Physiology of pain pathway with flowchart

Pain occurs whenever tissues are being damaged, and it causes the individual to react to remove the pain stimulus.

Hyperalgesia : Increased sensitivity to pain

Types of pain – fast pain and slow pain

FAST PAIN		SLOW PAIN
1. Felt within 1 second after a pair stimulus is applied.		1. Felt after 1 second or more then increases slowly over many second and sometimes over minutes.
2. Sharp pain, pricking pain, acute pain and electric pain		2. Slow burning pain, aching pain, throbbing pain, nauseasis pain and Chronic pain
3. Not felt in most deep tissues of the body.		3. Can occur both in the skin and in almost any deep tissue or organ.
4. Stimulus: mechanical and Thermal		4. Stimulus : mechanical, thermal and chemical
5. A-delta fibres		5. C fibres
6. Velocity : 6-30 m/s		6. 0.5-2 m/s
7. Neospinothalamic tract		7. Paleospinothalamic tract
8. Neurotransmitter: Glutamate		8. Substance P and glutamate

PAIN RECEPTORS AND THEIR STIMULUS

Pain receptors are free nerve endings and pain stimulus can be :

1- Mechanical

2-Thermal

3- Chemical –

bradykinin
serotonin
histamine
K⁺ ions
acetylcholine
proteolytic enzymes
prostaglandins : example – substance P – enhance the sensitivity of pain endings but do not directly excite them.

Non adapting nature of pain receptors : Unlike other receptors of the body, pain receptors adapt very little and sometimes not at all.

Rate of tissue damage as a stimulus for pain

The average person begins to perceive the pain when the skin is heated above 45^oC.

The intensity of the pain is closely (co-related) with the rate of tissue damage from –