Dermatomes, myotomes, segmental innervation of the limbs Flashcards
what does the sclerotome form and where is it found
vertebrae and ribs
found ventrally
what does the dermatomyotome form and where is it found
dermis and muscle
dorsal
how does the DMT form
develop in association with a specific neural level of spinal cord
take nerve supply with them from neural tube as spinal segmental nerve
skin and muscle derived from a single dermamyotome have a common spinal nerve supply
spinal nerve roots
roots connect each spinal nerve to a segment of cord which is continuous
dorsal roots contain
afferent/ sensory nerve fibres only
dorsal root ganglion
cell bodies of the sensory neurons from the periphery
ventral roots contain
efferent/ motor and autonomic nerve fibres only
where does the spinal cord run through
vertrebral foramen which join to form the spinal canal
where do spinal nerves leave the spinal canal
intervetrebral foramina
where does the spinal cord start and end
inferior margin of medulla oblongata and ends at the conus medullaris at L2
where do the first pair of spinal nerves emerge
emerge between occipital bone and atlas (C1)
where do the cervical spinal nerves emerge
c1 - c7 exit above corresponding vertebrae
where does the c8 spinal nerve emerge
between c7 and t1
where do the T1-L5 spinal nerves emerge
below corresponding vertebrae
where do S1 - S4 exit
Via 4 pairs of sacral foramina
where does s5 and Co1 exit
sacral hiatus
what does the posterior/ dorsal ramus supply
deep muscles and skin of dorsal trunk
divides again into medial and lateral branches
supply skin of back in ‘tidy’ segmental manner
narrow strip of muscle/ skin in line with intervetrebral foramen
what does the anterior/ ventral ramus supply
muscles and skin of the upper and lower limbs and lateral and ventral trunk
enter the plexuses to supply the limbs
what is the meningeal branch supply
re-enters spinal canal through intervetrebral foramen
supplues vetebrae, ligaments, blood vessels and meningies
where does the brachial plexus supply
upper limb
where does the lumbo-sacral plexus supply
lower limb
axial line
junction of two dermatomes supplied from discontinuous spinal levels
they mark the centre of either the ventral or dorsal compartments of the limb
how do the upper limbs rotate
lateral rotation away from the pre-axial border
how do lower limbs rotate
medial rotation towards the pre-axial border
in the upper limb what marks the pre/post-axial border
cephalic vein
basilic vein
in the lower limb what marks the pre/post-axial border
long saphenous vein
short saphenous vein
peripheral nerve territories
these are the areas of the skin supplied by the peripheral nerves
- branches of brachial plexus in upper limb
- branches of lumbosacral plexus in lower limb
they often overlap sections of multiple dermatomes (consistent with their spinal nerve content)
What is the difference between a myotome and motor unit
A myotome is a group of muscles supplied by a spinal nerve (which contains multiple motor
neurons), whereas a motor unit is a single motor neuron and the skeletal muscle fibres it
innervates.
what does the C5 myotome do
shoulder abduction and external rotation
C6 myotome
elbow flexion / wrist extension / supination
c7 myotome
elbow extension / wrist flexion / pronation
c8 myotome
finger flexion / finger extension
t1 myotome
finger abduction and adduction
l2 myotome
hip flexion
l3 myotome
knee extension
l4 myotome
ankle dorsiflexion
l5 myotome
great toe extension
s1 myotome
ankle plantar-flexion
s2 myotome
great toe flexion
what is hiltons law
The nerves crossing a joint supply:
• The muscles acting on it
• The skin over the insertion of those muscles
• The joint itself
dermatome
A dermatome is an area of skin supplied by a single spinal nerve.
Why do the areas of skin that constitute the dermatomes often differ from those supplied by
the peripheral nerves?
A dermatome is an area of skin supplied by a single spinal nerve. A peripheral nerve,
however, often contains fibres from multiple spinal nerves.
In the limbs, the spinal nerve fibres are distributed via the brachial (upper limb) and
lumbosacral (lower limb) plexuses into multiple different peripheral nerves. Fibres from one
spinal nerve can enter multiple different peripheral nerves, and peripheral nerves can
contain fibres from multiple spinal nerves.
State four factors that contribute to the stability and mobility of the vertebral column
- The thickness and compressibility of the intervertebral discs
- The shape and orientation of the intervertebral facet joints
- The tone of the back muscles
- The resistance of the ligaments of the vertebral column.
