Lecture 10: The Spinal Cord and Spinal nerves Flashcards
What is the term given to the termination of the spinal cord?
Conus medullaris
What is the cauda equina?
Spinal nerves emerge from lower levels of the cord to leave at their respective intervertebral foramina - these are called the cauda equina. Cauda equina - the horse tail. Though the nerve emerge from the end of the spinal around L1-L2, it will leave at its respective vertebrae e.g. lower lumbar or sacrum. This has the image of a horse tail.
What is the filum terminale?
From the tip of conus medullaris to insert into the coccyx is the filum terminale. It is an inferior attachment of the spinal cord. It therefore prevents excessive movement of the spinal cord. It is a thin sheath. of neural tissue, a remnant in development where the spinal cord extend all the way to the end of the coccyx.
Why is there 7 Cervical Spinal segments but 8 Cervical Spinal nerves?
The C1 spinal nerve can only leave form above the C1 vertebrae. C2 leaves above the C2 vertebrae. From C1-C8 the nerves emerge from above the vertebrae so C8 nerve leaves above C7 vertebra. At C7 there is a transition and spinal nerves emerge from below the vertebrae - from C8 - S5. Transmission point that nerves will go onto originate from below the vertebrae.
What is the origin of the epineurium?
As the spinal nerves leave the spinal cord they take with them a layer of meninges. The meningeal coverings go onto form the epineurium. This is an outer sheath of connective tissue for each spinal nerve.
What is the difference between spinal dura and cranial dura?
In the brain there is two dura layers - the meningeal layer and periosteal layer. There is normally no separation between the two only at specific point to form Dural folds. It is only the meningeal layer the continuous through the foramen magnum to cover the spinal cord. There is no periosteal layer. There is a real space between the dura and the vertebrae (epidural space) - this is filled with fat.
How does changes in cord length occur through development?
There is differential growth between the spinal cord and the vertebral column. In the foetus the spinal cord extends all the way to the end of the vertebrae as a result S1 for example spinal nerve roots exists near the level of the origin. As we grow the cord extends as the vertebrae grow. The cord ends at L1-L2. The lower nerve roost extend as the cauda equina.
How is a lumbar puncture performed?
In a lumbar puncture the patient lies in a knee to chest position/hunched over and a needle is used to obtain CSF from the lumbar cistern. This stretches the ligaments giving us more room to insert the needle. We need to insert the needle below where the spinal cord ends. Due to anatomical variations, it could extend to L3. Therefore we need to place it blow L3 - L3-L5. Here we are in the lumbar cistern. The cauda equina allows us to do this. When the needle is inserted, the nerves move away. It is very rare we will puncture them. You insert he needle through the ligamentum flavum.
Describe the vasculature of the spinal cord.
- Found in the anterior median fissure is the anterior spinal artery supplying the anterior aspect of the spinal cord
- In the posterior lateral sulci is the paired posterior spinal arteries
- The anterior spinal artery is reinforced by segmental spinal arteries. The segmental artery at each level gives a medullary branch to reinforce the anterior spinal in an anterolateral direction.
- The segmental artery also gives rise to anterior and posterior radicular arteries which supply the spinal nerve rootlets.
How is grey and white matter organised in the spinal cord?
In the spinal cord, the grey matter is confined to the inside of the cord and the white matter is confined to the outside.
Grey matter:
- Dorsal horn of the grey matter - many synapses occur mainly of sensory information
- Lateral grey horn - the origin of preganglionic visceral motor neurones of autonomic system
- Ventral grey horn
White matter - contains the somatic motor neurones that innervate the muscles
White matter:
- Dorsal white column
- Lateral White column
- Ventral white column
- Ventral white commissure - allows communication between the left and right side
At what level of the spinal cord do we see the lateral horn?
T1-L2 and S2-S3
How is the CNS connected to the PNS?
Spinal cord (CNS) is connected with PNS via its nerve rootlets. Each spinal level gives rise to 1 pair of spinal nerves (PNS).
What is contained in the dorsal root ganglion?
Sensory cell bodies
Why is the spinal nerve a mixed nerve?
Each spinal nerves starts as a collection of ventral rootlets leaving the anterior ventral sulci and the dorsal rootlets leaving the posterior lateral sulci. They merge to form roots. The dorsal roots is associated with dorsal root ganglia. The dorsal root ganglia is composed of cell bodies - these belong to primary sensory neurones. The ventral rootlets merge to form a ventral root. The ventral and dorsal root combine to form a segmental spinal nerve.
The afferent fibres, sensory fibres (can be somatic for visceral) that travel in the dorsal root of the spinal nerve to enter the dorsal horn. They have their cell bodies in the dorsal root ganglion. From the ventral horn have cell bodes of motor neurons that leave the cord to exit the cord and join the spinal nerve.
How is a reflex arc established?
A reflex arch happens at the same level of the cord or the brainstem. There is no time for the information to be sent to consciousness. A quick response needs to happen.
E.g. touching a hot object - afferent neurons transmit the sensory information via the spinal nerve and the dorsal aspect of the nerve. The cell body is in the dorsal root ganglion. They connect with the interneuron in the grey matter. This links via an interneuron. It can then leave towards to periphery to the muscle it innervates via the ventral root to withdraw from the hot object.
