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DPT 736 Neuroanatomy > PNS Clinical Considerations > Flashcards

Flashcards in PNS Clinical Considerations Deck (11)
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Class 1 Neurapraxia

-affected axons are demyelinated
-remyelination and conduction eventually resumes following removal of compression
-conduction is usually normal because the axon has not been disrupted
-usually temporary


Class 2 Axonotmesis

-crush injury
-axonal disruption at the site of injury
-wallerian degeneration: lose part of axon and myelin distal to injury
-preservation of endoneurial tubes so this may mean nerves are able to be regenerated: helps growing nerve sprout to reach their previous terminals and hopefully a functional connection
-regenerate 1 mm/day and 1 in in a month so less distance to travel means faster healing


Class 3 Neurotmesis

-severance of all neural and connective tissue components
-little hope of functional recovery without skilled surgery
-regenerating axons may enter inappropriate endoneurial tubes
-complex regional pain syndromes, severe pain, changes in sensation and skin
-look up to clarifyl


Nerve Regeneration in PNS

-clean cut: nerve sprouting occurs within a few hours
-crush or tear: sprouting may delay for a week due to retrograde degeneration
-successful regeneration requires that the fibers make contact
-failure to re-approximate these fibers may lead to formation of a neuroma
-no clear path means aberrant, abnormal growth
-step 1: proximal stump-multiple growth cones branch out
-step 2: simultaneously distal Schwann cells send out processes (filopodia) toward proximal stump and exert traction pull on the growth cones
-step 3: growth cones are mitogenic to Schwann cells
-filopodia recognize Schwann cells previously occupied by axons of a similar kind
-muscle atrophies and remains viable for 2 years
-during this time it is undergoing fibrosis: 30% atrophy in first month; 50-60% by 2 months; 60-80% by 4 months (stabilizes)
-functional re-innervation diminishes if the axon does not reach endplate within 12 mo of denervation


Nerve Regeneration in CNS

-distal degeneration occurs in a similar manner to the PNS
-slower clearance of debris by microglial cells and monocytes
-debris can be identified up to 6 months after an injury, whereas it is gone in 6 days in the PNS
-chromatolysis (change in cell body) is rare
-general rule = large scale neuron death, survivors are atrophied with permanent isolation from synaptic contacts
-transneuronal atrophy: CNS neurons have trophic affect upon each other, helper molecules help nerve make connections with neighbors
-small CNS lesion: neuronal debris replaced by glial scar tissue-primarily astrocytes
-large CNS lesion: scar tissue causes region to wall off and form cystic cavity containing CSF and blood
-neurons in CNS of humans do not regenerate axons, or at least do not do so effectively
-injured motor and sensory pathways do not re-establish their original connections
-regenerate only a few mm at most
-deterrents to spontaneous regeneration: obstruction by glial scar tissue, growth inhibition byproducts of the broken down oligodendorcytes


Ulnar Nerve Palsy

-elbow, wrist, brachial plexus, hand atrophy
-stimulate nerve and try to get them to move hand


Erb's Palsy

-pulling on baby to get out of birth canal may lead to shoulder dystocia
-stretching of brachial plexus-difficult time delivering shoulder during birth --> traction to get out --> stretched plexus --> paralysis of 1 arm usually affects C5, loos of fx of biceps, deltoid, brachialis --> IR --> inhibits flexion and supination


Hand Palsy

-wrist drop (radial palsy)
-preachers hand (median palsy)
-ulnar claw (ulnar palsy)
-simian hand (median and ulnar palsy)


Myasthenia Gravis

-severe muscle weakness
-immune system produces antibodies which bind to ACH receptors interfering with the normal action of ACH: autoimmune disease
-muscles most affected are those supplied by cranial nerves: face, mouth, eyes and limbs, especially proximal
-often see optic deficits
-swallowing and respiratory weakness may be life threatening
-anti ACHesterase drugs


Nerve Root Compression

-most frequently occurs where spine is most mobile (cervical and lumbar) either by spondylosis or HNP
-pain perceived/produced in myotome, sclerotome, and/or dermatome distributions
-dermatome: paresthesias, sensory loss
-myotome: motor weakness, loss of a tendon reflex
-discs degenerate as you age and sometimes inner part will come out and press on nerve root -->pain/weakness in dermatome, myotome, sclerotome


Guillain Barre Syndrome

-leg weakness noted first
-may be precipitated by respiratory infection, gastric infection, surgery, immunization
-immune system attacks body
-can be induced by a flu shot