1.1.2 Topography of the spinal cord

Question 1

How many segments of the spinal cord are there?

Answer 1

31 segments

Same number of somite

42-44 somites before they degenerate to 31 somites

Question 2

Describe the structure of the spinal cord

Answer 2

Central butterfly-shaped grey matter and an outer shell of white matter

Grey commissure joins both halves

Has an anterior and posterior median sulcus, which separates the cord into two halves

Question 3

What is the difference between the structure of the spinal cord and brain?

Answer 3

Brain follows the same structure as spinal cord but has additional cortex of grey matter

grey-white-grey

Question 4

What does the butterfly structure of grey matter consist of?

Answer 4

Dorsal horns, left and right
Ventral horns, left and right

Question 5

What do the dorsal and ventral horns do?

Answer 5

Dorsal and ventral nerve roots emerge here

Dorsal=sensory
Ventral=motor

Question 6

Where do sensory afferents and motor efferents meet?

Answer 6

Ventral horn

Question 7

What does each spinal cord segment connect with?

Answer 7

Connects with a spinal (mixed) nerve through dorsal and ventral roots

Question 8

What do spinal cord segments do?

Answer 8

Supply specific dermatomes and myotomes on both sides

Question 9

How can white matter be subdivided?

Answer 9

Divided into functionally relevant parts:
- Funiculus
- Tracts
- Fasciculus

Question 10

What is a funiculus?

Answer 10

Segment of white matter containing multiple distinct tracts

Impulses travel in multiple directions

Question 11

What is a tract?

Answer 11

Anatomically and functionally defined white matter pathway connecting two distinct regions of grey matter

Impulses travel in one direction

Found in funiculi

Question 12

What is a fasciculus?

Answer 12

Subdivision of a tract supplying a distinct region of the body

Question 13

How can grey matter be divided?

Answer 13

Organised into cell columns
Rexed’s laminae

Distinct histological and functional differences between different laminae

Question 14

How do motor neurones supplying a singlular muscle arise?

Answer 14

Arise from multiple segments and form a distinct population of neurones in the CNS- a nucleus

Question 15

What is the midbrain (mesencephalon) responsible for?

Answer 15

Eye movements and reflex responses to sound and vision

Remember CNIII and IV are responsible for eye movement and originate from the mid-brain

Question 16

What is the pons responsible for?

Answer 16

Feeding-trigeminal nerve comes from here (muscles of mastication)
Sleep

Question 17

What is the medulla responsible for?

Answer 17

Cardiovascular and respiratory centres (Vagus)

Major motor pathway, medullary pyramids

Question 18

Pure sensory loss in a single dermatome with no associated motor weakness suggests damage to what?

Answer 18

Dorsal root, ventral root damage would result in motor function loss