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
What is the main blood supply to the medial lemniscus and pyramids of the medulla?
anterior spinal A
Damage of the BS in the midbrain of the medial lemniscus would lead to what? Why?
CONTRALATERAL deficits of touch and proprioception because the fibers of the PCMLS crossed in the medulla via internal arcuate fibers to ascend as the ML
The ventral posterior nuclei are located in the caudal thalamus and are comprised of what?
ventral posterolateral and posteromedial nucleus (VPL/VPM) which are separated by arcuate lamina
What is the blood supply to the VPL and VPM, which if compromised can result in loss of touch and sensation over contralateral body/head?
thalamogeniculate branches of posterior cerebral A
The medial lemniscus terminates in the VPL with fibers from cuneatus and gracile nuclei terminating where?
cuneatus medially and gracile laterally within the VPL
The VPL for the trunk and extremities contain two populations of neurons?
- third order neurons **majority
2. local circuit interneurons (inhibitory to stop firing rate of 3rd order neurons)
From the VPL, most of the axons terminate in the third order neurons there which send axons that traverse what to where?
traverse the posterior limb of the internal capsule and terminate in primary/secondary somatosensory cortex
From the posterior limb of the internal capsule, the third order neurons from the thalamus terminate in the somatosensory cortex, which is comprised of what?
postcentral and posterior paracentral gyri
LE is medial, UE is medial, and face is lateral in the parital part of the brain. Which have the largest amt of receptors?
hands, feet, face
If the ACA or MCA blood supply was cut to the left side of the brain, primarily at the somatosensory cortex, what would be seen?
the RIGHT side (cause fibers crossed) would have no touch sense or proprioception
(aca is LE, mca is upper body and face)
What brodmann areas make up the primary somatosensory cortex from posterior to anterior? (4)
3a, 3b, 1, 2
The secondary somatosensory cortex lies deep in the lateral sulcus, and gets input from what?
ventral posterior inferior nucleus of thalamus
parietal cortical regions receive tactile inputs including areas 5 and 7 posterior to bordmann 2 area. Lesions here lead to agnosia which is?
limb is not recognized as part of the patients body
Trigeminal carries main sensory for head and motor for mastication M. Afferents extend from cell bodies to trigeminal (semilunar) ganlgion which then does what?
forms continous cell column that extends from spinomedullary junction to rostral levesl of midbrain
What are the two main sensory nucleus of the trigeminal inputs that relay info on touch and proprioceptions?
Main/cheif/princple sensory nucleus (msT) : touch and pressure Mesencephalic nucleus (mes): proprioceptive from TMJ/mastication M
The main sensory nucleus receives info on tacile and proprioceptive sensations. there is a dorsomedial and ventrolateral division which receive afferents from?
dorsomedial: oral cavity
Ventrolateral: V1,V2,V3
Afferents from trigmenal N synapse in trigeminal ganglion and send axons to the main sensory nucleus, ventro is V1-3 and dorsomedial is from oral cavity. What happens next?
2nd order fibers from dorsomedial division travel IPSILATERALLY via posterior trigeminothalamic tract
2nd order fibers from ventrolateral division travel CONTRALATERALLY via anterior trigeminothalamic tract
The posterior and anterior trigeminothalamic tracts have the same target of?
ventral posteromedial (VPM) nucleus in thalamus (oral cavity is medial and V1-3 is lateral)
3rd order axons/fibers from the VPM nucelus in the thalamus project to what to get to the primary somatosensory cortex?
posterior limb of the internal capsule
Tactile and proprioceptive information from UE/LE is relayed via PCMLS while head and neck is via
main sensory nucleus of trigeminal w some PCMLS
The mesencephalic nucleus is comprised of pseudounipolar neurons and is the only nucleus in the CNS. What does it convey?
unconscious proprioceptive and pressure info from muscles of oral region
What is this reflex: afferent limb: mesencephalic trigeminal neuron whose peripheral process innervates a masseter muscle and whose central process synapses on a trigeminal motor neuron (efferent)?
jaw-jerk reflex
Mesecephalic nucleus via spinal nucleus (pars interpolaris) allows proprioceptive input from jaw/chewing via?
supeiror cerebellar peduncle
From main sensory nucleus some 2ndary neurons project anterior to the vermis of the cerebellum via?
superior cerebellar peduncle
What is important information that is relayed via trigeminocerebellar pathways?
jaw placement during mastication
Cross sensory syndrome are different deficits that depend on where fibers cross. Brainstem: UE/LE is contralateral while face is ipsilateral. SC lesions can result in?
proprioceptive deficits on the right but anesthesia on the left (lack pain)
SI leasions usually include larger areas and frequenctly result in more what?
global deficits, as compared to brainstem/brain injuries
