MSK4: Dermatomes And Myotomes Flashcards
Describe the length of the spinal cord
Spinal cord travels from medulla of brain to conus medullaris under vertebral cord
Much shorter than column
Define a Dermatomes and describe their development
Area of skin supplied by a single sensory nerve fibre from a single spinal nerve
Can be overlap between adjacent Dermatomes so can be supplied by three successive sensory nerves (one from either side)
Describe how Dermatomes are useful clinically
Used to pinpoint areas of the skin with disturbed function
Predicts nerves and spinal segments which I may be affected by injury
Anaesthetise specific segments
Why is there an overlap of sensory innervation? Why useful clinically?
One from each side
Reduce probability of skin patches without natural sensory nerve supply. Anaesthesia would only occur if all three are damages together
Describe the lumbar plexus
Forms behind the psoas major muscle
Nerve emerge either side of the muscle
Supplies front of lower limb
Describe the sacral plexus
Lumbosacral trunk L4-S4 Sacral spinal segmental overflow Plexus ford within the pelvic cavity Supplies pelvic region, gluteal, perineal and lower limb
What is cutaneous innervation
Sensory divisions of the brachial and lumbar plexus
Not Dermatomes
They nerve fibres leave the spinal cord, through the dorsal spinal roots and are redistributed by the nerve plexus: peripheral nerves
Cutaneous distribution of a peripheral nerve is the area of skin the nerve innervates, which can be from several spinal roots
Describe a myotome
A muscle innervates from a single Spinal root. Most get innervates from more than one: multiple myotome said,
What is a motor unit
Muscle fibres innervated by a single motor nerve fibre
The smaller the motor unit the more presice the movement e,g eyes (5/6)
Describe the composition of a spinal nerve
Cylindrical made of millions of nerve cell bodies (grey mater)
Neuronal axons (white mater)
They are ascending (afferent) descending (efferent) or crossing over
