Spinal Pathways

Question 1

Which are the two motor tracts and which areas do they innervate?

Answer 1

The lateral corticospinal tract (motor supply to limbs) and the ventral corticospinal tract (motor supply to the trunk)

Question 2

Which are the two sensory pathways, and which modalities do they convey?

Answer 2

Spinothalamic / anterolateral system - pain and temperature

Dorsal columns - light touch, propioception, vibration

Question 3

Which are the two dorsal columns, and to which segments of the spine do they correlate?

Answer 3

Gracile fasiculus (more medial) - sensory information from T7 and below, present in entire spinal column

Cuneate fasciculus (more lateral) - sensory information from T6 and above, present at these levels only

Question 4

From where do the motor tracts originate?

Answer 4

The primary motor cortex (pre-central gyrus) of the frontal lobe in the cerebral cortex

Question 5

Where do the sensory tracts terminate?

Answer 5

The primary sensory cortex (post-central gyrus) of the parietal lobe in the cerebral cortex

Question 6

How many neurons are there in motor pathways, and how many in sensory pathways?

Answer 6

Two neurons in motor pathways - an upper motor and lower motor neuron.

Three neurons in sensory pathways - a first order, second order, and third order neuron

Question 7

Where does the spinothalamic tract decussate?

Answer 7

In the spinal cord. The STT first order neuron synapses at the ipsilateral L2 (after moving 1-2 segments in Lissaur’s tract), then the second order neuron decussates at the spinal cord anterior commissure before ascending contralaterally

Question 8

What is Lissaur’s tract and it’s significance?

Answer 8

An area of white matter lateral to the first lamina of the dorsal horn. The spinothalamic tract enters Lissaur’s tract via the dorsal root, then moves 1-2 segments up or down the spinal cord before emerging to synapse at the L2 of the new segment.

Question 9

Where do the dorsal columns decussate?

Answer 9

At the caudal medulla. The first order neurons synapse at the ipsilateral gracile or cuneate nucleus in the caudal medulla, before the second order neuron decussates and moves anteriorly to the medial lemniscus to ascend to the thalamus.

Question 10

Where does the ventral corticospinal tract decussate?

Answer 10

At the level of the spinal cord via the anterior commissure, to synapse at lamina 8 of the contralateral spinal cord.

Question 11

Where does the lateral corticospinal tract decussate?

Answer 11

At the pyramidal decussation segment (between the medulla oblongata and the spinal cord). From the descending pyramids the lateral corticospinal tract (approximately 85-90% of the neurons) decussate posteriorly to the contralateral spinal cord before descending in the lateral corticospinal tract to the spinal cord.

Question 12

Where does the spinothalamic tract have synapses?

Answer 12

First order neuron: synapses with second order neuron in ipsilateral L2 (substantia gelatinosa) of the spinal segment 1-2 levels above or below original segment.

Second order neuron: from L2, decussates at anterior commisure to ascend contralaterally. synapses with third order neuron in thalamus (VPL)

Third order neuron: synapses at primary sensory cortex of parietal lobe (contralateral to original sensory information)

Question 13

Briefly describe the locations of the synapses in the STT pathway

Answer 13

1. L2 (substantia gelatinosa) of ipsilateral spinal cord (1-2 segments above or below original segment)
2. thalamus (VPL), contralateral to original sensory information
3. primary sensory cortex of parietal lobe (contralateral to original sensory information)

Question 14

Describe the pathway of the dorsal columns pathway

Answer 14

First order neuron moves from PNS and enters spinal cord via dorsal root. Ascends in gracile or cuneate fasciculus ipsilaterally.

First order neuron synapses with second order neuron at the gracile or cuneate nucleus in the caudal medulla.

Second order neuron decussates and moves anteriorly at the caudal medulla into the medial lemniscus. Synapses with third order neuron in the VPL or VPM of the thalamus.

Third order neuron moves from the VPL or VPM of the thalamus to the primary sensory cortex of the parietal lobe (contralateral to original sensory stimuli)

Question 15

What are the gracile and cuneate nuclei?

Answer 15

Nuclei located in the caudal medulla.

This is where the first order neurons ascending via the gracile and cuneate fasciuli synapse with second order neurons.

The second order neurons then decussate and move anteriorly to ascend to the thalamus via the medial lemniscus.

The gracile nuclei is for neurons containing sensory information about T7 and below, and the cuneate nucleus is for neurons containing sensory information about T6 and above

Question 16

Describe the pathway of the lateral corticospinal tract

Answer 16

Upper motor neuron originates at the primary motor cortex (pre-central gyrus) of the frontal lobe.

Descends via corticospinal tract to the pyramidal decussation (between medulla and spinal cord).

Decussates laterally and posteriorly to enter the begining of the lateral corticospinal tract.

Upper motor neuron synapses with lower motor neuron at lamina 9 of the spinal cord, ipsilateral to side of original motor signal.

Lower motor neuron exits spinal cord via ventral root.

Question 17

Where is the synapse in the lateral corticospinal tract?

Answer 17

At lamina 9 of the grey matter in the spinal cord, contralateral to the side of original motor signal (decussation occurred at pyramidal decussation level)

Question 18

Describe the pathway of the ventral corticospinal tract

Answer 18

Upper motor neuron originates in the primary motor cortex (pre-central gyrus) of the frontal lobe.

Descends through the midbrain and pons anteriorly via the corticospinal tract.

Continues to descend in the pyramids after lateral tracts have decussated at the level of pyramidal decussation.

At spinal cord, decussates in anterior commisure.

Synapses with lower motor neuron in lamina 8 of the spinal cord contralateral to side of original motor signal.

exits spinal cord via ventral root.

Question 19

At which level does each of the 4 tracts decussate?

Answer 19

Dorsal columns - 2nd order neuron decussates at caudal medulla (after synapsing with 1st order neuron at gracile or cuneate nuclei)

STT - at spinal cord via anterior commissure. decussation is by the 2nd order neuron (synapse at L2 substantia gelatinosa) at the segmental level 1-2 segments above or below level of original impulse.

Ventral corticospinal tract - at spinal cord. upper motor neuron decussates from ventral corticospinaltract via anterior commissure to synapse with lower motor neuron at lamina 8 of the grey matter.

Lateral corticospinal tract - at level of pyramidal decussation. Upper motor neurons decussate laterally and posteriorly from the descending corticospinal tract to enter the lateral corticospinal tract.

Question 20

Which tract decussates at the level of the pyramidal decussation?

Answer 20

the ventral corticospinal tract

Question 21

Which tract decussates at the spinal cord?

Answer 21

The lateral corticospinal tract, and the STT (at segment 1-2 segments above or below)

Question 22

Which tract decussates at the caudal medulla?

Answer 22

The dorsal columns - second order neuron decussates from the gracile or cuneate nucleus to the medial lemniscus