mosby items and derived items © 2007, 2003 by mosby, inc.slide 1 chapter 15 sense organs

Mosby items and derived items © 2007, 2003 by Mosby, Inc.

Chapter 15Chapter 15Sense OrgansSense Organs


Sensory ReceptorsSensory Receptors Sensory receptors make it possible for the body to respond to Sensory receptors make it possible for the body to respond to

stimuli caused by changes occurring in the internal or external stimuli caused by changes occurring in the internal or external environmentenvironment

Receptor responseReceptor response General function—responds to stimuli by converting them General function—responds to stimuli by converting them

to nerve impulsesto nerve impulses

Different types of receptors respond to different stimuliDifferent types of receptors respond to different stimuli

Receptor potentialReceptor potential

• Develops when an adequate stimulus acts on a receptor; is a graded responseDevelops when an adequate stimulus acts on a receptor; is a graded response

• When a threshold is reached, an action potential in the sensory neuron’s axon is triggeredWhen a threshold is reached, an action potential in the sensory neuron’s axon is triggered

• Impulses travel over sensory pathways to the brain and spinal cord, where either they are Impulses travel over sensory pathways to the brain and spinal cord, where either they are interpreted as a particular sensation or they initiate a reflex actioninterpreted as a particular sensation or they initiate a reflex action

Adaptation—a functional characteristic of receptors; receptor potential Adaptation—a functional characteristic of receptors; receptor potential decreases over time in response to a continuous stimulus, which leads decreases over time in response to a continuous stimulus, which leads to a decreased rate of impulse conduction and a decreased intensity of to a decreased rate of impulse conduction and a decreased intensity of sensationsensation


Sensory ReceptorsSensory Receptors

Distribution of receptorsDistribution of receptors

Receptors for special senses of smell, taste, Receptors for special senses of smell, taste, vision, hearing, and equilibrium are grouped into vision, hearing, and equilibrium are grouped into localized areas or into complex organslocalized areas or into complex organs

General sense organs of somatic senses are General sense organs of somatic senses are microscopic receptors widely distributed microscopic receptors widely distributed throughout the body in skin, mucosa, connective throughout the body in skin, mucosa, connective tissue, muscles, tendons, joints, and visceratissue, muscles, tendons, joints, and viscera



Classification of receptors by the following: Classification of receptors by the following:

LocationLocation

Type of stimulus that causes responseType of stimulus that causes response


Sensory ReceptorsSensory Receptors Classification by locationClassification by location

ExteroceptorsExteroceptors• On or near body surfaceOn or near body surface

• Often called cutaneous receptors; examples are pressure, touch, pain, and Often called cutaneous receptors; examples are pressure, touch, pain, and temperaturetemperature

Visceroceptors (interoceptors)Visceroceptors (interoceptors)• Located internally—often within body organs, or visceraLocated internally—often within body organs, or viscera

• Provide the body with information about internal environment; examples are Provide the body with information about internal environment; examples are pressure, stretch, chemical changes, and hunger and thirstpressure, stretch, chemical changes, and hunger and thirst

Proprioceptors: specialized type of visceroceptorProprioceptors: specialized type of visceroceptor• Location limited to skeletal muscle, joint capsules, and tendonsLocation limited to skeletal muscle, joint capsules, and tendons

• Provide information on body movement, orientation in space, and muscle Provide information on body movement, orientation in space, and muscle stretchstretch

• Two types—tonic and phasic receptors provide positional information Two types—tonic and phasic receptors provide positional information on the body or body parts while at rest or during movementon the body or body parts while at rest or during movement



Classification by stimulus detectedClassification by stimulus detected Mechanoreceptors—activated when “deformed” to generate Mechanoreceptors—activated when “deformed” to generate

receptor potentialreceptor potential

Chemoreceptors—activated by amount or changing concentration Chemoreceptors—activated by amount or changing concentration of certain chemicals; e.g., taste and smellof certain chemicals; e.g., taste and smell

Thermoreceptors—activated by changes in temperatureThermoreceptors—activated by changes in temperature

Nociceptors—activated by intense stimuli that may damage tissue; Nociceptors—activated by intense stimuli that may damage tissue; the sensation produced is painthe sensation produced is pain

Photoreceptors—found only in the eye; respond to light stimuli if Photoreceptors—found only in the eye; respond to light stimuli if the intensity is great enough to generate a receptor potentialthe intensity is great enough to generate a receptor potential

Osmoreceptors—concentrated in the hypothalamus; activated by Osmoreceptors—concentrated in the hypothalamus; activated by changes in concentration of electrolytes (osmolarity) in changes in concentration of electrolytes (osmolarity) in extracellular fluidsextracellular fluids



Classification by structure (Figure 15-2)—divides sensory Classification by structure (Figure 15-2)—divides sensory receptors into either those with free nerve endings or those receptors into either those with free nerve endings or those with encapsulated nerve endingswith encapsulated nerve endings Free nerve endingsFree nerve endings

• Most widely distributed type of sensory receptorMost widely distributed type of sensory receptor

• Include both exteroceptors and visceroceptorsInclude both exteroceptors and visceroceptors

• Called nociceptors—are primary receptors for painCalled nociceptors—are primary receptors for pain

• Other sensations mediated include itching, tickling, touch, movement, and Other sensations mediated include itching, tickling, touch, movement, and mechanical stretchingmechanical stretching

• Primary receptors for heat and coldPrimary receptors for heat and cold

• Two types of nerve fibers carry pain impulses from nociceptors to the brain:Two types of nerve fibers carry pain impulses from nociceptors to the brain: Acute (A) fibers—mediate sharp, intense, localized painAcute (A) fibers—mediate sharp, intense, localized pain

Chronic (B) fibers—mediate less intense, but more persistent, dull or aching painChronic (B) fibers—mediate less intense, but more persistent, dull or aching pain



Classification by structure (cont.) Classification by structure (cont.)

Other free nerve ending receptorsOther free nerve ending receptors

• Root hair plexusesRoot hair plexuses

Weblike arrangements of free nerve endings around Weblike arrangements of free nerve endings around hair follicleshair follicles

• Merkel discsMerkel discs

Mediate sensations of discriminative touchMediate sensations of discriminative touch



Stretch receptors—two types; muscle spindles and Golgi tendon Stretch receptors—two types; muscle spindles and Golgi tendon receptors operate to provide body with information concerning receptors operate to provide body with information concerning muscle length and strength of muscle contractionmuscle length and strength of muscle contraction

Muscle spindle—composed of 5 to 10 intrafusal fibers lying between Muscle spindle—composed of 5 to 10 intrafusal fibers lying between and parallel to regular (extrafusal) muscle fibersand parallel to regular (extrafusal) muscle fibers

– Large diameter and rapid conducting, type Ia, and smaller diameter and Large diameter and rapid conducting, type Ia, and smaller diameter and slower conducting, type II, afferent fibers carry messages to brain slower conducting, type II, afferent fibers carry messages to brain concerning changes in muscle lengthconcerning changes in muscle length

– If length of a muscle exceeds a certain limit, a stretch reflex is initiated to If length of a muscle exceeds a certain limit, a stretch reflex is initiated to shorten the muscle, thus helping to maintain postureshorten the muscle, thus helping to maintain posture

Golgi tendon organs—located at junction between muscle tissue and Golgi tendon organs—located at junction between muscle tissue and tendon (Figure 15-2)tendon (Figure 15-2)

– Type Ib sensory neurons are stimulated by excessive contraction—when Type Ib sensory neurons are stimulated by excessive contraction—when stimulated, they cause muscle to relaxstimulated, they cause muscle to relax

– Golgi tendon reflex protects muscle from tearing internally as a result of Golgi tendon reflex protects muscle from tearing internally as a result of excessive contractile forceexcessive contractile force


Special SensesSpecial Senses

Characterized by receptors grouped closely Characterized by receptors grouped closely together or grouped in specialized organs; together or grouped in specialized organs; senses of smell, taste, hearing, equilibrium, senses of smell, taste, hearing, equilibrium, and visionand vision


Sense of SmellSense of Smell

Olfactory receptorsOlfactory receptors Olfactory sense organs consist of epithelial support Olfactory sense organs consist of epithelial support

cells and specialized olfactory receptor neurons cells and specialized olfactory receptor neurons (Figure 15-4)(Figure 15-4)

• Olfactory cilia—located on olfactory receptor neurons that touch the Olfactory cilia—located on olfactory receptor neurons that touch the olfactory epithelium lining the upper surface of nasal cavityolfactory epithelium lining the upper surface of nasal cavity

• Olfactory cells—chemoreceptors; gas molecules or chemicals Olfactory cells—chemoreceptors; gas molecules or chemicals dissolved in mucus covering the nasal epithelium stimulate dissolved in mucus covering the nasal epithelium stimulate olfactory cellsolfactory cells

• Olfactory epithelium—located in most superior portion Olfactory epithelium—located in most superior portion of nasal cavityof nasal cavity

• Olfactory receptors—extremely sensitive and easily fatiguedOlfactory receptors—extremely sensitive and easily fatigued


Sense of SmellSense of Smell

Olfactory pathway—when level of odor-Olfactory pathway—when level of odor-producing chemicals reaches a threshold producing chemicals reaches a threshold level, the following occurs (Figure 15-5):level, the following occurs (Figure 15-5):

Receptor potential, and then action potential, is Receptor potential, and then action potential, is generated and passed to the olfactory nerves in generated and passed to the olfactory nerves in the olfactory bulbthe olfactory bulb

The impulse then passes through the olfactory The impulse then passes through the olfactory tract and into the thalamic and olfactory centers of tract and into the thalamic and olfactory centers of brain for interpretation, integration, and memory brain for interpretation, integration, and memory storagestorage


Sense of TasteSense of Taste

Taste buds—sense organs that respond to gustatory, Taste buds—sense organs that respond to gustatory, or taste, stimuli; associated with papillaeor taste, stimuli; associated with papillae Chemoreceptors that are stimulated by chemicals dissolved Chemoreceptors that are stimulated by chemicals dissolved

in the salivain the saliva Gustatory cells—specialized cells in taste buds; gustatory hairs Gustatory cells—specialized cells in taste buds; gustatory hairs

extend from each gustatory cell into the taste poreextend from each gustatory cell into the taste pore Sense of taste depends on the creation of a receptor potential in Sense of taste depends on the creation of a receptor potential in

gustatory cells as a result of taste-producing chemicals in the salivagustatory cells as a result of taste-producing chemicals in the saliva Taste buds are similar structurally; functionally, each taste bud Taste buds are similar structurally; functionally, each taste bud

responds most effectively to one of four primary taste sensations: responds most effectively to one of four primary taste sensations: sour, sweet, bitter, and salty (and perhaps metallic and umami) sour, sweet, bitter, and salty (and perhaps metallic and umami) (Figure 15-6)(Figure 15-6)

Adaptation and sensitivity thresholds are different for each of the Adaptation and sensitivity thresholds are different for each of the primary taste sensationsprimary taste sensations


Sense of TasteSense of Taste

Neuronal pathway for tasteNeuronal pathway for taste Taste sensation begins with a receptor potential in gustatory Taste sensation begins with a receptor potential in gustatory

cells of a taste bud; generation and propagation of an action cells of a taste bud; generation and propagation of an action potential then transmits sensory input to the brainpotential then transmits sensory input to the brain

Nerve impulses from anterior two thirds of the tongue travel Nerve impulses from anterior two thirds of the tongue travel over the facial nerve; those from posterior one third of the over the facial nerve; those from posterior one third of the tongue travel over the glossopharyngeal nerve; vagus nerve tongue travel over the glossopharyngeal nerve; vagus nerve plays a minor role in tasteplays a minor role in taste

Nerve impulses are carried to the medulla oblongata, Nerve impulses are carried to the medulla oblongata, relayed into the thalamus, and then into the gustatory area relayed into the thalamus, and then into the gustatory area of the cerebral cortex in the parietal lobe of the brainof the cerebral cortex in the parietal lobe of the brain


Sense of Hearing and Balance: Sense of Hearing and Balance: The EarThe Ear

External ear—two divisions External ear—two divisions (Figures 15-7 and 15-8):(Figures 15-7 and 15-8):

Auricle, or pinna—visible portion of the earAuricle, or pinna—visible portion of the ear

External auditory meatus—tube leading from External auditory meatus—tube leading from auricle into the temporal bone and ending at the auricle into the temporal bone and ending at the tympanic membranetympanic membrane



Middle ear (Figure 15-8)Middle ear (Figure 15-8) Tiny, epithelium-lined cavity hollowed out of the temporal boneTiny, epithelium-lined cavity hollowed out of the temporal bone Contains three auditory ossiclesContains three auditory ossicles

• Malleus (hammer)—attached to inner surface of tympanic Malleus (hammer)—attached to inner surface of tympanic membranemembrane

• Incus (anvil)—attached to malleus and stapesIncus (anvil)—attached to malleus and stapes

• Stapes (stirrup)—attached to incusStapes (stirrup)—attached to incus

Openings into middle ear cavityOpenings into middle ear cavity

• Opening from external auditory meatus covered with tympanic Opening from external auditory meatus covered with tympanic membranemembrane

• Oval window—opening into inner ear; stapes fits hereOval window—opening into inner ear; stapes fits here

• Round window—opening into inner ear; covered by a membraneRound window—opening into inner ear; covered by a membrane

• Opening into the auditory (eustachian) tubeOpening into the auditory (eustachian) tube



Inner ear (Figure 15-9, A)Inner ear (Figure 15-9, A) Structure of the inner earStructure of the inner ear

• Bony labyrinth—made up of the vestibule, the cochlea, and Bony labyrinth—made up of the vestibule, the cochlea, and semicircular canalssemicircular canals

• Membranous labyrinth—made up of utricle and saccule inside the Membranous labyrinth—made up of utricle and saccule inside the vestibule, cochlear duct inside the cochlea, and the membranous vestibule, cochlear duct inside the cochlea, and the membranous semicircular canals inside the bony onessemicircular canals inside the bony ones

• Vestibule and semicircular canals are involved with balanceVestibule and semicircular canals are involved with balance

• Cochlea—involved with hearingCochlea—involved with hearing

• Endolymph—clear, potassium-rich fluid filling the membranous Endolymph—clear, potassium-rich fluid filling the membranous labyrinthlabyrinth

• Perilymph—similar to cerebrospinal fluid, surrounds the membranous Perilymph—similar to cerebrospinal fluid, surrounds the membranous labyrinth, filling space between the membranous tunnel and its labyrinth, filling space between the membranous tunnel and its contents and the bony walls that surround itcontents and the bony walls that surround it



Inner ear (cont.)Inner ear (cont.) Cochlea and cochlear duct (Figure 15-9, B)Cochlea and cochlear duct (Figure 15-9, B)

• Cochlea—bony labyrinthCochlea—bony labyrinth• Modiolus—cone-shaped core of the bone that houses the spiral Modiolus—cone-shaped core of the bone that houses the spiral

ganglion, which consists of cell bodies of the first sensory neurons ganglion, which consists of cell bodies of the first sensory neurons in the auditory relayin the auditory relay

• Cochlear ductCochlear duct Lies inside the cochlea; only part of the internal ear concerned with Lies inside the cochlea; only part of the internal ear concerned with

hearing; contains endolymphhearing; contains endolymph Shaped like a triangular tubeShaped like a triangular tube Divides cochlea into the scala vestibuli, the upper section, and the scala Divides cochlea into the scala vestibuli, the upper section, and the scala

tympani, the lower section; both sections filled with perilymphtympani, the lower section; both sections filled with perilymph Vestibular membrane—roof of cochlear ductVestibular membrane—roof of cochlear duct Basilar membrane—floor of cochlear ductBasilar membrane—floor of cochlear duct Organ of Corti—rests on basilar membrane; consists of supporting cells Organ of Corti—rests on basilar membrane; consists of supporting cells

and hair cellsand hair cells Axons of the neurons that begin around the organ of Corti, extend in the Axons of the neurons that begin around the organ of Corti, extend in the

cochlear nerve to the brain to produce the sensation of hearingcochlear nerve to the brain to produce the sensation of hearing



Inner ear (cont.)Inner ear (cont.) Sense of hearingSense of hearing

• Sound is created by vibrationsSound is created by vibrations

• Ability to hear sound waves depends on volume, pitch, and other Ability to hear sound waves depends on volume, pitch, and other acoustic propertiesacoustic properties

• Sound waves must be of sufficient amplitude to move the tympanic Sound waves must be of sufficient amplitude to move the tympanic membrane and have a frequency capable of stimulating the hair cells in membrane and have a frequency capable of stimulating the hair cells in the organ of Cortithe organ of Corti

• Basilar membrane is not the same width and thickness throughout its Basilar membrane is not the same width and thickness throughout its length; high-frequency sound waves vibrate the narrow portion near the length; high-frequency sound waves vibrate the narrow portion near the oval window, whereas low frequencies vibrate the wider, thicker portion oval window, whereas low frequencies vibrate the wider, thicker portion near the apex of the cochlea; this fact allows different hair cells to be near the apex of the cochlea; this fact allows different hair cells to be stimulated and different pitches of sound to be perceivedstimulated and different pitches of sound to be perceived

• Perception of loudness is determined by the amplitude of the Perception of loudness is determined by the amplitude of the movement of basilar membrane; the greater the movement, the louder movement of basilar membrane; the greater the movement, the louder the perceived soundthe perceived sound

• Hearing—results from stimulation of auditory area of cerebral cortexHearing—results from stimulation of auditory area of cerebral cortex



Sense of hearing (cont.)Sense of hearing (cont.)

• Pathway of sound waves (Figure 15-10)Pathway of sound waves (Figure 15-10)

Enter external auditory canalEnter external auditory canal

Strike tympanic membrane, causing vibrationsStrike tympanic membrane, causing vibrations

Tympanic vibrations move malleus, which in turn moves incus and Tympanic vibrations move malleus, which in turn moves incus and then stapesthen stapes

Stapes moves against oval window, which begins fluid conduction Stapes moves against oval window, which begins fluid conduction of sound wavesof sound waves

The perilymph in the scala vestibuli of cochlea begins “ripple” that The perilymph in the scala vestibuli of cochlea begins “ripple” that is transmitted through vestibular membrane to endolymph inside is transmitted through vestibular membrane to endolymph inside duct, to basilar membrane, then to organ of Cortiduct, to basilar membrane, then to organ of Corti

From basilar membrane, ripple is transmitted through perilymph in From basilar membrane, ripple is transmitted through perilymph in scala tympani and then expends itself against round windowscala tympani and then expends itself against round window



Sense of hearing (cont.)Sense of hearing (cont.)

• Neuronal pathway of hearingNeuronal pathway of hearing

A movement of the hair cells against tectorial membrane A movement of the hair cells against tectorial membrane stimulates dendrites that terminate around base of hair stimulates dendrites that terminate around base of hair cells and initiates impulse conduction by the cochlear cells and initiates impulse conduction by the cochlear nerve to the brainstemnerve to the brainstem

Impulses pass through “relay stations” in the nuclei in Impulses pass through “relay stations” in the nuclei in medulla, pons, midbrain, and thalamus before reaching medulla, pons, midbrain, and thalamus before reaching auditory area of temporal lobeauditory area of temporal lobe



Vestibule and semicircular canals (Figure 15-9, A)Vestibule and semicircular canals (Figure 15-9, A)

• Vestibule—the central section of the bony labyrinth; the utricle Vestibule—the central section of the bony labyrinth; the utricle and saccule are the membranous structures within the and saccule are the membranous structures within the vestibulevestibule

• Semicircular canals—three, each at right angles to the others, Semicircular canals—three, each at right angles to the others, are found in each temporal bone; within the bony semicircular are found in each temporal bone; within the bony semicircular canals are the membranous semicircular canals, each canals are the membranous semicircular canals, each containing endolymph and connecting with the utricle; near containing endolymph and connecting with the utricle; near this junction, each canal enlarges into an ampullathis junction, each canal enlarges into an ampulla



Vestibule and semicircular canals (cont.)Vestibule and semicircular canals (cont.)• Sense of balanceSense of balance

Static equilibrium—ability to sense the position of the head relative to Static equilibrium—ability to sense the position of the head relative to gravity or to sense acceleration or deceleration (Figure 15-11)gravity or to sense acceleration or deceleration (Figure 15-11)

– Movements of the macula, located in both the utricle and saccule almost Movements of the macula, located in both the utricle and saccule almost at right angles to each other, provide information related to head position at right angles to each other, provide information related to head position or accelerationor acceleration

– Otoliths are located within matrix of maculaOtoliths are located within matrix of macula

– Changing head position produces a change of pressure on the otolith-Changing head position produces a change of pressure on the otolith-weighted matrix, which stimulates hair cells that, in turn, stimulate weighted matrix, which stimulates hair cells that, in turn, stimulate receptors of vestibular nervereceptors of vestibular nerve

– Vestibular nerve fibers conduct impulses to the brain and produce a Vestibular nerve fibers conduct impulses to the brain and produce a sensation of the position of the head and also a sensation of a change in sensation of the position of the head and also a sensation of a change in the pull of gravitythe pull of gravity

– Righting reflexes—muscular responses to restore the body and its parts Righting reflexes—muscular responses to restore the body and its parts to their normal position when they have been displaced; caused by stimuli to their normal position when they have been displaced; caused by stimuli of macula and impulses from proprioceptors and from eyesof macula and impulses from proprioceptors and from eyes



• Sense of balance (cont.)Sense of balance (cont.)

Dynamic equilibrium—needed to maintain balance when head or Dynamic equilibrium—needed to maintain balance when head or body is rotated or suddenly moved; able to detect changes both in body is rotated or suddenly moved; able to detect changes both in direction and rate at which movement occurs (Figure 15-12)direction and rate at which movement occurs (Figure 15-12)

– Depends on functioning of cristae ampullaris, which are located in Depends on functioning of cristae ampullaris, which are located in ampulla of each semicircular canalampulla of each semicircular canal

– Cupula—gelatinous cap in which hair cells of each crista are Cupula—gelatinous cap in which hair cells of each crista are embedded; does not respond to gravity; moves with flow of embedded; does not respond to gravity; moves with flow of endolymph in semicircular canalsendolymph in semicircular canals

– Semicircular canals are placed at almost right angles to each other to Semicircular canals are placed at almost right angles to each other to detect movement in all directionsdetect movement in all directions

– When the cupula moves, hair cells are bent, producing a receptor When the cupula moves, hair cells are bent, producing a receptor potential followed by an action potential; action potential passes potential followed by an action potential; action potential passes through vestibular portion of eighth cranial nerve to medulla through vestibular portion of eighth cranial nerve to medulla oblongata, where it is sent to other areas of brain and spinal cord for oblongata, where it is sent to other areas of brain and spinal cord for interpretation, integration, and responseinterpretation, integration, and response


Vision: The Eye Vision: The Eye Structure of the eye (Figures 15-13 and 15-14)Structure of the eye (Figures 15-13 and 15-14)

Coats of the eyeball—three layers of tissues compose the eyeball:Coats of the eyeball—three layers of tissues compose the eyeball:

• Sclera—outer coatSclera—outer coat Tough, white, fibrous tissueTough, white, fibrous tissue Cornea—transparent anterior portion that lies over iris; no blood vessels found in Cornea—transparent anterior portion that lies over iris; no blood vessels found in

cornea or in lenscornea or in lens Canal of Schlemm—ring-shaped venous sinus found deep within anterior portion of Canal of Schlemm—ring-shaped venous sinus found deep within anterior portion of

the sclera at its junction with the corneathe sclera at its junction with the cornea

• Choroid—middle coatChoroid—middle coat Contains many blood vessels and a large amount of pigmentContains many blood vessels and a large amount of pigment Anterior portion has three different structures (Figure 15-14):Anterior portion has three different structures (Figure 15-14):

– Ciliary body—thickening of choroid, fits between anterior margin of retina and Ciliary body—thickening of choroid, fits between anterior margin of retina and posterior margin of iris; ciliary muscle lies in anterior part of ciliary body; posterior margin of iris; ciliary muscle lies in anterior part of ciliary body; ciliary processes—fold in ciliary bodyciliary processes—fold in ciliary body

– Suspensory ligament—attached to ciliary processes and blends with elastic Suspensory ligament—attached to ciliary processes and blends with elastic capsule of the lens, to hold it in placecapsule of the lens, to hold it in place

– Iris—colored part of eye; consists of circular and radial smooth muscle fibers Iris—colored part of eye; consists of circular and radial smooth muscle fibers that form a doughnut-shaped structure; attaches to ciliary bodythat form a doughnut-shaped structure; attaches to ciliary body


Vision: The EyeVision: The Eye

Coats of the eyeball (cont.)Coats of the eyeball (cont.)

• Retina—incomplete innermost coat of eyeballRetina—incomplete innermost coat of eyeball

Three layers of neurons make up the sensory retina (Figure 15-16):Three layers of neurons make up the sensory retina (Figure 15-16):

– Photoreceptor neurons—visual receptors, highly specialized for Photoreceptor neurons—visual receptors, highly specialized for stimulation by light raysstimulation by light rays

– Rods—absent from fovea and macula; increased in density toward Rods—absent from fovea and macula; increased in density toward periphery of retinaperiphery of retina

– Cones—less numerous than rods; most densely concentrated in fovea Cones—less numerous than rods; most densely concentrated in fovea centralis in macula luteacentralis in macula lutea

– Bipolar neuronsBipolar neurons

– Ganglionic neurons—all axons of these neurons extend back to the Ganglionic neurons—all axons of these neurons extend back to the optic disc; part of sclera, which contains perforations through which the optic disc; part of sclera, which contains perforations through which the fibers emerge from the eyeball as the optic nervefibers emerge from the eyeball as the optic nerve



Cavities and humorsCavities and humors

• Cavities—eyeball has a large interior space divided into Cavities—eyeball has a large interior space divided into two cavities:two cavities:

Anterior cavity—lies in front of lens; has two subdivisionsAnterior cavity—lies in front of lens; has two subdivisions

– Anterior chamber—space anterior to iris and posterior to corneaAnterior chamber—space anterior to iris and posterior to cornea

– Posterior chamber—small space posterior to iris and anterior to lensPosterior chamber—small space posterior to iris and anterior to lens

Posterior cavity—larger than anterior cavity; occupies all the Posterior cavity—larger than anterior cavity; occupies all the space posterior to lens, suspensory ligament, and ciliary bodyspace posterior to lens, suspensory ligament, and ciliary body



Cavities and humors (cont.)Cavities and humors (cont.)

• HumorsHumors

Aqueous humor—fills both chambers of anterior cavity; Aqueous humor—fills both chambers of anterior cavity; clear, watery fluid that often leaks out when eye is injured; clear, watery fluid that often leaks out when eye is injured; formed from blood in capillaries located in ciliary body formed from blood in capillaries located in ciliary body (Figure 15-17)(Figure 15-17)

Vitreous humor—fills posterior cavity; semisolid material; Vitreous humor—fills posterior cavity; semisolid material; helps to maintain sufficient intraocular pressure, with helps to maintain sufficient intraocular pressure, with aqueous humor, to give the eyeball its shapeaqueous humor, to give the eyeball its shape



Muscles—two types of eye muscles:Muscles—two types of eye muscles:

• Extrinsic eye muscles (Figure 15-18)—skeletal muscles that Extrinsic eye muscles (Figure 15-18)—skeletal muscles that attach to the outside of the eyeball and to the bones of the orbit; attach to the outside of the eyeball and to the bones of the orbit; named according to their position on eyeball; the muscles are named according to their position on eyeball; the muscles are superior, inferior, medial, and lateral rectus muscles and superior superior, inferior, medial, and lateral rectus muscles and superior and inferior oblique musclesand inferior oblique muscles

• Intrinsic eye muscles—smooth muscles located within the eye: irisIntrinsic eye muscles—smooth muscles located within the eye: iris—regulates size of pupil; ciliary muscle—controls shape of lens—regulates size of pupil; ciliary muscle—controls shape of lens



Accessory structures (Figure 15-19)Accessory structures (Figure 15-19)

• Eyebrows and eyelashes—give some protection against foreign Eyebrows and eyelashes—give some protection against foreign objects entering eye; cosmetic purposesobjects entering eye; cosmetic purposes

• Eyelids—consist of voluntary muscle and skin with a tarsal plate; lined Eyelids—consist of voluntary muscle and skin with a tarsal plate; lined with conjunctiva, a mucous membrane; palpebral fissure—opening with conjunctiva, a mucous membrane; palpebral fissure—opening between the eyelids; canthus—where upper and lower eyelids joinbetween the eyelids; canthus—where upper and lower eyelids join

• Lacrimal apparatus—structures that secrete tears and drain them from Lacrimal apparatus—structures that secrete tears and drain them from surface of eyeball (Figure 15-21)surface of eyeball (Figure 15-21)

Lacrimal glands—size and shape of a small almond; located at upper, Lacrimal glands—size and shape of a small almond; located at upper, outer margin of each orbit; approximately a dozen small ducts lead from outer margin of each orbit; approximately a dozen small ducts lead from each gland; drain tears onto conjunctivaeach gland; drain tears onto conjunctiva

Lacrimal canals—small channels that empty into lacrimal sacsLacrimal canals—small channels that empty into lacrimal sacs

Lacrimal sacs—located in a groove in lacrimal boneLacrimal sacs—located in a groove in lacrimal bone

Nasolacrimal ducts—small tubes that extend from lacrimal sac into Nasolacrimal ducts—small tubes that extend from lacrimal sac into inferior meatus of noseinferior meatus of nose


Vision: The EyeVision: The Eye The process of seeingThe process of seeing

Formation of retinal imageFormation of retinal image

• Refraction of light rays—deflection, or bending, of light rays produced by Refraction of light rays—deflection, or bending, of light rays produced by light rays passing obliquely from one transparent medium into another light rays passing obliquely from one transparent medium into another of different optical density; cornea, aqueous humor, lens, and vitreous of different optical density; cornea, aqueous humor, lens, and vitreous humor are the refracting media of the eyehumor are the refracting media of the eye

• Accommodation of the lens—increase in curvature of lens to achieve Accommodation of the lens—increase in curvature of lens to achieve the greater refraction needed for near vision (Figure 15-22)the greater refraction needed for near vision (Figure 15-22)

• Constriction of the pupil—muscles of iris are important to formation of a Constriction of the pupil—muscles of iris are important to formation of a clear retinal image; pupil constriction prevents divergent rays from clear retinal image; pupil constriction prevents divergent rays from object from entering eye through periphery of the cornea and lens; near object from entering eye through periphery of the cornea and lens; near reflex—constriction of pupil that occurs with accommodation of lens in reflex—constriction of pupil that occurs with accommodation of lens in near vision; photopupil reflex—pupil constricts in bright lightnear vision; photopupil reflex—pupil constricts in bright light

• Convergence of the eyes—movement of the two eyeballs inward so that Convergence of the eyes—movement of the two eyeballs inward so that their visual axes come together at the object viewed; the closer the their visual axes come together at the object viewed; the closer the object, the greater the degree of convergence necessary to maintain object, the greater the degree of convergence necessary to maintain single vision; for convergence to occur, a functional balance between single vision; for convergence to occur, a functional balance between antagonistic extrinsic muscles must existantagonistic extrinsic muscles must exist



The process of seeing (cont.)The process of seeing (cont.) Role of photopigments—light-sensitive pigmented Role of photopigments—light-sensitive pigmented

compounds undergo structural changes that result in compounds undergo structural changes that result in generation of nerve impulses, which are interpreted by generation of nerve impulses, which are interpreted by the brain as sightthe brain as sight

• Rods—photopigment in rods is rhodopsin; highly light-sensitive; Rods—photopigment in rods is rhodopsin; highly light-sensitive; breaks down into opsin and retinal; separation of opsin and breaks down into opsin and retinal; separation of opsin and retinal in the presence of light causes an action potential in rod retinal in the presence of light causes an action potential in rod cells; energy is needed to reform rhodopsin (Figure 15-24)cells; energy is needed to reform rhodopsin (Figure 15-24)

• Cones—three types of cones are present in retina, with each Cones—three types of cones are present in retina, with each having a different photopigment; cone pigments are less light-having a different photopigment; cone pigments are less light-sensitive than rhodopsin and need brighter light to break downsensitive than rhodopsin and need brighter light to break down



The process of seeing (cont.)The process of seeing (cont.)

Neuronal pathway of vision (Figure 15-25)Neuronal pathway of vision (Figure 15-25)

• Fibers that conduct impulses from rods and cones reach the Fibers that conduct impulses from rods and cones reach the visual cortex in occipital lobes via optic nerves, optic chiasma, visual cortex in occipital lobes via optic nerves, optic chiasma, optic tracts, and optic radiationsoptic tracts, and optic radiations

• Optic nerve contains fibers from only one retina, but optic Optic nerve contains fibers from only one retina, but optic chiasma contains fibers from the nasal portion of both retinas; chiasma contains fibers from the nasal portion of both retinas; these anatomical facts explain peculiar visual abnormalities these anatomical facts explain peculiar visual abnormalities that sometimes occurthat sometimes occur


Cycle of Life: Sense OrgansCycle of Life: Sense Organs

Sensory information is acquired through Sensory information is acquired through depolarization of sensory nerve endingsdepolarization of sensory nerve endings

Age, disease, structural defects, or lack of Age, disease, structural defects, or lack of maturation affect ability to identify and respondmaturation affect ability to identify and respond

Structure and function response capabilities Structure and function response capabilities are related to developmental factors are related to developmental factors associated with ageassociated with age


Cycle of Life: Sense OrgansCycle of Life: Sense Organs

Senses become more acute with maturationSenses become more acute with maturation

Late adulthood—loss of sensory capabilityLate adulthood—loss of sensory capability

Structural change in receptor cells or other sense Structural change in receptor cells or other sense organ structuresorgan structures

mosby items and derived items © 2007, 2003 by mosby, inc.slide 1 chapter 15 sense organs

Documents