MSK: nerves, dermotomes and myotomes Flashcards Preview

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Flashcards in MSK: nerves, dermotomes and myotomes Deck (48)
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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.


What does the anterior/ ventral rami supply? What size is it?

Muscles and skin of the upper and lower limbs and lateral and ventral trunk. It is large.


What is the meningeal branches of spinal roots? What do they innervate? What does it not innervate?

They branch off the spinal nerve before it splits into dorsal and ventral rami. They re-enter the spinal canal through the intervertebral foramina and innervate the facet joints, the anulus fibrosus of the intervertebral disc, blood vessels and the ligaments and periosteum of the spinal canal, carrying pain sensation. The nucleus pulposus of the intervertebral disk has no pain innervation.


What are rami comunicantes?

A communicating branch between the spinal nerve and the sympathetic trunk.


The dorsal/ posterior rami divide into which branches to supply the skin and muscle of the back in a tidy, segmental manner?

Medial and lateral branches.


How does the innervation of skin and muscles by the anterior rami differ from that of the posterior rami?

They innervate skin and muscles in a much more complicated way due to their entry into plexi which supply the upper and lower limbs (e.g. brachial plexus of upper limbs and lumbo-sacral plexus of lower limbs).


Which spinal segments supply the lower limb?



Which anterior rami form the lumbar plexus?



Which anterior rami form the sacral plexus?



What is the lumbosacral trunk?

It is the anterior division of the fifth and part of the fourth lumbar nerve which appears at the medial margin of the psoas major and runs downward over the pelvic brim to join the first sacral nerve. It therefore joins the lumbar and sacral plexi together.


Near which muscle/s is the lumbar plexus anatomically positioned?

It forms behind the psoas muscles and appears medially and laterally to psoas major.


What is a myotome?

A group of muscles supplied by a single spinal nerve (or spinal nerve root).