10.1 Somatosensory Tracts 1 (Dennis) Flashcards
What type of information is carried by the PCML pathway?
Two point touch
Deep Pressure
Vibration
Propriception
Crude touch
Thermal sensation
Nociception
Where are the cell bodies for first order sensory neurons?
What type of nerves are these?
From what layer are these nerves derived?
Dorsal root ganglion.
Pseudounipolar nerves.
Neuroectoderm.
Where do the afferent first order fibers of the PCML system enter the spinal cord?
At the medial division of the posterior root.
Where is the switch over from fibers coming together to form the fasciculus gracilis to becoming the fasciculus cuneatus?
T6
In the fasciculae gracilis and cuneatus, are the fibers from the upper extremity more lateral or more medial to the fibers from the lower extremity?
Upper extremity fibers are more lateral in the PCML system.
Where do we find the nuclei gracilis and cuneatus?
In the posterior medulla.
What is the specialization of the outer shell and inner core of the nuclei gracilis and cuneatus?
The outer shell of the nuclei gracilis and cuneatus specializes in proprioception.
The inner core specializes in sensation.
What do we call the decussation of the PCML secondary fibers immediately after the synapse of the nucleus gracile/cuneatus?
Anterior arcuate fibers.
At the level of the pons, are fibers from the nucleus gracilis medial or lateral to the fibers of the nucleus cuneatus?
Fibers from the nucleus gracilis are lateral in the pons.
What nucleus in the thalamus does the PCML pathway synapse onto?
The ventral posteriolateral nucleus of the thalamus.
Where do the third order neurons of the PCML system travel?
What important structure do they pass through?
What is the name of the pathway?
The fibers from the ventral posterolateral nucleus runs through the thalamocortical pathway, through the posterior limb of the internal capsule, and to the somatosensory cortex.
What artery supplies the PCML in the spinal cord?
What artery supplies the PCML in the medulla (and up from there)?
Spinal cord = posterior spinal artery
Medulla and up = anterior spinal artery
What artery supplies the ventral posterolateral nucleus?
What would happen if these were occluded?
The thalamogeniculate branches of the posterior cerebral artery.
Complete loss of discriminative touch, pressure sensation, and proprioception to the contralateral body.
Where would lesions to the middle cerebral artery cause loss of sensation?
Where would lesions to the anterior cerebral artery cause loss of sensation?
The anterior cerebral artery damage would eradicate sensation from the lower extremity.
Middle cerebral artery damage would eradicate damage from the upper extremity and face.
What symptom is associated with damage to the secondary somatosensory area?
Agnosia – the loss of ability to recognize a limb as part of the body.
What are the functions of the sensory nuclei of the trigeminal nerve?
Main sensory nucleus (msT)
- Touch and pressure.
Spinal nucleus
- Touch
- Pressure
- Proprioceptin
- Pain
- Temperature
Mesencephalic nucleus (mes)
- Proprioception for chewing.
What are the two divisions of the main sensory nucleus of the trigeminal nerve?
The main sensory nucleus has two divisions:
- Dorsomedial division
- Afferents just from the oral cavity.
- Ventrolateral division
- Afferents from V1, V2, and V3
What is the purpose of the mesencephalic nucleus?
Primarily relays proprioceptive information related to chewing.
What are the three parts of the spinal nucleus of the trigeminal nerve?
Pars caudalis,
Pars oralis,
Pars interpolaris
What are the targets of primary afferent nerves?
laminae I, II, and V of posterior horn
What is the other name for Lissauer’s tract?
posterolateral fasciculus
where afferents of ALS travel
ascending branches go up to brain
some descending branches terminate on interneurons in SC gray matter for reflexes
where are 3rd order neurons of the direct spinothalamic path located?
VPL
What are spinoreticular fibers?
branches from ALS that terminate in reticular formation of brainstem
third order neurons then project to medial thalamic nuclei
What are spinobulbar fibers?
info from sC that ascends to various brainstem nuclei
What are spinomesnecephalic fibers?
from ALS –> terminate in midbrain reticular formation or transition to form spinotectal fibers –> superior colliculus and anterior pretectum
What is the somatotopic relationship of the ALS?
axons from lower levels = lateral
axons from upper extremity = medial
What is the blood supply to the ALS?
vasa corona and sulcal branches of the anterior spinal A
What would occlusion of the arterial vasocorona and sulcal branches of Ant spinal A cause?
patchy loss of pain and thermal senses over contra side of body
What does hemisection of the SC cause?
contralateral loss of pain and thermal sensations about 2 segments below lesion
ipsi loss of tactile and vibratory sense
Where are medullary ALS fibers?
near anterolateral surface
anterior to spinal trigeminal nucleus
spearated from PCMLS
What artery supplies the ALS fibers in the medulla?
What happens if a lesion occurs here?
PICA
contra loss of discriminative touch and vibratory sense, but pain/thermal sense is WNL (one modality absent, but not the other)
How does the spinal trigeminal nucleus run?
afferents enter pons –> descend in spinal trigeminal tract, lateral to spinal nucleus –> becomes continuous w/ Lissauers tract in upper cervical cord
both nucleus and tract extend caudally to about 3rd cervical segment
What are the parts of the spinal trigeminal tract and nucleus?
pars caudalis: moust caudal, from C2, C3 to obes
pars oralis: most rostral, from main sensory nucleus to pontomedullary jxn
pars interpolaris: in btw, in rostral medulla
How are the spinal trigeminal tract and nucleus oriented in regard to dermatomes on face?
opposite: on face V1 = superior
in tract: V1 is inferior, V2 middle, V3 superior
How are fibers arranged in the pars caudalis?
oral fibers (most superior on face) = most superior
caudal and lateral fibers = most caudal
What is the pattern of sensory loss from a spinal trigeminal tract lesion?
onion-peel sensory loss
more caudal lesion –> larger the area surrounding the mouth that is spared from sensory loss
more reostral –> sensory loss starts and back of head and converges on mouth
Where do neurons decussate in the Trigeminal tract?
second order axons from spinal trigeminal nucleus –> decussate –> ascend in contra anterior trigeminothalamic tract
Where do nerves of the trigeminal system go once they are in the anterior trigeminothalamic tract?
(this is the medulla) –> ascend to trimeminal lemniscus in midbrain –> synapse is contra VPM of thalamus –> tertiary axons to posterior limb of internal capsule –> SI
What are trigeminoreticular fibers?
pain fibers project bilaterally to reticular formation
facilitates ascending reticular activating system (ARAS) = arousal and alertness
What happens in a unilateral lesion of the trigeminal N?
ipsi anesthesia
loss of jaw-jerk reflex
atrophy of muscles of mastication
loss of ipsi and consensual corneal reflex
What is alternating analgesia?
brainstem lesions in upper medulla may destroy primary fibers in spinal trigeminal tract and secondary fibers in spinal lemniscus
ipsi hemianalgesia of face and contra hemeanalgesia of the body
What is alternating trigeminal hemiplegia?
unilateral destruction of trigeminal n and CST in the pons
ipsi trigeminal anesthesia and paralysis
contra spastic hemiplegia
What nerves does the corneal reflex go through?
afferent through V –> trigeminal ganglion –> motor to VII
