10. Somatosensory Pathways 1 Flashcards
The somatosensory pathway transmits and analyzes touch or tactile info from external locations, such as discriminative touch, vibratiion, proprioception. Transmitted via what two pathways?
Posterior column/medial lemniscal
trigeminothalamic pathway
The posterior column - medial lemniscal system (PCMLS) is involed in what ?
perception and appreciation of stimuli (tactile/proprioception)
PCMLS has somatotopic organization (homunculus) and allows two-point discrimination, which is?
ability to discriminate between two stimuli simultaneously
Peripheral receptor density gradient exists between various parts of the body. Which areas would have more or less?
Digits and perioral have increase density of tactile recep Back and (legs) have decreased density of receptors
A receptive field is area of skin innervated by somatic afferent fibers, a small field has what?
high receptor density as compared to a large field with low density (back)
Primary afferent fibers consist of pseudounipolar cell body in the posterior/dorsal root ganglion (DRG) and has what processes?
Peripheral process to free nerve ending
Central process from DRG to CNS
dermatomes formed due to this
PCMLS specific afferent fibers enter the spinal cord via what?
medial division of poterior root and then branch
The largest set of branches will ascend to form the what? which collective are called posterior columns?
Fasciculus gracilis (LE/Lower Thoracics) or fasciculus cuneatus (UE/ Upper thoracics)
Fibers from medial to lateral within the fasciculus gracilis have sacral, then lumbar through T6. What about fasciculus cuneatus?
added laterally as they join the LE, thoracic levels above T6, lower cervical, upper cervical, which is the most lateral in the fasciculus cuneatus
A SC lesion in the fasciculus cuneatus or gracilis would result in?
ipsilateral loss of proprioception/touch to that level and below
What is it called when there is a loss of muscle stretch reflexes and proprioceptive loss from extremeties due to lack of sensory input?
Sensory Ataxia
The second order neurons of the PCMLS, which receive input from first order neurins, can be found in what, where?
in the nucleus gracile and nucleus cuneatus in the posterior medulla
From the second or neurons of the PCMLS, it sends axons to the contralateral thalamus via?
internal arcuate fibers
The internal arcuate fibers of the PCMLS cross the midline as the sensory decussation and ascend as what on the opposite side?
Medial Lemniscus ML
As the medial lemniscus moves rostrally, is rotates laterally in the pons, so the LE/UE fibers are located where inside?
UE are medial and LE are lateral
The medial lemniscus with the UE fibers medial and LE fibers lateral moves to the thalamus where is synapses where?
Ventral Posterolateral Nucleus (VPL)
What is the main blood supply to the cuneatus and gracilis fasciculus in the SC?
posterior spinal A