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