Pain perception , transmission, control & role of physical therapist
Assignment No 1:
“How pain is transmitted and perceived?
What pain controlling strategies are used by physical
“An unpleasant sensory & emotional experience associated with actual or
potential tissue damage, or described in terms of such damage”
Physiological response produced by activation of specific types of nerve
Experienced because of nociceptors being sensitive to extreme
mechanical, thermal, & chemical energy.
Composed of a variety of discomforts
Behavioral indicators of pain are crying, mood changes and from facial
One of the body’s defense mechanism
Fast Pain: Fast pain is transmitted through the A-delta neurons in the skin.
These are the mylinated neurons can transmit the impulse with rate of 40
Slow Pain: slow pain is transmitted via C fibers (unmylinated) , carry impulse
15 pulse /sec.
These are the Chemical substances that allow nerve impulses to move from
one neuron to other, found in synapses.
“Substance P - thought to be responsible for the transmission of painproducing impulses”
First Order Neuron:
These are stimulated by sensory receptors in the skin. End in the dorsal horn of
A-alpha – non-pain impulse
A-beta – non-pain impulse: Large, myelinated. Low threshold
mechanoreceptor; respond to light touch & low-intensity mechanical response
A-delta – pain impulses
due to mechanical pressure
Large diameter, thinly myelinated
Short duration, sharp, fast, bright, localized sensation (prickling, stinging,
C – pain impulses : due to chemicals or mechanical
Small diameter, unmyelinated
Second Order Neurons:
Receive impulses from the FON in the dorsal horn. Second order neurons then
send their information via two pathways to the thalamus: the dorsal column
medial-lemniscal system and the anterolateral system. The first is reserved
more for regular non-painful sensation, while the lateral is reserved for pain
Transmit impulses from the brain (corticospinal tract in the cortex) to
the spinal cord (lamina)
Periaquaductal gray area (PAG) – release enkephalins
Nucleus Raphe Magnus (NRM) – release serotonin
The release of these neurotransmitters inhibit ascending neurons
“Enkephalins” are endogenous opiod peptides produced by the body in
response to painful stimuli.
The transmission process occurs in three stages. The pain impulse is
from the site of transduction along the nociceptor fibres to the dorsal
horn in the spinal cord;
from the spinal cord to the brain stem;
through connections between the thalamus, cortex and higher levels of
The pain impulse is transmitted from the spinal cord to the brain stem and
thalamus via two main nociceptive ascending pathways. These are the
spinothalamic pathway and the spinoparabrachial pathway.
The brain does not have a discrete pain centre, so when impulses arrive in
the thalamus they are directed to multiple areas in the brain where they are
PERCEPTION OF PAIN
Perception of pain is the end result of the neuronal activity of pain
transmission and where pain becomes a conscious multidimensional
experience. The multidimensional experience of pain has affectivemotivational, sensory-discriminative, emotional and behavioural components.
When the painful stimuli are transmitted to the brain stem and thalamus,
multiple cortical areas are activated and responses are elicited.
MODULATION OF PAIN:
The modulation of pain involves changing or inhibiting transmission of pain
impulses in the spinal cord. The multiple, complex pathways involved in the
modulation of pain are referred to as the descending modulatory pain
pathways (DMPP) and these can lead to either an increase in the transmission
of pain impulses (excitatory) or a decrease in transmission (inhibition).
“Pain Gate Theory”
Gate control theory was described by Melzack and Wall in 1965.
This theory explains about a pain-modulating system in which a neural
gate present in the spinal cord can open and close thereby modulating
the perception of pain. The gate control theory suggested that
psychological factors play a role in the perception of pain.
The three systems located in the spinal cord act to influence perception
of pain, viz;
the substantia gelatinosa in the dorsal horn,
the dorsal column fibers, and
the central transmission cells.
The noxious impulses are influenced by a “gating mechanism.”
Stimulation of the large-diameter fibers inhibits the transmission of pain,
thus “closing the gate.” Whereas, when smaller fibers are stimulated, the
gate is opened.
When the gate is closed signals from small diameter pain fibers do not
excite the dorsal horn transmission neurons. When the gate is open pain
signals excite dorsal horn transmission cells. The gating mechanism is
influenced by nerve impulses that descend from the brain.
Factors which influence opening and closing the gate are:
The amount of activity in the pain fibers.
The amount of activity in other peripheral fibers
Messages that descend from the brain.
PAIN CONTROLLING STRATIGIES BY PHYSICAL THERAPIST
Pain controlling strategies used by a physical therapist involves the use of
physical agents,(electrotherapy )and exercise therapy ..
Physical agents involve manual therapy,mechanical therapy, hot and cold
packs, TENs , interferential therapy etc .This method remove stress from
nociceptors thus decreasing the stimuli of pain.
Other Exercises involves deep breathing and progressive muscle relaxation
exercise and mobilization techniques thus stimulating mechanoreceptors that
inhibit pain transmission.
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By: Tahir Ramzan