MSK - Dermatomes And Myotomes Flashcards
What is a neural level?
A segment of the central nervous system
What does the ‘somite’ differentiate into in the fourth week of embryological development?
- the sclerotome (ventral) which forms vertebrae and ribs
- the dermatomyotome (dorsal) which forms dermis and muscle
What do skin and muscle derived from a single dermatomyotome share?
A common spinal nerve supply
What do the ‘roots’ connect in the spine?
They connect each spinal nerve to a segment of spinal cord
What do dorsal (posterior) roots contain?
Afferent/sensory nerve fibres
What do ventral (anterior) roots contain?
Efferent/motor and autonomic nerve fibres
What are spinal nerves?
Parallel bundles of axons encased in connective tissue, which exist only briefly as they pass through the intervertebral foramen
How many spinal nerves are there?
31 pairs, which are numbered according to the level of vertebral column that they emerge from
What’s the difference between an epineurium, a perineurium and an endoneurium?
Epineurium covers the entire nerve, perineurium surrounds each fascicle and endoneurium is around each axon
What is a vertebral foramen?
A gap in the vertebra which the spinal cord runs through. Multiple vertebral foramina form the spinal canal.
What is a external segment?
The name given to a single vertebra, which differentiates from a sclerotome
Where does the spinal cord start and end?
Starts at inferior margin of medulla oblongata, ends as conus medullaris at L2
True or false - all spinal cord segments are perfectly aligned with their corresponding vertebrae?
False - long roots from inferior segments descend in cauda equina to exit at their respective foramina
Where does the first pair of spinal nerves emerge?
Between occipital bone and atlas
Where do C1-C7 emerge?
Above the corresponding vertebrae
Where does the spinal nerve (C8) exit?
Between vertebrae C7 and T1
Where do S1-S4 exit?
Via four pairs of sacral foramina
What are ‘rami’?
These are what the spinal nerve divides to form
What does the posterior/dorsal ramus innervate?
Deep muscles and skin of the dorsal trunk
What does the anterior/ventral ramus innervate?
Muscles and skin of the upper and lower limbs and lateral and ventral trunk
What is a myotome?
A group of muscles supplied by a single spinal nerve (or spinal nerve root)
What is a dermatome?
An area of skin supplied by a single spinal nerve or spinal nerve root
What is a motor unit?
A motor neuron and the skeletal muscle fibres it innervates
What’s the difference between a myotome and a motor unit?
1 spinal nerve contains the neurons of many motor units, but supplies one myotome
