Somatosensation (1)

Question 1

What are somatosensations?

Answer 1

Sensations from the body, mediated by the somatosensory system.

Question 2

What are the three interacting systems of the somatosensory system?

Answer 2

1) Exteroceptive system → senses external stimuli on skin (touch, temperature, pain).
2) Proprioceptive system → monitors body position via muscles, joints, and balance organs.
3) Interoceptive system → monitors internal body conditions like temperature and blood pressure.

Question 3

What are the three divisions of the exteroceptive system?

Answer 3

1) Mechanical (touch)
2) Thermal (temperature)
3) Nociceptive (pain)

Question 4

Name four major types of cutaneous receptors.

Answer 4

1) Free nerve endings → pain & temperature
2) Pacinian corpuscles → vibration, rapid adaptation
3) Merkel’s disks → slow adaptation, pressure
4) Ruffini endings → slow adaptation, skin stretch

fk patriarchy matriarchy rules

Question 5

What is the functional significance of fast vs. slow receptor adaptation?

Answer 5

Fast-adapting receptors respond quickly to changes in stimulation but stop firing during constant pressure.
* Function: Detect movement, vibration, or sudden changes on the skin.

Slow-adapting receptors keep firing as long as the stimulus is present.
* Function: Detect constant pressure, shape, and stretch of the skin.

Question 6

How do cutaneous receptors transduce stimuli?

Answer 6

Skin deformation or chemical changes alter receptor membrane ion permeability, producing a neural signal.

Question 7

Do specific receptors produce only one type of sensation?

Answer 7

No, tactile sensations involve interactions of multiple receptor types, and surrounding skin cells also influence perception.

Question 8

What are the two major somatosensory pathways?

Answer 8

1) Dorsal-Column Medial-Lemniscal (DCML) → touch & proprioception
2) Anterolateral system → pain & temperature

Question 9

Does damage to one pathway completely eliminate its sensations?

Answer 9

No, separation is incomplete. Lesions may reduce but not eliminate the sensations.

Question 10

Outline the DCML pathway.

Answer 10

Pathway:

• Sensory neurons enter the spinal cord via the dorsal root.
• Ascend ipsilaterally (same side) in the dorsal columns.
• Synapse in the dorsal column nuclei of the medulla.
• Axons decussate (cross to the other side).
• Ascend in the medial lemniscus to the ** contralateral ventral posterior** nucleus of the thalamus.

Then: Most neurons go to primary somatosensory cortex (SI); some go to secondary somatosensory cortex (SII) or posterior parietal cortex.

Question 11

How does the trigeminal nerve contribute to DCML?

Answer 11

Three branches carry somatosensory info from the face to ventral posterior nucleus of thalamus.

Question 12

What is notable about dorsal column neurons from the toes?

Answer 12

They are the longest neurons in the human body.

Question 13

Outline the anterolateral system.

Answer 13

1. Dorsal root neurons synapse immediately in spinal cord
2. Second-order neurons mostly decussate → ascend contralaterally; some ascend ipsilaterally
3. Ascend via spinothalamic, spinoreticular, spinotectal tracts
4. Trigeminal branches carry pain/temp info from face
5. Thalamus distributes info to somatosensory cortex & other brain areas

Question 14

What happens if both pathways are completely transected?

Answer 14

Complete loss of body sensations below the level of injury.

Question 15

Where is primary somatosensory cortex (SI) located?

Answer 15

In the postcentral gyrus of the parietal lobe.

Question 16

What is the somatosensory homunculus?

Answer 16

A somatotopic map of the body in SI, showing cortical regions corresponding to body parts.

Question 17

What is secondary somatosensory cortex (SII) responsible for?

Answer 17

Higher-level touch processing: texture discrimination and object recognition.

Question 18

What is the role of the posterior parietal cortex?

Answer 18

Integrates somatosensory info for spatial awareness and complex sensorimotor tasks.

Question 19

What are the free nerve endings?

Answer 19

They have no specialized structures and are sensitive to temperature changes and pain.

Question 20

What are the Pacinian corpuscles?

Answer 20

They are the largest, deepest, onion-like receptors. They adapt rapidly, responding to sudden skin displacements but not constant pressure.

Question 21

What are the Merkel’s disks?

Answer 21

They are slowly adapting receptors that respond to gradual skin indentation (pressure).

Question 22

What are Ruffini endings?

Answer 22

They are slowly adapting receptors that respond to skin stretch.