Sangari Lecture on Anterolateral System, Trigeminal System & Sensory Cortex

Question 1

What sensations travel through the Anterolateral System?

Answer 1

Pain, temperature and crude touch (non-discriminative)

Question 2

What are the three divisions of the Anterolateral System?

Answer 2

1. Neo-spinothalamic tract (sharp pain, temperature and crude touch travel in this tract and reach consciousness)
2. Paleospinothalamic tract / Spinoreticular (dull aching pain travels in a phylogenetically older pathway and may be felt at the level of thalamus / cerebral cortex
3. Spinomesencephalic (responsible for the modulation of pain)

Question 3

Where are the cell bodies of the first order neuron in the Anterolateral System?

Answer 3

Dorsal Root Ganglion

Question 4

Where are the cell bodies of the second order neuron in the Anterolateral System?

Answer 4

Spinal Dorsal Horn

(the first order neurons do not ascend all the way up to the thalamus like in the dorsal column, they synapse, and the second order neurons cross to the other side and go up to the thalamus)

Question 5

Where are the cell bodies of the third order neuron in the Anterolateral System?

Answer 5

VPL nucleus of the Thalamus

Question 6

What kinds of nerve fibers are in the Anterolateral System?

Answer 6

thin, slow conducting, free nerve endings

Aδ and C nerve fibers

Question 7

Do the Anterolateral nerve fibers pass through the lateral or medial part of the dorsal root entry zone?

Answer 7

LATERAL

Question 8

Which lamina do the the Anterolateral nerve fibers synapse in the dorsal horn of the spinal cord?

Answer 8

Lamina I, II and V

Question 9

Clinically, what would a lesion in the lateral part of the dorsal root will give rise to?

Answer 9

Loss of pain and temperature FROM THE SAME SIDE of the body (IPSILATERAL)

Question 10

What is the name of the area of white matter, which caps the dorsal horn where the central processes of first order neurons pass through and what happens once these pass through this area?

Answer 10

Dorsolateral tract of Lissauer

These fibers bifurcate, ascend (mostly) for 2-3 spinal segments before entering the dorsal horn

Question 11

What is the path of second order neurons (neospinothalamic tract)?

Answer 11

Their cell bodies are in Lamina I, II, V cross the ANTERIOR WHITE COMMISSURE to go to the opposite side in the ANTEROLATERAL FUNICULUS/ANTEROLATERAL SYSTEM

Question 12

What is syringomyelia?

Answer 12

It is characterized by cavity formation in the central part of the spinal cord including anterior white commissure

This condition will result in damage of the decussating fibers of ALS and will give rise to BILATERAL symmetrical loss of pain and temperature sensation 2-3 segments BELOW the site of the lesion

Question 13

Does the face have representation in the ALS?

Answer 13

NO

Question 14

If a tumor of the meninges is pressing on the spinal cord, where is the first place you will lose pain and temperature sensations?

Answer 14

The anterolateral funiculus is somatotopically arranged with the leg being the most superficial (Neck, Arm, Trunk, Leg)

So a tumor will first cause loss of pain and temperature sensations from the leg of the opposite side

Question 15

What is Brown-Sequard Syndrome?

Answer 15

Hemisection of the spinal cord will lead to:

1) Loss of all sensations on the same side at the level of the lesion (ipsilateral) bc the dorsal root is gone
2) Loss of dorsal column sensations (fine touch and proprioception) below the lesion on the same side of the body (ipsilateral)
3) Loss of pain and temperature sensations carried in ALS, 2-3 segments below the lesion on the opposite side of the body (contralateral)

Question 16

Describe the spinoreticular / paleospinothalamic tract and where does it terminate?

Answer 16

Carries more primitive sensations of DULL BURNING PAIN, mainly EMOTIONAL and AROUSAL aspects of pain.

These fibers project to RETICULAR FORMATION of medulla and pons and give rise to Central Tegmental Tract (CTT)

CTT further projects to the INTRALAMINAR NUCLEUS OF THE THALAMUS

Question 17

Describe the Spinomesencephalic tract and where does it terminate?

Answer 17

Synapses with neurons of the periaqueductal grey, reticular formation of the midbrain and superior colliculus which further project to amygdala

INVOLVED IN CENTRAL MODULATION OF PAIN / EMOTIONAL ASPECTS OF PAIN

Periaqueductal grey receives inputs from the hypothalamus, amygdala and cortex and inhibits pain transmission

TERMINATES @ mesencephalic nucleus

Question 18

Where is the ALS positioned in the medulla?

Answer 18

It is positioned laterally between the inferior olivary nucleus and the inferior cerebral peduncle

Question 19

Where is the ALS position in the pons and midbrain?

Answer 19

Part of the boomerang as all ascending tracts are closer to one another, but it is positioned lateral to the medial leminisces

Question 20

What are the branches of the trigeminal system giving sensory innervation to the face?

Answer 20

V1/Opthalmic Nerve

V2/Maxillary Nerve

V3/Mandibular Nerve

Question 21

What does V1/Opthalmic Nerve supply?

Answer 21

Supplies the skin of the tip of the nose, upper eyelid, conjunctiva, forehead and scalp until the vertex

Question 22

What does V2/Maxillary Nerve supply?

Answer 22

Supplies the skin of the ala of the nose, lower eyelid, upper lip, cheek and side of the temple

Question 23

What does V3/Mandibular Nerve supply?

Answer 23

Supplies the skin of the lower jaw, side of the mandible, temple and auricle

Question 24

What supplies the floor of the choncha/ear?

Answer 24

VII, IX, X cranial nerves

Question 25

What kinds of neurons make up the trigeminal system?

Answer 25

It is a collection of pseudounipolar neurons

Question 26

What does the trigeminal ganglion contain?

Answer 26

Trigeminal ganglion contains first order neurons for all sensations of the face EXCEPT proprioception from muscles of mastication (first order neurons for proprioception from these muscles lie in the mesencephalic nucleus of the trigeminal nerve) mesencephalic nucleus is the only example of a pseudo unipolar first order nerve cell in the brain stem

Question 27

What makes up the spinal nucleus of the trigeminal nerve?

Answer 27

second order neurons

Question 28

Where is the spinal nucleus of the trigeminal nerve and was are its 3 parts?

Answer 28

The spinal nucleus lies in the lower part of the pons, medulla and spinal cord and has three parts: PARS ORALIS (upper 1/3): carries fine/discriminative touch, pressure, proprioception from face PAS INTERPOLARIS & PARS CAUDALIS: carries pain, temperature and crude touch from the face

Question 29

What does the principal sensory/chief nucleus of V contain?

Answer 29

Cell bodies of second order neurons carrying discriminative touch, conscious proprioception and vibration from the face

Question 30

What does the mesencephalic nucleus & tract of trigeminal nerve contain?

Answer 30

First order neuron cell bodies, which failed to migrate from the neural tube and carry proprioception from muscles of mastication (only first order neuron that got stuck inside the brainstem, axons do not travel up)

Question 31

Describe the somatotopy of the spinal nucleus of trigeminal nerve?

Answer 31

- Opthalmic nerve (V1) is represented ventrally (back) - Maxillary nerve (V2) is dorsal to V1 - Mandibular nerve (V3) is dorsal to V2 - The area of the ear supplied by VII, IX, and X is most dorsal In addition, the face is concentrically represented like "onion skin": perioral area is more rostral in the nucleus and the area away from the mouth is represented more caudally

Question 32

Where do the second order neurons cross the midline?

Answer 32

Second order neurons (that lie either in the principal sensory/chief nucleus or the spinal nucleus) cross to the opposite side to from the Ventral Secondary Trigeminal Tract (VSTT)

Question 33

Where does the VSTT terminate?

Answer 33

VSTT passes through the pons and the midbrain tegmentum and terminates in the ventral posteromedial (VPM) nucleus of the thalamus

Question 34

Where are third order neurons of the trigeminal system located?

Answer 34

The neurons of VPM nucleus of the thalamus are third order neurons, their axons pass through the posterior limb of the internal capsule to terminate on the primary sensory cortex