2 - Spinal Chord Function and Dysfunction Flashcards
What is a spinal segment?
a portion of the spinal chord that gives rise to a pair of spinal nerves
How many spinal nerves (pairs)/segments are there?
31
Describe the discrepancy between the levels of the vertebral levels and the spinal levels
as you descend down the spinal chord, the vertebral level (the place where the nerve emerges from the vertebral column) becomes progressively more inferior than the spinal level (the place where the nerve emerges from the spinal chord)
Describe the relationship between the bones of the vertebral column and their corresponding nerves
above C8, the corresponding nerve emerges from above the vertebra
(7 cervical vertebra and 8 cervical nerves)
below C8, the corresponding nerve emerges from below the vertebra
What are the two enlargements in the spinal cord and what is their significance?
Cervical enlargement (C4-T1) – has extra motor neurons that go to the muscles of the upper limb Lumbosacral enlargement (L2-S3) – has extra motor neurons that go to the muscles of the lower limb
What are the layers of the meninges?
dura mater - outermost layer arachnoid mater (arachnoid and dura are closely associated) SUB ARACHNOID SPACE - CSF is found here pia mater
Which space is present in the spinal meninges but not in the cranial meninges?
Epidural space – this can be used for injecting anaesthetics/analgestics
Define dermatome
an area of skin innervated by (a pair) one single spinal nerve or spinal segment
Define myotome
muscles innervated by (a pair) one single spinal nerve or spinal segment
When does a spinal nerve form?
when the ventral and dorsal horns have fused (before the rami branch off)
they have a mixture of sensory and motor nerves
Which is larger out of the anterior and posterior rami?
anterior
What are the three most important tracts in spinal cord injury? State their roles.
Lateral corticospinal tract – fine motor movements (motor)
Dorsal columns – fine touch, pressure, vibration, proprioception (sensory)
Spinothalamic tract – pain and temperature (pain)
Where do the upper motor neurons within the lateral corticospinal tract decussate (cross over)?
Pyramidal decussation in the medulla
Usually, how many neurones in sensory pathways?
3
1 in skin, 1 in CNS and 1 going from the thalamus to the brain
2nd order sensory neurones cross over
Where do the sensory fibres of the dorsal columns decussate?
Sensory decussation in the medulla
How are pain neurons arranged differently to other sensory and motor neurons?
The first order neurons synapse in the dorsal horn and then the second order neuron crosses to the contralateral side immediately (at the level of the synapse with the first order neurone)
The second order neurons then ascend on the contralateral side
(dorsal crosses over in the medulla, hence ascends on the same side)
Describe autonomic outflow in relation to spinal segments
parasympathetic outflow - (craniosacral) cranial nerves III, VIII, IX and X and S2-S4
sympathetic outflow - (thoracocolumbar) T1-L2
What are the two stages of lateral corticospinal tract damage?
SPINAL SHOCK – you get loss of reflexes below the level of the lesion leading to flaccid paralysis. The limbs become floppy and there is little muscle tone
RETURN OF REFLEXES – you get hyperreflexia and spasticity. The patient experiences spontaneous muscle contraction and there is very high muscle tone – rigid paralysis
at what vertebral level does the spinal chord end at?
L2
What are are arachnoid granulations?
they are small protrusions of the arachnoid mater into the outer membrane of the dura mater. They protrude into the dural venous sinuses of the brain, and allow CSF to exit the subarachnoid space and enter the blood stream.
