Physiology of pain

Question 1

Which receptor senses pain?

Answer 1

Nociceptors

Question 2

What is pain?

Answer 2

It is a unpleasant sensory & emotional experience associated with actual or potential tissue damage

• It is a protective mechanism that brings conscious

Question 3

What are the different diseases that does not make us feel pain?

Answer 3

1) Congenital insensitivity to pain

2) Leprosy (bacterial infection)

3) Advanced diabetes

Question 4

Describe the nociceptors

Answer 4

• They are free nerve endings
• They are found in the skin, muscles, and most viscera
• They adapt slowly which is good so that our body is always sensitized to pain

Question 5

How can we measure pain?

Answer 5

• Pain is subjective and you cannot actually measure it
• It is influenced by:
  1) Behavioral response
  2) Emotional reaction
  3) Past experiences
• We can only measure the progress of pain in a given individual and not compare pain between two individuals

Question 6

What are the different types of pain?

Answer 6

1) Cutaneous pain (pin prick)

2) Visceral pain (kidney stones)

3) Deep somatic pain (muscle aches)

4) Psychogenic pain (emotional pain)

Question 7

How do we perceive pain?

Answer 7

1) Transduction (converting the stimulus into nerve impulses)

2) Transmission (transmitting the signals to the brain through the neurons and spinal cord)

3) Central processing (interpretation by the brain)

4) Modulation (controlling the pain signal along the pathway)

Question 8

What is a silent nociceptors?

Answer 8

They are nociceptors that are not activated unless their high threshold is reached and that is only in extreme pain cases

Question 9

What are the factors that affects the velocity of nerve impulse transmission? (transmission)

Answer 9

1) Prescence or absence of the myelin sheath

2) Thickness of the myelin sheath

3) Diameter of the axon

Question 10

What is the difference between fast and slow pain? (transmission)

Answer 10

1) Fast pain is acute, sharp, pricking, & electric pain, while on the contrary slow pain is chronic, burning, aching, throbbing, nauseous pain

2) Fast pain is in superficial tissues only, while slow pain is in both superficial and deep tissues

3) Fast pain is transmitted by large myelinated axons, while slow pain is transmitted by small unmyelinated axons

Question 11

Describe the types of pain axons

Answer 11

1) Type A
- Myelinated axons
- Fast pain
- Subtypes alfa 70-120 m/s, beta 35-75 m/s, gamma 15-50 m/s, & delta 6-30 m/s

2) Type C axons
- Unmyelinated axons
- Slow pain
- 0.5-2m/s

Question 12

What are the different pain pathways?

Answer 12

1) Dorsal column medial lemniscus system (carries touch, pressure, position senses to the brain and crosses the midline in the brainstem)

2) Anterolateral (spinothalamic) pathway (carries pain sensation, crosses the midline in the spinal cord)

Question 13

Which pathways carries pain sensation?

Answer 13

The anterolateral pathway and it carries both fast and slow pain

Question 14

What is the tract of fast pain from the anterolateral pathway?

Answer 14

Neo-spinothalamic tract it ends in the thalamus or cortex

Question 15

What is the type of neurotransmitter used by the neo-spinothalamic tract?

Answer 15

Glutamate

Question 16

What is the name of the tract responsible for transmitting slow pain of the anterolateral pathway?

Answer 16

Paleo-spinothalamic tract, the pathway commonly ends in the brain stem

Question 17

What is the neurotransmitter used by the paleo-spinothalamic tract?

Answer 17

Substance P

Question 18

What is the pathway of the anterolateral “spinothalamic” system

Answer 18

1) Receptor - spinal cord synapse

2) Spinal cord - Thalamus

3) Thalamus - Cerebral cortex

Question 19

What is the difference between the brainstem/thalamus and the cerebral cortex

Answer 19

Perception happens in the brain stem/thalamus while interpretation happens in the cerebral cortex

Question 20

What is the difference between the dorsal column medial lemniscus system and the spinothalamic system?

Answer 20

In the anterolateral “spinothalamic” pathway the first synapse occurs in the spinal cord while in the dorsal column medial lemniscus system the first synapse occurs in the brain stem

Question 21

What are the parts of the brain where pain is centrally processed?

Answer 21

1) Brain stem
2) Thalamus
3) Hypothalamus
4) Cortex
5) Limbic system

Question 22

What is the role of the brain stem in central processing of pain?

Answer 22

It detects:
1) Presence
2) Perception of dull, long lasting, crude, and diffuse pain

Question 23

What is the role of the hypothalamus in centrally processing pain?

Answer 23

It connects the perception of pain with the autonomic response

Question 24

What is the role of the thalamus in the central processing of pain?

Answer 24

It detects the perception of sharp, stabbing and acute pain

Question 25

What is the role of the cortex in centrally processing pain?

Answer 25

It interprets the quality of pain (spasm, burning or aching)

Question 26

What is the role of the limbic system when centrally processing pain?

Answer 26

It detects emotional pain and fear

Question 27

How are pain nerve impulse modulated?

Answer 27

• The brain reduces the pain sensation so that it can handle it better especially if it is consistent and severe

The brain and higher centers sends a signal to thalamus and brainstem, and they send an inhibitory signal to the meeting between the 1st and 2nd order neuron to reduce the 2nd order neuron and inhibit its excitation this signal is by enkephalins

Question 28

What is the role of enkephalins in pain sensation?

Answer 28

It inhibits/reduces the severity of the pain impulse

Question 29

In order of pathway how is pain modulated?

Answer 29

1) Substance P or glutamate is secreted by the 1st order neuron to excite the 2nd order neuron

2) Periaqueductal & periventricular grey matter excites the inhibitory neuron

3) Inhibitory neurons secretes enkephalin which will inhibit and decrease the excitement by increasing the threshold required to generate an AP making it harder to feel pain

Question 30

What is the gate control theory?

Answer 30

For example rubbing around a pain site (stimulating the tactile receptors)would inhibit the nerve impulses from nociceptors 1st order neurons thus decreasing the pain

Question 31

What is meant by referred pain?

Answer 31

In structures sharing the same second order neurons like the heart and the shoulder, the heart might be the one stimulating the nociceptors but because it shares the same 2nd order neuron the patient might also feel the pain in his shoulder

• When skin seems normal then think of referred pain

Question 32

What happens if we removed the limbic system?

Answer 32

We wont feel empathy for one another and there wont be any pain sensation if anyone but ourselves are in hurt