Session 4 - Dermatomes Flashcards
What are embryonic precursors of skin and muscle known as?
Dermamyotomes
From what do dermamyotomes arise?
Somites
What do dermamyotomes differentiate into?
Dermis (dermatome) and muscle (myotome)
What does a spinal segmental nerve comprise of?
Dorsal roots (sensory or afferent) Ventral roots - efferent Efferent can be - Motor to skeletal muscle - Autonomic to smooth muscle and glands
What happens as the mixed spinal nerve emerges through intervertebral foramen?
It divides into dorsal and ventral ramus
What is a dermatome?
An area of skin supplied by a single spinal nerve
What is a myotome?
Group of muscles innvervated by a single spinal nerve
What is the cutaneous distribution of a peripheral nerve?
An area of skin a peripheral nerve innervates - it is NOT a dermatome
What is a motor unit?
made up of a motor neuron and the skeletal muscle fibers innervated by that axon
What is the nerve supply root to the lower limb?
Lumbar and Sacral spinal segments
L1 - L4
L4 - S4
Describe the lumbar plexus
Forms behind the psoas major muscle
Nerves emerge either medial or lateral to the borders of the psoas major muscle
What nerves emerge lateral to the psoas major muscle in the lumbar plexus?
The femoral (L2-L4)
•Iliohypogastric
•Ilioinguinal
•Lateral cutaneous nerve of the thigh
What nerves emerge medial to psoas major muscle?
- The obturator nerve
* The lumbosacral trunk
What is the sacral plexus composed of?
Lumbosacral trunk (Half of L4 and all L5) Sacral spinal segmental out flow (S1-S4)
Where does the sacral plexus form?
Plexus forms within the pelvic cavity
• Plexus lies in relation to piriformis
