The Spinal Cord, Dorsal Root Ganglion and Peripheral Nerves Flashcards
The spinal grey matter is divided into 3 horns. Name these horns, and note the horn that is not in all spinal cord segments.
a) ventral horn
b) intermediate/lateral horn: found in T1-L2 segments only because they have preganglionic sympathetic neurons; lateral horn only has intermediolateral nuclei
c) dorsal horn
The spinal cord has a central canal.
a) What type of cells line the central canal?
b) What are the functions of those cells?
c) Where does the central canal extend to proximally?
a) simple columnar ciliated epithelial cells (these are called ependymal cells, so the ependyma lines the central canal)
b) secrete and promote flow of CSF by ciliary action
c) into the caudal half of medulla oblongata and opens into the fourth ventricle
What are some important histological features of the spinal grey matter?
- 4 linked cellular masses (i.e. the ventral and dorsal horns)
- dorsal and ventral grey commissures
- cell bodies of multipolar neurons
- dorsolateral tract of Lissauer (note that it is not part of grey matter and not part of dorsal horn): basically it is the route through which white matter passes as it enter grey matter
-
anterior horn cells:
a) these cells are larger than other cells in the spinal grey matter
b) these are lower motor neurons of spinal cord
c) their nuclei contain euchromatin (hence lightly stained)
d) their nuclei are open phased nuclei (open phased nuclei are consistent with active protein synthesis)
The spinal grey matter is organised into 10 cell layers, referred to as ________.
Rexed laminae
What are the functions of each lamina of Rexed?
Laminae I to IV - main site of termination of primary cutaneous afferents (1st order sensory neurons)
Laminae V and VI - receive both proprioceptive and descending projections and regulate movement
Lamina VII - level of the lateral horn, with multiple morphologies and functions - mainly regulate posture, movement, and autonomic functions
Laminae VIII - IX - the ventral horn, somatic motor functions (lamina IX houses bodies of lower motor neurons)
Lamina X - pericentral grey matter and grey commissures
State the nucleus in each lamina of Rexed.
Lamina I - Dorsomarginal nucleus
Lamina II - Substantia gelatinosa
Lamina III and IV - Nucleus proprius
Lamina V - Reticular nucleus
Lamina VI - Commisural nucleus
Lamina VII - Clarke’s nucleus, intermediolateral (has sympathetic preganglionic neurons [T1-L2]) and intermediomedial nuclei (has parasympathetic preganglionic neurons [S2-S4])
Lamina VIII - Medial motorneuron nucleus
Lamina IX - Lateral motorneuron nucleus
Lamina X - Central grey nucleus
[Diagram]
The spinal white matter is made up of myelinated axons that run parallel to one another in the longitudinal plane. It is organised into 3 major columns (funiculi) of nerve fibres. Name them.
- Dorsal funiculus - consists of ascending fibres that relay proprioceptive information. The other columns consist of ascending and descending tracts
- Lateral funiculus
- Ventral funiculus
The areas of the gray and white matter vary in different parts of the spinal cord because there is more white matter at the cervical than at the sacral level. Account for this statement.
This is because axons that form the descending pathways from the brain “peel off” to terminate at each segment, while there are increasing ascending pathways in a caudal-cranial direction.
The amount of grey matter at any one level of the spinal cord depends on the amount of the peripheral tissue innervated by the respective segments. Therefore, the spinal grey matter is consequently greatly enlarged in the lumbosacral and lower cervical segments because of the _________ and _________ plexuses, which innervate the limbs.
lumbosacral and brachial
The spinal arachnoid mater’s outer surface is lined with a ______________ epithelium.
simple squamous
Account for this statement: The cervical region of the spinal cord is larger than other regions of the spinal cord.
The region contains many more ascending and descending nerve fibres than the other regions of the cord.
Account for this statement: The ventral horn in the lumbosacral region of the spinal cord is larger than the ventral horn in other regions of the cord.
This is mainly due to the large cell bodies of lower motor neurons (Golgi type I cells).
NOTE: It is the large ventral horn of the lumbosacral region of the cord rather than the white matter of this region that accounts for the lumbosacral enlargement of the cord.
State the clinical relevance of the large lower motor neurons in the lumbosacral region.
They are affected in poliomyelitis with subsequent paralysis of the lower limbs.
What do you consider when determining the segment of a spinal cord when viewing histological slides? [This is just a guide. Rate it a 5.]
- Size of white matter
- Relative sizes of the grey matter; ventral horn:dorsal horn ratio
- Presence of intermediate horn
- Size/volume of dorsal funiculus, and partitioning* [Partitioning has been marked with an asterisk because absence of partitioning in the dorsal funiculus doesn’t show the segment since fasciculus gracilis is throughout while fasciculus cuneatus begins from T6 segment upwards. That will be better understood when tractology is covered.]
- Number of visualised collateral spinal nerve roots* - more at level near/around cauda equina [few or absence of those roots doesn’t tell us much because they could have been removed during slide preparation]
Here’s an opinion on the specific order to be followed when determining the spinal cord segment.
1. Ventral horn expansion; presence indicates cervial/lumbar
2. Shape; oval (cervical) or circular (lumbar)
3. Presence of the lateral horn (T1-L2/S2-S4)
Here are some histological slides of cross-sections at various levels of the spinal cord. Click on Answer to view them. It’s important to know how to identify the level of the cross-section of the spinal cord, giving reasons why.
