SPECIAL SENSES

•General senses – all throughout the body.

•Special senses – confined in the head, eyes and ears ( hearing and balance, sight, taste, smell) - conveyed by

cranial nerves

•TYPES OF RECEPTORS based on Location:1. SUPERFICIAL2. DEEP3. CORTICAL (combination of superficial and deep) Info: ↓ ↓ Exteroreceptors Proprioceptors - pain, temp., light

touch, pressure-from OUTSIDE the body

-position sense, kinesthesia, vibration-- from inside the body (muscle spindle, tendons, ligaments)

•Visceral Sensation – relayed by the autonomic efferent fibers - hunger, nausea, visceral pain - visceral pain receptors are only in

the viscera and respond differently to stimulation not localized

Referred pain – as if coming from other parts of the body

Ex: liver and gall bladder problem may be referred to the right shoulder

I. MECHANORECEPTORS Respond to mechanical deformation of

receptors A. CUTANEOUS SENSORY RECEPTORS Free nerve ending – pain and temp Merkel’s disk - two-pt discrimination,

localization of touch Ruffini – warmth (above 25 deg C) Krause end bulb – cold (100-200 deg C)

Meissner’s – discriminative touch (texture recognition)

Pacinian – deep touch and vibration B. DEEP/JOINT RECEPTORS Muscle Spindle – velocity of movement GTO- monitors tension Free nerve endings- pain and temp PacinianII. THERMORECEPTORS – for temperature

changesIII. NOCICEPTORS – noxious stimuli ( damage to

tissues)

III. ELECTROMAGNETIC RECEPTORS – respond to light (rods and cones)

IV. CHEMORECEPTORS – respond to chemical substance

A. Taste- receptors of taste buds B. Smell - receptors of olfactory nerves in

olfactory epithelium C. Arterial O2- receptors of Aortic and

carotid bodies D. Osmolality - neurons of supraoptic

nuclei

E. Blood CO2 - receptors in or on surface of medulla and in aortic and carotid bodies F. Blood Glucose, amino acid and fatty acids - receptors in hypothalamus Projection – the brain projects sensation back to the source - person pinpoints region of

stimulation

Pathways From Sensation to Perception (Example of an Apple)

•ACUTE PAIN

A-delta fibers Fast

Sharp pain Localized

•CHRONIC PAINC fibers

Slowassociated with dull aching pain

diffused (difficult to pinpoint)

ACUTE PAIN VS. CHRONIC PAIN

•OLFACTION - sense of smell, occurs in response to odors that stimulate sensory receptors

- receptors located in the extreme superior region of the nasal cavity, called the olfactory recess

PATHWAY:Once olfactory receptors are stimulated, nerve impulses travel through olfactory nerves → olfactory bulbs → olfactory tracts →limbic system (for emotions) olfactory cortex (for interpretation)

•olfactory receptors undergo sensory adaptation rapidly•sense of smell drops by 50% within a second after stimulation

•Mechanism of olfactory discrimination- unknown-wide variety of detectable (4000) smells actually combinations of a smaller number of primary odors

7 primary scents•Camphor•Musk•Floral•Peppermint•Ether•Pungent•Putrid GUSTATION/Taste

- a chemical sense that requires dissolving substance before it can be tasted.

GUSTATORY RECEPTORSLocated at the taste budsCan also be found on the soft palate, pharynx

and larynxTaste buds declines with ageTaste budOrgans of tasteLocation

a. Tongue Papillaeb. Mouth(roof)c. Cheeks(lining)d. Pharynx(wall)e. Lips

Taste receptors• Chemoreceptors• Taste cells-function as receptors• Taste hairs- microvilli that protude from taste

cells;sensitive parts of taste cells

4 major types of Papillae according to shape:1. Vallate- largest; V-shaped

-between anterior and posterior border of tongue

2. Fungiform-mushroom-shaped-contains most sensitive to taste

buds-folds on the sides of the tongue

-most numerous in CHILDREN-decreases with age

4.Filiform-filament-shaped-most numerous-no taste function

Five Primary Sensations• Sweet- stimulated by carbohydrates• Sour- stimulated by acids• Salty- stimulated by salts• Bitter- stimulated by many organic compounds•Umami

Spicy foods activate pain receptorsTaste PathwayImpulses from taste receptors → cranial nerves97,9,10) →medulla →thalamus

↓limbi syste,hypothalamus↓

Gustatory cortex

Visual System

oComponents

1.Eyes- respond to light and initiate afferent action potentials.

2. Accessory structures- help protect the eyes from direct sunlight and damaging particles

-includes:eyebrows, eyelids, eyelashes, lacrimal apparatus,conjunctiva, extrinsic eye muscles3. Optic nerves (II), tracts, and pathways

Eyebrows- Protects eyes1. Perspiration2. Shade from the sun

Eyelid(PALPEBRA)-for blinking (protects the eye from foreign objects)

-Average blinking: 25x/min Muscles

a. Orbicularis Oculi- closesb. Levator Palperbrae Superiosis- opens

• Canthi: angels where the eyelids join at the medial and lateral margins of the eye

• Caruncle: small reddish, on the medial canthi; contains modified sabaceous and sweat galnds

CONJUNCTIVE-mucous membrane; lines eyelid and covers portion of eyeballConjunctivitis-”pink eye”

- Inflammation caused by infection or irritation

Extrinsic Eye MusclesLateral rectus- outward; paralysis of both lateral will cause eyes to deviate inward (internal strabismus)Medial rectus- inward; paralysis of both medial will cause eyes to deviate outward (external strabismus)Superior rectus- up and inInferior rectus- down and inSuperior oblique- down and outInferior oblique- up and out

EYELASHES-double or triple row of hairs to the free edges of the eyelids-lubricates lids and restrains tears from flowing over the margin of the eyelids; openings behind the lashes

•Lacrimal ApparatusLacrimal• Lateral to eye• Secretes tears

Canaliculi• Collect tears

Lacrimal Sac• Collects from canaliculi

Punctum•Opening of each lacrimal canaliculis

Nasolacrimal Duct• Collects from lacrimal sac• Empties tears into nasal cavity

Optical Components:

•LAYERS/TUNICS:1. Outer Fibrous Tunis Sclera

Cornea

2. Middle/Vascular Tunic ChoroidCiliary BodyIris

3.Inner RetinaCorneaAnterior portionAVASCULARTransparentLight permission

Light refractionOne of the first organs transplantedCentral part of the cornea receives oxygen from

the outside air.soft plastic contact lenses worn for periods must

be permeable to air to reach the cornea.ScleraPosterior portion; firm, opaque, white functions:ProtectionMuscle attachmentShape of the eye

IrisAnterior portionpigmented

Smooth muscleControls light intensityPupil is the hole in irisDim light stimulates radial muscles and pupil

dilatesBright light stimulates circular muscles and pupil

constricts-blue eyes: decreased melanin-black/brown: increased melanin

•Ciliary BodyAnterior portionPigmentedHolds lensMoves lens for focusingForms internal ring around front of eyeCiliary processes-radiating foldsCiliary muscles-contract and relax to move lens

•Choroid CoatProvides blood supplyPigments absorb extra light

•RetinaContains visual receptorsContinuous with optic nerveMacula lutea- yellowish spot in retinaFovea centralis-center of macula lutea;produces

sharpest visionOptic disc-blind spot; contains no visual receptorsVitreous humor- thick gel that holds retina flat

against choroid coat fluid in anterior cavity of eye

•Aqueous Humor Fluid in the anterior cavity; provides nutrients Maintains shape of anterior portion of eye

•LensTransparentBiconvexLies behind irisHeld in place by suspensory ligaments of ciliary

body

Accomodation Changing of lens shape to view objects

•RefractionBending of lightOccurs when light waves pass at an oblique angle

into mediums of different densitiesConvex lenses cause light waves to convergeConcave lenses cause light waves to diverge

•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

Visual Receptors•RodsoContain light sensitive pigment called rhodopsinoMore sensitive to light than conesoProvide vision in dim lightoProduce colorless visionoProduce outlines of objects•ConesoShort, blunt projectionsoProvide vision in bright lightoProduce sharp imagesoProduce color vision

Clinical Correlation•Myopia-nearsightedness, too ↑ refraction•Hyperopia- farsightedness, ↓ refraction•Astigmatism- curvature of either lens or cornes is

greater in 1 axis or meridian• Scotomas- abnormal blind spot in visual fields

Visual Pathway and Visual field cuts

Lesions:a.Blindness in one eyeb.Bitemporal Hemianopiac.Homonymous Hemianopiad.Quadrantanopsiae.Homonymous Hemianopsia

HEARING AND BALANCEEAR

External ear• Consists of: auricle and external auditory meatus• Function: hearing only

Middle Ear/Tympanic Cavity• Consist of: air-filled CAVITY within the temporal

bone, and auditory ossicles• Function in both hearing balance

Auricle/Pinna:• Fleshy part of the external ear on the outside of

the head• Shape helps to collect sound waves and direct

them toward the external auditory meatus• Elastic cartilage covered with skin, extrinsic and

intrinsic mm

External auditory meatus• Sinus tube that leads to tympanic cavity• Isthmus: narrowest potion of meatus

Functions:1. Conduct sounds waves from auricle to tympanic

membrane2. Prevents foreign objects from reaching the

delicate eardrum thru the lined hairs and ceremonous glands, which produce cerumen(earwax)

o Tympanic Membrane/Eardrum Thin, semitransparent, nearly oval Separates the external ear from the middle ear.

Auditory Ossicles:1. Malleus: largest; handle is attached to the

center of the eardrum2. Incus: attached to the other side of malleus

:Whenever malleus moves, incus moves with it.

3. Stapes: attatched to opposite end of incus- Lies against the membranous labyrinth in

the opening of oval window where sound waves are conducted into inner ear.

Middle earChorda tympani

-branch if the facial nerve carrying taste impulses from the anterior two-thirds of the tongue-no function in hearing

Inner earBony Labyrinth:

1. Vestibule: for balance2. Semicircular canals: for balance3. Cochlea: for hearing

Membranous labyrinth1. Utricle2. Saccule

3.Semilunar ducts4. Cochlear ducts

STEPS IN HEARING1. The auricle collects sound waves that are then

conducted through the external auditory meatus to the tympanic membrane, causing it to vibrate.

2. The vibrating tympanic membrane causes the malleus, incus, and stapes to vibrate.

3. Vibration of the stapes produces vibration in the perilymph of the scala vestibuli.

4. The vibration of the perilymph produces simultaneous vibration of the vestibular membrane and the endolymph causes in the cochlear duct.

5. Vibration of the endolymph causes the basilar membrane to vibrate.

6. As the basilar membrane vibrates, the hair cells attached to the membrane move relative to the tectorial membrane, which remains stationary.7. The hair cell microvilli, embedded in the tectorial membrane, become bent.8. Bending of the microvilli causes depolarization of the hair cells.9. The hair cells induce action potentials in the cochlear neurons.10. The action potentials generated in the cochlear neurons are conducted to the CNS.11. The action potentials ate translated in the cerebral cortex and are perceived as sound.

Auditory Pathway:Sensory axons from the cochlear

↓Ganglion terminate in the cochlear nucleus in the brainstem

↓Superior olivary nucleus or to the inferior colliculus

↓Medial geniculate nucleus of the thalamus

↓Auditory cortex

↓Neurons in the superior olivary

Neurons in the superior olivary nucleus send axons to the inferior colliculus, back to the inner ear, or to motor nuclei in the brainstem that send efferent fibers to the middle ear muscles.Clinical correlation:1. Tinnitus- ringing, buzzing, roaring or “paper

crushing” noises in the ear, frequently an early sign of peripheral cochlear disease

2. Deafnessa. conduction- impaired conduction through the

external canal and ossicles to endolymph and tectorial membrane

-cause:external/middle ear diseases

b. sensorineural/nerve- interruption of cochlear nerve fibers from hair cells to BS

-cause: cochlear nerve/ inner nerve

VESTIBULAR SYSTEMFor maintenance of stance and body posture; coordination of the body, head and eye movements; and visual fixationSTATIC LABYRITH

-Stuctures involved:1. Saccule2. Utricle

-involved in evaluating the position of the head relative to gravity

-responds to linear acceleration deceleration, such as when a person is in a car that is increasing or decreasing speed

•Macula of the Utricllie: determines person’s head position w/ respect to gravitational force when person is in upright position•Macula of the saccule: equilibrium in lying down

OTOLITHS/OTOCONIA: small Ca Carbohydrates crystals in saccule and utricle

-displaces the hair cells and excites the saccule and utricle in response to Vertical and Horizontal acceleration

•KINETIC LABYRITH- Detects head rotation: Angular Rotation- When head begins to rotate-endolymph in S.D.

remain stationary while S.D moves w/ the head direction-cause flow to flow into ampula, bending cupula to side

- From hair cells- vestibular nerve to apprise the N.S of change in the rate of direction

-Pathway For Balance1. Sensory axons from the vestibular ganglion

pass through the vestibular nerves to the vestibular nucleus, which also receives input from several other sources, such as proprioception from the legs.

2. Vestibular neurons send axons to the cerebellum, which influences postural muscles, and to the motor nuclei (oculomotor, trochlear, andabducents), which control extrinsic eye muscles.3. Vestibular neurons also send axons to the posterior ventral nucleus of the thalamus. 4. Thalamic neurons project to the vestibular area

of the cortex. OTOSCLEROSIS

-Is an ear disorder in which spongy bone grows over the oval window and immobilizes the stapes, leading to progressive loss of hearing

TINNITUSConsists of noises such as ringing, clicking, whistling, or booming in the ears

MOTION SICKNESSConsists of nausea, weakness and other dysfuntions caused by stimulation of the semicircular canals during motion, such as is boat, automobile, airplane, swing or amusement park ride

OTITIS MEDIAInfections of the middle ear

VERTIGO