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The SensesThe Senses
Anatomy & Physiology IIChapter 11
The SensesThe Senses
Sensory receptors detect and respond to stimuli (environmental change)
Activation of receptors initiates nerve impulse (signal)
Signal interpreted by cerebral cortex
Sensation experienced
Sensory ReceptorsDistribution of sense receptorsSpecial senses in sense organ
◦Vision◦Hearing◦Equilibrium◦Taste◦Smell
General senses throughout body◦Pressure, temperature, pain, touch◦Sense of position
Sensory Receptors
Sensory receptors◦ Nociceptors – respond to tissue damage
(painful stimuli)◦ Chemoreceptors - respond to chemicals ◦ Photoreceptors - respond to light◦ Thermoreceptors - respond to heat◦ Mechanoreceptors - respond to
movement
The Eye and VisionThe Eye and Vision
Eye protection structuresEye cavity bonesEyelidsEyelashes and eyebrowConjunctivaLacrimal glands
Coats of the Eyeball
Eyeball has three separate coats (tunics)
Sclera ChoroidRetina
Note the three tunics, the refractive parts of the eye (cornea, aqueous humor, lens, vitreous body), and other structures involved in vision.
The Eye
Pathway of Light Rays and RefractionTransparent parts of the eye that
refract lightCorneaAqueous humorLensVitreous body
Function of the RetinaPigmented layer
◦Sensitive to lightRods
◦Function in dim light◦Shades of gray◦Blurred images
Cones◦Function in bright light◦Color sensitive◦Sharp images
Connecting neurons
Rods and cones form a deep layer of the retina, near the choroid. Connecting neurons carry visual impulses toward the optic nerve.
Structure of the Retina
Muscles of the Eye
Two muscle groups adjust eye so retina can receive clear image
The Extrinsic MusclesOuter surface of eyeballVoluntaryControl convergence for three-
dimensional vision
The medial rectus is not shown. ZOOMING IN • What characteristics are used in naming the extrinsic eye
muscles?
Extrinsic Muscles of the Eye
The Intrinsic MusclesWithin eyeballIris regulates amount of light
entering eyeCiliary muscle shapes lens for
near and far vision
Contraction of the ciliary muscle relaxes tension on the suspensory ligaments, allowing the lens to become more round for near vision.
Ciliary Muscle and Lens
Nerve Supply to the Eye
Optic nerve (cranial nerve II)Oculomotor nerve (cranial nerve
III)Trigeminal nerve (cranial nerve
V)Trochlear (cranial nerve IV)Abducens (cranial nerve VI)
ZOOMING IN • Which of the nerves shown moves the eye?
Nerve Supply to the Eye
Errors of Refraction
Hyperopia (farsightedness) – difficulty focusing on objects near the face.
Myopia (nearsightedness) – difficulty focusing on distant objects.
Astigmatism - An irregular shaped cornea or lens prevents light from focusing properly on the retina. Images focus at muliple points on retina
Eye DisordersStrabismus – inability to align both eyes
simultaneously due to a lack of muscle coordination◦ Convergent (cross-eyed) – affected eye deviates
toward nose◦ Divergent – affected eye deviates laterally
Amblyopia (lazy eye) – loss of vision in a healthy eye due to inadequate muscle balance◦ not correctable by glasses or contact lenses◦ The brain, for some reason, does not fully
acknowledge the images seen by the amblyopic eye.
Other Eye DisordersInfections
◦Conjunctivitis◦Inclusion conjunctivitis ◦Ophthalmia neonatorum
InjuriesCataractGlaucomaDisorders involving the retina
◦Diabetic retinopathy◦Macular degeneration
The EarThe Ear
Sense organ for hearing and equilibrium
Outer earMiddle earInner ear
The ear. Structures in the outer, middle, and inner divisions are shown
The Outer EarPinna (auricle)
◦Directs sound waves into earExternal auditory canal (meatus)
◦Ceruminous glandsTympanic membrane
◦Vibrates as sound waves enter ear
The Middle Ear and OssiclesMiddle ear cavity contains ossicles
(small bones) that amplify sound waves and transmit sounds to inner ear
Malleus (hammer) Incus (anvil)Stapes (stirrup)
Eustachian TubeConnects middle ear cavity with
throat (pharynx)Allows pressure to equalize on
both sides of tympanic membrane
Continuous mucous membrane from pharynx to middle ear cavity
The Inner EarBony labyrinth
◦Vestibule◦Semicircular canals◦Cochlea◦Perilymph fluid
Membranous labyrinth◦Vestibule◦Semicircular canals◦Cochlea◦Endolymph fluid
The vestibule, semicircular canals, and cochlea are made of a bony shell (labyrinth) with an interior membranous labyrinth. Endolymph fills the membranous labyrinth and perilymph is around it in the bony labyrinth.
The Inner Ear
Hearing
Organ of CortiLocated in membranous cochlea
(cochlear duct)Ciliated receptor cellsTectorial membrane
Cochlea and the organ of Corti.
The arrows show the direction of sound waves in the cochlea.
EquilibriumCiliated equilibrium sensory
receptors are located in vestibule and semicircular canals
Types of equilibrium◦Static
Maculae receptors Otoliths fluid
◦Dynamic Cristae receptors
Action of the receptors (maculae) for static equilibrium. As the head moves, the thick fluid above the receptor cells, weighted with otoliths, pulls on the cilia of the cells, generating a nerve impulse.
Action of the receptors (cristae) for dynamic equilibrium. As the body spins or moves in different directions, the cilia bend as the head changes position, generating nerve impulses.
Otitis and Other Disorders of the Ear
Otitis mediaOtitis externaHearing loss
◦Conductive hearing loss◦Sensorineural hearing loss◦Presbycusis
Other Special Sense Other Special Sense OrgansOrgansTaste and smell sense organs
respond to chemical stimuli
Sense of TasteTaste receptors
(buds) on tongue◦ Stimulated by
substance in solution
Basic tastes◦ Sweet◦ Salty◦ Sour◦ Bitter
Other tastes◦ Water◦ Alkaline◦ Metallic◦ Umami
Cranial nerves◦ Facial (VII)◦ Glossopharyngeal
(IX)
Special senses that respond to chemicals.(A)Organs of taste (gustation) and smell (olfaction). (B) A taste map of the tongue.
Sense of SmellSmell receptors in nasal cavity
◦Stimulated by substances in solution in nasal fluids
◦Smells stimulate appetite and flow of digestive juices
Olfactory nerve (cranial nerve I)
The General SensesThe General Senses
Receptors scattered throughout the body sense
TouchPressureHeatColdPositionPain
Sense of TouchTactile corpuscles Found mostly in dermis of skin and around
hair folliclesSensitivity varies with the number of
receptorsBaroreceptors in walls of large arteries
monitor blood pressure and trigger responses that control BP as vessels stretch.
Sense of PressureSense of PressureReceptors for deep touch locatedIn subcutaneous tissuesNear joints, muscles, and other deep
tissues
Sense of Temperature
Temperature receptors Are free nerve endingsAre widely distributed in the skinAre separate for heat and cold Occur in hypothalamus of brain
◦Help to adjust body temperature according to temperature of circulating blood
Sense of Position
Proprioceptors (position receptors)Are located in muscles, tendons,
jointsRelay impulses of body parts in
relation to each otherSend impulses to the cerebellum
for coordination
Sense of PainPain receptors
◦Are free nerve endings◦Are found in skin, muscles, joints and (to
a lesser extent) in most internal organsPain relief
◦Analgesic drugs◦Anesthetics◦Endorphins◦Heat or cold◦Relaxation or distraction techniques
Sensory AdaptationSensory AdaptationOccurs when receptors are
exposed to continuous stimulusSome receptors can adjust
themselves so sensation becomes less acute
Receptors adapt at different ratesPain receptors do not adapt
End of PresentationEnd of Presentation
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