Structure and Function of the Spinal Cord

Question 1

What is the conus medullaris?

Answer 1

Where the spinal cord narrows

Question 2

At what level is the conus medullaris?

Answer 2

L1/L2

Question 3

What do spinal nerves connect?

Answer 3

Connect the periphery to the spinal cord

Question 4

How many pair of spinal nerves are there?

Answer 4

31 pairs

Question 5

What is each pair of spinal nerves formed of?

Answer 5

• Dorsal root (afferent)

- Ventral root (efferent)

Question 6

What is the inner core of the spinal cord?

Answer 6

• H shaped (dorsal, lateral and ventral horns)

- Gray matter (due to neuronal cell bodies)

Question 7

What is the outer part of the spinal cord?

Answer 7

• White matter (due to myelinated axons)

- Can be divided into dorsal, lateral and ventral columns

Question 8

Describe the horns of the inner core

Answer 8

• Dorsal horn is made up neurons that receive sensory inputs
• Lateral horn is made up of preganglionic sympathetic neurons
• Ventral horn is made up of motor neurons

Question 9

What are the tracts in the white matter of the spinal cord?

Answer 9

• Long ascending tracts which carry afferent (sensory) impulses to centres in the brain
• Long descending tracts which carry efferent (motor) impulses from centres in the brain

Question 10

What are the columns in the white matter of spinal cords?

Answer 10

• Dorsal column which consists of long ascending tracts
• Lateral column which consists of both long ascending tracts and long descending tracts
• Ventral column which consists of long descending tracts (and some ascending tracts)

Question 11

What happens to long ascending and descending tracts when they travel to/from cerebral hemispheres?

Answer 11

They get crossed which means that the left hemisphere controls the right side of the body and the right hemisphere controls the left side of the body.

Question 12

What are the two types of sensory information that long ascending tracts carry?

Answer 12

• Proprioceptive: Information that originates from the inside of the body (e.g. muscles, tendons and joints)
• Exteroceptive: Information that originates from the outside of the body (e.g. pain, temperature and touch)

Question 13

What are the different neurons in an ascending tract circuit?

Answer 13

• First order neurons (primary sensory) which enter the spinal cord via a dorsal root
• Second order neurons which ascend the spinal cord or brainstem
• Third order neurons which project to the cerebral cortex

Question 14

What is the difference between the Fasciculus gracilis and the Fasciculus cuneatus?

Answer 14

• Fasciculus gracilis is medial and carries information from the lower limbs (T7 and below)
• Fasciculus cuneatus is lateral and carries information from the upper limbs (T6 and above)

Question 15

Where do the Fasciculus gracilis and the Fasciculus cuneatus terminate?

Answer 15

• Fasciculus gracilis terminates in the nucleus gracilis (gracile)
• Fasciculus cuneatus terminates in the nucleus cuneatus (cuneate)

Question 16

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

Answer 16

They cross over in the medulla and then ascend to the thalamus to form the medial lemniscus (ribbon).

Question 17

What happens to third order neurons in the dorsal column-medial lemniscus pathway?

Answer 17

Projects from the thalamus to the somatosensory cortex.

Question 18

What is sensory ataxia?

Answer 18

The loss of coordination and balance without visual cues (no positional information)

Question 19

What can a lesion on a side of the spinal cord lead to?

Answer 19

Loss of tactile discrimination and proprioception on the same side.

A symptom of this would be sensory ataxia.

Question 20

What is Romberg’s sign?

Answer 20

A clinical test for sensory ataxia. It is when there is severe swaying when standing with your eyes closed and feet together.

Question 21

What is the spinothalamic tract?

Answer 21

A sensory pathway that goes from the skin to the thalamus through nociceptors and it detects pain, temperature and touch.

Question 22

What route do the first order neurons of the spinothalamic tract take?

Answer 22

• Enter the dorsal horn to form the tract of Lissauer

- They then snaps in the dorsal horn with second order neurons

Question 23

What route do the second order neurons of the spinothalamic tract take?

Answer 23

• They cross at each level of the dorsal horn

- Ascend in the anterolateral column to the thalamus

Question 24

What would happen if there was a lesion on one side of the spinal cord (anterolateral column)?

Answer 24

There would be a loss of pain, temperature and crude touch on the opposite side.

Question 25

What does the corticospinal tract consist of?

Answer 25

• Upper motor neuron that goes from the cerebral cortex to the ventral horn
• Lower motor neuron that goes from the ventral horn to skeletal muscle

Question 26

The disruption to what tract can lead to motor neuron disease?

Answer 26

Corticospinal tract