MVC - Nociception

Question 1

What are examples of First order neurones?

Answer 1

Dorsal root ganglion (DRG) neurons

Question 2

Describe the characteristics of first-order neurons in the somatosensory system, including their branches and locations

Answer 2

First-order neurons are mechanosensory, entering the dorsal root and joining the dorsal column.

They have two axon branches:

• one to the periphery (PNS)
• the other to the spinal cord (CNS).

Cell bodies are located in the dorsal root ganglia (DRG)

Question 3

What are features of Mechanosensory neurons?

Answer 3

Myelinated
Have large diameters

Question 4

CLASSES OF SOMATOSENSORY AFFERENTS (4)

Answer 4

Proprioreception
Receptor Type: Muscle spindle
Diameter (micrometer): 13-20
Conduction velocity (m/s): 80-120

Touch
Receptor Type: Merkel, Meissner, Pacinian
Diameter (micrometer): 6-12
Conduction velocity (m/s): 35-75

Pain, Temperature
Receptor Type: Free nerve endings
Diameter (micrometer): 1-5
Conduction velocity (m/s): 5-30

Pain, Temperature, Itch
Receptor Type: Free nerve endings
Diameter (micrometer): 0.2-1.5
Conduction velocity (m/s): 0.5-2

Question 5

What determines the speed of action potential propagation in somatosensory fibers?

Answer 5

Fiber diameter and myelination

Question 6

What are the key steps in the sensory transduction cascade?

Answer 6

Signal transduction → Current → Generator potential → Action potentials

Question 7

What is the distinction between tonic and phasic receptors?

Answer 7

Tonic receptors convey static qualities

Phasic receptors convey dynamic qualities of a stimulus

Question 8

Describe ascending pathways for somatosensation

Answer 8

Unconcious
Proprioception

• Spinocerebellar tract

Concious
Mechanosensation

• Pain and temperature

Question 9

What is the role of dermatomes, and how do they help in understanding specific conditions affecting the body?

Answer 9

Dermatome: innervation arising from a single dorsal root ganglion and its spinal nerve (some overlap)

Helpful in determining how certain conditions, such as shingles and some other neurological conditions (spinal cord injury), affect specific regions of the body (pain and temperature more informative - less dermatome overlap

Question 10

How is cortical integration and signaling achieved in the somatosensory system?

Answer 10

Thalamic input predominantly layer IV

• Cortex sends projections in turn to limbic structures such as the amygdala and hippocampus
• Cortex also sends descending signals (thalamus, brainstem, and spinal cord)

Question 11

What is Nociception?

Answer 11

The neural process of encoding noxious stimuli

Question 12

What are nociceptive afferents?

Answer 12

Nociceptors lie near blood vessels between epithelial layers of the skin, the cornea, muscle joints, viscera, the alimentary tract, and in connective tissues.

• Essentially innervate all tissue except brain!

Activated by stimuli that are damaging or potentially damaging.

Noxious mechanical, thermal, chemical stimuli.

Nociceptor properties can change: inflammation, damage, pathology.

Question 13

How do noxious stimuli influence ion channels in nociceptors, and what is an example of this process?

Answer 13

Noxious stimuli influence ion channels, such as TRPV1 channels opening in C fiber endings due to painful heat (>43°C), causing Ca and Na ions to enter and depolarize the cell, leading to action potentials

Question 14

How does mechanotransduction work in the somatosensory system?

Answer 14

Mechanotransduction involves stretch-sensitive cation channels leading to the depolarization of afferent neurons