Lab 3 (ƒ5) - Somatosensory, Viscerosensory and Spinocerebellar Pathways
Brainstem and Diencephalon
The images move from the brainstem to the diencephalon. At each level read the corresponding section of text and identify the bold structures.
Lower Medulla
Fibers that travel in the anterolateral quadrant of the spinal cord in close association with spinothalamic tract terminate in the medullary and pontine reticular formation and constitute the spinoreticular pathway. Some regions of the brainstem reticular formation, in turn, project back to the posterior horns of the spinal cord in the dorsolateral fasciculus (DLF) to modify the transmission of nociceptive information in the spinal cord. This neural feedback mechanism is believed to modulate the perception of painful stimuli.
Mid Medulla
In the medulla, the spinothalamic tract lies near the lateral surface just posterior to the inferior olive. The spinoreticular fibers, which ascend with the paleospinothalamic tract, continue to give off branches that terminate in the medullary reticular formation.
Upper (Open) Medulla
The fibers of the spinothalamic tract have been shifted further posteriorly by the inferior olives. Spinoreticular fibers continue to travel with the spinothalamic fibers while giving off branches to the medullary reticular formation.
Caudal Pons
The spinothalamic tract is located at the lateral tip of the medial lemniscus. Some of the spinoreticular fibers traveling with the spinothalamic fibers are leaving to terminate in the pontine reticular formation.
Mid Pons
The spinothalamic tract is located near the lateral tip of the medial lemniscus. The spinoreticular fibers, which continue to travel with the spinothalamic tract, continue to give off branches to the pontine reticular formation.
Rostral Pons
The spinothalamic tract is located at the posterolateral tip of the medial lemniscus. Spinoreticular fibers continue to leave the spinothalamic tract to end in the pontine reticular formation and in the periaqueductal gray surrounding the cerebral aqueduct.
Lower Midbrain
The crossed (predominantly) and uncrossed 2° and 3° spinothalamic tract afferents continue to be located at the posterolateral tip of the medial lemniscus. The spinoreticular fibers continue to send branches to the periaqueductal gray. Also identify the cerebral aqueduct.
Upper Midbrain (Transverse)
The spinothalamic tract is located at the posterolateral tip of the medial lemniscus. It contains 2° neospinothalamic afferents and 3° paleospinothalamic afferents that are predominantly crossed. Identify the periaqueductal gray surrounding the cerebral aqueduct.
Midbrain (Coronal)
In the thalamus, the spinothalamic tract bifurcates and terminates in the ventral posterolateral nucleus (VPL) of the thalamus (the neospinothalamic 2° afferents) and in the intralaminar thalamic nuclei (the paleospinothalamic 3° afferents). Locate the intralaminar thalamic nuclei, which include the centromedian nucleus and nucleus parafascicularis. The axons of the VPL travel in the posterior limb of the internal capsule to end in the postcentral gyrus of the parietal lobe. The thalamic intralaminar projection to the cerebral cortex is more diffuse and includes most cortical areas.