Blumenfeld Somatosensory Pathways

Front 1

2 major somatosensory pathways

Back 1

posterior column (medial lemniscal pathway)

anterolateral pathway

Front 2

posterior column-medial lemniscal pathway

Back 2

proprioception, vibration sense, fine discriminative touch

Front 3

anterolateral pathway

Back 3

includes spinothalamic tract and other assoc tracts - pain, temp, crude touch. also spinoreticular and spinomesencephalic tracts

Front 4

dorsal root ganglia

Back 4

contain sensory neuron bodies, have axons that bifurcate, w/ one process extending to periphery and other into SC thru dorsal nerve roots

Front 5

posterior column pathway

Back 5

large diameter myelinated axons enter SC in ipsilateral posterior column and ascend to posterior column nuclei in medulla- decussate as internal arcuate fibers and become medial lemnisus tract- terminate in ventral posterior lateral nucleus (VPL) of thalamus- project thru internal capsule to somatosens cortex. some axon collaterals enter SC gray matter and synapse onto interneurons and motor neurons.

Front 6

spinothalamic tract

Back 6

smaller diameter, unmyelinated axons synapse immediately in gray matter of SC, cross over in SC anterior commissure to sscend in anterolateral WM, altho it takes 2-3 spinal segments to cross, so lesion will affect contralateral pain a few segments below level of lesion.

Front 7

gate control theory of pain

Back 7

sensory inputs from nonpain fibers (A-beta) reduce pain transmission through dorsal horn. e.g., TENS devices reduce chronic pain by activating these fibers.

Front 8

thalamic nuclear groups

Back 8

medial, lateral and anterior groups that are separated by Y-shaped WM (internal medullary lamina), which has its own nuclear group (intralaminar nuclei), midline thalamic nuclei, thalamic reticular nucleus

Front 9

ventral posterior medial (VPM) and ventral posterior lateral (VPL) nuclei of thalamus

Back 9

somatosensory pathways from CN and SC, respectively. These project to primary somatosensory cortex

Front 10

lateral geniculate nucleus (LGN) of thalamus

Back 10

input from retina, relays to primary visual cortex

Front 11

MEDIAL GENICULATE NUCLEUS OF THALAMUS (mgn)

Back 11

inputs from inferior colliculus, relays to primary auditory cortex

Front 12

ventral lateral (VL) and ventral anterior (VA) nucleus of thalamus

Back 12

inputs from GP, cerebellar nuclei, SN, relays to motor cortex. fx is to relay info from BG and cerebellum to cortex

Front 13

Pulvinar of thalamus

Back 13

inputs from tectum, relays to P-T association areas. fx is behavioral orientation to relevant visual or other stimuli

Front 14

mediodorsal nucleus of thalamus

Back 14

inputs from amygdala, OLF cortex, BG, relays to frontal cortex

Front 15

intralaminar nuclei

Back 15

connections to BG and ascending RAS to maintain alert, conscious state

Front 16

reticular nucleus of thalamus

Back 16

does not connect to cortex, has inputs from other areas of thalamus and is mostly inhibitory to regulate thalamic activity

Front 17

paresthesias

Back 17

can be caused by lesions to somatosensory pathways. characteristic of paresthesias have localizing value (e.g., anterolateral pathway damage leads to sharp, burning, or searing pain. posterior column-tingling or numb sensation)

Front 18

radicular pain

Back 18

lesion to nerve root that causes radiating limb pain in a dermatomal distribution

Front 19

Dejerine-Roussy syndrome

Back 19

severe contralateral pain caused by thalamic lesions

Front 20

allodynia

Back 20

painful sensation provoked by normally nonpainful stimuli

Front 21

hyperpathia or hyperalgesia

Back 21

enhanced pain to normally painful stimuli

Front 22

myelopathy

Back 22

SC dysfx

Front 23

SC infarction

Back 23

usu due to anterior spinal artery occlusion, leading to anterior cord syndrome. causes are traumatic, aortic dissection, thromboembolic and disc emboli

Front 24

myelitis

Back 24

can be infectious or inflammatory, usu presents w/ SC dysfx and develops quickly