2. ascending sensory pathways

longitudinal organization

walk through this graphic

dorsal column-medial lemniscus pathway

how many and which ascending pathways are testable?

• 2

• dorsal column/medial lemniscus pathway and

• spinothalamic pathway

ascending tracts {organization of white matter (funiculi)} are segregated by?

sensory modality

• dorsal column/medial lemniscus pathway and

• spinothalmic pathway

there are two clinically testable conscious ascending somatosensory pathways that convey info from periphery to cerebral cortex

relays sense vibration sense and discriminatory touch (2 point) from periphery → cortex

function of dorsal column/medial lemniscus pathway

relays pain, temp, crude touch from periphery → cortex

function of spinothalamic pathway

ascending pathway conveys unconscious sensory info muscles → cerebellum

spinocerebellar pathway

fasciculus gracilis and cuneatus

dorsal column pathway

• anterior spinothalamic tract- crude (non-discriminative) touch and pressure

• lateral spinothalamic tract (pain and temp)

spinothalamic pathways

• posterior/dorsal (blank) tract

• anterior/ventral (blank) tract

• cuneocerebellar tract

spinocerebellar pathways

why do long tracts have to decussate during ascent or descent?

left cortex deals w right side of body

right cortex deals w left side of body

longitudinal organization

somatotopic organization

the two sensory modalities (sensory endings/structures sensitive to specific stimuli) relative to dorsal column:

• proprioception

  • muscle spindles

  • golgi tendon organ

• fine/discriminatory touch

the three sensory modalities (sensory endings/structures sensitive to specific stimuli) relative to spinothalamic pathway:

• crude touch

• pain

• temp

describe the 3 neuron pathway:

• 1: first order neuron cell body in DRG and terminates in brainstem or spinal cord synapse w 2

• 2: second order neuron axon crosses the midline of brainstem or spinal cord, terminates in thalamus

• 3: third order neuron cell body in thalamus and terminates in cerebral cortex/post central gyrus, somatosensory

all info heading to cerebral cortex must stop at (blank) except olfaction

thalamus-relay for cortex

*thalamus also good for higher level cortical function and cortical activation

cortical activation

he process of increased neuronal activity in the cerebral cortex

what pathway is this? talk through graphic

dorsal column/posterior

where does the second neuron of posterior/dorsal pathway cross?

at medulla and form medial lemniscus; injury consistent with same side

where does posterior/dorsal column first order neuron enter?

• for T5 and above receives input from cuneate

• T6 and below receives input from gracilis

is gracile or cuneate more medial in posterior funiculus?

gracile

describe somatosensory cortex somatotopic organization

proprioception

sense of where body is in space

what is wrong in this picture? what would you expect to observe upon examination?

there is demyelination of the dorsal column pathway (posterior funiculi); loss of proprioception: would not know where low extremities are without seeing them; loss of vibration

what about demyelination of just fasciculus gracilis?

no proprioception and vibration too BUT gracilis is medial so that means lower part of body is affected

what about demyelination of just fasciculus cuneatus?

no proprioception and vibration too BUT cuneatus is lateral so that means upper part of body is affected

what findings would you expect to see in an individual with this lesion?

lesion to L posterior funiculus so both L cuneatus and gracilis; second neuron crosses all the way up in medulla so injury affects the same side

what separates the L and R fasciculus gracili?

posterior median sulcus

what separates Cun vs Grac?

posterior intermediate sulcus

what pathway is this?

spinothalamic

spinothalamic neuron location and desiccates

in dorsal horn and crosses immediately at ventral white commissure

where do poorly myelinated pain and temp neurons enter

dorsal horn and follow path to ventral white commissure to desiccate (gray matter)

what would you expect to see on examination of this individual?

spinothalamic loss of pain and temp on L side of body

dorsalateral pathway vs spinothalamic tract

dorso: ipsilateral deficits and good myelination

spinothalamic: contralateral deficits and no or poorly myelinated

what is suspended sensory loss?

suspended sensory loss: pain and temperature sensation is lost at a particular spinal cord level, band-like effect

long tract lesion damage to any of the major sensory pathways in the spinal cord, causing sensory loss that extends below the lesion level and can affect multiple sensory modalities depending on which tract is involved

lesion at white commissure?

spinothalamic neurons could not desiccate so bilateral loss of pain and temp suspended sensory loss!

where do all pathways to the cerebellum end?

they (dorsal spinocerebellar, ventral spinocerebellar, and cuneocerebellar pathways) end ipsilaterally in cerebellum

what is the DSC pathway?

dorsal spinocerebellar/cuneocerebellar

spinocerebellar pathways; not testable; unconscious to limbs

• rare, after occlusion of anterior spinal artery

• motor: bilateral paralysis or weakness

• fine touch: normal

• pain/temp: bilateral loss

anterior cord syndrome (spinothalamic; @ and below)

• rare, after occlusion of posterior spinal artery

• motor: normal

• fine touch vibration: bilateral loss

• pain/temp: normal

posterior cord syndrome (dorsal column @ and below)

• damage to central area of spinal cord, damages crossing fibers first

• motor: immediate bilateral loss

• fine touch: normal

• pain/temp: progressive bilateral paralysis by direct damage on motor neurons

central cord syndrome

ventral white commissure-spinothalamic

• aka lateral spinal hemisection

• motor: ipsilesional paralysis (same side lesion)

• fine touch: ispilesional loss

• pain/temp: contralesional loss

• (symptoms show loss of both pathways)

Brown-sequard syndrome

(motor and touch = dorsal column and pain/temp is spinothalamic)

memorize! summary!