● Alteration in sensory function dysfunctions of the
general or special
senses
• Dysfunctions of the general senses chronic pain,
abnormal temperature regulation, tactile dysfunction
Definitions of pain
• Pain is a complex unpleasant phenomenon composed of
sensory experiences that include time, space, intensity,
emotion, cognition, and motivation
• Pain is an unpleasant or emotional experience
originating in real or potential damaged tissue
• Pain is an unpleasant phenomenon that is uniquely
experienced by each individual; it cannot be adequately
defined, identified, or measured by an observer
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The experience of pain
Three systems interact usually to produce pain:
1. sensory - discriminative
2. motivational - affective
3. cognitive - evaluative
1. Sensory - discriminative system processes information about
the strength, intensity, quality and temporal and spatial
aspects of pain
2. Motivational - affective system determines the individual´s
approach-avoidance behaviours
3. Cognitive - evaluative system overlies the individuals learned
behaviour concerning the experience of pain. It may block,
modulate, or enhance the perception of pain
Pain categories
1.Somatogenic pain is pain with cause (usually known)
localised in the body tissue
a/ nociceptive pain
b/ neuropatic pain
2. Psychogenic pain is pain for which there is no known
physical cause but processing of sensitive information
in CNS is dysturbed
Acute and chronic pain
Acute pain is a protective mechanism that alerts the
individual to a condition or experience that is immediately
harmful to the body
Onset - usually sudden
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Relief - after the chemical mediators that stimulate the
nociceptors, are removed
• This type of pain mobilises the individual to prompt action
to relief it
• Stimulation of autonomic nervous system can be observed
during this type of pain (mydriasis, tachycardia, tachypnoe,
sweating, vasoconstriction)
Responses to acute pain
- increased heart rate - diaphoresis
- increased respiratory rate - blood sugar
- elevated blood pressure - gastric acid secretion
- pallor or flushing, - gastric motility
dilated pupils - blood flow to the viscera,
kidney and skin
- nausea occasionally
occurs
Psychological and behavioural response to acute pain
- fear
- general sense of unpleasantness or unease
- anxiety
Chronic pain is persistent or intermittent usually defined as lasting at least 6 months
The cause is often unknown, often develops insidiously, very often is associated with a sense of hopelessness and
helplessness. Depression often results
Psychological response to chronic pain
Intermittent pain produces a physiologic response similar to acute pain.
Persistent pain allows for adaptation (functions of the body are normal but the pain is not reliefed)
Chronic pain produces significant behavioural and
psychological changes
The main changes are:
- depression
- an attempt to keep pain - related behaviour to a minimum
- sleeping disorders
- preoccupation with the pain
- tendency to deny pain
Pain threshold and pain tolerance
The pain threshold is the point at which a stimulus is perceived
as pain
It does not vary significantly among healthy people or in the same
person over time
Perceptual dominance- intense pain at one location may cause
an increase in the pain threshold in another location
• The pain tolerance is expressed as duration of time or the
intensity of pain that an individual will endure before initiation
overt pain responses.
It is influenced by - persons cultural prescriptions
- expectations
- role behaviours
- physical and mental health
• Pain tolerance is generally decreased:
- with repeated exposure to pain,
- by fatigue, anger, boredom, apprehension,
- sleep deprivation
• Tolerance to pain may be increased:
- by alcohol consumption,
- medication, hypnosis,
- warmth, distracting activities,
- strong beliefs or faith
Pain tolerance varies greatly among people and in
the same person over time
A decrease in pain tolerance is also evident in the elderly,
and women appear to be more tolerant to pain than men
Age and perception of pain
Children and the elderly may experience or express pain
differently than adults
Infants in the first 1 to 2 days of life are less sensitive to pain
(or they simply lack the ability to verbalise the pain experience).
A full behavioural response to pain is apparent at 3 to 12 month of life
Older children, between the ages of 15 and 18 years,
tend to have a lower pain threshold than adults
Pain threshold tends to increase with ageing
This change is probably caused by peripheral neuropathies and changes in the thickness of the skin
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Neuroanatomy of pain
The portions of the nervous system responsible for the
sensation and perception of pain may be divided into three
areas:
1. afferent pathways
2. CNS
3. efferent pathways
The afferent portion is composed of:
a) nociceptors (pain receptors)
b) afferent nerv fibres
c) spinal cord network
· Afferent pathways terminate in the dorsal horn of the
spinal cord (1st afferent neuron)
● 2nd afferent neuron creates spinal part of afferent
system
· The portion of CNS involved in the interpretation of
the pain signals are the limbic system, reticular
formation, thalamus, hypothalamus and cortex
● The efferent pathways, composed of the fibers
connecting the reticular formation, midbrain, and
substantia gelatinosa, are responsible for modulating
pain sensation
The brain first perceives the sensation of pain
• The thalamus, sensitive cortex :
perceiving
describing of pain
localising
• Parts of thalamus, brainstem and reticular formation:
- identify dull longer-lasting, and diffuse pain
• The reticular formation and limbic system:
- control the emotional and affective response to pain
Because the cortex, thalamus and brainstem are
interconnected with the hypothalamus and autonomic
nervous system, the perception of pain is associated with an
autonomic response
The role of the afferent and efferent pathways in
processing of pain information
Nociceptive pain
Nociceptors: Endings of small unmyelinated and lightly
myelinated afferent neurons
Stimulators: Chemical, mechanical and thermal noxae
Mild stimulation positive, pleasurable sensation
(e.g. tickling)
Strong stimulation pain
These differences are a result of the frequency
and amplitude of the afferent signal transmitted
from the nerve endings to the CNS
Location: In muscles, tendons, epidermis, subcutanous tissue,
visceral organs
- they are not evenly distributed in the body
(in skin more then in internal structures)
Nociceptive pain:
- mechanisms involved
in development
Afferent pathways:
• From nociceptors transmitted by small A-delta fibers and
C- fibers to the spinal cord form synapses with neurons
in the dorsal horn(DH)
• From DH transmitted to higher parts of the spinal cord
and to the rest of the CNS by spinothalamic tracts
*The small unmyelinated C- neurons are responsible for the
transmission of diffuse burning or aching sensations
*Transmission through the larger, myelinated A- delta fibers
occurs much more quickly. A - fibers carry well-localized,
sharp pain sensations
Efferent analgesic system
Its role: - inhibition of afferent pain signals
Mechanisms:
- pain afferents stimulates the neurons in periaqueductal
gray (PAG) - gray matter surrounding the cerebral
aqueduct in the midbrain results in activation of efferent
(descendent) anti-nociceptive pathways
- from there the impulses are transmitted through
the spinal cord to the dorsal horn
- there thay inhibit or block transmission of nociceptive
signals at the level of dorsal horn
Descendent antinociceptive systém
Enk – enkefalinergic
PAG – paraaqueductal gray
EAA – excitatory amino acids
RVM – rostral ventro-medial medulla
The role of the spinal cord in pain processing
• Most afferent pain fibers terminate in the dorsal horn of the
spinal segment that they enter. Some, however, extend
toward the head or the foot for several segments before
terminating
• The A- fibers, some large A-delta fibers and small C- fibers
terminate in the laminae of dorsal horn and in the substantia
gelatinosa
• The laminae than transmit specific information (about
burned or crushed skin, about gentle pressure) to 2nd
afferent neuron
• 2nd afferent neurons transmit the impulse from the substantia
gelatinosa (SG) and laminae through the ventral and lateral horn,
crossing in the same or adjacent spinal segment, to the other side
of the cord. From there the impulse is carried through the
spinothalamic tract to the brain. The two divisions of
spinothalamic tract are known:
1.the neospinothalamic tract - it carries information to the mid brain, thalamus and post central gyrus (where pain is perceived)
2. the paleospinothalamic tract - it