Dermatomes, Myotomes & Segemental Innervation of Limbs Flashcards
The central nervous system is segmented throughout, what are the neural segments otherwise known as?
Neural levels.
What does the neural tube contain? When are they surrounded by paired somites?
Precursor cells of the nervous system.
4th week of gestation.
Somites split into dorsal and ventral sections, what do these go on to become?
Ventral section is sclerotome –> vertebrae and ribs.
Dorsal section is dermatomyotome (DMT) –> dermis and muscles.
As dermatomyotomes develop, they do so in association with specific neural levels of the spinal chord and take the nerve supply with them as a spinal/segmental nerve, what are they consequences of this to innervation?
Skin and muscle derived from a single dermatomyotome have a common nerve supply.
What do roots connect?
Each spinal nerve to a ‘segment’ of the spinal chord (it’s continuous).
What are the differences between dorsal and ventral roots?
Dorsal roots contain only sensory, afferent nerve fibres and dorsal route ganglions are cells bodies of sensory neurones from the periphery.
Ventral roots contain efferent, motor and autonomic nerve fibres.
There are 31 pairs of spinal nerves, numbered according to the level of the vertebral column from which they emerge. What do they contain and where do they travel?
Spinal nerves contain parallel bundles of axons, encased in connected tissue - mixed motor and sensory fibres. They exist only for a short time, as they pass through the intervertebral foramen (division between CNS and PNS).
What are the different levels of connective tissue in the spinal nerves called?
Epineurium covers the entire nerve, perineurium is around each fascicle and the endoneurium around each individual axon.
Fill in the gaps:
Vertebral segments differentiate from ______. The spinal chord runs through the vertebral _____ and multiple vertebral _____ make up the spinal _____. Spinal nerves leave the spinal _____ via _____ _____.
Sclerotomes Foramen Foramina Canal Canal Intervertebral foramina
Where does the spinal chord start and finish?
It starts at the inferior margin of the medulla oblongata and ends as the conus medullaris at L2.
Most segments of the spinal chord are not aligned with corresponding vertebrae. Long roots from inferior segments descend in what to exit at respective foramina?
Cauda equina (bundle of nerve roots from the lumbar and sacral levels that branch off the bottom of the spinal cord like a horse’s tail).
The first cervical pair of spinal nerves (C1) emerge between the occipital bone and atlas. C1-7 exit above corresponding vertebrae, then what happens for C8, T1-L5, then S1-4 and S5 and Co1.
Spinal nerve C8 exits between vertebrae C7 and T1 so T1 - L5 exit below the corresponding vertebrae, then S1-4 exit via the 4 pairs of sacral foramina and S5 and Co1 exit via the sacral hiatus.
Mixed spinal nerves divide into Rami, which communicate with components of the ANS. Where do the dorsal and ventral rami travel?
The dorsal ramus heads to the deep muscle and skin of the dorsal trunk (it’s small). These rami divide again into medial and lateral branches, innnervating in a neat, segmental manner in line with the intervertebral foramina.
The ventral ramus heads to the muscle and skin of the upper and lower limbs and the lateral and ventral trunk (it’s large). These are complicated and enter plexuses before supplying the limbs.
Other than the dorsal and ventral rami, what does the spinal nerve give off and where does it go?
The meningeal branch, which reenters the spinal chord through the intervertebral foramen to supply the vertebrae, ligaments, blood vessels and meninges.
What is a myotome and how does it differ from a motor unit?
A myotome is a group of muscles supplied by a single spinal nerve/root.
A motor unit is a motor neuron and all the skeletal muscle fibres it innervates, so one spinal nerve will contain neurons of many motor units, but only supplies one myotome.
