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Pain, Temperature
Regulation, Sleep, and
Sensory Function
Chapter 15
1
Pain
“Pain is an unpleasant sensory and emotional
experience associated with actual or potential
tissue damage or described in terms of such
damage” —International Association for the Study of Pain
“Pain is whatever the experiencing person
says it is, existing whenever he says it does”
—McCaffrey
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Pain Theories
Specificity theory
Amount of pain is related to the amount of tissue
injury
Accounts for many types of injuries but does not
explain psychological contributions
Gate control theory
Developed to explain the complexities of the pain
phenomenon
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Neuroanatomy of Pain
Nociception
Perception of pain
Nociceptors
Bare nerve endings in skin, muscle, joints,
arteries, and the viscera that respond to chemical,
mechanical, and thermal stimuli
Can detect a wide range of stimuli
Aδ fibers
Unmyelinated C polymodal fibers
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Pathways of Nociception
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Pathways of Nociception
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Pathways of Nociception
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Neuromodulation of Pain
Segmental inhibition
Diffuse noxious inhibitory controls
Integration of:
Peripheral sensory axon terminals
Spinal interneurons
Top-down control pathways
All converge on the spinal dorsal horns
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Neuromodulation of Pain
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Neuromodulation of Pain
Chemicals and neurotransmitters
Pain excitatory
Pain inhibitory
Modulators of pain
Direct excitation
Threshold depolarization from direct stimuli
Indirect excitation
Threshold depolarization from inflammatory
mediators after tissue injury
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Endorphin Response
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Clinical Description of Pain
Pain threshold
Perceptual dominance
Point at which a stimulus is perceived as pain
Pain at one location may cause an increase in the
threshold in another location
Pain tolerance
Duration of time or the intensity of pain that a
person will endure before initiation of pain
responses
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Pain Classifications
Nociceptive pain
Pain with a cause of normal tissue injury
Somatic
Visceral
Non-nociceptive pain
Neuropathic pain
Peripheral and central
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Acute Pain
Protective mechanism
Alerts an individual to a condition or experience
that is immediately harmful to the body
Manifestations
Fear and anxiety
Tachycardia, hypertension, fever, diaphoresis, dilated
pupils, outward pain behaviors, elevated blood sugar
levels, decreased gastric acid secretion and intestinal
motility, and a general decrease in blood flow
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Acute Pain
Acute somatic
Arises from connective tissue, muscle, bone and
skin
Aδ fibers—pain is sharp and well localized
C fibers—dull, aching, and poorly localized
Acute visceral
Pain in the internal organs and abdomen
Poorly localized due to the lesser number of
nociceptors
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Acute Pain
Referred pain
Pain that is present in an 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
Myocardial infarction pain
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Referred Pain
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Chronic Pain
A situation; state of existence
May be sudden or develop insidiously
Usually defined as lasting at least 3 months
Response patterns vary
Produces significant behavior and
psychological changes
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Common Types of Chronic Pain
Myofascial pain syndromes
Injury to the muscle and fascia
Spasm, tenderness, and stiffness
Chronic postoperative pain
Cancer pain
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Neuropathic Pain
Result of trauma or disease of nerves
Most often chronic
Painful diabetic neuropathy
Postherpetic neuralgia
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Neuropathic Pain
Deafferentation pain
Sympathetically maintained pain
Complex regional pain syndromes (CRPS)
Central pain
Phantom limb pain
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Pediatrics and Pain
Pathways and chemicals associated with pain
are functional in preterm and newborn infants
Nociceptor system is functional by 24 weeks’
gestation
Expressions of pain
Facial expression
Crying
Body language
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Pediatrics and Pain
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Aging and Pain
Increase in pain threshold
Peripheral neuropathies
Skin thickness changes
Decrease in pain tolerance
Alteration in metabolism of drugs and
metabolites
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Temperature Regulation
Variable
Location
Activity
Environment
Circadian rhythm
Gender
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Temperature Regulation
Peripheral thermoreceptors
Hypothalamic control
Heat production and conservation
Chemical reactions of metabolism
Skeletal muscle contraction
Chemical thermogenesis
Vasoconstriction
Voluntary mechanisms
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Heat Loss
Radiation
Conduction
Convection
Vasodilation
Decreased muscle tone
Evaporation
Increased respirations
Voluntary measures
Adaptation to warmer climates
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Temperature Regulation
Pediatrics
Produce sufficient body heat but are unable to conserve
heat produced
Small body size and high body surface to weight ratio
Thin subcutaneous layer
Aging
Slow blood circulation, vasoconstrictive response, and
metabolic rate
Decreased sweating and perception of heat and cold
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Fever
Resetting of the hypothalamic thermostat
Activate heat production and conservation
measures to a new “set point”
Exogenous pyrogens
Endogenous pyrogens
Endogenous cryogens
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Fever
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Benefits of Fever
Kills many organisms
Decreases serum levels of iron, zinc, and
copper
Deprives bacteria of food
Promotes lysosomal breakdown and
autodestruction of cells
Increases lymphocytic transformation and
phagocyte motility
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Hyperthermia
Not mediated by pyrogens
No resetting of the hypothalamic set point
41o C (105.8o F): nerve damage produces
convulsions
43o C (109.4o F): death results
Forms
Heat cramps, heat exhaustion, heat stroke
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Heat Cramps
Severe spasmodic cramps in the abdomen and
extremities
Following prolonged sweating and associated
sodium loss
Common in individuals not accustomed to heat or
those performing strenuous work in warm climates
Fever, rapid pulse, and increased blood pressure
often accompany the cramps
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Heat Exhaustion
Collapse due to prolonged high core or
environmental temperatures
Prolonged vasodilation and profuse sweating
Dehydration, depressed plasma volumes,
hypotension, decreased cardiac output,
tachycardia
Manifestations
Dizziness, weakness, nausea, and syncope
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Heatstroke
Potentially lethal result of a breakdown in an
overstressed thermoregulatory center
Brain cannot tolerate temperatures >40.5o C
(104.9o F)
Temperature maintained by blood flow through
the veins in the head and face
Cardiovascular and thermoregulatory centers may
cease functioning with higher temperatures
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Heatstroke
Manifestations
Cerebral edema, degeneration of the CNS,
swollen dendrites, and renal tubular necrosis
Rapid peripheral cooling will cause peripheral
vasoconstriction and limit core cooling
Children are more susceptible
Produce more metabolic heat when exercising
Greater surface area to mass ratio
Sweating capacity is less than adults
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Malignant Hyperthermia
Complication of inherited muscular disorder
Precipitated by the administration of volatile
anesthetics and neuromuscular blocking
agents
Increased calcium release or decreased calcium
uptake with muscle contraction
Causes sustained muscle contractions
Increased oxygen consumption and lactic acid
production
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Hypothermia
Body temperature less than 35° C
Produces:
Vasoconstriction, alterations in the microcirculation,
coagulation, and ischemic tissue damage
Ice crystals, which form inside the cells, causing them to
rupture and die
Tissue hypothermia slows the rate of chemical
reactions; increases blood viscosity and slows blood
through the microcirculation; facilitates blood
coagulation and stimulates vasoconstriction
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Hypothermia
Accidental hypothermia
Commonly the result of sudden immersion in
cold water or prolonged exposure to cold
Therapeutic hypothermia
Used to slow metabolism and preserve ischemic
tissue during surgery or limb reimplantation
May lead to ventricular fibrillation and cardiac
arrest
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Trauma-Induced Temperature
Change
CNS trauma
Accidental injuries
Hemorrhagic shock
Major surgery
Thermal burns
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Sleep
Active, multiphase process
Hypothalamus is the major sleep center
Hypocreatins (ovexins)
Promote wakefulness and rapid eye movement (REM)
sleep
Two phases
Rapid eye movement (REM) sleep
Non–rapid eye movement (NREM) sleep
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EEG Stages of Wakefulness and
Sleep
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NREM Sleep
75% to 80% of sleep time
Four stages evaluated by EEG
Stage I
Stage II
Stage III
Stage IV
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REM Sleep
20% to 25% of sleep time
Also known as paradoxic sleep
Occurs every 90 minutes beginning after 1 to
2 hours of sleep
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Normal Sleep Cycles
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Pediatrics and Sleep
Newborns sleep 16 to 17 hours per day
53% of that time is spent in active (REM)
sleep
The infant sleep cycle is about 50 to 60
minutes
Infants enter REM sleep immediately upon
falling asleep
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Aging and Sleep
Total sleep time is decreased
Elderly take longer to fall asleep, and awaken
more frequently during the night
Amount of time in stage IV sleep decreases
Potential causes
Physical ailments, lack of daily routine, circadian
rhythm changes, and medications
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Sleep Disorders
Four classifications
Disorders initiating sleep
Insomnia
Sleep-disordered breathing
Upper airway resistance syndrome
Obstructive sleep apnea
Obesity hypoventilation syndrome
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Sleep Disorders
Four classifications (cont’d)
Disorders of sleep/wake cycle
Parasomnias
Somnambulism
Night terrors
Enuresis
Dysfunctions of sleep, sleep stages, or partial
arousals
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Sleep and Disease
Secondary sleep disorders
Alterations in the quality and/or quantity of sleep
due to primary diseases
Depression, pain, sleep apnea syndromes, and
alterations in thyroid hormone secretion
Sleep-provoked disorders
Sleep stage alterations produced in certain disease
states
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Vision
Blepharitis
Hordeolum (stye)
Infection of the sebaceous glands of the eyelids
Chalazion
Inflammation of the eyelids
Infection of the meibomian (oil-secreting) gland
Keratitis
Infection of the cornea
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Vision
Conjunctivitis
Inflammation of the conjunctiva
Acute bacterial conjunctivitis (pinkeye)
Highly contagious
Mucopurulent drainage from one or both eyes
Viral conjunctivitis
Allergic conjunctivitis
Trachoma (chlamydial conjunctivitis)
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The Eye
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Visual Field and Neuronal
Pathways
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Vision Changes and Aging
Cornea
Anterior chamber
Lens
Ciliary muscles
Retina
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Visual Dysfunctions
Alterations in ocular movements
Strabismus
Diplopia
Nystagmus
Pendular nystagmus
Jerk nystagmus
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Visual Dysfunctions
Alterations in visual acuity
Amblyopia
Scotoma
Retrobulbar neuritis
Cataracts
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Visual Dysfunctions
Alterations in visual acuity
Papilledema
Dark adaptation
Glaucoma
Age-related macular degeneration (AMD)
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Visual Dysfunctions
Alterations in accommodation
Accommodation is the process whereby the
thickness of the lens changes
Oculomotor nerve changes
Decreased flexibility of the lens
Manifestations:
Diplopia, blurred vision, and headache
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Visual Dysfunctions
Alterations in refraction
Myopia (nearsighted)
Hyperopia (farsighted)
Astigmatism
May coexist with myopia or hyperopia
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Alterations in Refraction
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Visual Dysfunctions
Alterations in color vision
Age-related yellowing of the lens
Colorblindness
Generally an X-linked recessive trait
Commonly red-green colorblindness
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Visual Dysfunctions
Neurologic disorders
Hemianopia
Injury to the optic chiasm
Homonymous hemianopsia
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Neurologic Disorders Causing
Visual Dysfunction
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The Ear
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The Ear
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Aging and Hearing
Cochlear hair cell degeneration
Loss of auditory neurons in spiral ganglia of
organ of Corti
Degeneration of basilar conductive membrane
of the cochlea
Decreased vascularity of cochlea
Loss of cortical auditory neurons
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Ear Infections
Otitis externa
Infection of the outer ear
Commonly caused by prolonged moisture
exposure (swimmer’s ear)
Otitis media
Acute otitis media
Otitis media with effusion
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Auditory Dysfunction
Conductive hearing loss
Sensorineural hearing loss
Impaired sound conduction
Impairment of the organ of Corti or its central
connections
Presbycusis (age-related hearing loss)
Mixed hearing loss
Functional hearing loss
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Olfaction
Cranial nerve I and part of V
Strong relationship between taste and smell
Olfactory stimulants
Camphoraceous
Musky
Floral
Peppermint
Ethereal
Pungent
Putrid
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Taste
Cranial nerve VII and part of IX
Nerves in the tongue, soft palate, uvula,
pharynx, and upper esophagus
Gustatory stimulants
Sour
Sweet
Salty
Bitter
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Age-Related Olfaction and Taste
Changes
Olfaction
Decline in odor sensitivity
Loss of olfactory sensory neurons and cells in the
olfactory bulbs
Causes diminished appetite and food selection
Taste
Higher concentration of flavors is required
Decline in the number of fungiform papillae
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Olfactory Dysfunction
Hyposmia
Anosmia
Olfactory hallucinations
Parosmia
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Taste Dysfunction
Hypogeusia
Ageusia
Parageusia
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Somatosensory Function
Touch
Sensation involves modality, intensity, location,
and duration
Receptors are present in the skin
Proprioception
Depends on inner ear, vision, and receptors in
joints and ligaments
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Proprioceptive Dysfunction
Vestibular nystagmus
Vertigo
Ménière disease
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