Pain & Temperature

Question 1

What is Pain (IASP definition)?

Answer 1

An unpleasant sensory and emotional experience associated with actual or potential tissue damage.

Question 2

What is Nociception?

Answer 2

The unconscious activity induced by a harmful/noxious stimulus applied to sense receptors.

Question 3

How does Hyperalgesia manifest?

Answer 3

An exaggerated response to a noxious (painful) stimulus.

Question 4

How does Allodynia manifest?

Answer 4

Pain resulting from a typically harmless (innocuous) stimulus (e.g., light touch on sunburned skin).

Question 5

What kind of pain is neuropathic pain?

Answer 5

Chronic or pathologic pain.

Question 6

What are the sensory neurons for nociception?

Answer 6

Unmyelinated C fibers or finely myelinated Aδ fibers.

Question 7

Which fiber mediates Fast Pain and what is its degree of myelination?

Answer 7

Aδ fibers (finely myelinated).

Question 8

Which fiber mediates Slow Pain and what is its degree of myelination?

Answer 8

C fibers (unmyelinated).

Question 9

What is the primary neurotransmitter of Aδ fibers for fast pain?

Answer 9

Primarily Glutamate.

Question 10

What two types of transmitters do C fibers release for delayed slow pain?

Answer 10

Glutamate and neuropeptides (e.g., Substance P).

Question 11

What temperature activates Thermal nociceptors?

Answer 11

Skin temperatures above 42∘C or severe cold.

Question 12

What is the name of the receptor family sensitive to chemicals, heat/cold, and mechanical stimuli?

Answer 12

Transient Receptor Potential (TRP) channels.

Question 13

Which TRP receptor is sensitive to Capsaicin and H+, and senses heat >42∘C?

Answer 13

TRPV1.

Question 14

Which TRP channels are activated by Cold?

Answer 14

TRPM8 and TRPA1.

Question 15

What two types of receptors did Ardem Patapoutian characterize (Nobel 2021)?

Answer 15

PIEZO1, PIEZO2 (pressure) and TRPM8 (menthol/temp).

Question 16

Name two chemical mediators released by injured cells that sensitize nociceptors.

Answer 16

K+, Bradykinin, and Prostaglandin E2​.

Question 17

How do NSAIDs alleviate pain?

Answer 17

They inhibit cyclooxygenases (COX-1/COX-2), reducing the production of Prostaglandin E2​.

Question 18

Where do Aδ and C fibers send ascending/descending branches upon entering the dorsal horn?

Answer 18

Dorsolateral tract of Lissauer (for 1-2 spinal segments).

Question 19

Where do C-fiber branches synapse on 2nd order neurons?

Answer 19

Lamina 1 (Marginal Zone) and 2 (Substantia Gelatinosa).

Question 20

Where do Aδ fiber branches synapse on 2nd order neurons?

Answer 20

Lamina 1 (Marginal Zone) and 5 (Nucleus Proprius).

Question 21

Where do axons of 2nd order neurons cross the midline and ascend?

Answer 21

They cross and ascend in the Ventrolateral tract.

Question 22

Name 3 common causes of Deep/Visceral Pain?

Answer 22

Ischemia, chemical stimuli, spasm/overdistention of hollow viscus.

Question 23

What is the mechanism for Referred Pain?

Answer 23

Convergence-Projection theory/hypothesis.

Question 24

What is the mechanism by which Aβ fibers modulate pain (Gate Theory)?

Answer 24

Aβ fiber activity activates inhibitory interneurons, suppressing C-fiber signal transmission.

Question 25

What two nuclei are involved in the Descending Pain Suppression Pathway from the midbrain?

Answer 25

Periaqueductal Gray matter (PAG) and Nucleus Raphe Magnus (Rostral Ventromedial Medulla).

Question 26

What is the function of the Enkephalin-containing interneurons in pain suppression?

Answer 26

They inhibit nociceptive transmission in the dorsal horn.

Question 27

How does Opioid/Enkephalin reduce transmitter release from the presynaptic 1st order neuron?

Answer 27

Decreases Ca2+ influx.

Question 28

How does Opioid/Enkephalin affect the postsynaptic 2nd order neuron membrane potential?

Answer 28

Hyperpolarizes it by activating a K+ conductance (efflux).

Question 29

Name two of the four potential causes of Hyperalgesia and Allodynia (Central Sensitization).

Answer 29

Peripheral nerve injury (C/Aδ hyperexcitable), Central sensitization (NMDA overactivation), Loss of inhibitory control (GABAergic/Glycinergic loss), Abnormal rewiring (Aβ forming synapses in Lamina II).

Question 30

How does Neuropathic Pain fundamentally differ from Nociceptive pain?

Answer 30

Neuropathic pain involves direct nerve stimulation, while nociceptive pain requires transduction.

Question 31

What type of pain is Diabetic Neuropathy?

Answer 31

Neuropathic pain.