Somatosensory Tracts 1: Proprioception and Tactile Pathways Flashcards
What are some important somatosensory pathways?
PCMLS (touch/vibration and proprioception)
Trigeminothalamic pathway (pain and temp)
Spinocerebellar pathway (proprioception)
ALS (pain and temp)
What is the PCMLS involved with?
Tactile information (3D recognition), two-point discrimination, and conscious awareness of body/limb position
How do primary fibers enter the spinal cord in the PCMLS?
Via medial division of posterior root
Where are deficits located in SC lesions?
Ipsilateral side = reduction/loss of discriminative, positional, and vibratory tactile sensations at/below level of injury
What is sensory ataxia?
Loss of DTRs and proprioceptive losses from extremities. Wide-based stance seen.
Where are second order cell bodies located in the PCMLS?
In gracile nucleus or cuneate nucleus in the medulla
What do second order neurons do in the PCMLS?
Synapse with ipsilateral first order neurons in the gracile/cuneate nuclei and then arc and cross at midline (sensory decussation) to medial lemniscus. Go up medial lemniscus to contralateral thalamus
What happens to the fibers as they run up the ML in the PCMLS?
They rotate laterally, UE fibers lie medially, LE fibers lie latearlly
Where does the ML terminate?
Ventral posterolateral nucleus (VPL) of the thalamus
What do third order neurons do in the PCMLS?
Synapse with second order neurons in the VPL and then go through the posterior limb of the internal capsule to the primary/secondary somatosensory cortices
What are the VPL and VPM called?
The ventral posterior nuclei
What are the Brodmann areas of the primary somatosensory cortex?
3a, 3b, 1, 2 (higher integration of sensory info)
What is the blood supply to the S1?
ACA and MCA
What is agnosia?
Don’t know what your limb is doing but still have sensation
What are the trigeminal nuclei?
Mesencephalic nucleus (TMJ, oral cavity, extraocular muscles)
Principle/chief sensory nucleus (discriminative touch, pressure, and proprioception)
Trigeminal motor nucleus
Spinal nucleus (pain and temperature)
What are the two divisions of the trigeminal principle sensory nucleus?
Dorsomedial division (oral cavity) Ventrolateral division (major - V1, V2, V3)
How does the trigeminal principle sensory nucleus work?
Primary afferent cell bodies located in trigeminal ganglion. Enter laterally at mid pons to synpase in the principle sensory nucleus with secondary fibers. Secondary fiber cell bodies located in principle sensory nucleus, go either to ventrolateral/anterior (contralateral) division or dorsomedial/posterior (ipsilateral) division. Synapse with third order neurons in VPM of thalamus which travel via the posterior limb of the internal capsule to the primary somatosensory cortex (face region)
What is the blood supply to the trigeminothalamic tract in the midbrain?
PICA/PSA
What does the trigeminal mesencephalic nucleus/tract do?
Unconscious proprioceptive and pressure info from jaw/TMJ and eyes. Also forms circuit for jaw-jerk reflex.
How does the jaw-jerk reflex work?
Mesencephalic trigeminal neuron (afferent) innervates masseter muscle. Synapses with trigeminal motor neuron (efferent), causes muscles to contract bilaterally
What is the blood supply to the mesencephalic and principle sensory nuclei?
Located in midbrain and mid-pons:
Long circumferential branches of basilar a
Branches of AICA
Branches of superior cerebellar a
