Peripheral Nerve system disorders Flashcards
what is a peripheral nerve
many bundles of nerve fibres
motor and sensory
what is the structure of the peripheral nerve - epineurium
dense CT surrounds nerve
binds bundes (fascicles) togethe
what is the structure of the peripheral nerve - perineurium
surrounds bunches of axons + endoneurium sheath
nerve bundle = fascicle (CT around each bundle with common destination)
what is the structure of the peripheral nerve - enoneurium
delicate CT surrounds each axon
important for nerve fibre regeneration
describe neuropraxia
blocked nerve conduction
transient = rapid recovery
cold, ischaemia, tourniquet, saturday night palsy
decribe axonotmesis
axon + myelin sheath interrupted but endoneurium/nerve sheath intact
axon transmission interrupted
nerve crush, stretch injury
describe neurotmesis
axon and nerve sheath interrupted
long term partial/complete loss of motor/sensory
nerve transection
what are the 2 segments of PNS repair and the 4 series of changes
proximal (attached cell body) vs distal
cell body
proximal axon
distal axon
target muscle
describe the proximal changes
chromatolysis = cell body wells, nucleus moves to eccentric position, rER fragments (breakdown Nissl bodies)
metabolic switch = from secretory to regenerating phase
describe the distal changes
synatpic/NMJ stripping
wallerian degen of distal aon
myelin breakdown => mac clear debris
muscle atrophy
if endoneurium intact = good chance of recovery
what’s a nissl body
clump of ER
what happens to chances of recovery if endoneurium is intact
good chance of recovery
what are the 4 steps for pn injury repair
- proximal axon sprouts
- axon sprouts find way to endoneurium tube schwann cells
- tube guides axonal growth
- complete recovery if possible
what can happen without proper innervation
muscles can atrophy
what happens when end of damaged nerve cells aren’t aligned
no repair
tangled axons form neuroma/glioma
what are overall factors that affect nerve repair outcomes
type of injury
restoring contact with target muscle in periphery
proximal vs distal injury
age
what is a motor unit
basic unit of motor function
a motor neuron + group of muscle fibres it innervates
significance of motor unit
depends on dexterity of mvm + mass body part to be moved
smaller units recruited first, then larger units as muscle force increases
what are the 3 disease targets of the motor unit
cell body (MN disease), can affect CNS + PNS
axon: peripheral neuropathies
nmj: myasthenia gravis, botulism
what are the symptoms of peripheral neuropathy
motor + sensory axons are bundles together => sensory + motor functions affected
- Pos symptoms = numbness, tingling, pins/needles, hyperexcitability
- neg symptoms = weakness, loss of tendon reflexes (fasciculations and atrophy are rare), loss sensation eg pain + temp (prominent distally = glove and stocking)
demyelinating vs axonal peripheral neuropathy classifications
demyelinating: conduction velocity of ap slows + conduction synchrony between diff axons of nerve is list. linked to mutations in genes that code for myelin proteins
axonal: linked to cellular proteins eg neurofilaments, microtubule motors (kinesin), cytosolic enzymes etc
what is acute neuropathy - guillain-barre syndrome
often follows resp infection or infectious diarrhea, tho illness not always necessary
mild or sever => ventilator
spreading paralysis
autoimmune attack on peripheral nerved by circulating antibodies
pathogenesis of guillain barre syndrome
pathogens trigger humoral immune = autoimmune response through molecular mimicry
antibodies produced cross-react with peripheral nerve proteins (for myelin)
activates membrane attack complex
results in myelin detachment, dec Na+ channels -> nerve dysfunction + symptoms
describe chronic neuropathy - diabetic peripheral neuropathy
- capillary damage = compromised vasculature
- nerves dont get nutrient supply
- impaired transmission of sensory input
- loss sensation + circulation => increased risk infection
what are the 2 categories of disease at NMJ
block ntsm action (myasthenia gravis)
block ntsm release (botulism)
describe myasthenia gravis
- weakness, fatigue of muscle groups (worse on sustained/repeated exertion)
- autoimmune block of ACh receptors at nmj
- autoimmune antibodies produced by muscle
- reduced no. functional receptors
- treat w/acetylcholinesterase inhibitors -> inc ACh availability
describe botulism
botulinum toxin produced by clostridium botulinum bacteria
blocks vesicle binding to membrane -> blocks ACh release at nmj => muscle paralysis, dec sweat gland stim
therapeutic = spasticity, painful muscle spasms, wrinkles, reduce sweating
infection => respiratory paralysis & death
