somatosensory pathways

Question 1

Posterior column-medial lemniscal system (PCMLS)

Answer 1

perception and appreciation of mechanical stimuli
conscious awareness of body position and limb
movement in space

Question 2

two-point discrimination

Answer 2

ability to discriminate between two separate stimuli simultaneously
related to density of peripheral nerve endings

Question 3

where can you find a high density of peripheral receptors

Answer 3

digits and perioral region

Question 4

where can you find a low density of peripheral receptors

Answer 4

back

Question 5

what is a receptive field

Answer 5

area of skin innervated by a somatic afferent fiber

Question 6

how do primary sensory fibers enter the spinal cord

Answer 6

via medial division of the posterior root

Question 7

where can you see the fasciculus cuneatus

Answer 7

above T6 (lateral to fasciculus gracilis)

Question 8

SC lesion of Fasciculi gracilis and cuneatus

Answer 8

ipsilat. reduction or loss of discriminative touch, vibration, positional sense at and below level of injury

Question 9

where are the second order neurons of the PCMLS?

Answer 9

gracile and cuneatus nuclei – posterior medulla

input from ipsilat. DRG

Question 10

what is the segregation of tactile inputs in the nuclei

PCMLS

Answer 10

core clusters: inputs from rapidly and slowly adapting
afferents
outer shells: muscle spindles, joints, pacinian
corpuscles

Question 11

when do the internal arcuate fibers of the second order neurons become the medial lemniscus
(PCMLS)

Answer 11

after sensory decussation in the medulla

Question 12

where are the third order neurons of the PCMLS

Answer 12

VPL (ventral posterolateral nucleas)

Question 13

damage @ brainstem causes

PCMLS

Answer 13

loss of discriminative touch, vibration, positional sense of contralat. side

Question 14

what comprises the ventral posterior nuclei

what separates them

Answer 14

ventral posterolateral nucleas (VPL) – receives PCMLS
ventral posteromedial nucleas (VPM) – receives
trigeminal sensory info

separated by arcuate lamina

Question 15

blood supply to ventral posterior nucleas

Answer 15

thalamogeniculate branches of posterior cerebral a

Question 16

compromise of thalamogeniculate branch of PCA can cause

Answer 16

loss of all tactile sensation on contralat. body and head

Question 17

VPL receives input from

Answer 17

medial lemniscus (PCMLS) fibers from contralat. nucleas cuneatus and nucleas gracile

Question 18

populations of neurons in VPL

Answer 18

third order neurons – travel along posterior limb of IC
to get to primary and secondary somatosensory
cortices
local circuit interneurons (inhibitory)

Question 19

blood supply to primary somatosensory cortex (SI)

Answer 19

both ACA and MCA

Question 20

MCA lesion –>

Answer 20

loss of tactile sense over contralat. face and upper body

Question 21

ACA lesion –>

Answer 21

loss of tactile sense over contralat. lower limb

Question 22

SI divisions from ant –> post

Answer 22

3a, 3b, 1, 2

Question 23

lesion of parietal cortical region

Answer 23

can produce agnosia
sensory not affected too much, but contra lat limbs
no longer on body map. not recognized as part of
own body

Question 24

trigeminal nuclei (4) and f(x)

Answer 24

main sensory nucleas – touch and pressure
trigeminal motor nucleas – m of mastication
spinal nucleas – pain and temp
mesencephalic nucleas – proprioceptive afferents of
TMJ and masticatory m

Question 25

Main sensory nucleas divisions

Answer 25

dorsomedial division: afferent input from oral cavity | ventrolateral division: afferents from V1, V2, V3

Question 26

2nd order fibers of ventrolateral division follows what tract

Answer 26

anterior trigeminothalamic tract --> contralat. VPM | --posterior limb of IC--> SI

Question 27

2nd order fibers of dorsomedial division follow what tract

Answer 27

posterior trigeminothalamic tract --> ipsilat. VPM | --posterior limb of IC--> SI

Question 28

somatotropic arrangement of VPM

Answer 28

``` medial = oral cavity input lateral = external face input ```

Question 29

what classification of neurons is the mesencephalic nucleas comprised of

Answer 29

psuedounipolar neurons

Question 30

jaw jerk reflex

Answer 30

stretching masseter m causes it to contract bilat. mesencephalic nucleas --> trigem. motor nucleas --> masseter m intensity enhanced w/ UMN lesion

Question 31

cross sensory syndrome/findings | brainstem? SC?

Answer 31

brainstem or sc lesions that result in deficits that differ on either side of the body brainstem: sensory deficit contralat. trunk/extremities sensory deficit ipsilat. face SC: proprioceptive defecit one side, anesthesia other

Question 32

SI lesions can lead to

Answer 32

loss of proprioception, position sense, vibratory sense, pain, temp on contralat. side

Question 33

lesion in area 1 of SI -->

Answer 33

loss of texture discrimination

Question 34

lesion in area 2 of SI -->

Answer 34

loss of shape and size discrimination

Question 35

lesion in area 3b of SI -->

Answer 35

loss of texture, shape, and size discrimination

Question 36

modalities of sensation conveyed by anterolateral system (ALS)

Answer 36

nondiscriminative touch, pain, temp

Question 37

ALS (spinothalamic) pathway

Answer 37

body --> thalamus --> somatosensory and limbic cortices similar to anterior trigeminothalamic tract, but from body not face/head

Question 38

disruption of ALS pathway produces

Answer 38

numbness, tingling, parasthesia, anesthesia

Question 39

how do cutaneous nociceptors and primary neurons enter the spinal cord

Answer 39

lateral division of the posterior root entry zone travel in posterolateral fasciculus

Question 40

direct ALS pathway | spinothalamic

Answer 40

(nondistinctive tactile, pain, temp) enters SC at posterolateral fasciculus and bifurcates ascending branches synapse on posterior horn axons decussate via anterior white commisure travel through lateral spinothalamic tract on contralat. side travel to VPL in thalamus

Question 41

fate of descending branches of direct ALS pathway

Answer 41

synapse with interneurons in gray matter to contribute segmental spinal reflexes

Question 42

indirect ALS pathway | spinothalamic

Answer 42

(noxious and innocuous mechanical and temp info to reticular formation) similar pathway as direct, but third order neurons in reticular formation of brainstem take signal to medial thalamic nuclei synapse in lamina 2&3 of posterior horn to influence cells in 5 to 8

Question 43

somatotropic arrangement of ALS

Answer 43

axons from lower levels are more posterolateral | higher levels are added anteromedially

Question 44

blood supply of ALS

Answer 44

originates from arterial vasocorona and via sulcal brances of anterior spinal a

Question 45

occlusion of vessels supplying ALS results in

Answer 45

patchy nociception, thermal and nondistinctive touch over contralat. side of body anterolateral cordotomy = complete loss of these

Question 46

hemisection of the SC (brown-sequard syndrome)

Answer 46

contralat. loss of pain and temp (ALS) ipsilat. loss of discriminative tactile, vibratory, positional sensation @ and below level (PCMLS)

Question 47

syringomyelia effects on somatosensory pathways

Answer 47

impinge on AWC bilat. loss of nondiscriminative tactile, pain, temp seen 2 levels down?

Question 48

effect of vascular lesions/tumors in lower brainstem on sensory modalities (medullary ALS fibers)

Answer 48

dissociated sensory loss: deficit of one modality with the other modality within normal limits ALS: i.e. deficit of pain/temp, normal vibration/discriminitive touch or vice versa i.e. PCMLS and ALS stay separate

Question 49

where are medullary ALS fibers positioned

Answer 49

near anterolateral surface, anterior to spinal trigeminal nucleas remains separated from PCMLS

Question 50

divisions of the spinal trigeminal tract

Answer 50

pars oralis, pars interpolaris, pars caudalis(pain and temp procession for face and head)

Question 51

how far does the spinal trigeminal tract extend

Answer 51

pontomedullary jxn to 3rd cervical segment

Question 52

f(x) of pars caudalis

Answer 52

allows for smooth transition of cutaneous info from posterior head (spinal) with cutaneous anterior face/head (brainstem)