Lecture 9: Somatosensory Pathways Part 1

Question 1

If the PCML pathway is affected from a spinal cord lesion, what can happen?

Answer 1

Ipsilateral reduction or loss of discriminative, positional, and vibratory tactile sensations
Will happen at and below level of injury

Question 2

If there is a lesion to the Anterior Cerebral Artery, where would there be tactile loss?

Answer 2

Contralateral lower limb

Question 3

If there is a lesion to the Middle Cerebral Artery, where would there be tactile loss?

Answer 3

Contralateral upper body and face

Question 4

What supplies the Ventral Posterolateral Nucleus of the Thalamus?

Answer 4

Thalamogeniculate Branches of Posterior Cerebral Artery

Question 5

Which fibers are found more medially?

Answer 5

Sacral and the more rostral you go, the more lateral those fibers are found

Question 6

What is the role the mesencephalic nucleus?

Answer 6

Conveys unconscious proprioceptive afferents and pressure afferents from TMJ, masticatory, and extraocular muscles

Question 7

What supplies the Principal/Chief Sensory Nucleus?

Answer 7

Superior Cerebellar Artery

Long Circumferential branches of Basilar Artery

Question 8

How does the dorsomedial division reach the thalamus?

Answer 8

Travels ipsilaterally via posterior trigeminothalamic tract to

Question 9

What are the Brodmann Areas of the Primary Somatosensory Cortex?

Answer 9

31, 3b, 1, and 2

Question 10

In the Sensory Trigeminothalamic Pathway, where are primary afferents from?

Answer 10

Trigeminal Ganglion

Question 11

What areas would have high density of tactile receptors?

Answer 11

Digits

Perioral region

Question 12

How does the ventrolateral division reach the thalamus?

Answer 12

Travels contralaterally via anterior trigeminothalamic tract

Question 13

What is two point discrimination?

Answer 13

Ability to discriminate between two stimuli simultaneously

Question 14

In the medial lemniscus, where do the upper and lower extremity fibers now reside after the rotation in the pons?

Answer 14

Upper: Medial
Lower: Lateral

Question 15

Where are the gracile and cuneate nuclei receiving their input from?

Answer 15

First order neurons (primary afferents) from ipsilateral dorsal root ganglion

Question 16

In the PCML pathway, what do primary afferent fibers after entering the spinal cord?

Answer 16

Posterior Columns: Fasciculus Gracilis and Cuneatus

Question 17

What are the two divisions of the principal/chief sensory nucleus and what do they receive information from?

Answer 17

Dorsomedial: Oral Cavity
Ventrolateral: V1, V2, V3

Question 18

What type of axons are primary afferent fibers?

Answer 18

Sensory

Question 19

What happens if the parietal cortical region is lesioned?

Answer 19

Agnosia: cannot recognize own limb

Question 20

What is the role the principal/chief sensory nucleus?

Answer 20

Discriminative touch and pressure from face

Question 21

In the Sensory Trigeminothalamic Pathway, where are 2nd order neurons found?

Answer 21

Principal/Chief Sensory Nucleus

Question 22

Where is Fasciculus Gracilis found?

Answer 22

Sacral Region to T6

Question 23

What is the role the spinal nucleus?

Answer 23

Pain, temperature, and non-discriminative touch from face

Question 24

What is the pathway of a jaw-jaw reflex?

Answer 24

1. Innervation of Mesencephalic Trigeminal Neuron
2. Innervation of masseter muscle spindle
3. Synapse on trigeminal motor neuron

Question 25

Small receptive fields have ____ receptor density. | Large receptive fields have ____ receptor density.

Answer 25

Small receptive fields have HIGH receptor density. | Large receptive fields have LOW receptor density.

Question 26

Where do primary afferent fibers have their cell bodies?

Answer 26

Dorsal Root Ganglion

Question 27

What are internal arcuate fibers?

Answer 27

After synapsing at the gracile and cuneate nuclei, they are the fibers that cross anteromedially in the medulla

Question 28

Where does the medial lemniscus terminate?

Answer 28

Ventral Posterolateral Nucleus of the Thalamus

Question 29

What information does the PCML and trigeminothalamic pathway transmit?

Answer 29

Discriminative Touch Pressure Vibration Proprioception

Question 30

Where does secondary somatosensory cortex gets its input from?

Answer 30

Ipsilateral SI cortex and Ventral Posterior Inferior Nucleus of the Thalamus

Question 31

What reflex is initiated when there is a downward tap on the chin?

Answer 31

Jaw-Jaw Reflex: Stretching of masseter muscle causes it to contract bilaterally

Question 32

What does the secondary somatosensory cortex sense?

Answer 32

Inner face

Question 33

In the PCML pathway, where are 2nd order neurons found?

Answer 33

Gracile and Cuneate Nuclei in the posterior medulla

Question 34

What is medial lemniscus?

Answer 34

The new name of the fibers after they cross at the medulla until they terminate

Question 35

Where do both anterior and posterior trigeminothalamic tracts synapse at?

Answer 35

Ventral Posteromedial Nucleus of the Thalamus - Oral Cavity: Medial part of nucleus - External Face: Lateral part of nucleus

Question 36

In the PCML pathway, where do primary afferent fibers enter the spinal cord?

Answer 36

Medial division of posterior root

Question 37

How do third third order neurons reach the somatosensory cortices?

Answer 37

Via Posterior Limb of Internal Capsule

Question 38

What is sensory ataxia?

Answer 38

Loss of muscle tendon reflex and proprioceptive losses from extremities due to lack of sensory input Can lead to difficulty walking and wide based stance

Question 39

What supplies the posterior columns?

Answer 39

Posterior Spinal Artery

Question 40

Where is Fasciculus Cuneatus found?

Answer 40

T6 and above

Question 41

From the Ventral Posterolateral Nucleus of the Thalamus, where do the third order neurons go to?

Answer 41

Primary and Secondary Somatosensory Cortices

Question 42

From the Ventral Posteromedial Nucleus of the Thalamus, where do the third order neurons go to?

Answer 42

Primary somatosensory nucleus via posterior limb of internal capsule

Question 43

What compromises the Primary Somatosensory Cortex (S1)?

Answer 43

Postcentral gyrus and Posterior Paracentral Gyrus

Question 44

What areas would have low density of tactile receptors?

Answer 44

Back

Question 45

What supplies the medial lemniscus?

Answer 45

Anterior Spinal Artery