Lecture 12

Question 1

What are the four main modalities of somatosensation?

Answer 1

• Touch (mechanoreceptors)
• Temperature (thermoreceptors)
• Pain (nociceptors)
• Proprioception (muscle spindles)

Question 2

What are the four main types of mechanoreceptors and their properties?

Answer 2

• Meissner corpuscle (RA1): Light touch, low-frequency vibration, superficial, rapidly adapting
• Merkel disk (SA1): Sustained pressure, superficial, slowly adapting
• Pacinian corpuscle (RA2): Deep pressure, high-frequency vibration, deep, rapidly adapting
• Ruffini ending (SA2): Skin stretch, deep, slowly adapting

Question 3

What are the fibre types associated with somatosensory modalities?

Answer 3

• Aα: Proprioception
• Aβ: Touch
• Aδ / C: Pain and temperature

Question 4

What channels mediate thermal sensation?

Answer 4

Transient Receptor Potential (TRP) channels, each tuned to specific temperature ranges

Question 5

What is the function of muscle spindles in proprioception?

Answer 5

• Detect muscle stretch via stretch-sensitive ion channels
• Provide feedback on muscle length and movement

Question 6

How does distortion of the skin from pressure/stretch activate mechanoreceptors?

Answer 6

1. Direct activation through lipid membrane tension
2. Direct activation through structural proteins interacting with extracellular structures

Question 7

What is a receptive field?

Answer 7

The region of space that activates a sensory neuron; determines location and acuity of sensation

Question 8

How do receptive field size and adaptation affect sensation?

Answer 8

• Small fields: High acuity
• Large fields: High sensitivity
• Rapidly adapting: Detect change
• Slowly adapting: Detect sustained stimuli

Question 9

What are the two main ascending somatosensory pathways?

Answer 9

• Dorsal column/medial lemniscus: Touch and proprioception
• Spinothalamic tract: Pain, temperature, itch

Question 10

What are the thalamic targets for somatosensory input?

Answer 10

• VPL: Touch from body
• VPM: Touch from face
• VPS: Proprioception

Ventro-posterior- nuclei

Question 11

What is a pseudo-unipolar neuron?

Answer 11

A sensory neuron with a single axon that splits into peripheral and central branches; action potentials are initiated near the receptor

Question 12

What are the Brodmann areas of the primary somatosensory cortex (S-I)?

Answer 12

• 3a: Muscle spindles
• 3b & 1: Touch
• 2: Proprioception

Question 13

What is columnar processing in S-I?

Answer 13

Neurons are organised into vertical columns that process the same modality from a specific body region

Question 14

What is the sensory homunculus?

Answer 14

A cortical map showing overrepresentation of body parts with high receptor density (e.g., hands, lips)

Question 15

What are the functions of S-II?

Answer 15

• Integrates sensory and cognitive processes
• Direction, orientation, speed
• Higher order decision making

Question 16

What are the functions of areas 5/7?

Answer 16

• Combining sensory and motor information
• Movement planning and feedback
• Supports active touch and interaction with the environment