Lecture 10: Somatosensory Pathways Part 2 Flashcards
What does the Spinothalamic/ALS system do?
Relays information about pain, temperature, and crude touch from the body to the brain
What is the direct pathway of the ALS?
Spinal Cord –> Lateral Thalamus –> Somatosensory Cortices
What is the indirect pathway of the ALS?
Spinal Cord –> Reticular System –> Medial Thalamus –> Cingulate, Frontal, and Limbic Cortices
What picks up pain/temperature sensation?
Free nerve endings found all over the body
Where does nerve fibers from the free nerve endings travel to?
Lateral division of the posterior root of the spinal cord
What happens to fibers that stay at the same level?
Terminate on interneurons for reflexes
What laminae are targeted by primary afferents of the ALS tract?
Laminae I, II, and V
What happens to most fibers that enter the lateral spinal cord?
Will ascend or descend (mostly ascend) 1-2 levels in Lissauer’s Tract
In the direct pathway what happens after the fibers ascend?
- They synapse at a cell body in the dorsal horn of gray matter
- They decussate (cross over) at the same level and continue upwards, contralaterally
What is anterior white commissure?
The name of the fibers in the ALS tract that have decussated and continuing upwards toward thalamus
In the direct pathway where does the anterior white commissure synapse?
Synapses at Ventral Posterolateral Nucleus of thalamus (VPL)
In the direct pathway, where do fibers go after synapsing at the VPL?
Somatosensory cortex via posterior limb of internal capsule
What does the indirect pathways of the ALS tract do?
Relay awareness of pain rather than specific sensation
In the indirect tract, what laminae do the fibers synapse in?
Laminae II and III and influences Laminae V-VIII
Where do spinoreticular fibers terminate?
Terminates in reticular formation (upper pons)
For the spinoreticular fibers that does continue upward, where does it terminate?
Medial Thalamus
In the ALS tract, where are axons from the lower and upper extremities found?
Lower: Posterolaterally
Upper: Anteromedially
Where do primary afferents for the ALS tract come from?
Trigeminal Ganglion
Where do the primary afferent fibers for the ALS tract synapse?
Spinal Trigeminal Nucleus
Why do the primary afferent fibers descend to join Lissauer’s Tract?
The blending allows cross over of sensation in the upper cervical area
Where do second order axons terminate at?
They decussate and ascend contralaterally to the VPM where they terminate
Where do fibers go from the VPM?
Primary Somatosensory cortex via posterior limb of internal capsule
What supplies the trigeminal structures in the medulla?
Posterior Inferior Cerebellar Artery
Posterior Spinal Artery
What are the divisions of the spinal trigeminal nucleus?
Pars Caudalis
Pars Oralis
Pars Interpolaris
In the spinal trigeminal tract, how are the branches of the trigeminal nerve oriented?
Ophthalmic is inferior
Mandibular is superior
Where is pars caudalis?
Starts around C2/C3 and extends to obex of medulla
What happens if there is a caudal lesion in pars caudalis?
Area around mouth more likely to be spared from sensory loss
What happens if there is a rostral lesion in pars caudalis?
Sensory loss starts back of head and converges on mouth
Where is pars oralis?
What does it do?
Superior medulla to lower ons
Receives tactile info from central face
Where is pars interpolaris?
What does it do?
Superior medulla to obex
Receives info from peripheral face and projects info to cerebellum
What is the function of the trigemino-reticulo-thalamic pathway?
Facilitates Reticular Activating System in arousal and alertness
What supplies the ALS tract in the spinal cord?
Sulcal Branches of Anterior Spinal Artery - symptoms start two levels below lesion
What are signs of a Brown-Sequard Syndrome?
Contralateral: loss of pain/temp sensation over body two segments below lesion
Ipsilateral: Loss of general sensory info at or below lesion and motor loss with paralysis of extremities
What is syringomyelia?
Cystic cavitation of central regions of spinal gray matter that can impinge on anterior white commissure that contains decussating ALS fibers?
What are signs of a syringomyelia?
Bilateral loss of pain/temp sensation
C4/C5: cape like distribution
What are symptoms of shingles?
Diminished sensibility over affected dermatomes and severe pain
What are symptoms of [Medial] Medullary Syndrome?
Contralateral loss of discriminative touch and vibratory sense but intact pain/temp sensation
What are symptoms of Lateral Medullary/Wallenberg Syndrome?
Contralateral loss of pain/temp over body and ipsilateral loss of pain/temp over face
What artery can be damaged in Lateral Medullary/Wallenberg Syndrome?
PICA
