Neurophysiology: Pain Flashcards
what is pain
Pain is defined as a response to noxious stimuli which is damaging or potentially damaging to the normal tissues. Pain can be decribed in a lot of ways including:
-pricking
-stabbing
-ache
-shooting
-burning
-throbbing
what is the importance of pain sensation
- Pain gives warning signal about the existence of
a problem or threat. It also creates awareness of
injury. - Pain prevents further damage by causing reflex
withdrawal of the body from the source of injury - Pain forces the person to rest or to minimize the
activities thus enabling rapid healing of injured part - Pain urges the person to take required treatment to
prevent major damage.
what are the various ways of classifying pain
-based on the duration
-pathophysiological classification
-anatomical classification
-depending on components
what are the types of pain according to its components
Fast pain and Slow pain
what is fast pain
Fast pain is the1st sensation of pain when a stimulus is applied. It is a bright sharp, localized pain. it is followed by slow pain.
Fast pain is carried by Aδ fibres
what is slow pain
Slow pain is the pain that follows after fast pain. It is a dull, diffused, unpleasant pain.
It is carried by C fibers.
what are the classifications of pain under its duration
-Acute pain
-Chronic pain
dwhat is acute pain?
An acute pain is a sharp and intense (severe) pain that is localized and easily identified.
-It is usually localized before spreading to other areas
-It is caused by injury to muscle, bone, or other visceral organs
-The injury stimulates nociceptors
-The pain usually disappears after the source of the pain is treated, and the injury heals. It is usually treated with mediciations.
what is chronic pain
Chronic pain lasts for a longer period of time
-It is not easily described
-It is usually associated with a long term disease like osteoarthritis
-It is resistant to treatment by medication
what are the pathophysiological classifications of pain
-Nociceptive pain
-Neuropathic pain
What is nociceptive pain
This kind of pain results from activation of nociceptors, on injury to the tissues.
It has 2 types
-somatic pain
-visceral pain
wetin be somatic pain
This is pain resulting from stimulation of
-skin
-mucus membrane
-bone
-cartilage
-muscles
-ligament
-tendons
-joints
-connective tissue
what is visceral pain
This is due to stimulation of receptors in the visceral organs.
It is unpleasant and poorly localised.
The pain receptor in the visceral organs are stimulated by:
->substances like bradykinin and proteolytic enzymes released during ischemic reactions
->chemical substances like gastric juice that leak from ruptured ulcers into the peritoneal cavity
->spastic contraction of hollow organs (GIT esp.)
->Over distension of hollow organs
the pain receptors in visceral organs is stimulated by
The pain receptor in the visceral organs are stimulated by:
->substances like bradykinin and proteolytic enzymes released during ischemic reactions
->chemical substances like gastric juice that leak from ruptured ulcers into the peritoneal cavity
->spastic contraction of hollow organs (GIT esp.)
->Over distension of hollow organs
what is neuropathic pain
Neuropathic pain is due to the dysfunction, damage, compression or disease of a nervous structure.
It is either peripheral neuropathic pain or central neuropathic pain
what is peripheral neuropathic pain
This pain is caused by a damage or lesion of a peripheral nerve or dorsal root or dorsal root ganglion
what is central neuropathic pain
this occurs due to a lesion or disease of the structures of the spinal cord or brain
what is the anatomical classification of pain
the location on the body of affected tissue. Examples:
shoulder pain
neck pain
tooth ache
stomach ache
muscle cramps
neurological pain
myofascial pain
what is referred pain?
Referred pain is a pain perceived adjacent to or at a site away from the site of origin.
Deep pain of the visceral organs is referred to other areas, BUT superficial pain is not referred.
give examples of referred pain
- Cardiac pain is felt at inner part of left arm and left
shoulder - Pain in ovary is referred to umbilicus
- Pain from testis is felt in abdomen
- Pain in diaphragm is referred to shoulder
- Pain in gallbladder is referred to epigastric region
- Renal pain is referred to loin.
where is cardiac pain referred
at the inner part of the left arm and left shoulder
where testiscular pain felt
abdomen
where is kidney pain felt
loin
where is gallbladder pain felt
epigastric region
where is ovary pain felt
umblical region
what is the the mechanism of referred pain (dermatomal rule)
According to dermatomal rule, pain is referred to a
structure, which is developed from the same dermatome
from which the pain producing structure is developed.
A dermatome includes all the structures or parts of
the body, which are innervated by afferent nerve fibers
of one dorsal root.
-For example, the heart and inner
aspect of left arm originate from the same dermatome.
So, the pain in heart is referred to left arm.
comment on the pathway of pain from the skin and deeper structures
A. FIRST ORDER NEURONS
first order neurons are from the posterior nerve root ganglia which receive pain sensations from pain receptors via their dendrites and then transmit those impulses to the spinal cord via their axons.
-fast pain fibers are carried by Aδ fibres that end in the marginal nucleus of the posterior grey horn
-slow pain fibres are carried by C fibres and the end in the substantia gelatinosa of rolando in the posterior grey horn
B. SECOND ORDER NEURONS
Generally they ascend as the lateral spinothalamic tract (i.e from the marginal nucleus and substantia gelatinosa of rolando)
-fast pain fibers originate from the marginal nucleus and cross the midline and ascend as the neospinothalamic fibres of the lateral spinothalamic tracts.
These nerves terminate in the ventral posterolateral nucleus of the thalamus, and some in the ascending reticular activating system of the brainstem.
-slow pain fibers originate from the substantia gelatinosa of rolando and also cross the midline and ascend as the paleospinothalamic fibers of the lateral spinothalamic fibers. They end in the:
=> 1/5th terminate in the ventral posterolateral nucleus with the fast fibres
=>Nuclei of the reticular formation of the brainstem
=>Tectum of the midbrain
=>Grey matter surrounding the aqueduct of sylvius
C. THIRD ORDER NEURONS
The third order neurons are in:
-thalamic nucleus
-reticular formation
-tectum
-grey matter around the aqueduct of sylvius
D. CENTER OF PAIN SENSATION
-> the postcentral gyrus of the cerebral cortex
->Hypothalamus: for arousal associated with pain stimuli
comment on t
comment on the pain pathway from the face
It is carried by the trigeminal nerve
comment on the pain pathway from the pelvic region
It is conveyed by the sacral parasympathetic nerves (S1-S4)
Comment on the pain pathway from the viscera
=>The viscera are insensitive to:
-Touching
-Cutting
-Pinching
=>Sensitive to
-Pain
Visceral stimulants include, distention, excessive contraction,
irritation by toxins and chemicals
-Pain sensation from thoracic and abdominal viscera is transmitted by sympathetic (thoracolumbar) nerves.
-Pain from esophagus, trachea and pharynx is carried by vagus and glossopharyngeal nerves.
-By the way, sensations like satiety, hunger, thirst, nausea are transmitted by the vagus nerves.
what are the NT’s of pain sensation
Glutamate and substance P are the neurotransmitters
secreted by pain nerve endings.
=>Aδ afferent fibers,which transmit impulses of fast pain secrete glutamate.
=>The C type fibers, which transmit impulses of slow pain
secrete substance P.
comment on the first order neurons of the pain pathway from skin and deeper regions
The first order neurons are in the posterior nerve root ganglia that receive impulses via their dendrites from receptors for pain, and then transmit those impulses to the spinal cord.
-Fast pain sensations are transmitted via Aδ fibres which end in the marginal nucleus of the posterior grey horn.
-slow pain sensation is transmitted via C fibres in the susbtantia gelatinosa of rolando of the posterior grey horn
comment on the second order neurons of the pain pathway from the skin and deeper regions
-Slow pain from the substantia gelatinosa (of rolando) of the spinal cord cross over the midline and ascend as the paleospinothalamic part of the lateral spinothalamic tract. They end in:
-1/5th end in the ventral spinothalamic nucleus of the thalamus
-tegmentum of the midbrain
-grey matter surrounding the aqueduct of sylvius
-nuclei of reticular formation of the brainstem
comment on the 3rd order neurons of the pain pathway of the skin and deeper regions
They are in:
-thalamic nucleus
-Tegmentum
-grey matter surrounding aqueduct of sylvius
-reticular formation
what is the pain centre (last part of the pain pathway of the skin and deeper regions)
-The parietal cerebral cortex: postcentral gyrus
-The hypothalamus: arousal associated with pain
comment on the visceral sensory fibers
-Similar to those in the skin but are sparser and smaller in
diameter
-Free nerve endings in the gut wall are the receptors for
pain
-Nerve fibres are small myelinated and unmyelinated
fibres
-Nerve fibres traverse through the splanchnic nerve and
sympathetic ganglia ( no synapsis)
-Enter posterior roots by way of white rami
communicantes
-The cell bodies are in the posterior root ganglia and the
central processes synapse in the posterior horn
-The nerve fibres cross over and ascend close to the
spinothalamic tract to reach the thalamus
outline visceral organs an their sensory innervation
=>Heart – sensory fibres from the cardiac nerve
connected centrally with T1- T5
=>Liver, stomach, duodenum, small intestines
and kidneys – receive splanchnic nerve T6 –
T12
=>Large intestines – receive sympathetic
sensory supply via hypogastric plexus;
impulses pass through T10 – L2 segments
=>Pelvic organs – parasympathetic sensory
nerve which pass through posterior roots of
S1 –S4
WHAT IS DEEP PAIN
-Pain initiated by stimulation of nociceptors
in the ligaments, tendons, bones, blood
vessels fasciae and muscles
-Deep pain is dull, aching and poorly
localised. Examples are seen in sprain and broken
bone
-Dull pain is persistent or chronic pain but
usually does not stop one from daily
activities
outline the processes of pain sensation
Transduction
Transmission
Perception
Modulation
what are the types of noxious stimuli
Chemical
Thermal
Mechanical
what is phantom pain
pain felt in a part of the
body that has been removed eg amputation
what is total pain
includes emotional, social and
spiritual factors that affect a persons
perception of pain
lol
what is psychogenic pain
It is affected by psychological factors, often times have
physical origin (tissue or nerve damage) but the pain is increased in intensity or prolonged by fear, stress, anxiety or depression
what are the structures of pain sensation in the forebrain
cerebral cortex, thalamus, hypothalamus
what are the structures of pain sensation in the midbrain
periaqueductal grey matter, reticular formation, locus coeruleus
what are the structures of pain sensation in the medulla
nucleus reticularis, gigantocellularis, nucleus raphe
- Neospinothalamic (fast pain)
- paleospinothalamic tract(slow pain)
what are the structures of pain sensation in the spinal cord
-Dorsal root ganglion
-Dorsal horn ( laminae I – vI)
-Nerve fibres – C- fibres, delta- fibres
what is pain threshold
This is the set point peculiar to each individual for the perception of a stimulus as pain
what are the symptoms of pain
Negative:- this refers to sensation of
numbness
Positive :- this is sensation of abnormal
experience
what are the processes of pain modulation
They are adaptive changes for information reception-:
=>Sensory end organs - cease to respond after
variable period of stimulation
=>Presympathetic inhibition of adjacent nerve cells
by collaterals from active nerve cells
=>Regulation of synaptic transmission in sensory
nuclei by the motor cortex
=>Pyramidal tract fibres send collaterals to the
cuneate, gracile and trigeminal nuclei and the
ventrobasal thalamus
=>Alterations in the state of awareness at a cortical
or subcortical level
what is pain modulation
Pain modulation is the process by which the body alters pain signals along the transmission pathway of the pain. These alterations are adaptive changes for the reception of information. This explains why individuals respond to the same stimulus differently. Pain modulation is in form of a circuit with inputs arising from areas like the hypothalamus, the amygdala and rostral anterior cingulate cortex and outputs from the midbrain (periaqueductal gray region) to the medulla.
