Somatosensory Paths Flashcards
What does the posterior column transmit
Perception of mechanical stimuli
Size, shape, and texture discrimination, and recognition of 3D shape
Proprioception
What is 2 pt discrimination
Can discriminate b/w 2 stimuli simultaneously
Related to density of peripheral nerve endings
Density seen in a small receptive field?
Density send in a small receptive field?
High receptor density
Low receptor density
Where are the cell bodies of the primary afferent fibers?
Where do these cell bodies terminate?
Dorsal root ganglion
On neurons in spinal gray matter
Where do primary afferent fibers for the posterior columns enter the spinal cord?
Enter via medial division of the posterior root then branch
What does the fasciculus gracilis transmit?
Sensory info and proprioception from
BELOW T6
What does the fasciculus Cuneatus do?
Transmits sensory info from AT and ABOVE T6
As you go up fasciculus gracilis and Cuneatus, how are fibers added?
Sacral fibers medially
Rostral fibers laterally
What happens to the posterior columns if they are lesioned at the spinal cord?
Ipsilateral reduction or loss of discriminative, positional, and vibratory tactile sensation at and below segment lesion
What is sensory ataxia?
What 2 things could it be caused from?
Loss of muscle tendon reflexes
Loss of proprioception from extremities
Wide based stance and place feet with force
Lesion to posterior column
Neurosyphylis
Where are the nuclei for gracile and Cuneatus?
Posterior medulla
What are the gracile nucleus and cuneate nucleus supplied by?
Posterior spinal a.
Where do the posterior columns cross midline?
Internal arcuate fibers in medulla
After crossing in the medulla, how do the posteiror columns ascend?
Ascend as medial lemniscus
Topographically, how are the medial lemniscus fibers set up?
upper ext. = medial
Lower extr. = lateral
Where does the ML go to?
VPL nucleus in thalamus
What is the blood supply of ML?
Anterior spinal a.
Where are the ventral posterior nuclei?
What supplies them?
In caudal thalamus
Thalamogeniculate branches
WHat happens if there is a lesion of thalamogeniculate branches of PCA?
Loss of all tactile sensation over opposite body and head
Thalamogeniculate supplies ML - aka posterior columns
The third order neurons of posterior column go where?
Posterior limb of internal capsule
What is the final destination of the GF/CF/ML posterior column pathways?
Primary and seocndary somatosensory cortices
What makes up the primary somatosensory cortex?
What is is boarded by?
Post central gyrus and posterior paracentral gyrus
Central and post central sulcus
What is the primary somatosensory cortex divided into?
Brodmann areas
3a,3b, 1 and 2
What supplies the primary somatosensory cortex?
ACA and MCA
What would a lesion to MCA cause (looking to primary somatosensory cortex)?
Tactile loss over contralateral upper body and face
What would a lesion to ACA cause (looking to primary somatosensory cortex)?
Affect contralateral lower limb
Where is the secondary somatosensory cortex?
What sends it inputs?
Upper bank of lateral sulcus
Input from somatosensory cortex and VPI of thalamus
What can a lesion to the parietal cortical region produce?
Agnosia = contralateral body regions lost from body map, limbs are not recognized
(Sensory intact)
What does the Mesencephalic nucelsu?
Proprioceptive info from masticatory ms., extraocular ms. And periodontal l.
What does the principle sensory nucleus do?
Discriminative tactile and proprioceptive info
What supplies the prinicpal sensory nucleus?
SCA
Principle Sensory A.
What does the dorsomedial division of the principal sensory nucleus?
Oral cavity
Travels ipsilaterally via anterior trigeminothalamic tract
What does the ventrolateral division of the principal sensory nucleus?
V1, V2, V3
Travels contralaterally via posterior trigeminothalamic tract
Where do the principal sensory nucleus go?
VPM nucleus
What is the somatotopic arrangement of the VPM nucleus?
Oral cavity medial
External face lateral
What is the only nucleus within the CNS?
Mesencephalic nucleus
Where does the Mesencephalic nucleus go to?
To principal sensory nucleus and spinal nucleus
What is the jaw jerk reflex ?
What is the afferent limb?
What is the efferent limb?
Stretching masseter by downward tap on chin - causes it to contract bilaterally
A: Mesencephalic nucleus to trigeminal motor neurons
E: trigeminal motor neuron
What is mononeuropathy?
Damage to a nerve outside outside the brain and spinal cord
What is a dermatomal sensory loss?
Big overlap of dermatomal sensory distribution
What is peripheral neuropathy?
How does it present?
Who does it commonly affect?
Symmetrical damage to peripheral nerves
Stocking-glove loss of sensation
Diabetes Mellitus
How does hemisection of the spinal cord present?
Brown-sequard
Dorsal column lost = ipsilateral sensation body lost
ALS lost = contralateral loss of pain/temp
CST lost = ipsilateral paralysis
what does the als convey?
Pain, temp, non-discriminative touch from body, itching
What is the direct pathway of ALS?
Spinal Cord —> Lateral thalamus —> S1
What is the indirect pathway of ALS?
SC —> RF —> ML —> cingulate, frontal and limbic cortices
What are cutaneous nociceptors?
1st strustcutres that pick up the sensation transmitted
C fibers and a-delta
How is sensation transmitted thru free nerve endings?
Ligand gated ion channels
Glutamate receptors
GPCRs
How do free nerve endings enter the SC?
Lateral division of the posterior root
Body sensation was medial
What are the targets of the ALS free nerve endings?
Lamina 1, 2, and 5 of the posterior horn
After the free nerve endings of the ALS enter the SC where do they go?
Ascend and descend via Lissauer’s tract
How does the ALS cross? And where?
Cross to what?
Cross anterior white commissure to ascend via ALS
2 levels above the fiber entry zone
What does the direct ALS pathway target?
VPL of thalamus
Where does the indirect ALS pathway terminate?
Where do those 3rd order neurons go?
Reticular formation
RF to intralaminar nuclei and posterior group nuclei
Where do the spinothalamic fibers go?
Spine -> thalamus -> VPL
Where do the spinomesencephalic fibers go?
Spine -> RF and PAG
Where do the spinobulbar fibers go?
Spine —> various nuclei of brain
Where do the spinohypothalamic fibers go?
Spine -> hypothalamus and other nuclei
How is the ALS organized?
Arms- medial
Legs - lateral
What would an intramedullar tumor cause?
Medial= arms hit first
What would an extramedullary tumor cause?
Lateral = sacral and coccygeal and lumbar hit first
How does Herpes zoster manifest?
Viral etiology that has dermatomal distribution
Can reactivate from NS when under stress
Postherpetic neuralgia
What is syringomyelia?
How does this first present
Cystic cavitation of central regions of spinal gray matter
Can impinge on AWC and take out both ALS fibers
Patient unknowingly burns hands on stove, curling iron, etc.
What is the blood supply to the ALS?
Arterial vasocorona
Sulcal branches of ASA
What could happen if the arterial vasocorona or Sulcal branches of ASA is occluded?
Where would sxs show up?
Patchy loss of pain, temp., and touch of contralateral side of body
2 spinal segments below lesion
What does a medial medulla lesion cause?
Contralateral loss of touch and vibratory
Still has pain and touch
Lateral medullary syndrome presents how?
Caused by what?
PICA lesion
Spinal V lost - ipsilateral pain loss to face
ALS lost - contra pain loss to body
What is the target of the spinal trigeminal pathway?
VPM of thalamus
What is the blood supply to the trigeminal strucutres in the medulla?
PICA
What are the division of the spinal V nucleus?
Pars caudalis
Pars oralis
Pars interpolaris
where is the pars caudalis located?
Spinal cord C2, C3 to obex
Where is the pars oralis?
Pons to superior medulla
What is pars interpolaris?
From superior medulla to obex
What happens if the spinal trigeminal tract is lesioned…
Caudally?
Rostrally?
Onion peel sensory loss
Caudal lesion - mouth okay
Rostral lesion - sensory loss at mouth and back of head
What is the indirect pathway for Trigeminal pathway?
What does this facilitate?
Pain fibers to RF bilaterally as Trigeminoreticular fibers
Helps ascending RAS system in arousal and alertness
What does a unilateral lesion of trigeminal n. Cause?
Loss of jaw jerk reflex
Atrophy of Ms. of ma stication
Anesthesia in trigeminal dermatomes
Loss of ipsilateral and consensual corneal reflex
What could cause alternating analgesia?
Brainstem lesion in upper medulla
Damaging spinal V tract before it crosses
What causes alternating trigeminal hemiplegia?
Unilateral destruction of trigeminal n. And CST in PONS
What would a lesion to the trigeminal n. Or central nuclei cause?
Ipsilateral loss of pain, temp and touch sensation cause
Loss of sensation in mouth
Paralysis in masticatory Ms.
Could lose afferent limb of corneal reflex
How does the corneal reflex work?
Aff. Limb to CN V
Travel on V1 to cell bodies in trigeminal ganglion
Trigeminothalamic fibers BILATERALLY to facial motor nucleus
Causes both eyes to blink
