Somatosensory tracts

Question 1

postecentral gyrus

Answer 1

aka somatosensory cortex or Broadmann’s areas 3,1,2

the final destination for somatosensory information from thalamic relay neurons

Question 2

thalmaic relay neurons

Answer 2

NEVER decussate, receive info from the prethalamic relay neurons (which do decussate

final synapse onto the primary somatosensory cortex

Question 3

Labeled line code

Answer 3

MODALITY
any stimulus, at any point along a SPECIFIC TRACT, there is the same modality
i.e. stimulate the visual tracts at any point, it will synapse onto the visual cx and transmit a visual stimuli

Question 4

population code

Answer 4

as intensity of stimulus the number of receptors activated increases—->increased Intensity

Question 5

frequency code

Answer 5

increased intensity of stimulus increases the rate of AP generation —–> increased intensity

Question 6

receptive field

Answer 6

the area of which a particular neuron can respond to a particular stimuli

• large receptive field=low density=low resolution=dec localizing ability=decreased cortical neurons
• small RF=high density=high resolution=localizing ability=large number of associated cortical neurons

Question 7

PCML

Answer 7

posterior column medial lemniscus

• ascending tract GSA from THE BODY Only (C1-S5)
• Conscious
• Modalities: somatosensation: proprioception, discriminative (fine) touch, vibratory sense
• very rapid conduction (A alpha)

Question 8

Discriminative touch

Answer 8

ability to have fine, two point discrimination with high degree accuracy in location

graphesthesia, stereognosis

Question 9

sensory ataxia

Answer 9

lack on conscious proprioception

causes dymetria: incorrect metering of limb in space. Base wide stance, stumbling, difficulty turning, truncal sway, inaccurate voluntary movement

results from a lesion of the dorsal columns

Question 10

anterolateral system

Answer 10

GSA somatosensation
Pain, temp, CRUDE touch
Tested clinically
small, unmyelinated Abeta (touch temp) and Adela and C=pain

**spinothalamic is contralateral projections
all other tracts are bilateral

Question 11

spinothalamic tract

Answer 11

most axons in ALSO, projects to primary SS cx via thalamus

Conscious perception

Question 12

Spinoreticular tract

Answer 12

projects to reticular formation, important for alerting the cx of stimulus focusing attention and some autonomic fxns

Question 13

spinomesensephalic tract

Answer 13

to midbrain
some fibers project to the PAG for pain modulation

also sends fibers to the spinotectal system (visual-grasp reflex)

Question 14

spinohypothalamic tract

Answer 14

projects to the hypothalamus
controls autonomic responses to stimuli (think tearing up, or become nauseated after a painful stimuli)
provides fibers into the limbic systems—>emotional response to pain

Question 15

Adelta fibers

Answer 15

part of the anterolateral system
small unmyelinated neurons
control fast pain (short lived and well localized

Question 16

A C fibers

Answer 16

part of the anterolateral system
small unmyelinated
control slow, long lasting pain that is not well localized (think GVA)

Question 17

GVA

Answer 17

Sensory info to the gut
some conscioius, but mostly unconcious that drive local reflexes
small C fibers with nociceptive or stretch receptors

info goes into tracts other than STT (i.e. spinoreticular, spinohypothalamic-anything that is NOT headed into the cortex)

Question 18

opthalmic n.

Answer 18

V1

sensory from nose, around eyes and forehead

Question 19

maxillary n.

Answer 19

V2

sensory from lat nose, masilla

Question 20

mandibular

Answer 20

V3
sensory and motor
sense from chin, cheek and lateral head

Question 21

trigeminal GSA

Answer 21

brought in from primary afferents in all three 3brs
most cell bodes in the trigeminal ganglion
mesencephalic nuc (within CNS) is also a location for cell bodies- EXCEPTION TO THE RULES

Question 22

spinal nuclei of V

Answer 22

prethalamic relay nuclei
analagous to the dorsal horn neurons in the ALS
relay info form V1-3 about pain, temp and crude touch

Question 23

Pontine nuclei

Answer 23

aka sensory nuc.
prethalamic relay nuclei for proprioception for fine touch, somatosensation, vibration
aka gracillis and cuneatus
off to the thalamus (Ventroposteriormedial nuc. of the thalamus)

Question 24

somatotopy of the Spinal V nuc.

Answer 24

V3=posterior
V1=anterior
ear= inferior
face=superior

Question 25

spinal tract of V

Answer 25

descending tract of primary afferents carrying pain, temp, and crude touch to the spinal nuclei of V

Question 26

ventrotrigeminal thalamic tract

Answer 26

VTT

carries all secondary ascending neurons of the trigeminal system up to the VPM