Module 4.13 Pain, Temperature, Sleep, and Sensory Function

Pain

an unpleasant but protective phenomenon that is uniquely experienced by each individual; cannot be defined, identified, or measured by an observer

Nociception

processing harmful stimuli through normally functioning nervous system

Nociceptors

free nerve endings in skin, muscles, joints, arteries, and the viscera that respond to chemical, mechanical, and thermal stimuli; can detect a wide range of stimuli

A-delta myelinated fibers

localized fast pain sensations

Unmyelinated C fibers

poorly localized dull pain

Four phases of nociception

transduction→transmission→perception→modulation

Transduction

activation of nociceptors

transmission

conduction to dorsal horn and up spinal cord

Perception

conscious awareness of pain; sensory-discriminative system, affective-motivational system, cognitive evaluation system, pain threshold, perceptual dominance, and pain tolerance

Modulation

increase or decrease in transmission before, during, or after perception

Neurotransmitters of pain modulation

modulate control in periphery, spinal cord, and brain; triggered by tissue injury and/or inflammation

Excitatory neurotransmitters of pain

glutamate(main), asperate, substance P, and calcitonin

Inhibitory neurotransmitters of pain

GABA, glycine, serotonin, norepinephrine

Endogenous opioids

morphine-like neuropeptides; bind with opioid receptors to inhibit pain impulses in periphery, spinal cord, and brain; opioid receptors throughout body, responsible for sensations of well-being and modulation of many physical processes

Enkephalins

most prevalent natural opioids, have pharmacologic actions similar to morphine, bind as direct agonist to opioid receptors; endorphins, dynorphins, and endomorphins

Endocannabinoids

synthesized from phospholipid, classified as eicosanoids, cannabis produces a resin containing cannabinoids, analgesic in humans, drawbacks are the psychoactive and addictive properties

Descending inhibitory of facilitory pathways

inhibitory pathways activate opioid pathways, inhibit release if excitatory neurotransmitters, release inhibitory neurotransmitters, stimulate inhibitory interneurons

Stimulation of efferent pathways inhibit pain signals

Segmental inhibition of pain

A-beta fibers stimulate inhibitory interneurons and decrease pain transmission

Diffuse noxious inhibitory control(DNIC)

pain relieved when two noxious stimuli occur at the same time from different sites

Expectancy-related cortical activation

placebo effect, cognitive expectations cause physiologic effects

Acute pain

protective mechanism, alerts an individual to a condition or experience that is immediately harmful to the body, mobilizes individual to take prompt action, transient, begins suddenly and relieved after pain stimulus removed

Somatic pain

arises from skin, joints, and muscles; can be sharp or dull pain

Visceral pain

arises from internal organs and body cavity linings; poorly localized with aching, gnawing, throbbing, or cramping quality; often radiates or is referred

Referred pain

felt in area removed or distant from its point of origin, the area of referred pain is supplied by the same spinal segment as the actual site, can be acute or chronic

Chronic pain

pain lasting longer than the expected healing time, usually defined as lasting 3-6 months, may be ongoing or intermittent, manifestations thought to be due to stress, produces behavior and psychologic changes, persistent pain causes physiologic adaptation

Neuropathic pain

dysfunction that causes long-term changes in pain pathway structures and abnormal processing of sensory information, amplification of pain without stimulation

Neuropathic pain feeling

often described as shooting, burning, shocklike, or tingling

Neuropathic pain classifications

peripheral neuropathic pain and central neuropathic pain

Thermoregulation

maintained through heat production, heat conservation, and heat loss; varies in response to location, activity, environmental, circadian rhythm, and gender

Temperature mediator

hypothalamus and endocrine system

Peripheral thermoreceptors

skin, liver, and skeletal muscle

Central thermoreceptors

hypothalamus, spinal cord, and viscera

Heat production

chemical reactions of metabolism, skeletal muscle tone and contraction, and chemical thermogenesis

Heat conservation

vasoconstriction, shivering, and voluntary mechanisms(warm clothes)

Heat loss

radiation, conduction, convection, vasodilation, evaporation, decreased muscle tone, increased respiration, voluntary measures, adaptation to warmer climates

Thermoregulation in infants

produce sufficient body heat but are unable to conserve heat produced; small body size and high body surface-to-weight ratio, thin subcutaneous layer, can’t shiver, lower sweating rate, higher peripheral blood flow in the heat

Thermoregulation in the elderly

respond poorly to temperature extremes; slow blood circulation, skin changes, decreased heat-producing activities, disease, decreased shivering and sweating response, metabolic rate, vasoconstrictive response, and perception of heat and cold

Fever

temporary resetting of the hypothalamic thermostat to a higher level, person feels colder and dresses warmer or curls up to get warm; increase in heat production and conservation, exogenous pyrogenes, and endogenous pyrogenes

Fever of unknown origin

high fever for longer than 3 weeks that is undiagnosed

Benefits of fever

helps body to respond to infections

kill many microbes; decrease serum levels of iron, zinc, and copper; promotes lysosomal breakdown and autodestruction of cells; increases lymphocytic transformation and phagocyte motility; augments antiviral interferon production and phagocytosis

Hyperthermia

elevation of the body temperature without an increase in the hypothalamic set point; can produce nerve damage, coagulation of cell proteins, and death; may be associated with stroke or head trauma

Therapeutic hyperthermia

local, regional, or whole-body hyperthermia used to destroy microorganisms or tumor cells

Accidental hyperthermia

heat cramps, heat exhaustion, heat stroke, malignant hyperthermia

Heat cramps

spasmodic cramps in the abdomen and extremities after sweating(sodium loss)

Heat exhaustion

profound vasodilation and profuse sweating resulting from prolonged high core or environmental temperatures

Heat stroke

failure of heat loss mechanisms at core temperatures >40C(104F), may be lethal

Malignant hyperthermia

uncoordinated muscle contractions and increased lactic acid, complication of inherited muscular disorder

Hypothermia

body temperatures less than 35C(95F); produces depression of nervous and respiratory system, vasoconstriction and changed in microcirculation and coagulation, ischemic tissue injury; in severe cases ice crystals form inside cells causing them to rupture and die

Tissue hypothermia

slows rate of cellular metabolism; increases blood viscosity, facilitates blood coagulation, and stimulates vasoconstriction

Therapeutic hypothermia

used to slow metabolism and preserve ischemic tissue during surgery or limb reimplantation

Accidental hypothermia

results from immersion in cold water, prolonged exposure to cold, or altered thermoregulation

Trauma and temperature

CNS trauma leads to central fever→inflammation, increased ICP, intracranial bleeding; does not induce sweating; resistant to antipyretic therapy

Other trauma that alters temperature are accidental injuries, hemorrhagic shock, major surgery, and thermal burns

Sleep

active multiphase process that restores functions and promotes memory consolidation, hypothalamus is major sleep center, hypocretins(orexins) promote wakefulness and REM sleep

Two phases of sleep

rapid eye movement(REM) sleep and non-rapid eye movement(NREM) sleep

REM sleep

20-25% of sleep time, occurs every 90 minutes beginning after 1-2 hours of non-REM sleep, called paradoxical sleep cause EEG is similar to normal awake person

increased parasympathetic activity and variable sympathetic activity; rapid eye movement, muscle relaxation, loss of thermoregulation, altered heart rate, blood pressure, respiration, and memorable dreams

Non-REM sleep

75-80% of sleep time, sympathetic tone decreased and parasympathetic activity increased, state of reduced activity; decreases in metabolic rate, temperature, heart rate, respiration, blood pressure, and muscle tone

Sleep disorder classifications

insomnia, sleep related breathing disorders, central disorders of hypersomnolence, circadian rhythm sleep-wake disorders, parasomnias, and sleep related movement disorders

Dysomnias

inability to fall or stay asleep; accompanied by fatigue, malaise, and difficulty with performance while awake; can be mild, moderate, or severe and may be transient or chronic

Common dysomnias

obstructive sleep apnea syndrome, hypersomnia, narcolepsy, and circadian rhythm sleep disorders

Obstructive sleep apnea syndrome

most commonly diagnosed sleep disorder, results from total or partial upper airway obstruction→excessive loud snoring, gasping, multiple apneic episodes longer than 10 seconds; disrupts total sleep time and produces hypercapnia and low oxygen saturation, diagnosed with polysonography

Risk factors for obstructive sleep apnea

obesity, male sex, older age, and being postmenopausal

Untreated obstructive sleep apnea

polycythemia, hypertension, stroke, heart failure, dysrhythmias, liver congestion, and edema

Hypersomnia

excessive daytime sleepiness; falling asleep during activities, impaired mood and cognitive function

Narcolepsy

primary hypersomnia with disruptions of sleep-wake cycles, usually sporadic, associated with immune-mediated destruction of hypocretin-secreting cells in the hypothalamus; causes hallucinations, sleep paralysis, and rarely cataplexy

Circadian rhythm sleep disorders

common disorder of the 24hr sleep-wake schedule that desynchronize circadian rhythm, long term health consequences

Extrinsic causes of circadian rhythm sleep disorders

rapid time zone change, alternating sleep schedule, changes in total sleep

Intrinsic causes of circadian rhythm sleep disorders

advanced sleep phase disorder, delayed sleep phase disorder

Parasomnias

unusual behaviors occurring during NREM stage 3 sleep; sleepwalking(somnambulism), night terrors, rearranging furniture, eating food, sleep sex, violent behaviors, restless leg syndrome

Special senses

vision(eyes), hearing(ears), olfaction(smell; cranial nerves I and V), and taste(gustation; cranial nerves VII and IX)

Eyes

3 layers; sclera, choroid, and retina; nerve impulses pass through optic nerves to optic chiasm; light entering eye is focused on retina by the lens which is a flexible bioconcave structure; has anterior chamber

Sclera

thick, white, outermost layer of the eye; becomes transparent at the cornea

Choroid

deeply pigmented middle layer of eye; pupil and iris

Retina

innermost layer of the eye, contains rods and cones

Accomodation

lens flexibility allows eye to focus at different distances

Anteriorchamber

aqueous chamber filled with aqueous humor, vitreous chamber filled with vitreous humor

Alterations in ocular movements

strabismus, nystagmus, and paralysis of individual extraocular muscle

Strabismus

one eye deviates; amblyopia(reduced vision in affected eye) and diplopia(double vision)

Nystagmus

involuntary rhythmic movement; pendular nystagmus(regular back and forth movement) or jerk nystagmus(one phase of eye movement is faster)

Paralysis of individual extraocular muscle

limited abduction, abnormal closure of eyelid, ptosis, diplopia

Alterations in visual acuity

caused by amblyopia(reduced or dimmed vision), scotoma(blind spot), cataracts(cloudy area in lens), papilledema(edema of optic nerve), dark adaptation, glaucoma(high intraocular pressure), retinal detachment, age-related macular degeneration

Visual acuity

the ability to see sharp detail

Alterations in accomodation

oculomotor nerve changes

manifestations: diplopia, blurred vision, headache

Presbyopia

loss of accommodation with age

Alterations in refraction

most common visual problem; causes include irregularities in corneal curvate, focusing power of lens, length of eye

myopia, hyperopia, astigmatism

Myopia

nearsighted

Hyperopia

farsighted

Astigmatism

unequal curvate of cornea; may coexist with myopia, hyperopia, or presbyopia

Alterations in color vision

age-related yellowing of the lens or color blindness

Color blindness

generally an X-linked trait(commonly red-green color blindness), acquired color vision with diseases

Neurologic vision disorders

vision disrupted at points along the visual pathway, optic nerve or optic chiasm; causes defects or blindness, blindness in entire visual field of blindness in half of the visual field(hemianopia)

External eye disorders

blepharitis, hordeolum(stye), chalazion, entropin, conjunctivitis, and keratitis

Conjunctivits

inflammation of the conjunctiva; can be acute bacterial conjunctivits(pinkeye), allergic conjunctivits, and trachoma(chlamydial conjunctivits)

The Ear

divided into three areas: external ear, middle ear, and inner ear

External ear

only involved with hearing

Middle ear

only involved with hearing

Inner ear

involved with both hearing and equilibrium

Eustachian tube

connects the middle ear with the nasopharynx

Conductive hearing loss

occurs when physical anomalies in the outer ear or middle ear impair conduction of sound from the outer ear to the inner ear

Conductive hearing loss symptoms

diminished hearing and a soft-speaking voice

Sensorineural hearing loss

caused by impairment of the organ of Corti of its central connections to the auditory cortex; the loss may occur gradually or suddenly