearing,  Vestibule and semicircular canals: organs of balance

Copyright 2010, John Wiley & Sons, Inc. Hearing and Equilibrium: Ear Structure

Copyright 2010, John Wiley & Sons, Inc. Inner Ear Structure: Three Regions Vestibule includes  Two sacs: utricle and saccule Semicircular canals: at right angles  Contain membranous semicircular ducts  Each ends in a swelling known as ampulla Cochlea: 3 levels  Cochlear duct: membranous, has endolymph Contains spiral organ (sensory organ for hearing)  Above: scala vestibuli: ends at oval window  Below: scala tympani: ends at round window

Copyright 2010, John Wiley & Sons, Inc. Spiral Organ Sits on basilar membrane  Floor of cochlear duct Contains supporting cells + hair cells Hair cells  Covered with jellylike tectorial membrane  Are receptors for auditory sensations  Synapse with sensory neurons in cochlear branch of vestibulocochlear nerve cranial nerve VIII)

Copyright 2010, John Wiley & Sons, Inc. Inner Ear Structure

Copyright 2010, John Wiley & Sons, Inc. Inner Ear Structure

Copyright 2010, John Wiley & Sons, Inc. Physiology of Hearing Sound waves in air  auditory canal Tympanic membrane  ossicle movement  stapes strikes oval window Pressure waves in perilymph  Conveyed from scala vestibuli  scala tympani Pressure waves in endolymph cause  Hair cells bend against tectorial membrane  Neurotransmitter released to sensory neurons Pitch (wavelength): location in cochlea Volume (loudness): intensity of waves

Copyright 2010, John Wiley & Sons, Inc. Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 12 Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 12 3 Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti)

Copyright 2010, John Wiley & Sons, Inc. Auditory Pathway Cochlear neurons (in cranial nerve VIII) end in medulla  On same side: R ear  R side medulla  Midbrain  thalamus  Auditory cortex in temporal lobe  Each side of brain receives input from both ears

Copyright 2010, John Wiley & Sons, Inc. Physiology of Equilibrium Static equilibrium: senses position relative to gravity  As when head is tilted or a car is speeding up or slowing down Dynamic equilibrium: senses position in response to head movement  As in spinning movements

Copyright 2010, John Wiley & Sons, Inc. Static Equilibrium Sensed in maculae of utricle and saccule Mechanism  Gravity pulls on otoliths in otolithic membrane  Bends hair cells in otolithic membrane  Triggers nerve impulses in vestibular branch of vestibulochochlear nerve

Copyright 2010, John Wiley & Sons, Inc. Static Equilibrium

Copyright 2010, John Wiley & Sons, Inc. Static Equilibrium

Copyright 2010, John Wiley & Sons, Inc. Dynamic Equilibrium Semicircular canals (3)  At right angles to each other Cristae in each ampulla contain  Hair cells embedded in jellylike cupula  Supporting cells Mechanism  When head turns, hair cells move  Endolymph lags and bends hair cells   Nerve impulses in vestibular branch

Copyright 2010, John Wiley & Sons, Inc. Dynamic Equilibrium

Copyright 2010, John Wiley & Sons, Inc. Dynamic Equilibrium

Copyright 2010, John Wiley & Sons, Inc. Equilibrium Pathways Axons from vestibular branch  medulla or cerebellum Medulla  motor control: eye, head, neck  Spinal cord tracts for adjusting muscle tone and postural muscles

Copyright 2010, John Wiley & Sons, Inc. End of Chapter 12 Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.