Nerves Flashcards
Define Motor unit
An efferent neurone and all the muscle fibres it innervates
If a nerve is damaged through traumatic injury or disorder of NS, the muscle group innervated by the nerve will cease to function. Loss of the posterior forearm muscle group leads to what?
Wrist-drop
In what 2 ways do somatic nerves emerge from the spinal cord?
Sensory dorsal (posterior) nerve root
Motor ventral (anterior) nerve root
Sensory dorsal (posterior) nerve root and motor ventral (anterior) nerve root join to form what? Where do they join
They form a mixed spinal nerve, in the intervetebral foramen
The mixed spinal nerve exits the intevertebral foramen laterally and branches into what?
A dorsal and a ventral ramus
What does the ventral ramus supply?
Skin, muscles and bones of anterolateral sides of the trunk, and the entire upper body and lower limbs
What does the dorsal ramus supply?
Posterior side of trunk only
Do dorsal rami supply the limbs?
No
What does the dorsal root carry?
Afferent fibres
What does the ventral root carry?
Motor fibres
What does the mixed spinal nerve carry?
Motor and sensory fibres
What does the dorsal and ventral rami carry
Motor and sensory fibres
Define cutaneous iinnervation
The area of skin which is supplied by a specific cutaneous nerve.
It contains fibres from several spinal nerves
Define dermatome
An area of skin served by a single spinal nerve - arising from only one level of the spinal cord
In which part of the body are cutaneous nerves and dermatomes the same?
Thorax and abdomen
In which part of the body are cutaneous nerves and dermatomes different, and why?
In the limbs. This is due to plexus formation of spinal nerves.
During development, limbs are “pulled out” from the trunk
Why is it important for clinicians to understand dermatomal distribution?
To identify the cutaneous nerve involved in a deficit, and pinpoint the exact single spinal nerve that is responsible for non-function
Partial overlap of adjacent dermatome means if nerve supply to one dermatome is lost, what happens?
A reduction in sensitivity of the skin of that dermatome, but not complete loss.
Generally, nerve damage nearer the spinal cord involves what?
What about peripheral injuries?
Individual nerve roots and dermatomes
Peripheral - more than one nerve root and dermatome
What joint occurs in the midline of the trunk at dermatome T2
Sternocostal joint
What surface features of the body are found at dermatome T4
Nipples
What surface feature of the body marks the dermatome T10?
Navel
In what region of the body is the dermatome L1 found?
Groin
The dermatomes of the thoracic trunk at the sternomanubrial joint jum from C5, just above the joint, directly to T2, just below the joint.
Where have dermatomes C5-T1 been diverted?
Posterior - neck and shoulders
Define myelin
A fatty white substance that surrounds the axon of some nerve cells, forming an electrically insulating layer
What secretes myelin?
Schwann cells
Define endoneurium
A layer of delicate connective tissue around the myelin sheath of each nerve fibre
Each fascicle lies in a protective sheath called what?
Perineurium
In sufficiently large nerves, multiple fascicles may be bundled in a sheath called what? What are their features
Epineurium
Each has a blood supply and fatty tissue
What surrounds:
Individual axons
Nerve fascicles
A nerve?
Individual axons - endoneurium
Nerve fascicles - perineurium
A nerve - epineurium
