3.14 Ch. 12.1 Flashcards
peripheral nerves consist of
parallel bundles of axons surrounded by three connective tissue sheaths
3 connective tissue sheaths of peripheral nerves
- endoneurium
- perineurium
- epineurium
endoneurium
Separates individual axons.
perineurium
Surrounds fascicles
epineurium
Encloses the entire nerve trunk
peripheral nerves supply
- visceral
- somatic structures
somatic peripheral nerves
usually mixed and include sensory, autonomic, and motor axons
cutaneous branches supply
- skin
- subcutaneous tissues
muscular branches supply
- muscles
- tendons
- joints
peripheral axon classification
- speed of conduction
- diameter
nerve plexuses formed by
anterior rami
What are the plexuses?
- cervical
- brachial
- lumbar
- sacral
cervical plexus innervates
- anterior neck muscles
- diaphragm
cervical plexus provides cutaneous sensory info from
posterior scalp to the clavicle
brachial plexus innervates
entire UE
lumbar plexus innervates
skin and muscles of anterior and medial thigh
sacral plexus innervates
posterior thigh and most of the leg and foot
What type of axons does the sacral plexus contain?
parasympathetic
How does movement affect nerve health?
promotes blood flow through the nerves and flow of axoplasm through the axons
How does movement affect the axoplasm?
causes it to thin and flow more easily
Where do motor axons synapse with motor fibers?
at NMJ
summation of action potentials and NMJ
no summation needed to depolarize the postsynaptic membrane
depolarization of motor axon in a normal motor unit
every depolarization releases sufficient ACh to initiat AP in the innervated muscle fibers
Signs of peripheral nerve damage
- sensory
- autonomic
- motor
**All signs are in a peripheral nerve distribution.
sensory changes in peripheral nerves
decreased or lost sensation
abnormal sensations
- hyperalgesia
- dysesthesia
- paresthesia
- allodynia
autonomic changes: signs depend on
pattern of axonal dysfunction
autonomic changes: single nerve dysfunction signs
usually observed only if the nerve is completely severed
autonomic changes: many nerves
problems include:
difficulty regulating
- BP
- HR
- sweating
- bowel/bladder functions
- impotence
motor changes: signs of peripheral nerve damage
paresis
paralysis
EMG activity for denervated muscles
recordings show no activity for +/- 1 week after injury
What happens to muscle fibers with peripheral nerve damage?
- muscle atrophy progresses rapidly
- fibers develop a sensitivity to ACh along muscle membrane (get fibrillation)
fibrillation and lesions
fibs are not diagnostic of a specific lesion
When do trophic changes begin in denervated tissues?
when nerve supply is interrupted
appearance of tissues with trophic changes
- muscles atrophy
- skin becomes shiny
- nails become brittle
- subcutaneous tissues thicken
- ulceration
trophic changes and neurological/blood flow issues
- poor healing
- neurogenic joint damage
- blood supply changes
- loss of sensation
- lack of movement
