Chapter 15
Pain, Temperature Regulation,
Sleep, and Sensory Function
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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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2
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 psychologic contributions
Gate control theory

Explains the complexities of the pain phenomenon
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Neuroanatomy of Pain

Nociception


Primary order neurons: nociceptors




Perception of pain
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
• A-delta fibers
• Unmyelinated C polymodal fibers
Secondary order neurons
Third order neurons
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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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Segmental Inhibition

Low-threshold mechanical information


Touch, vibration, and pressure
Can distract from injury pain
• Example: sucking thumb after hitting with hammer
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Neuromodulation of Pain
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Neuromodulation of Pain

Chemicals and neurotransmitters





Pain excitatory (glutamate, aspartate)
Pain inhibitory (serotonin, GABA, endorphins)
Modulators of pain
Direct excitation
• Threshold depolarization from direct stimuli
Indirect excitation
• Threshold depolarization from inflammatory mediators
after tissue injury


Hyperalgesia
Allodynia
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Indirect Excitation

Increased sensitivity due to inflammatory
mediators

Example: sunburn
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Endorphin Response
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Clinical Description of Pain

Pain threshold



Point at which a stimulus is perceived as pain
Does not vary significantly among people or in the
same person over time
Intense pain at one location may cause an
increase in the threshold in another location
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Clinical Description of Pain

Perceptual dominance

Pain at one location may cause an increase in the
threshold in another location
• An individual with many painful sites may report only the
most painful
• After the dominant pain is diminished, the individual may
then identify other painful areas
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Clinical Description of Pain

Pain tolerance

Duration of time or the intensity of pain that a person
will endure before initiating pain responses
 Influenced by cultural perceptions, expectations, role
behaviors, and physical and mental health
 Decreased with repeated pain, fatigue, anger,
boredom, apprehension, and sleep deprivation
 Generally increased by alcohol consumption,
persistent use of pain medication, hypnosis, warmth,
distracting activities, and strong beliefs or faith
 Varies greatly among people and in the same person
over time
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Clinical Description of Pain

Pain threshold


Perceptual dominance


Point at which 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 initiating pain responses
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Pain Classifications

Nociceptive pain


Pain with normal tissue injury
• Somatic
• Visceral
Non-nociceptive pain

Neuropathic pain
• Peripheral and central
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Acute Pain

Protective mechanism


Alerts 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
 A-delta 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 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 misinterpretation of nociceptive input


Imbalance of neuromodulation controls
Examples
• Decreased level of endorphins
• Predominance of C-neuron stimulation
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Chronic Pain


A situation; state of existence
Cause often unknown





Does not respond to usual therapy
May be sudden or develop insidiously
Usually defined as lasting at least 3 months
Response patterns vary
Significant behavior and psychologic changes
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Common Types of Chronic Pain

Back pain


Myofascial pain syndromes



Most common
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 syndrome (CRPS)
Central pain
Phantom limb pain
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Neuromatrix and Pain:
Emerging Concepts

In neuropathic pain consider:

Psychologic components (e.g., depression or
anxiety)
 Sleep disturbances
 Work-related issues of impairment and disability
 Treatment expectations
 Availability of social support
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Pediatrics and Pain



Pathways 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


Research studies are conflicting
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
41° C (105.8° F): nerve damage produces
convulsions
43° C (109.4° F): death results
Forms

Heat cramps, heat exhaustion, heat stroke
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Heat Cramps




Severe spasmodic cramps in the abdomen
and extremities
Follow prolonged sweating and associated
sodium loss
Common in people not accustomed to heat or
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, profuse sweating


Dehydration, depressed plasma volumes,
hypotension, decreased cardiac output,
tachycardia
Manifestations

Dizziness, weakness, nausea, and syncope
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Heat Stroke


Potentially lethal result of a breakdown in an
overstressed thermoregulatory center
Brain cannot tolerate temperatures greater
than 40.5° C (104.9° F)

Temperature maintained by blood flow through the
veins in the head and face
 Cardiovascular and thermoregulatory centers may
cease functioning in high temperatures
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Heat Stroke

Manifestations



Cerebral edema, degeneration of the CNS, swollen
dendrites, and renal tubular necrosis
Rapid peripheral cooling causes peripheral
vasoconstriction and limits 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 (95° F)
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 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 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
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 on
falling asleep
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Aging and Sleep




Total sleep time is decreased
Older adults take longer to fall asleep;
awaken more frequently during the night
Amount of time in stage IV decreases
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


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 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
Color blindness
• Generally an X-linked recessive trait

Commonly red-green color blindness
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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, 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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