Ascending and Descending Pathways

Question 1

What is the term for when a neuron which crosses over the midline of the spinal cord?

Answer 1

Axonal decussation

Question 2

How many neurons are involved in the spine-thalamic pathway?

Answer 2

X3

Question 3

What type of sensory information does the spinal-thalamic pathway carry?

Answer 3

Pain, temperature, light touch

Question 4

Where does the first order neuron of the spino-thalamic pathway enter the spinal cord?

Answer 4

Via the dorsal root into the dorsal horn

Question 6

Where does the first order neuron synapse with the second order neuron in the spino-thalamic pathway?

Answer 6

In the dorsal horn of the spinal cord

Question 7

What happens to the second order neuron in the spino-thalamic pathway?

Answer 7

It undergoes axonal decussation and also travels centrally into the spine-thalami tract, which from here ascends to the thalamus

Question 8

Where do the second and third order neurons in the spinal-thalami tract synapse?

Answer 8

In the thalamus

Question 9

Where is the soma for the third order neuron of the spino-thalamic pathway?

Answer 9

In the VPL, ventro-posterior lateral nucleus of the thalamus

Question 10

Which tract does the 3rd order neuron in the spino-thalami pathway use to reach the somatosensory cortex?

Answer 10

The thalamo-cortical tract

Question 11

Where is the 3rd synapse in the cortico-spinal pathway?

Answer 11

It is the 3rd order neuron synapsing in the somatosensory cortex.

Question 12

What sensory information does the dorsal column - medial lemniscus pathway carry?

Answer 12

Touch, proprioception and vibrations

Question 13

What is the name of the X2 tracts which relay sensory information from different levels of the the body in the dorsal column - medial lemniscus pathway?

Answer 13

The gracile and cuneate tracts

Question 14

Where does the gracile tract relay information from?

Where does this sit in relation to the cuneate fascicles in the dorsal horn?

Answer 14

It relays information from below T6

It sits in the dorsal horn, medially to the cuneate fascicles

Question 15

Where does the cuneate tract relay information from?

Where does this sit in relation to the gracile fascicles in the dorsal horn?

Answer 15

It relays information from above T6

It sits in the dorsal horn, laterally to the cuneate fascicles

Question 16

Where is the soma of the first order neuron of the dorsal column - medial lemniscus pathway?

Answer 16

In the dorsal root ganglia

Question 17

What is the journey of the first order neuron in the dorsal column - medial lemniscus pathway?

Answer 17

It travels into the dorsal horn and into either the gracile or cuneate fascicles (depending on level of entry) and ascends in these dorsal columns until it reaches the gracile/cuneate nucleus in the medulla

Question 18

Where do the first and second order neurons in the dorsal column - medial lemniscus pathway synapse?

Answer 18

In the gracile/cuneate nucleus of the medulla

Question 19

Where is the soma of the second order neuron in the dorsal column - medial lemniscus pathway?

Answer 19

In the medulla

Question 20

What happens to the second order neuron in the dorsal column - medial lemniscus pathway?

Answer 20

It undergoes axonal decussation and also travels ventrally into a tract called the medial lemniscus. It ascends via this tract into the thalamus where it synapses with the third order neuron of the pathway.

Question 21

Where is the soma of the third order neuron of the dorsal column - medial lemniscus pathway?

Answer 21

In the VPL of the thalamus

Question 22

What tract does the third order neuron of the dorsal column - medial lemniscus pathway use to ascend to the somatosensory cortex?

Answer 22

The thalamo-cortical tract

Question 23

Where is the third synapse in the dorsal column - medial lemniscus pathway?

Answer 23

At the somatosensory cortex involving the third order neuron

Question 24

What type of pathway is the cortical-spinal pathway?

Answer 24

A descending pathway

Question 25

How many neurons are involved in the cortical-spinal pathway?

Answer 25

X2

Question 26

What information does the cortical-spinal pathway carry?

Answer 26

Somatic motor command

Question 27

Where is the soma of the first order neuron in the cortical-spinal pathway?

Answer 27

In the primary motor cortex, located in the frontal lobe just in front of the central sulcus.

Question 28

Where does the first order neuron in the cortical-spinal pathway terminate?

Answer 28

At a level close to that of its target motor neuron

Question 29

85% of axons in the cortical-spinal pathway undergo axonal decussation at which level?

What is this type of decussation called?

What type of cortical-spinal tract do these axons form?

Answer 29

In the pyramids of the ventral medulla

This is called pyramidal decussation

They form the LATERAL cortical-spinal tract

Question 30

15% of axons in the cortical-spinal pathway undergo axonal decussation at which level?

What type of cortical-spinal tract do these axons form?

Answer 30

They decussate at a level close to where they terminate

They form the ANTERIOR/VENTRAL cortico-spinal tract

Question 31

Where is the soma of the second order neuron in the cortico-spinal pathway?

Answer 31

It is in the ventral horn of the CNS at the level at which it is exiting the CNS, as it is a motor neuron.

Question 32

Which ascending pathway is fast and which is slow conducting?

Answer 32

Spino-thalamic = slow conducting

Dorsal column - medial lemniscus = fast conducting

Question 33

How many neurons are involved in the dorsal column - medial lemniscus pathway?

Answer 33

X3