LO5 Exteroception: somatosensory (lemniscal system)

Question 1

Two major subdivisions of somatosensory system

Answer 1

Dorsal column/Posterior column/Lemniscal system

and

Anterolateral system

Question 2

Rapidly adapting vs SLowly adapting receptors

Answer 2

Rapid:
- stimulated→ fires AP → stops (even if skin is still being pressed)

Slow:
- Stim → keeps firing AP throughout time skin is pressed.

Question 3

Meissner’s Corpuscle

• Receptive field size
• Adaptation rate

Answer 3

• Small fields
  (MM: fine tactile sense of finger tips)
• Fast adaptation

(discriminative touch finger tips)

(small fields - mickey mouse MM)

Question 4

Pacinian corpuscles

• Receptive field size
• Adaptation rate

Answer 4

• Large fields
• Fast adaptation

(vibratory, texture - palm)

Question 5

Merkel’s disc

Answer 5

• Small fields (MM: fine tactile sense of fingertips)
• Slow adaptation

Light touch

Question 6

Ruffinis ending

Answer 6

• Large field size
• Slow adaptation

Grip

Question 7

Lemniscus pathway

Answer 7

skin mechanoreceptors cell body in dorsal root (touch, P, Vib) → posterior/dorsal horn → ascending branches enter dorsal columns (fasciculus cuneatus or gracilis) → ascend spinal cord to superior medulla (nucleus cuneatus/gracilis)→
synapse on 2nd order neurons →cross midline to FORM medial lemniscus → synapse on ventro-basal complex of thalamus (VPM+VPL nucleus) →
primary somatosensory area, SI →
primary motor cortex → secondary somatosensory area SII → association somatosensory cortical areas in parietal cortex.

Question 8

Why is the map of the body surface considerably distorted?

Answer 8

distortion due to innervation density

- More primary afferents (higher density) → more cortical surface devoted to them

Question 9

Cortical barrels

Answer 9

referred to as the Columnar organization of the cortex

• the vertical arrangement of functionally related cells
• transforms info recieved from thalamus and redistributes it to other regions of brain

ie: Barrel 1: orientation and direction
- horiz columns are found in barrels

Question 10

Cortical Barrels/Column 1 sensory modality

Answer 10

Orientation and direction

Question 11

Cortical Barrels/Column 2 sensory modality

Answer 11

Orientation and direction (just like 1)

But also Shape

Question 12

Cortical Barrels/Column 3b sensory modality

Answer 12

Skin (slow and rapid adapting cutaneous receptors)

Question 13

Cortical Barrels/Column 3a sensory modality

Answer 13

Deep tissue (muscle stretch receptors)
Proprioreceptive

Question 14

The dorsal root ganglion of the head?

Answer 14

Trigeminal ganglion

- afferent info regarding touch, proprioception,, pain, T on the head flows through this nerve

Question 15

Lemniscal system for trigeminal nerve

Answer 15

Mechanoreceptors of the skin receives sensory input (Soma in trigem gang) →
main sensory nucleus aka principle nucleus (dorsal column nuclei analog) →
synapses on second order cells in main sensory nucleus → immediately crosses midline →
Joins medial lemniscus fibers → end in VPM nucleus of thalamus → face area of somatosensory cortex

Question 16

Afferents that run in the trigeminal nerve have their cell bodies located where?

Answer 16

trigeminal ganglion 
(for mechanoreceptors of the skin - sensory input)

trigeminal mesencephalic nucleus

• centrally located
• proprioceptive afferents
• muscle stretch receptors
• cell bodies for muscle spindles in the m of mastication and mechanoreceptors of the mouth
• monosynaptic conxn w/ motorneurons to the m of mastication