Lab 6: Somatosensory Systems II

Question 1

Marginal Zone

Answer 1

Thin rim of cells dorsal to the size able substantia gelatinosa

Question 2

Substantia Gelatinosa

Answer 2

(Rexed’s lamina II)

Receives terminations of first order pain and temperature neurons

Question 3

Ventral (anterior) White Commissure

Answer 3

Crossing of the axons from pain/temperature projection neurons to reach the lateral funiculus of the opposite side

Question 4

Anterolateral System

Answer 4

Consists of the crossed pain/temperature fibers that ascend to the brain stem and thalamus on the opposite (contralateral to) the stimulated receptors.

Question 5

Reticular Formation

Answer 5

Receives some fibers of the ALS that take a multisynaptic course to terminate in the intralaminar nuclei of the thalamus (slow pain pathway)

Question 6

Raphe Nuclei

Answer 6

Pale nuclei near that midline that:

• receive descending fibers from the periaqueductal gray of the midbrain
• project fibers to the dorsal horn of the spinal cord for inhibition of ascending pain transmission

Question 7

Dissociated Sensory Loss

Answer 7

-a small stroke in the medulla can affect one sensory system but not the other
-the ALS is in the posterolateral vascular territory (ventrolateral tegmentum) and the medial lemniscus is in the paramedian zone (close to the midline)
This occurs in Wallenberg (lateral medullary) Syndrome which results from an infarct in the vascular territory of PICA

Question 8

Caudal Pons

Answer 8

The Medial Lemniscus has begun to move laterally towards the ALS

Question 9

Rostral Pons

Answer 9

The medial lemniscus meets the ALS in the lateral tegmentum at this level and they travel adjacent to each other en route to the thalamus

Question 10

Periaqueductal Gray Nuclei of the Midbrain

Answer 10

• receive fibers from ALS

- send descending fibers to raphe nuclei of brainstem for inhibition of pain transmission

Question 11

Ventral Posterolateral (VPL) Nucleus of the Thalamus

Answer 11

Synapse site of fibers of the ALS

Question 12

Posterior limb of internal capsule

Answer 12

Path of fibers from the VPL to the somatosensory cortex

Question 13

Internal Medullary Lamina

Answer 13

Sheet of fibers in thalamus

Question 14

Intralaminar nuclei

Answer 14

Nuclei in internal medullary lamina that:

• receive pain/temperature fibers from the reticular formation
• send axons to widespread areas of cortex

Question 15

Posterior Limb, internal capsule

Answer 15

Contains fibers (thalamic radiations) from the VPLs to the somatosensory cortex (postcentral gyrus and posterior paracentral gyrus, Brodmann Areas 3,1,2)

Question 16

Postcentral Gyrus and Posterior part of Paracentral Lobule

Answer 16

Where sensations of discriminative touch/pressure (medial lemniscus) and pain/temperature (ALS) are detected

Question 17

Posterior Parietal Cortex

Answer 17

Where sensations are recognized

Question 18

Ophthalmic and maxillary divisions of Trigeminal Nerve

Answer 18

• course in the wall of the cavernous sinus

- contain sensory fibers only

Question 19

Mandibular Division of Trigeminal Nerve

Answer 19

-contains sensory and motor fibers

Question 20

Trigeminal Ganglion

Answer 20

Consists of cell bodies of sensory fibers from face, ear, orbit, oral cavity, nasal cavity, paranasal sinuses meninges

Question 21

Trigeminal Nerve Roots

Answer 21

Located in the lateral tegmentum, between the motor and main sensory nucleus of V

Question 22

Motor Nucleus (V)

Answer 22

Medial to the trigeminal nerve roots; supplies the muscles of mastication

Question 23

Main Sensory Nucleus (V)

Answer 23

Lateral to the trigeminal nerve roots

Question 24

Properties of Main Sensory Nucleus (V)

Answer 24

• receive axons from large-fiber neurons of trigeminal ganglion
• are comparable to dorsal column nuclei in that they’re involved in discriminative touch
• send axons across the midline (decussation not visible) to joint the ventral trigeminothalamic tract

Question 25

Mid Pons

Answer 25

Main sensory and motor nuclei of the trigeminal nerve (V): in the dorsolateral tegmentum of the pons Trigeminal nerve roots: easy to see between the main sensory and motor nuclei in the slice on the left

Question 26

Spinal Trigeminal Tract

Answer 26

The pain/temperature neurons in the trigeminal ganglion from the anterior head have central processes that enter the pons and descend into the medulla and rostral spinal cord

Question 27

Caudal Medulla

Answer 27

Spinal Trigeminal Tract: central processes of neurons for pain/temperature from the ipsilateral face and teeth Spinal Trigeminal Nucleus: medial to the spinal trigeminal tract; receives fibers from the spinal Trigeminal tract; contains neurons that process pain and temperature information from the face and send axons across the midline to become the VENTRAL TRIGEMINOTHALAMIC TRACT (VTTT)

Question 28

Spinal Trigeminal Nucleus and Substantia Gelatinosa

Answer 28

The spinal trigeminal nucleus is continuous caudally with the substantia gelatinosa of the dorsal horn of the spinal cord. Neither of these structures are visible in a clinical scan, but the general position can be determined because both are located in the lateral tegmentum, with the tract being peripheral to the nucleus

Question 29

Mid/Rostral Medulla

Answer 29

Spinal Trigeminal tract: lateral to spinal trigeminal nucleus Spinal trigeminal nucleus: has cells whose axons cross (crossing not visible) and ascend as the ventral trigeminothalamic tract to the thalamus

Question 30

VTTT Fiber Organization

Answer 30

They're not gathered into a discrete bundle in the medulla, but in the caudal Pons they are found dorsal to the medial Lemniscus

Question 31

Mid Pons (trigeminal nerve system locations)

Answer 31

Ventral Trigeminothalamic Tract (VTTT): -has fibers from the contralateral spinal Nucleus of V plus some from the contralateral main sensory nucleus of V -travels dorsal to the medial lemniscus -projects to the ventral posterior medial (VPM) nucleus of the thalamus Main sensory nucleus of V: Receives input from discriminative touch and vibration receptors via fibers of the trigeminal nerve Motor Nucleus of V: BE motor nucleus to the muscles of mastication Trigeminal Nerve Roots: pass between the main sensory and motor nuclei of V

Question 32

Midbrain

Answer 32

VTTT: dorsal to the medial lemniscus: carries sensory information from contralateral face Medial Lemniscus: carries discriminative touch sensation from the contralateral trunk and limbs ALS: carriers pain and temperature sensation from the contralateral trunk and limbs

Question 33

Ventral Posterior Medial (VPM) Nucleus of the Thalamus

Answer 33

- synapse for fibers of the VTTT - located medial to the VPL nucleus - is a sensory relay nucleus of the thalamus for general sensations from the face and for taste

Question 34

Posterior Limb of Internal Capsule

Answer 34

Lateral to the thalamus; has fibers from the VPM and VPL en route to the postcentral gyrus and posterior paracentral gyrus