C: Ascending Sensory Pathways 1

Question 1

What kind of modalities are carried in the spinothalamic pathway? 4

Answer 1

Modalities that are essential to survival:

1) Pain
2) Temperature
3) Some touch
4) Pressure

Question 2

Modalities carried in the spinothalamic pathway are carried via neurons with what characteristics? How fast is conduction?

Answer 2

Thin, poorly myelinated or unmyelinated fibres

Conduction is slow

Question 3

What kind of modalities are carried in the dorsal column pathway? 2

Answer 3

Modalities that increase detail:

1) Discriminative touch: 2-point discrimination and vibration
2) Proprioception

Question 4

Modalities carried in the dorsal column pathway are carried via neurons with what characteristics, how fast is conduction?

Answer 4

Large diameter, heavily myelinated fibres

Fast conduction

Question 5

General sensory pathways involve how many neurons?

Answer 5

3

A primary, secondary and tertiary

Question 6

Where is the cell body of the primary neuron in a general sensory pathway located?

Answer 6

Ipsilateral dorsal root ganglion - outside the CNS

Question 7

On which side does a primary neuron enter the CNS?

Answer 7

Same side as the receptor

Question 8

Which neuron in a general sensory pathway crosses the midline?

Answer 8

Axon of the secondary neuron

Question 9

In a general sensory pathway where does the cell body of a secondary neuron reside?

Answer 9

Ipsilateral grey matter of the CNS

Question 10

In a general sensory pathway cell bodies of the tertiary neuron reside where?

Answer 10

In the contralateral thalamus

Question 11

Axons of the tertiary neurons in a general sensory pathway project to where?

Answer 11

The somato-sensory cortex

Question 12

Is synaptic transmission in a general sensory pathway a simple relay?

Answer 12

No, it can be modified by other inputs such as descending pathways

Question 13

What 2 kinds of circuits can exist in the relaying of sensory information?

Answer 13

1) Diverging circuit - emphasises input

2) Converging circuit - diminishes input

Question 14

In a spinothalamic pathway where does the axon of the secondary neuron cross the midline?

Answer 14

At the level that it enters the spinal cord - crosses anterior to the canal via the ventral white commissure

Question 15

How does the axon of a secondary axon in the spinothalamic pathway ascend the spinal cord?

Answer 15

In the spinothalamic tract

Question 16

Where do the primary and secondary neurons in a spinothalamic pathway synapse?

Answer 16

In the ipsilateral dorsal grey horn at the level of entry to the spinal cord

Question 17

What is meant by the statement that the spinothalamic tract is somatotypically organised?

Answer 17

Input from a specific sensory receptor will go to a specific region in the spinothalamic tract

Question 18

What name is given to the spinothalamic tract once it enters the brainstem?

Answer 18

The spinal/lateral lemniscus

Question 19

Where do primary and secondary neurons synapse in the dorsal column pathway?

Answer 19

In the cuneate and gracile tubercles

Question 20

Cuneate fascicle carries sensory info from approximately what level?

Answer 20

Above T6

Question 21

Gracile fascicle carries sensory info from approximately what level?

Answer 21

Below T6

Question 22

Where are the cell bodies of secondary neurons in the dorsal column pathway located?

Answer 22

In the gracile and cuneate nuclei (within the tubercles)

Question 23

How do the axons of primary neurons ascend the spinal cord in the dorsal column pathway?

Answer 23

In the ipsilateral cuneate or gracile fascicle

Question 24

Where are the cell bodies of tertiary neurons located in the dorsal column pathway?

Answer 24

Contralateral thalami

Question 25

At what level do the axons of secondary neurons cross the midline in the dorsal column pathway?

Answer 25

At the level of the closed medulla

Question 26

Axons of the secondary neurons in the dorsal column pathway cross the midline via what?

Answer 26

Internal arcuate fibres

Question 27

After crossing the midline fibres in the dorsal column pathway ascend to the thalami via what?

Answer 27

The medial lemniscus - which is somatotopically organised

Question 28

Which lies more lateral the cuneate fascicle or the gracile fascicle?

Answer 28

The cuneate fascicle

Question 29

Fibres travel from the thalami to the post central gyri via what?

Answer 29

The posterior limb of the internal capsule

Question 30

Do fibres carrying pain and temperature travel ipsilaterally or contralaterally in the spinal cord?

Answer 30

Contralaterally

Question 31

Do fibres carrying discriminative touch and proprioception travel ipsilaterally or contralaterally in the cord?

Answer 31

Ipsilaterally

Question 32

What kind of neuron is a primary neuron in a general sensory pathway?

Answer 32

Pseudounipolar

Question 33

Do all the fibres in the spinothalamic tract decussate at the level of entry to the spinal cord?

Answer 33

No, MOST do but some fibres ascend ipsilaterally for a few vertebral levels in the spinal cord before decussating, these are fibres in the spinothalamic tract carrying light touch and pressure sensation.