The Spinal Cord - Lecture 4

Question 1

Where do segmental spinal nerves leave the vertebral column?

Answer 1

The inter-vertebral foramina

Question 2

Where does the spinal cord end in human adults?

Answer 2

At ~L1, the spinal column stops growing hence is shorter than the actual vertebral column.
Anaesthesiologists inject drugs below L1 so needle doesn’t damage spinal cord

Question 3

How do spinal cord cross sections change as you go down caudally?

Answer 3

C3 - a large cross section, with a larger lateral extension of the ventral horn, large white matter

T4 - small gray matter ; a small gray/white matter ratio

L2 - more gray matter ; large gray/white matter ratio

S2 - smallest white matter ; biggest gray/white matter ratio

Question 4

What are Rexed Lamina?

Answer 4

These are the cytoarchitechtonic divisions also found in the spinal cord

Question 5

In relation to movement, what parts of the Rexed Lamina are of interest?

Answer 5

Area 8 - motor interneurons, these coordinate the activity of the lower motor neurons

Area 9 - motor neuron columns, these govern limb musculature

Question 6

Motor neurons axons leave the cord through Ventral roots to terminate where?

Answer 6

On ipsilateral (same side) muscles

Question 7

When the spinal cord is injured, what do the injured neurons do?

Answer 7

Release glutamate at high levels, over exciting neighbouring neurons. Glutamate (and cysts) kill myelin producing cells.

Question 8

What is the most common type of spinal injury in humans?

Answer 8

Injury at C5-C6 leads to an inability to control elbow extensor and all the finger muscles

Question 9

How does neural prosthesis (functional electrical stimulation) work?

Answer 9

The system replaces the output from the damaged spinal cord

Question 10

What better system tried on monkeys could be adopted for spinal injury?

Answer 10

Use a signal directly recorded from the brain and bypass the spinal cord. Brain activity is recorded and decoded and the paralysed muscles are stimulated to restore grasping function

Question 11

What is a motor pool?

Answer 11

All the motor neurons that innervate a single muscle

Question 12

Where are the cell bodies of motor neurons located?

Answer 12

Ventral horn of the spinal cord

Question 13

Why are there enlargements in the cervical and lumbar regions?

Answer 13

There are large number of motor pools responsible for arm (cervical) and leg (lumbar) movements

Question 14

What is the appearance of a slow (S) motor unit in acid/alkaline and what is its description

Answer 14

Dark in acid / lighter in alkaline
Typically innervate relatively few muscle fibres and generate small forces, contract slowly but are fairly fatigue resistant

Question 15

What is the appearance of a fast fatiguable (FF) motor unit in acid and alkaline, and provide a description

Answer 15

Light in acid and dark in alkaline

Large motor neurons innervate larger more powerful units.

Question 16

What is the appearance of FR motor unit in acid / alkaline and give a description

Answer 16

Lighter in acid and intermediate in alkaline

An intermediate size, not as fast as FF units but less fatiguable

Question 17

What muscle fibres transformation occurs in strength training? What transformation occurs in paralysis ?

Answer 17

Type IIb is slowly transformed to IIa

In paralysis, type I is turned to type IIb

Question 18

Discuss motor unit activity as voluntary force is increased

Answer 18

As voluntary force increases, the number of units recruited increases and the firing rate also increases.

Question 19

What did desmedt(1977) find when looking at motor units?

Answer 19

Motor units that are activated later tend to produce more force and have faster contraction time