Somatosensory Tracts 1 Flashcards
What is the DCML pathway used for?
general sensation and proprioception
What is the ability to discriminate between two stimuli simultaneously?
two-point discrimination
what is the area of skin that is innervated by somatic afferent fibers?
receptive field
small receptive fields have what type of receptor density?
high
large receptive fields have what type of receptor density?
low
where are the cell bodies located for primary afferent fibers?
in the dorsal root ganglion
how do the primary afferent fibers enter the spinal cord?
via the medial division of the posterior root
what are the two posterior columns?
the fasciculus gracilis and the fasciculus cuneatus
The fasciculus gracilis is responsible for what region of the body?
sacral–> T6 region
the fasciculus cuneatus is responsible for what region of the body?
T6–> superior
sacral level fibers in the posterior column are positioned how?
medially
fibers from progressively more rostral levels are added to the posterior column how?
laterally
Lesions of the fasciculus gracilis or fasciculus cuneatus? spinal cord lesions result in what?
ipsilateral reduction or loss of discriminative, positional, and vibratory tactile sensations AT AND BELOW the segmental level of injury
what is sensory ataxia?
loss of muscle stretch (tendon) reflexes and proprioceptive losses from the extremities due to lack of sensory input
where are the gracile nucleus and cuneate nucleus found?
in the posterior medulla
what do the gracile nucleus and cuneate nucleus contain?
2nd order neurons on the DCMLS
once the second order neurons receive input from the primary afferents (1st order neurons), what happens next?
they send their axons to the contralateral thalamus
what is the name of the location of where the crossing over takes place?
internal arcuate fibers
once the sensory decussation occurs, what do the fibers ascend as?
the medial lemniscus (ML)
where does the medial lemniscus terminate?
in the ventral posterolateral nucleus (VPL) of the thalamus
what is housed in the VPL of the thalamus?
3rd order neurons that project to the cortex
if we have damage in the medulla or other portions in the brainstem, what will the deficits look like?
they will be on the contralateral side
Before reaching the VPL of the thalamus, what happens to the ML?
it rotates
what is the blood supply of the thalamus nuclei?
thalamogeniculate branches of the posterior cerebral artery
what would a lesion of the thalamogeniculate branches of the posterior cerebral artery result in?
loss of all tactile sensation over the contralateral body and head
What happens after the 3rd order neurons in the thalamus receive input from the 2nd order neurons?
they traverse the posterior limb of the internal capsule to get to the cortex
where specifically on the cortex do the third order neurons go?
the primary and secondary somatosensory cortices
Where is the primary sensory cortex located?
in the parietal lobe
what makes up the primary sensory cortex?
the postcentral gyrus and the posterior paracentral gyrus
what is the blood supply of the SI cortical areas?
anterior and middle cerebral arteries (ACA and MCA)
what would a MCA lesion produce?
tactile loss over the contralateral upper body and face
what would an ACA lesion produce?
tactile loss over the contralateral lower limb
where is the secondary somatosensory cortex located?
inner face of the upper bank of the lateral sulcus
where does the secondary somatosensory cortex get its input from?
inputs from the ipsilateral SI cortex and ventral posterior inferior nucleus (VPI) of the thalamus
besides the primary and secondary somatosensory cortices, where else can also receive tactile inputs?
parietal cortical regions
what would a lesion in the parietal association area produce?
agnosia- the contralateral body region(s) are lost from the body map- limb is not recognized as part of the patient’s own body- sensation is not radically altered
where do the primary afferents of the face come from?
the trigeminal ganglion
how many trigeminal nuclei are there?
4
where is the mesencephalic nucleus of the trigeminal nuclei located?
midbrain
where is the principal sensory nucleus of the trigeminal nucleus found?
the midpons
what is the role of the principal sensory nucleus of the trigeminal nucleus?
discriminative touch and pressure
where is the spinal nucleus of the trigeminal nucleus found?
obex of the spinal cord–> C2/C3
what is the role of the spinal nucleus of the trigmeinal nucleus?
temperature and non-discriminative touch
where do the primary afferents of the face target their axons?
they target 2nd order neurons in the principal sensory nucleus
where are the V1 (opthalmic) fibers located in the principal sensory nucleus?
anterior
where are the V2 (maxillary) fibers located in the principal sensory nucleus?
in between the V1 fibers and the V3 fibers
where are the V3 (mandibular) fibers located in the principal sensory nucleus?
posterior
Once the 2nd order neurons receive input from the primary afferent neurons of the face, we have two options. what are those two options?
the anterior trigeminothalamic tract or the posterior trigeminothalamic tract
If you have the anterior trigeminothalamic tract, what happens to the 2nd order neurons?
they cross the midline and then ascend on the contralateral side to the contralateral VPM in the thalamus
if you have the posterior trigeminothalamic tract, what happens to the 2nd order neurons?
they stay ipsilateral, ascend, and target the ipsilateral VPM nucleus in the thalamus
the posterior trigeminothalamic tract is specific to what?
the oral cavity
where do the third order neurons from the VPM project?
via the posterior limb of the internal capsule, project to the primary somatosensory cortex
what type of neurons make up the mesencephalic nucleus?
pseudounipolar neurons
why would you use the jaw-jerk reflex?
if you suspect upper motor neuron damage
what is the mesencephalic nucleus responsible for?
regulating the oral cavity/ proprioception of the face-specifically the jaw, tongue and lips
what nucleus is in charge of the specific way we chew food?
the mesencephalic nucleus
what is the blood supply of the primary sensory nucleus of the trigeminal nucleus?
long circumferential branches of the basilar artery and branches of the anterior inferior cerebellar artery as well as a smidge of the superior cerebellar artery
