Flashcards in Module D-03 Deck (27):
Describe the 3 neuron chain spinal touch pathway
- 1st order neuron (somatosensory receptor neuron): afferent fibers in peripheral nerve (pseudounipolar with cell body in dorsal root ganglia) enter through dorsal roots
- 2nd order neuron: fibers crossing the midline(at cuneate or gracile nuclei) and terminating in the thalamus
- 3rd order neuron: fibers running in posterior limb of internal capsule and ending in S1 (primary somatosensory cortex)
Where does the pathway for touch and vibration start ?
on the body surface (dermatomes)
Where does the pathway for proprioception start?
Where are the cell bodies of the 2nd order neurons found?
Cuneate and Gracilis nuclei
Which order fibers cross over in Touch pathway?
2nd order neurons
Which nucleus of the thalamus do the 2nd order touch neurons synapse?
ventral posterior lateral (VPL) nucleus
Where is the primary somatosensory cortex located?
postcentral gyrus of the parietal lobe and the part of the paracentral lobule on the medial side
From Where does input of the trigeminal pathway for
touch, vibration and proprioception come?
cutaneous mechanoreceptors and muscle proprioceptors of the face
Where are the cell bodies for the primary afferent neuron found?
Describe the 3 neuron pathway for the trigeminal pathway
1) primary afferent fibers enter the brainstem at the pons and synapse in the principal (chief) sensory nucleus of CN V in upper half of the pons
2) second order neurons fibers exit the principal nucleus of CN V and immediately cross over to the contralateral side, where they ascend in the ventral trigeminothalamic tract and synapse in the ventral posterior medial (VPM) nucleus of the thalamus.
3) Third order neurons in the VPM nucleus of the thalamus send their axons through the posterior limb of the internal capsule, close to the genu, and then through the corona radiata then synapse in the primary somatosensory cortex
What part of the brainstem are the fibers for somatosensory information of touch, vibration and proprioception from the face found?
Upper Pons and midbrain
Name the 4 nuclei of the Trigeminal
1) Principal (chief) nucleus
2) Spinal nucleus of V
3) Motor nucleus of V
4) Mesencephalic nucleus of V ( in midbrain)
Which brodmann's areas make up the Primary somatosensory cortex
the somatosensory Homonculus , shows where on the primary somatosensory cortex is which part of the body's sensation
Sensation of which regions of the body are found on the Lateral side of the primary somatosensory cortex?
from top to bottom:
Sensation of which regions of the body are found on the Medial side of the primary somatosensory cortex
from top to bottom:
What are the organizing units of the sensory cortex called
cortical columns (slow and rapid adapting neurons processing columns)
Which layer of the primary somatosensory cortex receives inputs from the thalamus (VPL and VPM) through thalamocortical fibers?
Lower threshold (distance) for 2 point discrimination the ________ the spatial resolution
Which are areas of highest two point discrimination thresholds (= lowest spatial resolution) ?
the upper arm and forearm, thigh, calf and the back of the trunk.
Factors Contributing to High Spatial Resolution
- High density of cutaneous mechanoreceptors
- Small receptive fields of the sensory receptors (which is characteristic of Merkel's disks and Meissner’s corpuscles)
- Lateral inhibition
Which sense is often lost first in peripheral neuropathies?
What is Stereognosis ?
Ability to perceive the properties of a coherent object, like its size, shape, and texture, by holding it in the hand (tested with eyes closed)
What is Graphesthesia ?
Ability to distinguish letters drawn on the skin (tested with eyes closed)
What is Tabes Dorsalis?
consequence of a syphilitic infection.
Destruction of dorsal root ganglion cells with large diameter myelinated axons
What senses are lost in Tabes Dorsalis?
Deficit in touch and proprioception.
Nociception and temperature sense remain almost unaffected.