Organisation of the Spinal Cord

Question 1

What is the spinal cord and what is it protected by?

Answer 1

• The spinal cord is the connection between the brainstem and the spinal nerves.
• It is protected by the bony vertebral canal.

Question 2

What are the 3 parts of the brainstem?

Answer 2

Midbrain
Pons
Medulla Oblongata

Question 3

What are the 3 protective layers (meninges) surrounding the central nervous system?

Answer 3

-	Surrounding the central nervous system are 3 protective layers;
o	Dura mater
o	Arachnoid mater
o	Pia mater
(see lecture notes for images)

Question 4

What is the spinal cord composed of?

Answer 4

• The spinal cord is composed of white and grey matter. The white matter is made up of axons, covered in myelin, and the grey matter is composed of non-myelinated components (cell bodies, synapses).
  (see lecture notes for diagram)

Question 5

Where is the lateral horn of grey located?

Answer 5

• Lateral horn of grey is only associated with sympathetic nervous system, so will only be located at the vertebral levels associated with the sympathetic nervous system also

Question 6

Where are the vertebral bodies of motor and sensory neurons located?

Answer 6

• Motor neurons have their cell bodies located in ventral horn of grey
• Sensory cells bodies not located in the spinal cord at all, actually located just outside in dorsal root ganglion (blue circle on diagram)

Question 7

How many pairs of spinal nerves are there? How many of each type?

Answer 7

-	31 pairs of spinal nerves
o	8 cervical
o	12 thoracic
o	5 lumbar
o	5 sacral
o	1 coccygeal

Question 8

How are the spinal nerves named in the cervical region? How about in the rest of the spine?

Answer 8

In cervical region = spinal nerve is named according to the vertebrae below
In the rest of the spine = spinal nerve is named according to the vertebrae above

Question 9

Where does the spinal cord end in relation to the vertebral column? What is formed afterwards?

Answer 9

• The spinal cord is substantially shorter than the vertebral column, ending at the level of L1/2 in the adult. The lumbar region of the spinal cord is mainly in the thoracic part of the vertebral column. Below L1/2 the spinal nerves are bunched together, forming the cauda equina (horse’s tail - filum terminale is at the end of this)

Question 10

How is the spinal cord different in children to adults?

Answer 10

• As bone grows quicker than nervous tissue, the spinal cord in children will end lower down than it does in adults, as their bone has not fully grown yet

Question 11

Where are lumbar puncture and epidural anaesthesia performed and why?

Answer 11

• Lumbar puncture and epidural anaesthesia are both performed below the level of L3 to avoid damage to the spinal cord.

Question 12

How does the proportion of white and grey matter vary along the spinal cord?

Answer 12

-	The proportion of white and grey matter varies along the spinal cord. 
o	Cervical:
	Large amount of white matter
	Large ventral and dorsal horns
o	Thoracic
	Large proportion of white matter
	Lateral horn of grey
o	Lumbar
	Little white matter
	Large ventral and dorsal
o	Sacral
	Very little white matter
	Predominantly grey matter

(see lecture notes for pictures)

Question 13

What is a dermatome and why are they useful?

Answer 13

• A dermatome is an area of skin which receives its sensory supply from a single spinal nerve. Dermatomes are useful to help localise neurologic levels

Question 14

Where does the spinal cord receive its blood supply from?

Answer 14

• The spinal cord receives its blood supply from the anterior and posterior spinal arteries. These arteries are not enough to supply the whole cord, so they are reinforced by radiculospinal arteries which are derived from arteries of the body wall.

Question 15

Where does venous drainage from the spinal cord come from?

Answer 15

• Venous drainage is via 3 anterior and 2-3 posterior spinal veins.

Question 16

What does the spinal tract do?

Answer 16

This is the pathway to transmit signals from the spinal cord to the brain

Question 17

What does the spinothalamic tract transmit?

Answer 17

• Transmitting the sensations of crude touch, pain and temperature from the spinal cord to the thalamus.
  (see diagram in lecture notes for pathway)

Question 18

What is the process of transmission in the spinothalamic tract?

Answer 18

• The first order neuron transmits the sensation along the spinal nerve and travels via the dorsal root into the spinal cord.
• In the spinal cord the first order neuron synapses with the second order neuron in the dorsal horn of grey
• The second order neuron then decussates to reach the contralateral spinothalamic tract
• The second order neuron travels via the spinothalamic tract up to the thalamus
• In the thalamus the secondary order neuron synapses with the third order neuron
• The third order neuron travels via the internal capsule to the primary somatosensory cortex

Question 19

What does the dorsum column medial lemniscus transmit?

Answer 19

• Transmitting the sensations of vibration, proprioception and discriminative touch from the periphery to the brain via the dorsal columns and medial lemniscus.

Question 20

What is the process of transmission via the dorsum column medial lemniscus transmit?

Answer 20

• The first order neuron transmits the sensation along the spinal nerve and travels via the dorsal root into the spinal cord.
• In the spinal cord the first order neuron does not synapse but runs into the dorsal column (fasiculus gracilis from the lower limb, fasciculus cuneatus from the upper limb)
• The first order neuron ascends in the spinal cord along the ipsilateral dorsal column to enter the medulla
• In the medulla the first order neuron synapses with the second order neuron within the cunate or gracile nucleus respectively and then decussates to reach the medial lemnisus
• The second order neuron travels via the medial lemnisus to reach the thalamus
• In the thalamus the secondary order neuron synapses with the third order neuron
• The third order neuron travels via the internal capsule to the primary somatosensory cortex

Question 21

What does spinocerebellar transmit?

Answer 21

• Transmitting the sensations of subconscious proprioception (position in space) from the spinal cord to the cerebellum.

Question 22

What is the process of transmission via the spinocerebellar? What is special about this tract?

Answer 22

• The first order neuron transmits the sensation along the spinal nerve and travels via the dorsal root into the spinal cord.
• In the spinal cord the first order neuron synapses in the dorsal horn of grey
• The second order neuron enters the ipsilateral spinocerebellar tract and ascends to the cerebellum
  (this is the only tract where the body is controlled by the same side of the brain, rather than right brain controlling left body etc.)

Question 23

What does the corticospinal tract transmit?

Answer 23

• Transmitting the motor signals from the cortex to the spinal cord.

Question 24

What is the process of transmission via the corticospinal tract?

Answer 24

• The first order neuron has its cell body in the primary motor cortex and the axon projects along the internal capsule to reach the brainstem
• The first order neurons run anteriorly in the brainstem, and enter the medullary pyramids
• In the pyramids the majority of fibres decussate to enter the corticospinal tract.
• From the corticospinal tract the first order neurons descend to the level of innervation and enter the ventral horn of grey and synapse with the second order neurons
• The second order neuron travels out of the spinal cord via the ventral root and into the spinal nerve to reach skeletal muscle

Question 25

What is a complete spinal cord injury and what effect does it have?

Answer 25

• Complete spinal cord injuries occur when the spinal cord is fully compressed or severed. A complete injury will result in a complete loss of sensory and motor information below the level of the lesion.

Question 26

What is an incomplete spinal cord injury and what effect does it have?

Answer 26

• Incomplete spinal cord injuries occur when the spinal cord is compressed or injured, but the brain’s ability to send signals below the site of the injury is not completely removed.
• The pattern of injury will vary depending which tracts are involved and what level the injury is at.

Question 27

What is a central cord injury, why do they occur and what effect effect do they have?

Answer 27

• Central cord injury (often due to hyperextension)
• Patients present with upper limb weakness, and sensory loss below the level of the injury. The upper extremities are classically more affected than the lower extremities, with motor function more severely impaired than sensory function.
• Usually affects corticospinal tract and sometimes spinothalamic

Question 28

What is Brown-Sequard syndrome and what effect does it have?

Answer 28

• Brown-Séquard Syndrome (damage to only one side of side cord)
• Paralysis and loss of proprioception/ vibration/discriminative touch on the ipsilateral (same) side as the injury.
• Loss of pain and temperature sensation on the opposite (or contralateral) side as the lesion.