Lecture - Dermatomes and Segmental Innervation Flashcards
Where do anterior and posterior nerve roots combine to form a mixed spinal nerve?
At the intervertebral foramina
Which nerve roots are sensory and which are motor?
Sensory - posterior
Motor - anterior
Through what do spinal nerves leave the vertebral canal?
The intervertebral foramina
After leaving the vertebral canal, what happens to spinal nerves?
They split into:
- Posterior rami
- Anterior rami
What areas are supplied by posterior rami of spinal nerves?
Vertebrae, deep back muscles and overlying skin
What areas are supplied by anterior rami?
Give an example
Everywhere except the vertebrae, deep back muscles and overlying skin, both motor and sensory
E.g. - upper limb supplied by anterior rami of C5 to T1 inclusive
Define a dermatome
The area of skin supplied by sensory nerve fibres from a single spinal nerve
How does the adult dermatome map result?
As the limb buds grow and rotate during development, the nerves are “dragged” with the skin.
Why does injury to a single spinal nerve usually not result in loss of sensation over the whole dermatomal area?
The dermatomes overlap
Where do the dermatomes not overlap?
Either side of the axial line, as the contiguous areas are not supplied by contiguous nerves
What is a myotome?
A muscle/group of muscles innervated by a single spinal nerve root
What is a “motor unit”?
The muscle fibre(s) innervated by a single nerve fibre
Where is the lumbar plexus located?
Within psoas major muscle, anterior to transverse processes of the lumbar vertebrae.
What forms the lumbar plexus?
Anterior rami of the lumbar spinal nerves (L1 - 4) and some contribution from T12
How many peripheral nerves result from the lumbar plexus?
6
