Somatic Sensations Somatic Sensations IIII

PAIN & THERMAL PAIN & THERMAL SENSATION:SENSATION:

2.1.112.1.11

DEFINITION: A protective / warning DEFINITION: A protective / warning sensation, when a noxious stimulus is sensation, when a noxious stimulus is applied to a part of the body. Part applied to a part of the body. Part becomes flexed & withdrawn from becomes flexed & withdrawn from source of noxious stimulus & this source of noxious stimulus & this prevents tissue damage.prevents tissue damage.

Pain in a viscera Pain in a viscera warning to seek warning to seek the treatment. (example: pain of the treatment. (example: pain of appendicitis or MI is a warning).appendicitis or MI is a warning).

Types of pain:Types of pain:

2 types of pain:2 types of pain: FIRST / FAST PAINFIRST / FAST PAIN SECOND / SLOW PAINSECOND / SLOW PAIN

FIRST / FAST PAINFIRST / FAST PAIN

is pricking, sharp, short & is is pricking, sharp, short & is localized. localized.

Example: pin prick or cut with a Example: pin prick or cut with a sharp weapon. Fast pain impulses sharp weapon. Fast pain impulses are carried by A delta fibers from are carried by A delta fibers from periphery to spinal cord periphery to spinal cord

(5-30 m/sec).(5-30 m/sec).

SECOND / SLOW PAINSECOND / SLOW PAIN is burning, dull, diffuse & of prolong duration. is burning, dull, diffuse & of prolong duration.

It indicates tissue damage. It indicates tissue damage.

Example: if fingers touch something very hot. Example: if fingers touch something very hot. Slow pain impulses are carried by C fibers Slow pain impulses are carried by C fibers from periphery to spinal cord (unmyelinated, from periphery to spinal cord (unmyelinated, velocity: 0.5 to 2 m/sec).velocity: 0.5 to 2 m/sec).

Pain impulses are carried by lateral Pain impulses are carried by lateral spinothalamic tract.spinothalamic tract.

Noxious stimuli are of different types: Noxious stimuli are of different types: Mechanical, thermal, chemical.Mechanical, thermal, chemical.

Mechanical noxious Mechanical noxious stimuli:stimuli:

Pin prick, Pin prick, cut with a sharp edge, cut with a sharp edge, heavy pressure. heavy pressure. In viscera, distention or increase in In viscera, distention or increase in

pressure (example: a segment of gut pressure (example: a segment of gut is distended). Increased intracranial is distended). Increased intracranial pressure pressure headache. headache.

Thermal noxious stimuli:Thermal noxious stimuli:

Extremes of temperature: Extremes of temperature:

burning hot or freezing cold.burning hot or freezing cold.

Chemical noxious Chemical noxious stimuli:stimuli:

Histamine, Histamine, bradykinin, bradykinin, serotonin, serotonin, insect bites, insect bites, ischemic products (like substance P).ischemic products (like substance P).

PAIN SENSITIVITY IN PAIN SENSITIVITY IN BODY TISSUES:BODY TISSUES:

All body tissues are not pain sensitive.All body tissues are not pain sensitive. Compact bone is without pain receptors (receptors are Compact bone is without pain receptors (receptors are

in periosteum).in periosteum). If a patient gets osteomyelitis If a patient gets osteomyelitis no pain till periosteal no pain till periosteal

involvement.involvement. In brain, no pain receptors. In meninges, pain In brain, no pain receptors. In meninges, pain

receptors. In brain disorder, until meninges are receptors. In brain disorder, until meninges are involved, no pain.involved, no pain.

In lung tissue, no pain receptors, but in pleural In lung tissue, no pain receptors, but in pleural membrane.membrane.

In intestines, pain receptors are in peritoneum.In intestines, pain receptors are in peritoneum. In liver & spleen tissue, no pain receptors, but in their In liver & spleen tissue, no pain receptors, but in their

capsule.capsule. Pain receptors are free nerve endings called Pain receptors are free nerve endings called

nociceptors.nociceptors.

ASPECTS OF PAIN:ASPECTS OF PAIN:

Pain sensation has 2 aspects:Pain sensation has 2 aspects: Pain perception (feeling of pain).Pain perception (feeling of pain). Reaction to pain (emotional aspect Reaction to pain (emotional aspect

of pain).of pain).

INDIVIDUAL PAIN INDIVIDUAL PAIN SENSITIVITY:SENSITIVITY:

Reaction to pain varies in individuals. It Reaction to pain varies in individuals. It includes:includes:

vocalization (noise making), vocalization (noise making), clenching of hand, clenching of hand, facial muscle contraction, facial muscle contraction, narrowing of palpebral fissure, narrowing of palpebral fissure, fall or increase in B.P, fall or increase in B.P, sweating & skin pallor. sweating & skin pallor. In some individuals violent movements of In some individuals violent movements of

body.body.

SIGNIFICANCE OF PAIN SIGNIFICANCE OF PAIN RECEPTORS:RECEPTORS:

Pain receptors are almost non-Pain receptors are almost non-adapted & that is beneficial. adapted & that is beneficial.

As long as there in noxious stimulus, As long as there in noxious stimulus, pain is felt, this has got a protective pain is felt, this has got a protective value.value.

LOCALIZATION OF PAIN LOCALIZATION OF PAIN DEPENDS UPON No. OF DEPENDS UPON No. OF

RECEPTORS:RECEPTORS: Regarding (visceral pain), it is not so Regarding (visceral pain), it is not so

localized, because there are less number of localized, because there are less number of pain receptors in viscera. Superficial pain is pain receptors in viscera. Superficial pain is more localized.more localized.

Visceral pain is also referred.Visceral pain is also referred.

It radiates to a distant structure.It radiates to a distant structure.

Ischemic pain (behind upper sternum Ischemic pain (behind upper sternum left left shoulder shoulder left arm left arm neck neck may radiate to may radiate to right arm. right arm.

Cause: Dermatomal rule.Cause: Dermatomal rule.

Dermatomal rule:Dermatomal rule:

The viscera where pain is produced The viscera where pain is produced & where pain is referred are & where pain is referred are supplied by same sensory / supplied by same sensory / dermatome of spinal cord.dermatome of spinal cord.

Fast pain is more localized than Fast pain is more localized than slow. Touch receptors also play a slow. Touch receptors also play a role in pain localization.role in pain localization.

Pain sensitivity can be tested in Pain sensitivity can be tested in different ways:different ways:

Pricking the skin with a measured Pricking the skin with a measured pressure.pressure.

Pinching the skin (rough method).Pinching the skin (rough method). Applying a hot stimulus (temp: above Applying a hot stimulus (temp: above

45 degrees centigrade).45 degrees centigrade).

Crude Touch or pain Sensation.flv

THERMAL SENSATION:THERMAL SENSATION: Human beings can perceive various grades Human beings can perceive various grades

of thermal sensation.of thermal sensation.

2 types of thermal receptors:2 types of thermal receptors: Cold receptorsCold receptors Warmth receptorsWarmth receptors

At extremes of temperature, pain receptors At extremes of temperature, pain receptors are also stimulated. When there is burning are also stimulated. When there is burning hot / freezing cold hot / freezing cold pain receptors are pain receptors are also stimulated along with thermal.also stimulated along with thermal.

THERMAL RECEPTORS:THERMAL RECEPTORS: Present just beneath the skin in the form of Present just beneath the skin in the form of

aggregations / spots (cold spots & warm spots).aggregations / spots (cold spots & warm spots).

4-10 times more cold spots as compared to 4-10 times more cold spots as compared to warm spots.warm spots.

From warmth receptors impulses are carried From warmth receptors impulses are carried by C fibers.by C fibers.

From cold receptors impulses are carried From cold receptors impulses are carried mainly by A delta fibers & some by C fibers.mainly by A delta fibers & some by C fibers.

Mucus membrane of mouth is relatively insensitive Mucus membrane of mouth is relatively insensitive to warm as compared to cold temperature.to warm as compared to cold temperature.

Exposed areas are relatively less sensitive to Exposed areas are relatively less sensitive to temperature changes as compared to covered temperature changes as compared to covered areas of body like face, scalp & hand.areas of body like face, scalp & hand.

In exposed areas, temperature change can be In exposed areas, temperature change can be detected: 0.5 to 1 degree centigrade while covered detected: 0.5 to 1 degree centigrade while covered areas can detect change of 0.2 degrees even.areas can detect change of 0.2 degrees even.

*Neutral zone (adaptation of thermal receptors) is *Neutral zone (adaptation of thermal receptors) is between 29 to 36 degrees centigrade. We don’t between 29 to 36 degrees centigrade. We don’t feel warmth / cold in this zone. When temperature feel warmth / cold in this zone. When temperature is below 29 or above 36, we feel warmth / cold. is below 29 or above 36, we feel warmth / cold.

Here humidity factor is important. If humid, even Here humidity factor is important. If humid, even 36 degrees is uncomfortable. In dry weather, even 36 degrees is uncomfortable. In dry weather, even 45 degrees is tolerable. 45 degrees is tolerable.

If we take 2 meterials:If we take 2 meterials: WoodWood Metal Metal With same temperature, metal is felt cooler, because it With same temperature, metal is felt cooler, because it

conducts more heat.conducts more heat.

Thermal receptors respond to static temperature but Thermal receptors respond to static temperature but much more to changing temperature.much more to changing temperature.

If temperature is falling, we feel more cold, as If temperature is falling, we feel more cold, as compared to fixed cold temperature (during snow compared to fixed cold temperature (during snow fall).fall).

When there are thermal changes, these effect metabolic When there are thermal changes, these effect metabolic rate in receptors, so accordingly receptors are rate in receptors, so accordingly receptors are stimulated.stimulated.

thermal sensation.flv