The Spinal cord

Question 1

Where does the spinal cord originate, travel and terminate?

Answer 1

The spinal cord is travels from the temporal lobe and is continuous with the brainstem. It is located within the vertebral column and terminates at the spinal level of L1/2 vertebrae.

Question 2

What is the vertebral level?

Answer 2

The level corresponding to which part of the vertebral column you are at e.g. T12.

Question 3

What is the spinal level?

Answer 3

The level corresponding to which spinal cord you are referring to. This does not always correspond to the vertebral level, e.g. C8 spinal level is at the C7 vertebrae.

Question 4

What are the 3 main functions of the spinal cord?

Answer 4

1. To act as a protective mechanism to facilitate reflexes
2. To transmit sensory information from sensory receptors to the primary sensory cortex in the parietal lobe of the cerebral cortex.
3. To transmit motor information from the primary motor cortex to effectors such as muscles/glands.

Question 5

Where are the 2 main enlargements of the spinal cord found?

Answer 5

The cervical enlargement - at C5-T1

The lumbar enlargement - at L1-S3

Question 6

What is the name of the cone-shaped ending of the spinal cord?

Answer 6

The conus medullaris

Question 7

What is the filum terminale?

Answer 7

A delicate piece of fibrous tissue travelling from the apex of the conus medullaris

Question 8

What is the caude equine?

Answer 8

A bundle of spinal nerves consisting of L2-L5 and S1-S5 spinal levels. It occupies the lumbar cistern which is a sub-arachnoid space below the conus medullaris. It innervates the bladder, pelvic organs and the lower body.

Question 9

Draw out/describe the descending tracts of the cross section of the spinal cord.

Answer 9

Right side starting from top to bottom:
Lateral CST
Rubrospinal tract
Lateral RST
Vestibulo spinal tract
Medial RST
Anterior CST

Question 10

Draw out/describe the ascendongside of the cross section of the spinal cord.

Answer 10

Left side starting from top to bottom:
Gracile tract
Cuneate tract
Posterior spinocerebellar tract
Anterior spinocerebellar tract 
Spinothalamic tract

Question 11

What is an upper motor neurone?

Answer 11

A motor nerve fibre travelling from the cerebral cortex to the anterior horn cell of the spinal cord - within the CNS.

Question 12

What is a lower motor neurone?

Answer 12

e.g. the Alpha MN - a motor nerve fibre travelling from the anterior horn cell of the spinal cord to the muscle/groups of muscle fibres that it innervates - within the PNS.

Question 13

What is an alpha motor neurone?

Answer 13

A multipolar lower motor neurone travelling from the anterior horn cell of the spinal cord to the skeletal muscle, namely the extrafusal fibres.

Question 14

Describe the course of a gamma motor neurone and it’s function.

Answer 14

A lower motor neurone that travels from the AHC of the spinal cord to the intrafusal fibres of a muscle spindle to ‘reset’ the fibre and set it’s sensitivity to stretch so that it can continue to transmit somato-sensation to the dorsal horn of the spinal cord. It is involved in muscle tone/posture and balance.

Question 15

What is a motor unit?

Answer 15

The motor neurone and the muscle fibre/groups of muscle that it innervates. Many motor units are called a motor pool and helps to regulate/coordinate muscle contractions.

Question 16

What is a myotome?

Answer 16

A muscle/groups of muscles innervated by a single nerve root. e.g. the biceps is innervated by C5/6

Question 17

What is a dermotome?

Answer 17

An area of skin innervated by a single nerve root. e.g. the dorsal surface of the little toe is innervated by S1.

Question 18

What is reciprocal innervation?

Answer 18

The process by which an antagonist to a movement lowers the amount of tension produced/relaxes to allow the agonist to contract/cause movement e.g. hamstrings relax/lower tone to allow the quadriceps to cause knee extension.

Question 19

Describe the simple stretch reflex

Answer 19

A stimulus e.g. patellar hammer on the patellar tendon causes the muscle spindle to stretch, this sends sensory information to the spinal cord via the dorsal root ganglion and synapses with the alpha motor neuron which causes the knee to extend. This is monosynaptic, unilateral and intrasegmental.

Question 20

What is the role of a reflex?

Answer 20

To act as a protective mechanism e.g. to stop the patellar tendon tearing when stretched.

Question 21

What is the flexor withdrawal reflex?

Answer 21

A withdrawal of a limb away from a dangerous stimulus to act as a protective mechanism e.g. foot stepping on a pin, the knee will flex to move away. This is intersegmental, polysynaptic and unilateral.

Question 22

What is the crossed extensor reflex?

Answer 22

This occurs when the flexor withdrawal relfex occurs. e.g. you step on a pin and the knee flexes to move the moot away from the dangerous stimuli. However, if both knees were to flex, you would fall over. Therefore weight bearing occurs on the opposite limb and muscle tone increases to aid balance and posture and prevents you falling over. This is therefore polysynaptic, contralateral and intersegmental.

Question 23

State the root value for the:
Biceps/brachioradialis
Triceps 
Patellar tendon
Achilles tendon
Plantar surface of the foot (Babinski's sign)

Answer 23

C5/6
C6/7
L2,3,4
S1,2,3
S1,2,3