unit 15

sensory receptors classified into 2 major categories

general senses, touch & smell

special senses, include the eye and ear

exteroceptors

located close to body surface (cutaneous receptors)

ex: touch, pressure, temperature, pain

visceroreceptors

located internally around the viscera

abdominal, uterus, etc

proprioceptors

muscle sense

mechanoreceptors

stimulated by mechanical force(s)

touch, pressure, equilibrium, hearing

chemoreceptors

change in chemical concentration

taste, smell

thermoreceptors

stimulated by change in the temperature

warm and cold receptors

photoreceptors

respond to light

rods and cones in the retina

nociceptors

respond to any tissue damage

results in pain

osmoreceptors

recognize changes in the osmolarity of body fluids

concentrated in the hypothalamus

eye - photoceptors

light rays enter the eye through the cornea

pass through the lens to the receptor cells of the retina

• rods: black and white vision

• cones: color vision

visual stimuli are conducted by the optic nerve to the occipital lobe

• interpretation and processing

• info sent to other appropriate areas of the brain

protection for the eye

protected by bony orbit of the skull

eyelids and eyelashes

• deflect foreign material from eyes

• protect against excessive sunlight and drying

conjunctiva

• mucous lining of eyelids

• covers sclera

tears

• produced by lacrimal glands

• contain lysozyme - antibacterial enzyme

muscles of the eyeball

six extraocular skeletal muscles for movement of the eyeball

muscles controlled by cranial nerves III and IV

eyeball outer layer

touch fibrous coat

posterior portion - sclera

• “white” of the eye

anterior portion - cornea

• transparent portion

• light rays pass and are refracted

• does not contain blood vessels

• nourished by fluids around it

• oxygen diffusing from atmosphere

eyeball middle layer - uvea

choroid: dark vascular layer interior to the sclera

absorbs scattered light

located in anterior segment of the eyeball

• choroid is specialized as ciliary body that controls shape of the crystalline lens

• iris is pigmented muscle of pupil

  • dilation occurs as a result of increased SNS activity

  • constriction occurs as a result of increased PNS activity

eyeball inner layer - retina

contains no pain receptors

multilayered - in posterior two thirds of the eye

photoreceptor cells, rods and cones

forvea Centralia

• cones for most acute vision

fluids in the eye - posterior cavity

space between lens and retina

contains vitreous humor

• formed during embryonic development

fluids in the eye - anterior cavity

between cornea and lens

divided into the anterior chamber and the posterior chamber

filled with aqueous humor

visual pathway

light rays pass through cornea

• refraction of rays

• through aqueous humor and pupil

• to the retina (rods and cones)

nerve fibers form the optic nerve (CN II)

optic chiasm

• fiber cross

• left occipital lobes receive images from right visual fields, right occipital lobes from left visual fields

perception occurs in visual sensory and association areas of the occipital lobes of the cortex

diagnostic tests for vision

snellen chart: measures visual acuity

visual field test: checks for central and peripheral vision

tonometry: assessment of IOP, numb eyes prior to measurement

ophthalmoscope: examines internal structures

gonioscopy: determines angle of anterior chamber

muscle function and coordination tests

myopia

nearsightedness

image focused in front of the lens

hyperopia

farsightedness

eyeball is too short

image focused behind the retina

presbyopia

farsightness associated with aging

loss of elasticity reduces accommodation

astigmatism

irregular curvature in the cornea or lens

strabismus (squint or cross-eye)

results from deviation of one eye

double vision (diplopia)

may be caused by weak or hypertonic muscle, short muscle, neurological defect

in children: must be treated immediately to prevent development of amblyopia

nystagmus

involuntary abnormal movement of one or both eyes

may result from neurological causes, inner ear or cerebellar disturbances, drug toxicity

diplopia (double vision)

may be caused by trauma to cranial nerves, resulting in paralysis of extraocular muscles

may occur in stroke

loss of depth perception occurs

stye

infection involving a hair follicle on the eyelid

usually caused by staphylococci

swollen, red mass forms on eyelid

purulent exudate

conjunctivitis

redness itching excessive tears

superficial inflammation or infection involving the conjunctiva (lining of eyelids)

redness, itching, excessive tearing

trachoma

preventable with inoculation of antibiotic at birth

caused by Chlamydia trachomatis

follicles develop on inner surface of eyelids

can occur in any age group

“scratchy” eye

antibiotic treatment

globally, most common cause of vision loss where water is scarce and inadequate hygiene occurs

scarring of lid leads to eyelashes abrading cornea → loss of transparency

keratitis

inflammation of the cornea from infection or irritation

severe pain and photophobia

risk of ulceration eroding the cornea that can lead to scarring and vision loss

etiologies:

• herpes simplex can cause

• transfer from herpes lesion around mouth

• transfer by fingers, dental office, spray of contaminated saliva

• trauma to cornea

• damage from chemicals, splashes, fumes

treatment: flushing and oral and ophthalmic steroids and antibiotics

eye trauma

direct contact and chemical burns

presentations:

• black eye / swelling

• visual defects

• eye pain, edema, blurry vision, diplopia, dry eyes, photophobia, floaters, pupil dilation, and pupils that are unresponsive to light

treatment:

• flushing irritant out of the eye with sterile saline

• avoiding rubbing the eye

• covering the eye with a sterile dressing or cloth

subconjunctival hemorrhage

capillaries under that conjunctiva rupture

causes: trauma, anti-coagulant use, coughing, vomiting, sneezing, heavy lifting

manifestations: bright red blood on the sclera that does not cross the cornea

diagnosis: H&P

treatment: avoid rubbing the eye, self-limiting withing 1-2 weeks

glaucoma

group of eye conditions that damage the optic nerve

increased pressure from blocked outflow of aqueous humor or increased production of aqueous humor

result of increased increase ocular pressure (IOP) caused by excessive accumulation of aqueous humor that decreases blood flow to nerve and can cause ischemia and degeneration

can be acute or chronic

glaucoma signs and symptoms and diagnosis

halos around lights at night

loss of peripheral vision

pain may occur if IOP is greatly increased, as in acute form

gonioscope exam reveals a closed angle into the canal of schlemm and corneal edema

diagnosis: H&P, ophthalmic exam

acute glaucoma

acute or narrow angle

angle between cornea and iris is decreased

may be caused by aging, developmental abnormalities, or scar tissue from trauma or infection

chronic or open-angle glaucoma

higher incidence after age 50 years

thickening of trabecular network, which allows for resorption of fluid so absorption diminished

has insidious onset

pressure increases over time

treated by regular administration of eye drops

minimally invasive surgical options to open aqueous humor outflow channels

cataracts

progressive opacity or clouding of the lens

• interferes with light transmission

size, site, and density of clouding vary among individuals

changes may be:

• age-related or caused by metabolic abnormalities

• excessive exposure to sunlight

• congenital - can occur at birth

• traumatic

cararacts signs and symptoms

blurred vision over visual field

• becomes darker with time

• night driving especially difficult with halos around lights

• photosensitivity and decrease color intensity perception

rate of impairment varies and can be different in each eye

outpatient surgery involves lens replacement

cataract diagnosis & treatment

diagnosis: H&P, opthalmic examination includes visual acuity testing, retinal exam, and slit lamp exam

treatment: surgery and managing or eliminating contributing factors

detached retina

separation of retina from supporting structures

acute emergency

• retina tears away from underlying choroid

• decreased blood flow and retinal ischemia can lead to irreversible loss of receptors

• no pain or discomfort

• visual field contains areas of blackness (scotomas), as if a curtain has fallen over the eye

mucular degeneration

common cause of visual loss in older adults

risk factors: age, smoking, FH, obesity, female

central vision becomes blurred then lost

two types: dry or atrophic, wet or exudative

new therapies being investigated

dry type of macular degeneration

blood vessels under macula become thin

deposits form in retinal cells and proliferate causing blurring of central vision

wet type of macular degneration

neovascularation: to replace thinning vessels

new vessels leak blood and fluid leading to more rapid vision loss

external ear

pinna and external auditory meatus (canal)

middle ear

tympanic membrane

bony ossicles

auditory tube connects to upper respiratory tract

inner ear

cochlea

semicircular canals

• balance and equilibrium

eustachian tube

located in the middle ear and opens into the pharynx

acts as a pressure valve

normally, the tube remains closed but opens with as yawning and swallowing

opening the eustachian tube open air flow and equalizes the internal and external pressure on the tympanic membrane

pathway of sound

sound waves enter the external ear canals

vibration of the tympanic membrane causes the ossicles to vibrate

motion of staples against oval window initiates movement of the fluid in the cochlea

impulses conducted to the auditory area in the temporal lobe of cerebral cortex for interpretation of sound

semicircular canals

three structures at right angles with each other

structure of semicircular canal

contain receptor hair cells

stimulated by motion of the endolymph in response to head movements

stimuli conducted to vestibule which relays to the cochlea

vestibular branch of the auditory nerve then receives the positioning in space and sends signals to cerebellum and medulla

two types of hearing loss

conduction deafness

sensorineural impairment

conduction deafness

sound is blocked in the external ear or middle ear

accumulation of wax, foreign object, scar tissue

osteosclerosis of the ossicles

hearing loss from traumas

direct physical trauma (foreign objects and insects) and excessively loud noises (explosions and gunshots)

manifestation: bloody or clear exudate, tinnitus, dizziness, ear pain, hearing deficits, nausea, vomiting, edema, and a sensation that an object is in the ear

hearing loss treatment

newborns are screened for hearing deficits

hearing aids

cochlear implants

ear infections: otitis media

inflammation or infection of the middle ear

• exudate builds up in cavity

• causes pressure on tympanic membrane

• auditory tube may be obstructed by inflammation

• prolonged infection is likely to produce scar tissue and adhesion

• chronic infection may lead to mastoiditis

otitis media signs and symptoms, treatment

signs and symptoms

• most often, severe pain or earache

• tympanic membrane red and bulging

• mild hearing loss or feeling of fullness

• fever, nausea might be present

treatment

• ibuprofen or acetaminophen to reduce discomfort in first 48 hours

• use of antibacterial infection

• decongestant may be useful in draining auditory tube

surgery may be done to insert temporary tubes in tympanic membrane to allow for drainage

otitis externa

also called swimmer’s ear

usually bacterial, may be fungal

infection of the external auditory canal and pinna

pain usually increased with movement of pinna

purulent discharge and hearing defict

otosclerosis - cause of hearing loss

imbalance in bone formation and resorption

development of excess bone in middle ear cavity

blockage of conduction sounds to cochlea

may be caused by genetic or environmental factors

treatment: surgical removal of stapes and replacement prosthesis to restore hearing

meniere’s syndrome

inner ear labyrinth disorder causing severe vertigo and nausea

intermittent, with remissions and exacerbations

excessive endolymph produced

attack may last minutes or hours

balance test, electronystagmography, electrocochleography, MRI

treatment with drugs

meniere’s disease signs and symptoms

severe vertigo: a sensation of whirling and weakness, is often accompanied by loss of balance and falls

attack may last minutes or hours

tinnitus: excess noise like a roaring motor or ringing

unilateral hearing loss

nausea and sweating

inability to focus

diagnostic and treatment for miniere’s disease

diagnostic test:

• balance tests such as rotary-chair and video head impulse

• electronystagmography (ENG): evaluating balance by assessing eye movement

• fluid test: checking for an abnormal buildup in the inner ear

• electocholeography (ECOG): tests response to sounds

• MRI

treatment with drugs

tinnitus

hearing abnormal noises in the ear

may be described as a ringing, buzzing, humming, whistling, roaring, or blowing

diagnosis: H&P

treatment: treating the underlying cause

vertigo

patient feels like they are in motion, not dizziness

can be associated with nauseas and vomiting

types based on origin

• peripheral: problem with vestibular labyrinth, semicircular canals or vestibular nerve

• central: problem in the brain - stem or cerebellum

vertigo diagnosis and treatment

diagnosis: H&P to determine underlying etiology

treatment: anticholinergic agents, antihistamines

benign paroxysmal positional vertigo

one of the most common causes of vertigo, can be mild to severe

causes: idiopathic, trauma, otoliths stuck. risks: aging, females, recent URI or allergies

manifestations: sudden sensation of spinning, often after specific head movements

diagnosis: H&P, Dix-Hallpike test

treatment: epley maneuver, treat underlying causes, anti-histamine

hyposmia

impaired sense of smell

ansonia

complete loss of smell

olfactory hallucinations

smelling odors that are not currently present

parosmia

abnormal sense of smell

hypogeusia

decrease in taste sensation

ageusia

absence sense of taste

dysgeusia

perversion of taste

often unpleasant flavor (metallic)

may cause anorexia and affect nutrition

insomnia

inability to fall asleep or stay asleep

drugs, alcohol, pain, depression, obesity, aging

hypersomnia

excessive daytime sleepiness

narcolepsy

daytime sleepiness and unability to regulate sleep-wake cycles

primary hypersomnia of central (hypothalamus) origin

parasomnias

unusual behaviors during sleep

somnambulism

sleepwalking, often in children

night terrors

sudden apparent arousal in a child, experiencing fear, actually not awake & hard to arouse, not associated with dreaming

pain

unpleasant sensation

• discomfort caused by stimulation of pain receptors

body defense mechanism

• warning of a problem

subjective scales

• developed to compare pain levels over time

causes: inflammation, infection, ischemia, and tissue necrosis, stretching of tissue, stretching of tendons, ligaments, joint capsule, chemicals, burns, muscle spasm

signs and symptoms of pain

important to identify in H&P

location of pain

descriptive terms: aching, burning, sharp, throbbing, widespread, cramping, constant, periodic, unbearable, moderate

timing

associated symptoms: nausea & vomiting, fainting and dizziness, etc

physical evidence: pallor and sweating, high BP, tachycardia, clenched fists, guarding area

referred pain

source may be difficult to determine

pain may be perceived at site distant from source

• characteristic of visceral damage in the abdominal organs

• heart attacks or ischemia in the heart

phantom pain

usually in adults

more common is chronic pain has occurred

can follow an amputation

pain tolerance

degree of pain, intensity, or duration

may be increased by endorphin release

may be reduced because of fatigue or stress

varies among people in different situations

pain perception

subjective but can be compared from day to day in same person

response to pain

influenced by personality, emotions, and cultural norms

acute pain

usually sudden and severe, short term

indicates tissue damage

may be localized or generalized

myelinated A delta fibers

initiates physiologic stress response

vomiting may occur

strong emotional response may occur

chronic pain

more complex than acute pain

occurs over extended time; may be recurrent

often perceived to be generalized

unmyelinated C fibers

individual may be fatigued, irritable, depressed and sleep disturbances common

specific cause may be less apparent

frequently affects daily activities

somatic pain

from skin

bone muscle

conducted by sensory fibers

visceral pain

originates in organs

conducted by sympathetic fibers

may be acute or chronic

pain pathways

nociceptors (pain receptors) are free sensory nerve endings

pain threshold: level of stimulation required to elicit a pain response

may be stimulated by temp, chemicals, physical means

sensory changes with aging

senses become less acute and less able to distinguish details

aging increases the threshold needed to perceive sensory input so the amount of sensory input needed to be aware becomes greater

physical changes account for most of the other sensation changes

age-related eye changes may begin as early as 30

visual changes with aging

less tear production

structural deteriorations

• corneas become less sensitive

• pupil size decreases and react more slowly

• lens becomes yellowed, less flexible and slightly cloudy

• fat pads supporting eye decrease and eyes sinks back into the skull

• eye muscles weaken, decreasing the ability to rotate the eye fully and limiting the visual field

• presbyopia: difficulty focusing the eyes

ear function decline with aging

presbycusis: hearing may decline slightly, especially with high-frequency sounds. can occurs as early as 50

treatment: surgery or hearing aid