Flashcards in MSK: nerves, dermotomes and myotomes Deck (48):
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?
What structure do multiple vertebral foramen create?
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?
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).
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 is the difference between a myotome and motor unit?
A motor unit is a motor neuron and the skeletal muscle fibres it innervates.Many motor units are innervated by a single spinal nerve. It It is A myotome is muscle innervated by a single spinal nerve.
What is an axial line?
A junction between two dermatomes supplied from discontinuous spinal levels. Limbs have anterior and posterior axial lines.
What are pre-axial and post-axial compartments of limbs?
Pre-axial compartments are compartments of limbs in front of the axial line of the limb and post-axial behind. E.g. anterior and posterior compartments of the forearm. Therefore these compartments are separated by the axial line.
Which structures mark the boundaries of the pre-axial and post-axial comparments of limbs?
They are marked by veins. E.g. the basilic and cephalic veins in the upper limb and the great saphenous and small saphenous veins in the lower limbs.
What are peritheral nerve territories? How do they differ from dermatomes?
These are areas of the skin supplied by the peripheral nerves. These are not the same as dermatomes because within each peripheral nerve may be fibres from more than one spinal nerve.
What is notable about the distribution of viral infection? Give an example of a virus.
Viral infection almost always affects the skin of a single dermatome. For example in the reactivation of Varicella zoster (chickenpox called shingles) the virus travels through a cutaneous nerve and remains dormant in a dorsal root ganglion after chickenpox. When host is 'immunosupressed', VZV reactivates and travels through peripheral nerve to the skin of a single dermatome.
What dermatome crosses the nipple?
What dermatome crosses the groin?
What dermatome crosses the umbilicus?
How is the neural level of a spinal injury determined?
It is defined as the lowest level of full SENSATION and FUNCTION.
What myotomes are involved in shoulder:
2. C6, C7, (C8).
Which myotomes are involved in elbow:
1. C5 and C6
2. C7 and C8.
Which myotomes are involved in wrist:
1. C7 and C8
Which myotomes are involved in wrist:
1. C6 and C7
2. C6 and C7
Which myotomes are involved in finger: