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