Spinal Cord

Question 1

How many spinal cord segments are there?

How are they divided?

Answer 1

31 spinal cord segments

• 8 cervical segments (C1-C8)
• 12 thoracic segments (T1 - T12)
• 5 lumbar segments (L1-L5)
• 5 sacral segments (S1-S5)
• 1 coccygeal segment (Co1)

Question 2

What are the functions of dorsal and ventral roots of the spinal cord?

Answer 2

• the spinal cord receives sensory information via dorsal roots
• this information is transmitted to higher centres in the brain via ascending tracts
• the spinal cord receives information from the brain via descending tracts
• it transmits motor information to somatic and visceral target sites via ventral roots

Question 3

What does each spinal cord segment give rise to?

Answer 3

• each spinal cord segment gives rise to a pair of spinal nerves
• in total, there are 31 pairs of spinal nerves

Question 4

What is the role of the cervical and lumbar enlargements?

Why is there not a thoracic enlargement?

Answer 4

Cervical enlargement:

• allows for mass of motor neurones supplying the brachial plexus to exit the spinal cord

Lumbar enlargement:

• allows for mass of motor neurones suplying the lumbosacral plexus to exit the spinal cord

Thoracic enlargement?

• there is not one as there is not a mass of motor neurones exiting the spinal cord in the thoracic region
• there is not as much musculature present in the thoracic region compared to the upper and lower limbs

Question 5

Where does the spinal cord start and end?

Answer 5

• the spinal cord extends from the foramen magnum to the rostral edge of L2 vertebra
• it terminates in the conus medullaris

Question 6

Where does the C1 spinal nerve emerge relative to its corresponding vertebra?

Answer 6

• at each level, the spinal cord gives off several spinal nerve rootlets that join together to form a single spinal nerve
• C1 spinal nerve emerges between the base of the skull and C1 vertebra
• it emerges ABOVE the corresponding vertebra

Question 7

What is the transition in nomenclature of nerves and where does this occur?

Answer 7

• cervical spinal nerves all arise ABOVE the corresponding vertebra
• C8 spinal nerve arises above T1 vertebra
• From this point onwards, the spinal nerves arise BELOW the corresponding vertebra
• T1 spinal nerve emerges below T1 vertebra and so on…
• this point is called the transition in nomenclature of nerves

Question 8

What is the cauda equina and why does it form?

Answer 8

• during development, the spinal cord lengthens at a slower rate than the vertebral column
• the spinal cord only occupies the upper 2/3 of the vertebral column in an adult
• the spinal cord terminates at the rostral end of L2 vertebra, so lumbar and sacral nerve roots have to descend in the vertebral canal before exiting via their respective intervertebral foramina
• lumbosacral nerve roots surround the filum terminale and form a cluster that resembles the tail of a horse

Question 9

What is the filum terminale?

Answer 9

• a region of pia mater that extends from the conus medullaris
• it runs from the apex of the conus medullaris to the coccyx

Question 10

How can the filum terminale be divided?

Answer 10

Filum terminale internum:

• runs from apex of conus medullaris to the lumbar cistern at level of S2 vertebra

Filum terminale externum:

• runs from S2 vertebra to the coccyx
• despite the name change, this is all one continuous piece of tissue that is either running within or outside of the lumbar cistern

Question 11

Where is the lumbar cistern located?

What is found in this space?

Answer 11

• it runs from the conus medullaris to the S2 vertebra
• it is part of the subarachnoid space and contains no CNS structures except for the filum terminale internum and cauda equina
• as it contains CSF, it is often the site of lumbar puncture

Question 12

Where is grey and white matter located in the spinal cord?

Answer 12

• grey matter containing cell bodies is located centrally within the spinal cord
• white matter containing ascending & descending tracts (fasciculi) of myelinated and unmyelinated axons is located more peripherally

Question 13

How can the dorsal and ventral horns be distinguished on a spinal cord section?

Answer 13

• the dorsal horn of grey matter reaches the surface where the dorsal rootlets of the spinal nerves enter
• the ventral gey horn does not reach the ventral surface of the spinal cord

Question 14

What is the grey commissure and anterior white commissure?

Answer 14

Grey commissure:

• this is a band of grey matter that connects the grey matter on both sides of the spinal cord
• the central canal is located within the grey commissure

Anterior white commissure:

• this is located ventral to the grey commissure and contains decussating axons