MSK: nerves, dermotomes and myotomes Flashcards
What is segmentation?
Segmentation is the division of the body plan into distinct levels. In the case of nerves they are divided into neural levels which correspond to the intervertebral foramen level at which each pair of spinal nerves leave the spinal cord.
What are spinal nerve roots?
A nerve fiber bundle that emerges from either side of the spinal cord and joins with a complementary bundle to form each spinal nerve in the series of spinal nerves
What type of nerves fibres does the dorsal root contain?
Afferent/ sensory nerve fibres only.
What type of nerves fibres does the ventral root contain?
Efferent/ motor and autonomic nerve fibres only.
What marks the division between the CNS and the PNS?
Intervertebral foramen. Spinal nerves that have exited are considered part of the peritheral nervous system.
What is a spinal nerve?
They are paralell bundles of axons of mixed nerve fibres (sensory and motor) encased in connective tissue. They exist briefly as they exit the vertebral column through intervertebral foramen.
What two bundles do spinal nerves divide into after they have exited the vertebral column?
Dorsal and ventral ramus.
What is the dorsal root ganglion?
A collection of cell bodies of sensory nerves found in the dorsal root of a spinal nerve.
How many pairs of spinal nerves are there?
31 pairs.
What structure do multiple vertebral foramen create?
Spinal canal
Where does the spinal cord start and end?
Starts - inferior margin of medulla oblongata
End - conus medullaris (L2 level)
How do spinal cord segments align with their corresponding vertebrae?
Most do not align at the same level.
What nerve structure do long nerve roots from the lumbar, sacral and coccygeal regions create as they pass inferiorly and exit through their respective foramina?
Cauda equina.
Where do the first pair (C1) of spinal nerves exit?
Intervertebral foramina between the occipital bone and atlas.
What is the relationship of the spinal nerves to the cervical and thoracic vertebrae?
C1-C7 exit above their corresponding vertebrae. C8 exits below the C7 vertebrae. T1- L5 exit below their corresponding vertebrae.
How many cervical, thoracic, lumbar, sacral and coccyx vertebrae are there?
7,12,5,5 and 4
Where do spinal nerves S1-S4 exit?
Via 4 pairs of sacral foramina.
How do S5 and Co1 exit?
Via the sacral hiatus.
What does the posterior/ dorsal rami supply? What size is it?
Deep muscles and skin of dorsal trunk. It is small.