Somatosensory Tracts 1

Question 1

What is the DCML pathway used for?

Answer 1

general sensation and proprioception

Question 2

What is the ability to discriminate between two stimuli simultaneously?

Answer 2

two-point discrimination

Question 3

what is the area of skin that is innervated by somatic afferent fibers?

Answer 3

receptive field

Question 4

small receptive fields have what type of receptor density?

Answer 4

high

Question 5

large receptive fields have what type of receptor density?

Answer 5

low

Question 6

where are the cell bodies located for primary afferent fibers?

Answer 6

in the dorsal root ganglion

Question 7

how do the primary afferent fibers enter the spinal cord?

Answer 7

via the medial division of the posterior root

Question 8

what are the two posterior columns?

Answer 8

the fasciculus gracilis and the fasciculus cuneatus

Question 9

The fasciculus gracilis is responsible for what region of the body?

Answer 9

sacral–> T6 region

Question 10

the fasciculus cuneatus is responsible for what region of the body?

Answer 10

T6–> superior

Question 11

sacral level fibers in the posterior column are positioned how?

Answer 11

medially

Question 12

fibers from progressively more rostral levels are added to the posterior column how?

Answer 12

laterally

Question 13

Lesions of the fasciculus gracilis or fasciculus cuneatus? spinal cord lesions result in what?

Answer 13

ipsilateral reduction or loss of discriminative, positional, and vibratory tactile sensations AT AND BELOW the segmental level of injury

Question 14

what is sensory ataxia?

Answer 14

loss of muscle stretch (tendon) reflexes and proprioceptive losses from the extremities due to lack of sensory input

Question 15

where are the gracile nucleus and cuneate nucleus found?

Answer 15

in the posterior medulla

Question 16

what do the gracile nucleus and cuneate nucleus contain?

Answer 16

2nd order neurons on the DCMLS

Question 17

once the second order neurons receive input from the primary afferents (1st order neurons), what happens next?

Answer 17

they send their axons to the contralateral thalamus

Question 18

what is the name of the location of where the crossing over takes place?

Answer 18

internal arcuate fibers

Question 19

once the sensory decussation occurs, what do the fibers ascend as?

Answer 19

the medial lemniscus (ML)

Question 20

where does the medial lemniscus terminate?

Answer 20

in the ventral posterolateral nucleus (VPL) of the thalamus

Question 21

what is housed in the VPL of the thalamus?

Answer 21

3rd order neurons that project to the cortex

Question 22

if we have damage in the medulla or other portions in the brainstem, what will the deficits look like?

Answer 22

they will be on the contralateral side

Question 23

Before reaching the VPL of the thalamus, what happens to the ML?

Answer 23

it rotates

Question 24

what is the blood supply of the thalamus nuclei?

Answer 24

thalamogeniculate branches of the posterior cerebral artery

Question 25

what would a lesion of the thalamogeniculate branches of the posterior cerebral artery result in?

Answer 25

loss of all tactile sensation over the contralateral body and head

Question 26

What happens after the 3rd order neurons in the thalamus receive input from the 2nd order neurons?

Answer 26

they traverse the posterior limb of the internal capsule to get to the cortex

Question 27

where specifically on the cortex do the third order neurons go?

Answer 27

the primary and secondary somatosensory cortices

Question 28

Where is the primary sensory cortex located?

Answer 28

in the parietal lobe

Question 29

what makes up the primary sensory cortex?

Answer 29

the postcentral gyrus and the posterior paracentral gyrus

Question 30

what is the blood supply of the SI cortical areas?

Answer 30

anterior and middle cerebral arteries (ACA and MCA)

Question 31

what would a MCA lesion produce?

Answer 31

tactile loss over the contralateral upper body and face

Question 32

what would an ACA lesion produce?

Answer 32

tactile loss over the contralateral lower limb

Question 33

where is the secondary somatosensory cortex located?

Answer 33

inner face of the upper bank of the lateral sulcus

Question 34

where does the secondary somatosensory cortex get its input from?

Answer 34

inputs from the ipsilateral SI cortex and ventral posterior inferior nucleus (VPI) of the thalamus

Question 35

besides the primary and secondary somatosensory cortices, where else can also receive tactile inputs?

Answer 35

parietal cortical regions

Question 36

what would a lesion in the parietal association area produce?

Answer 36

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

Question 37

where do the primary afferents of the face come from?

Answer 37

the trigeminal ganglion

Question 38

how many trigeminal nuclei are there?

Answer 38

4

Question 39

where is the mesencephalic nucleus of the trigeminal nuclei located?

Answer 39

midbrain

Question 40

where is the principal sensory nucleus of the trigeminal nucleus found?

Answer 40

the midpons

Question 41

what is the role of the principal sensory nucleus of the trigeminal nucleus?

Answer 41

discriminative touch and pressure

Question 42

where is the spinal nucleus of the trigeminal nucleus found?

Answer 42

obex of the spinal cord--> C2/C3

Question 43

what is the role of the spinal nucleus of the trigmeinal nucleus?

Answer 43

temperature and non-discriminative touch

Question 44

where do the primary afferents of the face target their axons?

Answer 44

they target 2nd order neurons in the principal sensory nucleus

Question 45

where are the V1 (opthalmic) fibers located in the principal sensory nucleus?

Answer 45

anterior

Question 46

where are the V2 (maxillary) fibers located in the principal sensory nucleus?

Answer 46

in between the V1 fibers and the V3 fibers

Question 47

where are the V3 (mandibular) fibers located in the principal sensory nucleus?

Answer 47

posterior

Question 48

Once the 2nd order neurons receive input from the primary afferent neurons of the face, we have two options. what are those two options?

Answer 48

the anterior trigeminothalamic tract or the posterior trigeminothalamic tract

Question 49

If you have the anterior trigeminothalamic tract, what happens to the 2nd order neurons?

Answer 49

they cross the midline and then ascend on the contralateral side to the contralateral VPM in the thalamus

Question 50

if you have the posterior trigeminothalamic tract, what happens to the 2nd order neurons?

Answer 50

they stay ipsilateral, ascend, and target the ipsilateral VPM nucleus in the thalamus

Question 51

the posterior trigeminothalamic tract is specific to what?

Answer 51

the oral cavity

Question 52

where do the third order neurons from the VPM project?

Answer 52

via the posterior limb of the internal capsule, project to the primary somatosensory cortex

Question 53

what type of neurons make up the mesencephalic nucleus?

Answer 53

pseudounipolar neurons

Question 54

why would you use the jaw-jerk reflex?

Answer 54

if you suspect upper motor neuron damage

Question 55

what is the mesencephalic nucleus responsible for?

Answer 55

regulating the oral cavity/ proprioception of the face-specifically the jaw, tongue and lips

Question 56

what nucleus is in charge of the specific way we chew food?

Answer 56

the mesencephalic nucleus

Question 57

what is the blood supply of the primary sensory nucleus of the trigeminal nucleus?

Answer 57

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