Somatosensory

Question 1

Free Nerve Endings

Answer 1

Pain
Heat
Cold

Question 2

Meissner’s Corpuscles (encapsulated)

Answer 2

Touch - not present in hairy skin
Aß fibre
Stroking, flutter (RA)

Question 3

Merkel’s Discs

Answer 3

Touch - also present in moderate numbers in hairy skin
Aß fibre
Pressure, texture (SA)

Question 4

Krause end bulbs

Answer 4

Touch - at the border of dry skin and mucous membranes

Question 5

Ruffini endings (encapsulated)

Answer 5

Pressure - within dermis and joint capsule
Aß fibre
Skin stretch (SA)

Question 6

Pacinian corpuscles

Answer 6

Vibration and pressure - within dermis and fascia
Aß fibre
Vibration (very RA)

Question 7

Hair (G), guard (long)

Answer 7

Aß fibre

Stroking, flutter

Question 8

Hair (D), down (short)

Answer 8

A∂ fibre

Light stroking

Question 9

Nociceptors (Fibre class and termination in dorsal horn)

Answer 9

A∂ / C fibre

Laminae I,II

Question 10

LTMs (Fibre class and termination in dorsal horn)

Answer 10

Aß fibre

Laminae III - VI

Question 11

Proprioceptors (Fibre class and termination in dorsal horn)

Answer 11

Aa fibre

Laminae VII - IX

Question 12

DCML pathway

Answer 12

Decussation occurs at the level of the brainstem.

Touch and proprioceptive information

Question 13

Spinothalamic tract

Answer 13

Decussation occurs at point of synapse

Pain and thermosensation

Question 14

Fasciculus Gracilis

Answer 14

Sensory input to T6 and below (legs and lower trunk)

Question 15

Fasciculus Cuneatus

Answer 15

Input about T6 (arms and upper trunk)

Question 16

DCML pathway capabalities

Answer 16

Stereogenesis - ability to recognise an object by feeling it
Vibration detection
Fine touch
Conscious proprioception
Weight discrimination

Question 17

Somatosensory Cortex (SI)

Answer 17

Location: Post central gyrus of parietal cortex - posterior to central sulcus.

Brodmann areas: 1, 2, 3a, and 3b (3b primary somatosensory cortex - SI)

Question 18

BA 3a (input, modality, effect of lesion)

Answer 18

Input: Proprioceptors (muscle spindles)
Modality: Body position

Question 19

BA 3b (input, modality, effect of lesion)

Answer 19

Input: BA 3a, Merkel, Meissners
Modality: Touch (texture, shape, stimulus size)
Lesion: Deficits in texture, shape, discrimination

Question 20

BA 1 (input, modality, effect of lesion)

Answer 20

Input: BA 3b, Cutaneous RA mechanoreceptors
Modality: Texture discrimination
Lesion: Loss of texture discrimination

Question 21

BA 2 (input, modality, effect of lesion)

Answer 21

Input: BA 3a, 3b, Joint afferents, Golgi tenon organs
Modality: Object perception (size, shape, stereogenesis)
Lesion: Impaired grasping and size and shape discrimination (astereogenesis)

Question 22

Somatosensory Cortex Layers

Answer 22

Molecular (lamina I)
External Granular (lamina II)
External Pyramidal (lamina III)
Internal Granular (lamina IV)
Internal Pyramidal (lamina V)
Multiform (lamina VI)

Question 23

Posterior Parietal Cortex (SII)

Answer 23

Receives information from SI and other cortical areas (visual, auditory) and subcortical areas (thalamus).

Neglect syndrome, damage to the right posterior parietal cortex. Pts believe the left side of the world does not exist etc.