Chapter 34: The Sensory System Vocabulary Flashcards

Fundamentals of the Sensory System

  • General Purpose of the Sensory System

    • Allows humans to perceive, interact with, and experience the surrounding environment.

    • Serves a critical biological role in protecting the body from environmental hazards and harm.

  • The Five Primary Senses

    • Sight (Vision)

    • Hearing (Audition)

    • Taste (Gustation)

    • Smell (Olfaction)

    • Touch (Somatosensation)

Somatosensation and Pain Perception

  • Mechanisms of Touch

    • Tactile sensory nerves are embedded throughout the layers of the skin.

    • Tactile sensitivity varies across different anatomical regions of the body.

    • Deep touch sensory nerves detect mechanical pressure and signal the body to alter physical positions to relieve pressure and prevent tissue ischemia.

  • Pathophysiology of Pain

    • Pain functions as the body's primary distress signal indicating potential or actual damage.

    • Referred (Radiating) Pain

      • Pain perceived in an anatomical location distant from the true origin or site of tissue injury.

      • Example: Radiating left arm pain experienced during a myocardial infarction (heart attack).

    • Phantom Pain

      • Neuropathic pain or sensory perception experienced in a limb or body part that has been surgically or traumatically amputated.

Chemical Senses: Taste and Smell

  • Gustatory System (Taste)

    • Taste receptors (tastebuds) are situated primarily on the surface of the tongue.

    • Five distinct taste modalities:

      • Sweet

      • Salty

      • Bitter

      • Sour

      • Umami (savory)

  • Olfactory System (Smell)

    • Sense organs and chemical receptors responsible for olfaction are located within the superior nasal cavity.

  • Age-Related Alterations and Geriatric Implications

    • The total number of operational chemoreceptors for taste and smell declines progressive with age.

    • Reduction in chemoreceptor density decreases the intensity of gustatory and olfactory sensations.

    • Diminished taste and smell intensity leads to a reduced appetite in elderly individuals.

    • Geriatric Risk: Decreased appetite predisposes geriatric clients to severe nutritional deficiencies, unintended weight loss, and dehydration.

Anatomy and Physiology of Vision

  • Primary Functions of the Eye

    • Detects light levels, spatial forms, visual colors, and physical shapes.

  • Structural Layers (Tunics) of the Ocular Globe

    • Sclera (Outer Layer)

      • Tough, fibrous protective outer coating, commonly referred to as the "white of the eye."

      • Cornea: The transparent anterior portion of the sclera that allows ambient light rays to enter the eye.

    • Choroid (Middle Layer)

      • Vascular layer containing blood vessels that supply oxygen and essential nutrients to eye tissues.

      • Ciliary Body: Tiny muscular structures connected directly to the lens; contracts and relaxes to alter lens shape and curvature, enabling visual accommodation and focusing.

      • Iris: Pigmented colored ring of the eye containing a central dynamic aperture called the pupil; regulates the volume of light entering the inner eye by adjusting pupil diameter.

    • Retina (Innermost Layer)

      • Sensory layer housing specialized photoreceptor cells:

        • Rods: Responsible for vision in dim light and black-and-white perception.

        • Cones: Responsible for high-acuity color vision and detail.

      • Transduces light energy into electrical nerve impulses.

      • Nerve impulses travel out of the eye along the optic nerve directly to the visual cortex of the brain for interpretation.

  • Internal Fluid Chambers

    • Anterior Chamber

      • Located in the space between the cornea and the lens.

      • Filled with clear, watery fluid termed aqueous humor.

    • Posterior Chamber

      • Located in the large space between the lens and the retina.

      • Filled with a clear, gelatinous substance termed vitreous humor, which maintains intraocular pressure and the structural shape of the eyeball.

  • Mechanics of Visual Perception

    • Visual mechanics function analogously to a camera:

      • The retina acts as the visual recording "film."

      • The iris and pupil function as the dynamic aperture control.

      • The cornea and lens act as optical lenses focusing light rays onto the retina to form a clear visual image, which the brain subsequently decodes.

Vision Impairments and Pathologies

  • Refractive Errors

    • Myopia: Nearsightedness (difficulty seeing distant objects clearly).

    • Hyperopia: Farsightedness (difficulty seeing close objects clearly).

    • Astigmatism: Visual distortion resulting from irregular curvature of the cornea or lens.

  • Age-Related Ocular Changes

    • Decrease in the operational photoreceptor cell count within the retina.

    • The crystalline lens becomes gradually opaque and cloudy.

    • The iris becomes rigid, impairing rapid pupil adjustment to altered lighting environments.

    • The crystalline lens loses elasticity, impairing near-distance focusing—a condition known as presbyopia.

    • Lacrimal fluid production decreases, causing ocular dryness and chronic surface irritation.

  • Pathological Eye Conditions

    • Conjunctivitis ("Pink Eye")

      • Infection or acute inflammation of the conjunctival tissue, causing the underlying sclera to appear bright red.

      • Chief Complaints: Itching, burning, excessive tearing, and sticky white or yellow mucopurulent discharge.

      • Transmission: Highly contagious; easily spread by rubbing the infected eye and touching clean surfaces or the uninfected eye.

      • Treatment: Ophthalmic antibiotic drops or ointments.

    • Cataracts

      • Progressive yellowing, hardening, and opacification of the lens, preventing light transmission to the retina.

      • Leads to cloudy vision and eventual blindness if left untreated; highly prevalent in geriatric populations.

      • Treatment: Surgical extraction of the clouded lens and insertion of an intraocular lens implant.

    • Glaucoma

      • Pathological elevation of fluid pressure within the anterior chamber of the eye.

      • Occurs when aqueous humor fails to drain or be absorbed properly.

      • Progressive intraocular pressure crushes the retina and optic nerve, leading to irreversible destruction and blindness.

      • Risk Factors: Age over 40 years, family history of glaucoma, and individuals with dark irises.

      • Treatment: Early detection screenings, daily hypotensive ophthalmic drops, and surgical procedures.

    • Macular Degeneration

      • Pathology characterized by the build-up of proteinaceous deposits (drusen) or abnormal blood vessel growth over the macula (the central area of the retina).

      • Destroys photoreceptors, resulting in loss of central vision fields.

      • Leading cause of legal blindness in adults over 65 years of age.

      • Risk Factors: Tobacco smoking, excessive ultraviolet (UV) sunlight exposure, high-cholesterol diets, and genetic predisposition.

Ophthalmic Prosthetics and Assistive Device Care

  • Understanding Blindness

    • Legal blindness spans a spectrum: some individuals experience absolute darkness, while others retain partial vision (detecting light, movement, broad shapes, or colors without sufficient acuity to identify distinct objects).

    • Individuals with congenital blindness typically adapt effectively and maintain functional independence.

    • Individuals acquiring blindness later in life face significant adjustment and psychological challenges.

  • Eyeglass Maintenance Protocols

    • Cleaning: Clean exclusively with designated microfiber cloths and specialized cleaning solutions designed specifically for optical lenses to prevent stripping anti-reflective or protective coatings.

    • Drying: Dry lenses using soft, clean cloths.

    • Contraindications: Never use paper towels, tissues, or napkins to dry glasses, as their abrasive wood fibers cause permanent lens scratches.

    • Storage: Keep glasses protected inside a hard-shell case stored within easy physical reach of the client.

  • Contact Lens Care

    • Clean and store contact lenses exclusively using dedicated sterile contact lens solutions.

    • Always place individual lenses into their designated left ("L") and right ("R") case compartments to avoid cross-contamination or power mix-ups.

  • Prosthetic Eye Care

    • Prosthetic eyes are constructed of durable ceramic or specialized plastic materials.

    • Formed as a thin, curved shell disc (not a solid sphere) engineered to fit directly beneath the eyelids over an ocular implant.

    • Assist clients with routine removal, cleaning, and storage when required.

    • Prosthetics are extremely expensive; handle with extreme caution.

    • Risk: Improper handling causing physical scratches or nicks will severely injure or irritate the delicate mucosal tissue lining the interior eyelids.

Anatomy and Physiology of Hearing and Balance

  • The Outer Ear

    • Pinna (Auricle): External cartilaginous structure that collects environmental sound waves and funnels them into the auditory canal.

    • External Auditory Canal: Passageway lined with fine hairs and ceruminous glands that secrete cerumen (earwax) to trap foreign dirt and airborne particles.

    • Tympanic Membrane (Eardrum): Thin, membrane barrier separating the outer ear from the middle ear cavity; vibrates in direct response to arriving sound waves.

  • The Middle Ear

    • An air-filled space housing the auditory ossicles (three tiny bones):

      • Malleus (Hammer)

      • Incus (Anvil)

      • Stapes (Stirrup)

    • The ossicular chain creates a physical mechanical bridge between the vibrating eardrum and the inner ear.

    • Eustachian Tube: Channel connecting the middle ear cavity directly to the pharynx (throat).

      • Equalizes atmospheric pressure on both sides of the tympanic membrane to prevent membrane rupture.

  • The Inner Ear

    • Contains sensory receptor structures dedicated to hearing and spatial balance.

    • Structures for Hearing:

      • Cochlea: Fluid-filled bony organ shaped like a snail shell.

    • Structures for Balance (Equilibrium):

      • Vestibular Apparatus: Composed of the vestibule and three semicircular canals.

  • Physiology of Auditory Processing

    • Sound waves are collected by the pinna and funneled down the external auditory canal to strike the tympanic membrane.

    • Tympanic membrane vibrations cause physical movement of the three auditory ossicles (malleus, incus, stapes).

    • The stapes transfers mechanical vibrations into fluid displacement waves inside the cochlea.

    • Fluid movement stimulates internal cochlear hair cell micro-receptors.

    • Receptors generate electrical nerve impulses that travel along the cochlear nerve directly to the auditory cortex of the brain for decoding into recognized sound.

  • Physiology of Balance and Equilibrium

    • Changes in body or head position move internal fluid, activating specialized mechanoreceptors within the vestibular apparatus (vestibule and semicircular canals).

    • Receptors transmit positional nerve signals along the vestibular nerve to the brain, detailing spatial orientation relative to gravity to maintain physical equilibrium.

    • Pathophysiology of Motion Sickness:

      • Occurs when sensory signals transmitted by the eyes conflict directly with positional signals transmitted by the vestibular inner ear apparatus.

      • Sensory mismatch confuses the central nervous system, triggering systemic symptoms of nausea, severe dizziness, and vomiting.

Otic Pathologies and Auditory Disorders

  • Presbycusis

    • Age-related progressive hearing loss caused by stiffening of the tympanic membrane and ossicles, coupled with a decline in inner ear sensory hair cells.

    • Results in a selective inability to perceive high-pitched acoustic frequencies.

    • Causes specific difficulty distinguishing high-frequency consonant sounds like "th" and "s".

    • Significantly impairs the ability to follow spoken conversations when ambient background noise is present.

  • Cerumen (Earwax) Impaction

    • Excessive accumulation and hardening of earwax within the external auditory canal.

    • Manifestations: Conductive hearing loss, sensation of fullness in the ear, persistent ringing (tinnitus), localized itching, and otalgia (ear pain).

    • Risk Factor: Insertion of foreign objects into the canal (such as hearing aids) significantly elevates impaction risks.

    • Treatment: Professional canal flushing/irrigation and administration of prescribed cerumenolytic ear drops performed by nursing staff.

  • Ear Infections

    • Otitis Media

      • Infection of the air-filled middle ear space.

      • Symptoms: Acute ear pain, fever (pyrexia), and diminished hearing capability.

      • Treatment: Pharmacological oral antibiotics or surgical insertion of tympanostomy tubes.

    • Otitis Externa ("Swimmer’s Ear")

      • Infection or inflammation of the cutaneous lining of the external auditory canal.

      • Symptoms: Canal redness and extreme localized pain when the outer ear is touched or manipulated.

      • Treatment: Topical antibiotic ear drops.

  • Ménière’s Disease

    • Chronic, progressive inner ear disorder characterized by excessive accumulation of endolymph fluid.

    • Occurs in sudden periodic episodes or paroxysmal attacks featuring a classic symptom tetrad:

      • Severe vertigo (dizziness)

      • Tinnitus (ringing in ears)

      • Temporary sensorineural hearing loss

      • Intense feeling of ear fullness or pressure

    • Systemic attack manifestations include severe motion nausea and violent vomiting.

    • Immediate Clinical Intervention: Instruct the patient to immediately lie completely flat (supine) and maintain visual focus on a single non-moving, stationary object.

Auditory Assistive Devices and Communication Strategies

  • Communication Guidelines for Hearing Impairments

    • Position yourself directly in front of the individual, facing them fully when speaking.

    • Avoid chewing gum, covering your mouth, or speaking at an unusually fast rate.

    • Utilize written communication notes or visual pads when necessary.

    • Actively confirm that the individual has accurately understood the message being communicated.

  • Hearing Aid Maintenance and Troubleshooting

    • Operational Checks:

      • Verify that the hearing aid unit is switched to the ON position.

      • Verify that the physical volume control wheel is set sufficiently high.

    • Troubleshooting Non-Functional Units:

      • Check battery charge levels and replace depleted batteries.

      • Inspect the opening of the ear mold and external ear canal for blockage secondary to impacted cerumen.