Lab 5 Somatosensory Systems I Flashcards
Dorsal Root Ganglia
Contain cell bodies of larger-diameter discriminative touch, pressure and vibration neurons
Dorsal Roots
Contain central processes of discriminative touch/pressure/vibration neurons
Dorsal Columns (gracile and cuneate fascicles)
Contain ascending axons of primary afferent neurons conducting discriminative touch/pressure sensation
Dorsal Intermediate Septum
Separates the gracile fascicle from the cuneate fascicle
Caudal Medulla Features
Termination site of the fibers of the dorsal column system
IV Ventricle: narrow, surrounded by nuclei associated with cranial and spinal nerves
Horizontal reference line is ventral to the tegmentum
Tegmentum: extends from the dorsal edge to the inferior olivary nuclei; includes the following: Periventricular zone (contains cranial nerve nuclei and some associated nuclei with the dorsal column system) Reticular formation (extends from the periventricular zone to the inferior olivary nuclei)
Walls: tracts that contribute to the inferior cerebellar peduncles
Base: the pyramids
DCML in the Caudal Medulla
Gracile Nucleus: axons of primary afferent neurons carrying discriminative touch info from the body below the T6 level synapse here
Cuneate Nucleus: axons of primary afferent neurons carrying discriminative touch info from the body above the level of T6 synapse here
These nuclei are the first processing center in the DCML pathway
Sensory decussation: crossing of gracile and cuneate fibers across the midline
DCML in Rostral Medulla
Medial Lemniscus: axons originating from neurons in the gracile and cuneate nuclei
It’s between the inferior olivary nuclei, ventral to the horizontal reference line here
Fibers bringing discriminative touch info from the upper body are located dorsal to those from the lower body
Medial Lemniscus in the Caudal Pons
The beginning of a change in orientation from vertical toward horizontal; upper and lower limb representations? Feet start to move out
Medial Lemniscus in the Rostral Pons
note the lateral movement of the lower limb part of the medial Lemniscus
Medial Lemniscus in the Cadual Midbrain
This tract continues to move laterally in the ventral tegmentum
Condenses in the lateral midbrain as it approaches its termination in thalamic nuclei
Medial Lemniscus in the Rostral Midbrain
Ventrolateral Tegmentum in close proximity to the surface and to the horizontal reference line
Ventral Posterior Lateral Nucleus of the Thalamus
Processing and integration center
Ass sensory systems (except olfaction) pass through and synapse in thalamic nuclei on their way to the cerebral cortex
Can easily be located on an MR by knowing axons pass from the VPL to the posterior limb of the internal capsule en route to the left somatosensory cortex
Posterior Limb of the Internal Capsule
Carries thalamocortrical fibers from the VPL to the postcentral gyrus
Spinocerebellar System for Unconscious Proprioception
Cerebellum modulates reflex activity and modifies outgoing motor commands from other brain regions based on the outcome of ongoing motor actions.
We’re not consciously aware of the info brought to the cerebellum by these tracts
They’re commonly involved along with descending motor tracts that cause paralysis. Realize that they travel in the peripheral area of the lateral white matter columns and carrying info to the same side (ipsilateral) of the cerebellum as the side of the receptor
It’s difficult, if not impossible, to identify abnormalities from damage to the spinocerebellar tracts
Discriminative touch Localization (spinal levels)
Shoulders (C4) Thumbs (C6) Little Finger (C8) Anterior surface of the thigh (L2) Medial surface of the leg (L4) Lateral surface of the leg (L5) Little toe (S1)
