Spinal cord development, CSF pathways and blood supply
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During neurulation the notochord induces overlaying ectoderm to become ...? And for a ...?
neuroectoderm, neural tube
What are the stages of neural tube formation?
- A neural plate forms (overlying ectoderm becomes a thickened neural plate)
- This becomes the a neural groove
- The dorsal margins of the neural groove merge medially forming a neural tube composed of neuroepithelial cells surrounding a neural cavity
The neural tube becomes the CNS/PNS?
CNS, which consists of the brain and spinal cord
What does the cavity of the neural tube become?
The ventricles of the brain and central canal of the spinal cord
What becomes the cells of the PNS?
The neural crest cells
What are enlargements of spinal cord segments that innervate the limbs a result of?
Greater numbers of neurones in these segments due to less neuronal degeneration compared to segments that do not innervate limbs
Describe the formation of the meninges and the subarachnoid space
The mesenchyme surrounding the neural tube aggregates into two layers. The outer layer forms the dura mater. The cavities develop and coalesce within the inner layer, dividing it into arachnoid and pia mater. The cavity becomes the subarachnoid space which contains CSF.
What do the dorsal grey column, intermediate grey column and ventral grey column of the spinal cord develop into?
- Dorsal grey column - sensory neurones
- Intermediate grey column - autonomic nervous system
- Ventral grey column - motor neurones
Describe the development of dorsal nerve roots
Axons energy from the segmental spinal ganglions (neural crest) and grow into the alar plate (dorsal horn of the neural tube)
Where are cell bodies of dorsal nerve roots located?
They are located in the spinal ganglion
What do dorsal nerve roots form?
Afferent (sensory) neurones
Describe the development of ventral nerve roots
Axons grow from the basal plate (ventral horn of the neural tube) out of the neural tube
Where are ventral nerve root cell bodies located?
In the spinal cord
What structure is the remnants of the notochord?
The nucleus pulposus of intervertebral discs
List the ventricles present in the brain
Lateral, 3rd and 4th ventricles
What structure does the 3rd ventricle surround?
The interthalamic adhesion
CSF passes from the 3rd ventricle through the ... to get to the 4th ventricle?
Where is CSF ultimately drained away through?
The dorsal sagittal sinus
How does CSF get into the subarachnoid space between the spinal cord and dura?
Through the lateral aperture
What structures produce CSF?
The choroid plexus of the lateral, 3rd and 4th ventricles
Describe cervical collection of CSF
The animal must be under anaesthesia. The neck is flexed and the needle inserted midline between C1 and C2. Stop advancing the needle when you enter the CSF space.
Describe lumbar collection of CSF
The animal is restrained. The needle is advanced to the floor f the spinal canal and withdrawn. The position of the lumbar tap varies between species depending on the caudal extent of the spin cord. It is ~L6.
What would a very turbid looking sample of CSF reflect?
A high cell count
What is a problem with lumbar taps?
They are more likely to be 'dry', especially in small fat patients or cats
Describe the arterial blood supply to the spinal cord
Lumbar arteries of the aorta, intercostal arteries and vertebral arteries --> paired spinal arteries ---> dorsal and ventral root artery per spinal cord segment ---> superficial and anastomosing arteries of the spinal cord ---> deep arteries in the spinal cord leading to 3 vascular zones
What are the three vascular zones in the spinal cord?
- Inner vascular zone - vertical arteries only
- Middle vascular zone - both vertical and radial arteries
- Outer vascular zone - radial arteries only
Describe the venous drainage of the spinal cord
Ventral spinal vein (drains spinal cord) ---> vertebral venous sinus ---> segmental spinal veins ---> vertebral veins, azygous vein and caudal vena cava ---> systemic circulation
Which vessel does the ventral spinous vein escort along in the ventral fissure of the spinal cord?
The ventral spinal artery
True or false: the vertebral venous sinuses have valves?
False - they are valveless
What is the significance of these sinuses being valveless?
Some infections can use these areas for transport as blood can move backwards and forwards freely.
Where are the vertebral venous sinuses located?
In the epidural space longitudinal on the floor of the vertebral canal
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