Chapter 12
The Senses
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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
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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
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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
• Projection• Process in which the brain projects the sensation back to the apparent source• It allows a person to pinpoint the region of stimulation
Sensations and Perception
• 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
Sensory Adaptation
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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
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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
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Touch and Pressure Receptors
Epidermis
Dermis
(a)
(b)
(c)
Section ofskin
Free nerveendings
Epithelialcells
Sensorynerve fiber
Epithelialcells
Tactile (Meissner’s) corpuscle(touch receptor)
Sensory nervefiber
Lamellated(Pacinian) corpuscle(pressure receptor)
Connective tissuecells
Sensory nervefiber
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b, c: © Ed Reschke
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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
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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
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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…
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Referred Pain• May occur due to sensory impulses from two regions following a common nerve pathway to brain
Appendix
Ureter
Lung and diaphragm
Heart
Stomach
Pancreas
Colon
Kidney
Urinary bladder
Liver andgallbladder
Smallintestine
Ovary(female)
Liver andgallbladder
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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
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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
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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
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Stretch Receptors
(a)
Muscle spindleSkeletal muscle fiber
Golgi tendon organ
Tendon
(b)
Sensorynerve fiber
Sensorynerve endings
Sensorynerve fiber
Connectivetissue sheath
Intrafusalfiber
Skeletal musclefiber
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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
Summary of Receptors of the General Senses
End of Section 1, chapter 12
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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
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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
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.
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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.
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Olfactory Stimulation
• Olfactory code• Hypothesis • Odor that is stimulated by a distinct set of receptor cells and its associated receptor proteins
• 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
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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
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Taste Receptors
Papillae
(a)
(b)
Connectivetissue
Sensorynerve fibers
Epitheliumof tongue
Supportingcell
Tastepore
Taste hair
Taste cell
Taste buds
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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
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Taste Nerve Pathways
• Sensory impulses from taste receptors travel along:• Cranial nerves to… • Medulla oblongata to…• Thalamus to… • Gustatory cortex (for interpretation)
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Sense of Hearing
• Ear• Organ of hearing
• Three (3) sections:• External ear• Middle ear• Inner ear
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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
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Round window
PharynxAuditory tube
Auricle
Oval window (under stapes)
Cochlea
Malleus
Incus Stapes
External acousticmeatus
Semicircularcanals
Vestibulocochlearnerve
Tympanic cavity
Tympanicmembrane
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Middle EarCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Round window
PharynxAuditory tube
Auricle
Oval window (under stapes)
Cochlea
Malleus
Incus Stapes
External acousticmeatus
Semicircularcanals
Vestibulocochlearnerve
Tympanic cavity
Tympanicmembrane
• Tympanic cavity• Air-filled space intemporal 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
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Auditory Tube
• Also known as the 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
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Round window
PharynxAuditory tube
Auricle
Oval window (under stapes)
Cochlea
Malleus
Incus Stapes
External acousticmeatus
Semicircularcanals
Vestibulocochlearnerve
Tympanic cavity
Tympanicmembrane
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
Cochlear nerve
Maculae
Utricle
(a)
Cochlea
Saccule
Ampullae
Endolymph
Perilymph
Membranous labyrinth
Bony labyrinth
Vestibular nerve
Scalavestibuli (cut)
Scalatympani (cut)
Cochlearduct (cut)containingendolymph
VestibuleOvalwindow
Roundwindow
Semicircularcanals
Bony labyrinth(contains perilymph)
Membranous labyrinth(contains endolymph)
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Inner Ear
• Three (3) parts of labyrinths:• Cochlea
• Functions in hearing• Semicircular canals
• Functions in equilibrium
• Vestibule• Functions in equilibrium
Cochlear nerve
Maculae
Utricle
(a)
Cochlea
Saccule
Ampullae
Endolymph
Perilymph
Membranous labyrinth
Bony labyrinth
Vestibular nerve
Scalavestibuli (cut)
Scalatympani (cut)
Cochlearduct (cut)containingendolymph
VestibuleOvalwindow
Roundwindow
Semicircularcanals
Bony labyrinth(contains perilymph)
Membranous labyrinth(contains endolymph)
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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
Stapes vibrating inoval window
Scala vestibulifilled with perilymph
Vestibularmembrane
Basilarmembrane
Scala tympanifilled withperilymph
Round window
Helicotrema
Membranouslabyrinth
Cochlear ductfilled with endolymph
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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
Spiral organ (organ of Corti)
Basilar membrane
(a)
Scala vestibuli(contains perilymph)Vestibular membrane
Cochlear duct(contains endolymph)
Scala tympani(contains perilymph)
Branch ofcochlearnerve
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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
Spiral organ (organ of Corti)
Hair cells
Basilar membrane
(a)
(b)
Scala vestibuli(contains perilymph)
Cochlear duct(contains endolymph)
Scala tympani(contains perilymph)
Branch ofcochlearnerve
Tectorialmembrane
Basilarmembrane
Supportingcells
Nervefibers
Branch ofcochlear nerve
Vestibular membrane
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Organ of Corti
Cochlear duct
Scala tympani Hair cells
(a)
(b)
Basilarmembrane
Tectorial membrane
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a: © John D. Cunningham/Visuals Unlimited; b: © Fred Hossler/Visuals Unlimited
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Auditory Nerve Pathways
Midbrain
Pons
Thalamus
Auditory cortex(temporal lobe)
Medial geniculatebody of thalamus
Superiorolivarynucleus
Medullaoblongata
Vestibulocochlearnerve
Cochlearnuclei
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Summary of the Generation of Sensory Impulses from the Ear
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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
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Vestibule
• Utricle• Communicates with saccule and membranous portion of semicircular canals
• Saccule• Communicates with cochlear duct
• Macula• Hair cells of utricle and saccule
Saccule
UtricleCochlea
Maculae
Ampullae ofsemicircularcanals
Vestibulocochlearnerve
Cochlearduct
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Vestibule
Macula
• Responds to changes in head position• Bending of hairs results in generation of nerve impulse
Hair cells
Sensory nerve fiber Supporting cells
Otoliths
(a) Head upright (b) Head bent forward
Maculaof utricle
Hairs ofhair cells bend
Gelatinousmaterial sags
Gravitationalforce
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Semicircular Canals
• Three (3) 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
Saccule
Utricle Cochlea
Maculae
Ampullae ofsemicircularcanals
Vestibulocochlearnerve
Cochlearduct
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Vestibule
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Crista Ampullaris
Hair cell
Supporting cells
Sensory nerve fibers
Hairs
Cupula Cristaampullaris
(a) Head in still position
(b) Head rotating
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(c)
Crista ampullaris
Semicircular canal
Endolymph
Ampulla
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End of section 2, chapter 12
section 3, chapter 12
vision
ivyanatomy.com
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Sense of Sight
• Visual accessory organs• Eyelids• Lacrimal apparatus• Extrinsic eye muscles
Eyelid• 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
Eyelash
Cornea
Conjunctiva
Eyelid
Tendon of levatorpalpebrae superioris
Superiorrectus
Orbicularisoculi
Inferiorrectus
Tarsal glands
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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
Lacrimal gland
Lacrimal sac
Superior andinferior canaliculi
Nasolacrimalduct
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Extrinsic Eye Muscles
Inferior rectus Inferior oblique
Medialrectus
Superiorrectus
Superioroblique
Lateralrectus(cut)
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• Superior rectus• Rotates eye up and medially
• Inferior rectus• Rotates eye down and medially
• Medial rectus• Rotates eye medially
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Extrinsic Eye Muscles
Inferior rectus Inferior oblique
Medialrectus
Superiorrectus
Superioroblique
Lateralrectus(cut)
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• Lateral rectus• Rotates eye laterally
• Superior oblique• Rotates eye down and laterally
• Inferior oblique• Rotates eye up and laterally
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Structure of the Eye
The eye has three distinct layers “tunics”1.Fibrous tunic 2.Vascular tunic3.Nervous tunic
Outer Tunic
• Sclera• Posterior portion• Opaque• Protection
• Cornea• Anterior 1/6th of eye• “window of the eye”• Transparent• Light transmission
Middle Tunic
• Iris “rainbow”• Anterior portion• Pigmented• Controls light intensity
• Ciliary body• Anterior portion• Pigmented• Suspensory ligaments holds lens• Ciliary muscles moves lens for focusing
• Choroid coat• Provides blood supply• Pigments absorb extra light
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
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Accommodation
• Changing of lens shape to view objects
(a)
Lens thick
Lens thin
(b)
Ciliary musclefibers contracted
Suspensoryligaments relaxed
Ciliary musclefibers relaxed
Suspensoryligaments taut
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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
Sclera
Iris
Lens
Aqueous humor
Cornea
Vitreous humor
Ciliary process
Ciliary muscles
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Posteriorchamber
Ciliarybody
Scleral venous sinus(canal of Schlemm)
Anteriorchamber
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.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
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Posterior Cavity
• Contains vitreous humor – thick gel that holds retina flat against choroid coat
Ciliary body
Retina
Choroid coat
Sclera
Fovea centralis
Optic nerve
Lens
Iris
Pupil
Cornea
Lateral rectus
Medial rectus
Optic disc
Posterior cavity
Vitreous humor
Posteriorchamber
Anteriorchamber
Aqueoushumor
Suspensoryligaments
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Anteriorcavity
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Layers of the Eye
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Light Refraction
• Refraction • Bending of light• Occurs when light waves pass at an oblique angle into mediums of different densities
Light wave
Perpendicular line
Air
Glass
Refractedlight wave
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Types of Lenses
• Convex lenses cause light waves to converge
• Concave lenses cause light waves to diverge
Air
Glass
(a) (b)
Diverginglight waves
Convexsurface
Lightwave
Converginglight waves
Concavesurface
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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
Light waves
ObjectCornea
Image
Retina
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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.
• 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
Visual Receptors
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.
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.
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12.6 Clinical Application
Refraction Disorders• Concave lens corrects nearsightedness
• Convex lens corrects farsightedness
Light waves
Light waves
Light waves
CorneaLens
Retina
(a) Eye too long (myopia)
(b) Normal eye
(c) Eye too short (hyperopia)
Pointof focus
Pointof focus
Pointof focus
Light waves
Concave lens
Convex lens
(a)
(b)
Uncorrectedpoint of focus
Correctedpoint of focus
Uncorrectedpoint of focus
Correctedpoint of focus
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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 light-sensitive 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
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Stereoscopic Vision
• Provides perception of distance and depth• Results from formation of two slightly different retinal images
Lightwaves
Right eyeLeft eye
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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.
Figure 12.41 The visual pathway includes the optic nerve, optic chiasma, optic tract, and optic radiations.
End of Chapter 12