Ner 18: Somatosensory System, Paths From Spinal Cord

Front 1

Types and definitions of tactile/light touch

Back 1

1) Awareness of the precise location of a very light touch
2) 2-point sense - distinguishing 2 separate points on the skin.
3) Stereognosis - ability to recognize an object based soley on touch.
4) Graphesthesia - Ability to identify numbers and letters drawn on the skin.

Front 2

Flutter vs vibration

Back 2

Flutter - Sensation of low frequency vibrations which can be precisely located.
Vibration - High frequency vibrations that give a humming feeling in deeper tissues.

Front 3

Pathway of tactile, vibration, and preconception senses from spinal nerves

Back 3

1) Unipolar cell bodies of sensory organs located in DRG. Axons pass into spinal cord and travel up dorsal folliculus. Below mid thoracic = gracile, above = cuneate tract.
2) Secondary neurons at dorsal column nuclei at caudal medula (closed medulla) (gracile and cuneate nuclei)
3) Decusate at sensory decussation as internal arcuate fibers
4) Ascend spinal cord as medial lemniscus.
5) Terminate on VPL nuc of thalamus. Axons enter posterior limb of internal capsule.
6) Synapse on dorsal half of poscentral gyrus and posterior part of paracentral lobule which make up primary sensory cortex.

Front 4

Fast pain vs slow pain and examples

Back 4

Fast pain - Sharp, prickling, well localized. Pin prick.
Slow pain - Dull, burning, poorly localized. Tissue damage.

Front 5

What type of nerves are thermoreceptors?

Back 5

Free nerve endings

Front 6

Pathway of fast pain and temperature sensation.

Back 6

1) Unipolar nucleus of sensory fibers located in DRG. Axons enter spinal cord then synapse at dorsolateral part of grey matter in marginal nucleus. Some travel up or down a few segments before synapsing via tract called tract of lissauer in dorsolateral fasciculus.
2) Axons decussate via ventral white commisure, at level of the marginal nucleus ascend up anteriolateral fasciculus in spinothalmic tract.
3) Axons terminate on VPL of thalamus. Axons go to primary sensory cortex.

Front 7

Class 1 somatosensory nerve fiber (Letter, myelination, diam, speed, ex)

Back 7

Letter = A alpha
Myelinated = Yes
Diam = 12-20
Speed = 75-120
Ex = limb position and motion

Front 8

Class 2 somatosensory nerve fiber (Letter, myelination, diam, speed, ex)

Back 8

Letter = A beta
Myelinated = Yes
Diam = 6-12
Speed = 30-75
Ex = tactile, pressure, vibration

Front 9

Class 3 somatosensory nerve fiber (Letter, myelination, diam, speed, ex)

Back 9

Letter = A delta
Myelinated = Yes
Diam = 1-6
Speed = 5-30
Ex = fast pain, temp

Front 10

Class 4 somatosensory nerve fiber (Letter, myelination, diam, speed, ex)

Back 10

Letter = C
Myelinated = no
Diam = <1.5
Speed = .5-2
Ex = slow pain, warmth

Front 11

Lateral vs medial distribution in the DRG

Back 11

Medial = large fibers (A alpha and Beta)
Lateral = small fibers (A delta and C)

Front 12

Somatotopic organization of gracile and cuneate tracts

Back 12

More caudal is more medial. More rostral is more lateral.