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Chapter 14 Sensory Function Sensory System • General senses include pain, light touch, pressure, temperature, and proprioception • Special senses include taste, smell, sight, hearing, and balance Sensory Receptors • Mechanoreceptors – activated by mechanical stimuli such as touch or pressure • Chemoreceptors – activated by chemicals in the blood, food, or air • Thermoreceptors – activated by heat or cold • Photoreceptors – activated by light • Nociceptors – activated by painful stimuli Pain • Associated with many conditions • Protective mechanism • Most common reason that people seek medical attention • Can be used to aid diagnosis • Subjective feeling • Pain threshold – perception of pain – Can be influenced by affective, behavior, cognitive, sensory, and physiologic factors • Unrelieved pain can delay healing, stimulate the stress response and result in pain tolerance Types of Pain • Somatic pain – Results from noxious stimuli to the skin, joints, muscles, and tendons – Generally easy to pinpoint • Visceral pain – Results from noxious stimuli to internal organs – Usually vague and diffuse – May be sensed on body surfaces at distant locations from the originating organ, called referred pain Types of Pain • Phantom pain – Exists after the removal of a body part – Severed neurons may result in spontaneous firing of spinal cord neurons because normal sensory input has been lost – Can be extremely distressing but usually resolves with time • Intractable pain – Chronically progressing pain that is unrelenting and severely debilitating – Does not usually respond well to typical pharmacologic pain treatments – Common with severe injuries, especially crushing injuries • Neuropathic pain – Results from damage to peripheral nerves by disease or injury – Tends to be chronic and intractable Eyes • • • • Perceive the environment Sclera – white area Cornea – lens on anterior surface Choroid – middle layer of the eye, which contains melanin to absorb stray light • Ciliary body – anterior portion of the choroid, which contains smooth muscle fibers that control the shape of the lens to focus on incoming light • Iris – colored portion • Pupil – dark opening in the center of the iris Eyes • Retina – innermost layer of the eye – Contains an outer, pigmented layer and an inner layer consisting of photoreceptors and nerve cells – Weakly attached to the choroid, making it vulnerable to damage – Contains two types of photoreceptors • Rods – sensitive to low light and function at night • Cones – only operate in bright light and are responsible for visual acuity and color vision Eyes • Optic nerve – form from the axons of the ganglion cells at the back of the eye – This area contains no photoreceptors and is insensitive to light • Visual images cast upside down onto the retina, and impulses are transmitted to the brain Eyes • Lens – transparent, flexible structure behind the iris • Anterior chamber - front of the lens • Posterior chamber – behind the lens • Aqueous humor - watery liquid in the anterior chamber that provides nutrients to the cornea and lens and carries away cellular waste products Eyes • Vitreous humor – clear, gelatinous material that fills the posterior chamber • Conjunctiva – fragile membrane that covers the inner surface of the eyelid and the exposed surface of the eye • Lacrimal glands keep surface moist • Blinking cleans the eye by sweeping the fluid • Tears drain on the inner side through two lacrimal ducts Ears • Detect and process sound, detect body position, and maintain balance • Outer ear – auricle (or pinna), ear lobe, and external ear canal • Middle ear – tympanic membrane and the ossicles • Inner ear – cochlea, semicircular canals, saccule, and utricle Sound Transmission • Enters through the auricle, an irregularly shaped cartilage that channels sound into the ear • Sound travels through the external ear canal until reaching the tympanic membrane, or eardrum • Sound hits the tympanic membrane, creating vibrations Sound Transmission • The vibrations transmit from the membrane to the ossicles—malleus (hammer), incus (anvil), and stapes (stirrup) • The malleus lies near the tympanic membrane, and vibrations from the membranes cause the malleus to rock back and forth • This rocking causes the incus to vibrate, which, in turn, causes the stapes to move in and out against the oval window, an opening to the inner ear covered with a membrane Sound Transmission • Vibrations created by the tympanic membrane amplify as they are transmitted through the structures to the inner ear • Movement of the oval window causes fluid within the cochlea to vibrate, creating waves • The organ of Corti contains hearing receptors, the hair cells, and vibrations at the organ of Corti stimulate hair movement • Dendrites wrap the bases of these hair cells • Hair movement causes the dendrites to form nerve impulses that travel to the brain via the vestibulocochlear nerve, cranial nerve VIII Position and Balance • Vestibular apparatus – located in the inner ear • Two parts – Semicircular canals – three ringlike, fluid-filled structures that house receptors for body position and movement; fluid movement stimulates dendrites to send impulses to the brain to report this movement – Vestibule – bony chamber positioned between the cochlea and semicircular canals that houses receptors that respond to body position and movement Ears • Eustachian tube – located in the middle ear and opens into the pharynx – Acts as a pressure valve – Normally, the tube remains closed – May become open with activities such as yawning and swallowing – Opening the eustachian tube allows air to flow in and out of the middle ear, equalizing the internal and external pressure on the tympanic membrane Understanding Sensory Conditions • Alterations result Altered Sensory Perception • Alterations may also result in: – Risk for Injury Congenital Cataracts • Clouding of the lens that is present at birth • Results in hazy vision • In most cases, no specific cause can be identified • Associated with several genetic and chromosomal conditions (e.g., Down syndrome, Patau syndrome, Lowe syndrome, and galactosemia) as well as intrauterine infection exposure (e.g., congenital rubella) Congenital Cataracts • Other manifestations: failure to demonstrate visual awareness and presence of nystagmus • Diagnosis: history, physical examination (including a thorough ophthalmology exam), and additional tests may be necessary to determine other associated conditions • Treatment: may not be required, surgical removal, artificial intraocular lens, patching, manage any underlying disorder Congenital Ear Conditions • • • • • Anotia – absence of the auricle Microtia – underdeveloped, small auricle Atresia – lack an external ear canal These conditions are more common in males Often associated with other congenital conditions affecting the head (e.g., hemifacial microsomia, Goldenhar syndrome, and Treacher-Collins syndrome) • May be unilateral or bilateral • Congenital hearing loss can occur because of damage associated with maternal rubella and syphilis infection during pregnancy Sensory Conditions Associated With Aging • The 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 of the sensation becomes greater • Physical changes account for most of the other sensation changes Sensory Conditions Associated With Aging • Age-related eye changes may begin as early as 30 • Eye changes include – Less tear production – Structural deteriorations – Corneas becomes less sensitive – Pupil size decrease 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 – Visual acuity may gradually decline – Presbyopia – difficulty focusing the eyes • Treatment: glasses or contact lenses, use red lighting, and lower lighting Sensory Conditions Associated With Aging • All the ear structures thicken with aging affecting balance and hearing • Hearing may decline slightly, especially with high-frequency sounds • Hearing loss accelerates in people who were exposed to excessive noise or smoking when they were younger • Presbycusis – age-related hearing loss • Hearing acuity may decline slightly beginning about 50 years of age, possibly caused by changes in the auditory nerve • The brain may have a slight decreased ability to process or translate sounds into meaningful information Sensory Conditions Associated With Aging • Impacted cerumen is another cause of impaired hearing and is more common with increasing age • Sensorineural hearing loss involves damage to the inner ear, auditory nerve, or the brain • Conductive hearing loss occurs when sound has problems transmitting through the outer and middle ear to the inner ear • Tinnitus is common • Treatment: surgery or a hearing aid may be helpful for conductive type of hearing loss, depending on the specific cause Conjunctivitis • Infection or inflammation of the conjunctiva • Caused by viruses (most common), bacteria (e.g., Staphylococcus, Chlamydia, and gonorrhea), allergens (e.g., pollen and dust), chemical irritants, and trauma • Can generate blurry vision and photophobia • Viral infections normally produce a watery or mucuslike exudate Conjunctivitis • Bacterial infections usually produce a yellow-green exudate • Allergens and irritants typically produce redness, itching, and excessive tearing • Risk factors: wearing contact lenses and using contaminated makeup or ophthalmic medications • Bacterial and viral is highly contagious through direct contact • Treatment: many resolve without treatment, vary depending on the underlying agents, treat infants with ophthalmic antibiotics shortly after birth, and warm moist compresses Keratitis • Inflammation of the cornea that can be triggered by an infection or trauma • The HSV type 1 can be self transmitted from the mouth and cause an ulcerated form • Manifestations: severe pain, photophobia, and visual disturbances • Treatment: varies depending on the underlying etiology, but includes ophthalmic or oral antibiotics and corticosteroid agents Otitis Media • Infection or inflammation of the middle ear • Common condition in young children because the eustachian tubes of young children are narrower, straighter, and shorter than those of adults and older children and an immature immune system • Additional cause: fluid accumulation in the middle ear due to adenoid enlargement, usually due to inflammation • Typically begins as a viral upper respiratory infection • More common in the winter months • Fluid collection from the viral infection provides a prime medium for secondary bacterial growth, usually Streptococcus pneumoniae and Haemophilus influenzae Otitis Media • Additional risk factors: child care in group settings, feeding infants in the supine position, environmental smoke exposure, and a history of allergic rhinitis • Complications: rupture of the tympanic membrane, scar tissue formation, conductive hearing loss, mastoiditis, cholesteatoma, meningitis, and osteomylitis • Manifestations: ear pain, crying or irritability, rubbing or pulling at the ear, mild hearing deficits, sleep disturbances, red and bulging tympanic membrane, indications of infection, purulent or clear exudate from the external ear canal (if the tympanic membrane ruptures), nausea, vomiting, and headache Otitis Media • Diagnosis – History and a physical examination – Otologic examination including visualization of the tympanic membrane, tympanometry, and acoustic reflectometry • Treatment – – – – – Oral or otologic antibiotics and analgesics Oral decongestant and antihistamine agents Antipyretics Tympanostomy tubes Removal of the adenoids Otitis Externa • Infection or inflammation of external ear canal or auricle • Usually bacterial in origin (often Pseudomonas aeruginosa) but may also be fungal • Generally arises from moisture in the ear that creates an environment for bacterial or fungal growth or introduction of the organisms from external sources Otitis Externa • Risk factors: swimming in contaminated water, scratching outside or inside of ear, and insertion of foreign objects • Complications: hearing loss, cellulitis, necrosis, osteomylitis, and meningitis • Manifestations: ear pain that worsens with auricle movement, purulent exudate, itching, a sensation of fullness in the ear, and hearing deficits Otitis Externa • Diagnosis: history, physical examination (including an otologic examination), and exudate analysis • Treatment – Otologic antibiotics, antifungals, corticosteroids, and analgesics – Clean the external canal • Prevention: drying the ears after swimming or bathing with an alcohol-based product, avoiding insertion foreign objects into the ear, and treating pools properly Eye Trauma • Causes: direct physical trauma or chemical burns • May vary in severity from mild (e.g., black eye) to sight threatening (e.g., corneal abrasions and closed-angle glaucoma) • Vision deficits often result Eye Trauma • Manifestations: eye pain, edema, blurry vision, diplopia, dry eyes, photophobia, floaters, pupil dilatation, and pupils that are unresponsive to light • Early diagnosis and treatment can prevent or limit the severity of visual deficits • Diagnosis: history and physical examination (including an ophthalmic examination often by an ophthalmologist) Eye Trauma • Treatment – Flushing irritant out of the eye with sterile saline – Avoiding rubbing the eye – Leaving an embedded object in the eye – Covering the eye with a sterile dressing or cloth – Applying eye patches to protect the eye during the healing process – Repairing any damage surgically Ear Trauma • Causes: direct physical trauma (e.g., foreign objects and insects) and excessively loud noises (e.g., explosions and gunshots) • Can result in permanent hearing deficits • Manifestations: bloody or clear exudate, tinnitis, dizziness, ear pain, hearing deficits, nausea, vomiting, edema, and a sensation that an object is in the ear Ear Trauma • Treatment – Removing the object if it is visible and easily removed – Performing surgery to remove objects or repair the damage – Limiting exposure to loud sounds as structures heal Glaucoma • Group of eye conditions that lead to damage to the optic nerve • Causes: increased intraocular pressure and decreased blood flow to the optic nerve • Pressures inside the eye can climb because of blocked outflow of aqueous humor or increased production of aqueous humor • These increased pressures cause ischemia and degeneration of the optic nerve • Second leading cause of blindness (diabetic retinopathy is number one) Open-Angle Glaucoma • Most common type • Intraocular pressure increases gradually over an extended period • Risk factors: family history and African American decent • Manifestations: painless, insidious, bilateral changes in vision (e.g., tunnel vision, blurred vision, halos around lights, and decreased color discrimination) Closed-Angle Glaucoma • Medical emergency • Result of a sudden blockage of aqueous humor outflow • Causes: trauma, sudden pupil dilatation (e.g., exposure to bright light after prolonged exposure to darkness), prolonged pupil dilatation (e.g., medications for eye examinations), and emotional stress Closed-Angle Glaucoma • Typically unilateral, but it may affect both eyes • Manifestations: sudden and severe eye pain, headache, nausea, vomiting, a nonreactive pupil, redness, haziness of the cornea, and vision changes (e.g., halos around lights) Glaucoma • Congenital glaucoma – Present at birth – Result of abnormal development of outflow channels (trabecular meshwork) of the eye – X-linked, recessive hereditary pattern – May go unnoticed for a few months – Manifestations: excessive lacrimation, photophobia, corneal edema, gray-white appearance to the cornea, enlarged eye globe, and vision deficits Glaucoma • Secondary glaucoma – Result of certain medications (e.g., corticosteriods), eye diseases (e.g., uveitis and nearsightedness), and systemic diseases (e.g., arteriosclerosis and diabetes mellitus) Glaucoma • Diagnosis – History and physical examination – Ophthalmic examination including gonioscopy, tonometry, optic nerve imaging, pupillary reflex response, retinal examination, slit lamp examination, visual acuity testing, and visual field measurement Glaucoma Treatment • Strategies for open-angle glaucoma – Ophthalmic medications • Beta blockers • Alpha agonists • Carbonic anhydrase inhibitors • Prostaglandin-like compounds • Miotic or cholinergic agents • Epinephrine compounds • Alpha-2 adrenergic agonists Glaucoma Treatment – Oral medications (not generally effective when used alone), including carbonic anhydrase inhibitors – N-methyl d-aspartate receptor antagonist – Laser surgery to open aqueous humor outflow – Filtering surgery – Drainage implants Glaucoma Treatment • The main strategy for treating closed-angle glaucoma is iridotomy • The main strategies for treating congenital glaucoma is surgery to open the aqueous humor outflow channels (e.g., laser, filtering, and drainage implants) • Strategies to treat secondary glaucoma include: – Chronic disease management – Treating or eliminating underlying causes – Previously discussed glaucoma pharmacologic and surgical treatments Cataracts • Opacity or clouding of the lens • Can occur as a congenital condition or develop later in life • Risk factors for adult-onset cataracts: family history, advancing age, smoking, ultraviolet (UV) light exposure (natural or artificial), metabolic conditions (e.g., diabetes mellitus), certain medications (e.g., corticosteroids), and eye injury (e.g., trauma and infection) • May affect one or both eyes and do not necessarily affect eyes symmetrically Cataracts • Other manifestations – Cloudy, fuzzy, foggy, or filmy vision – Color intensity loss – Diplopia – Impaired night vision gradually progressing to impaired day vision – Halos around lights – Photosensitivity – Frequent changes in eyeglass or contact prescription Cataracts • Diagnosis – History and physical examination – Ophthalmic examination includes visual acuity testing, retinal examination, and slit lamp examination • Treatment: surgery and managing or eliminating contributing factors Macular Degeneration • Deterioration of the macular area of the retina • Caused by impaired blood supply to the macula that results in the cellular waste accumulation and ischemia • The most significant risk factor for this condition is advancing age • Risk factors: family history, being female, Caucasian decent, smoking, high-fat diet, and obesity Macular Degeneration • Dry macular degeneration – Occurs when the blood vessels under the macula become thin and brittle – Small yellow deposits (drusen) form under the macula – Deposits increase in size and number, blurring vision and creating a dim spot in the central vision – Almost all people with macular degeneration start with the dry form – Progresses gradually (over years) Macular Degeneration • Wet macular degeneration – Occurs in only about 10% of people with macular degeneration – Brittle vessels break down, and new, abnormal, fragile blood vessels grow under the macula – Vessels leak blood and fluid, leading to macula damage – Not as common, but causes most of the vision loss associated with the condition – Progresses suddenly with rapid vision loss (over weeks or months) Macular Degeneration • Diagnosis – History and physical examination – Ophthalmic examination includes visual acuity using the Amsler grid, retinal examination, fluorescein angiogram, and optical coherence tomography Macular Degeneration Treatment • No treatment exists for dry macular degeneration • Age-Related Eye Disease Study formula can slow progression, but smokers should not use this treatment – 500 milligrams of vitamin C – 400 international units of beta-carotene – 80 milligrams of zinc – 2 milligrams of copper Macular Degeneration Treatment • No cure for wet macular degeneration • Strategies may include: – Laser surgery – Photodynamic therapy – Antiangiogenesis or anti-vascular endothelial growth factor therapy – Low-vision aids – Occupational therapy Otosclerosis • Abnormal bone growth in the middle ear, usually involving an imbalance in bone formation and resorption • Cause is unknown, but appears to be hereditary • Abnormal spongelike bone grows in the middle ear, preventing the ear structures from vibrating in response to sound waves • Conductive hearing loss progressively worsens • Nerve loss can also occur • Most common in young adults, women and Caucasians • Pregnancy may also trigger • Typically affects both ears • Tinnitus may also be present Otosclerosis • Diagnosis: history, physical examination (including a hearing test), and temporal-bone computed tomography • Treatment – Medications such as oral fluoride, calcium, or vitamin D may help to control the hearing loss, but the efficacy remains in question – Hearing aids to treat the hearing loss – Surgery to remove the stapes and replace it with a prosthesis – Laser surgery to create an opening in the stapes with or without the placement of the prosthetic device Meniere’s Disease • Disorder of the inner ear that results from endolymph swelling • This swelling stretches the membranes and interferes with the hair receptors in the cochlea and vestibule • The exact cause is unknown, but may be associated with head injuries, otitis media, and syphilis • Additional risk factors: allergic rhinitis, alcohol consumption, stress, fatigue, certain medications (e.g., aspirin), and respiratory infections Meniere’s Disease • Manifestations – Typically occur in waves of acute episodes that last several months followed by brief periods of relief – Attacks triggered by changes in barometric pressure or any of the risk factors – Include: intermittent episodes of vertigo, tinnitus, unilateral hearing loss, and a sensation of fullness • Complications: permanent hearing loss Meniere’s Disease • Diagnosis: history, physical examination (including a neurologic assessment), hearing test, balance test, electrocholeography, electronystagmography, caloric stimulation, head computed tomography, and head magnetic resonance imaging Meniere’s Disease • Treatment – – – – – – – – – – – – – No cure Antihistamine agents Benzodiazepines Anticholinergic agents Diuretics Antiemetic agents Limitation of dietary sodium intake (to promote fluid retention) Avoiding triggers (e.g., alcohol and stress) Middle ear injections of gentamicin (an ototoxic antibiotic that can reduce balance structures) or corticosteroids Partial or complete surgical removal of the endolymph or inner ear Vestibular nerve resection Hearing aids Physical therapy to improve balance Eye Cancer • Uncommon • Affecting genders and ethnic groups relatively evenly • Can affect any part of the eye • Most common intraocular cancers in adults are melanoma and lymphoma • Most frequent eye cancer in children is retinoblastoma Eye Cancer • May metastasize to the eye from other parts of the body • Manifestations: some sort of visual disturbance (e.g., losing part of the visual field and seeing flashing lights) • Diagnosis: history, ophthalmic examination, ultrasound, fluorescein angiography (imaging of blood vessels in the eye using contrast dye), biopsy, and other tests to detect and evaluate metastasis • Treatment: surgery, radiation, and prosthetic eye Strabismus • Gaze deviation of one eye • The eyes do not coordinate to focus on the same object together, resulting in diplopia • Most often appears at birth or shortly after • In children, the brain will begin to ignore input from one eye • If the brain continues to ignore one eye, the eye will never function properly, and permanent visual deficits may result (e.g., amblyopia) Strabismus • Causes: a weak or hypertonic eye muscle, a short muscle, or a neurologic deficit • Often associated with chromosomal defects (e.g., Down syndrome), intrauterine infection exposure (e.g., congenital rubella), eye cancers (e.g., retinoblastoma), and traumatic brain injuries • Diagnosis: history and physical examination (including an ophthalmic examination and a neurologic examination) • Treatment: glasses (e.g., prism glasses), eye muscle exercises, eye patching, and surgery Amblyopia • Loss of one eye’s ability to see details • Most common cause of vision problems in children • Occurs when the brain and eyes do not work together properly; the brain favors one eye • The preferred eye has normal vision, but because the brain ignores the other eye, vision does not develop normally • Normal eye attempts to compensate for affected eye, creating a viscous cycle where normal eye becomes stronger and affected eye becomes weaker Amblyopia • The brain stops growing between 5 and 10 years of age, at which time the condition becomes permanent • Causes: strabismus, family history, bilateral astigmatism, congenital cataracts, farsightedness, and nearsightedness • Diagnosis: history and physical examination (including an ophthalmic examination) • Treatment: wearing glasses (e.g., prism glasses), eye muscle exercises, eye patching, ophthalmic medication (atropine may be used to dilate the pupil of the normal eye to “chemically patch” it), and surgery Retinal Detachment • Acute condition that occurs when the retina separates from its supporting structures • Causes: spontaneously, severe nearsightedness, trauma, diabetes mellitus, inflammation, degenerative aging changes, and scar tissue • Occurs when vitreous humor leaks through a retinal tear and accumulates underneath the retina Retinal Detachment • Leakage can also occur through tiny holes where the retina has thinned due to aging or other retinal disorders • Less commonly, fluid can leak directly underneath the retina, without a tear or break • As vitreous humor collects underneath it, the retina peels away from the underlying choroid • These detached areas may expand over time • The retina becomes ischemic and stops functioning, causing vision loss Retinal Detachment • Manifestations: typically painless, flashes of light in the peripheral visual field, blurred vision, floaters, and darkening vision (like a curtain drawing across a visual field) • Diagnosis – History and physical examination – Ophthalmic examination including an electroretinogram, fluorescein angiography, intraocular pressure measurements, ophthalmoscopy, a refraction test, retinal photography, color discrimination, visual acuity testing, slit lamp examination, and eye ultrasound Retinal Detachment • Medical emergency • Treatment: surgery including a cryopexy (intense cold application to the area with an ice probe to form scar tissue, which holds the retina to the underlying layer), laser surgery (to seal the tears or holes in the retina), pneumatic retinopexy (placing a gas bubble in the eye to help the retina float back into place), scleral buckle (indents the eye wall), and vitrectomy (removes gel or scar tissue pulling on the retina) Tinnitus • Hearing abnormal noises in the ear • May be described as a ringing, buzzing, humming, whistling, roaring, or blowing • May be associated with presbycusis, exposure to excessive noise, cerumen impaction, otosclerosis, Meniere’s disease, stress, head injury, acoustic neuroma, atherosclerosis, hypertension, carotid stenosis, arteriovenous malformation, caffeine, and ototoxic medications (e.g., many antibiotics, aspirin, chemotherapies, and diuretics) Tinnitus • Diagnosis: history, physical examination (including a complete hearing test and otoscopic examination), and tests to identify underlying cause • Treatment: – Treating the underlying cause (e.g., removing cerumen and controlling blood pressure) – Tricyclic antidepressants – Alprazolam (Niravam, Xanax), a benzodiazepine – Acamprosate (Campral), a drug used to treat alcoholism – White noise machines and hearing aids – Avoiding things that can worsen tinnitus (e.g., caffeine, smoking, and ototoxic medications) Vertigo • Illusion of motion • Not the same as dizziness • Peripheral vertigo occurs when there is a problem with vestibular labyrinth, semicircular canals, or vestibular nerve – Causes: certain medications (e.g., aminoglycoside antibiotics), head injuries, Meniere’s disease, nerve compression, infections, and inflammation • Central vertigo occurs when there is a problem in the brain, particularly in the brain stem or cerebellum – Causes: arteriosclerosis, certain medications (e.g., antiseizure agents and aspirin), alcohol, migraines, multiple sclerosis, and seizures – Additional manifestations: nausea and vomiting Vertigo • Diagnosis: history, physical examination, and other tests to determine the underlying etiology • Treatment: anticholinergic agents, antihistamines (especially meclizine [Antivert]), benzodiazepines, antiemetics, and safety precautions