Peripheral Nerve system disorders

Question 1

what is a peripheral nerve

Answer 1

many bundles of nerve fibres
motor and sensory

Question 2

what is the structure of the peripheral nerve - epineurium

Answer 2

dense CT surrounds nerve
binds bundes (fascicles) togethe

Question 3

what is the structure of the peripheral nerve - perineurium

Answer 3

surrounds bunches of axons + endoneurium sheath
nerve bundle = fascicle (CT around each bundle with common destination)

Question 4

what is the structure of the peripheral nerve - enoneurium

Answer 4

delicate CT surrounds each axon
important for nerve fibre regeneration

Question 5

describe neuropraxia

Answer 5

blocked nerve conduction
transient = rapid recovery
cold, ischaemia, tourniquet, saturday night palsy

Question 6

decribe axonotmesis

Answer 6

axon + myelin sheath interrupted but endoneurium/nerve sheath intact
axon transmission interrupted
nerve crush, stretch injury

Question 7

describe neurotmesis

Answer 7

axon and nerve sheath interrupted
long term partial/complete loss of motor/sensory
nerve transection

Question 8

what are the 2 segments of PNS repair and the 4 series of changes

Answer 8

proximal (attached cell body) vs distal
cell body
proximal axon
distal axon
target muscle

Question 9

describe the proximal changes

Answer 9

chromatolysis = cell body wells, nucleus moves to eccentric position, rER fragments (breakdown Nissl bodies)
metabolic switch = from secretory to regenerating phase

Question 10

describe the distal changes

Answer 10

synatpic/NMJ stripping
wallerian degen of distal aon
myelin breakdown => mac clear debris
muscle atrophy
if endoneurium intact = good chance of recovery

Question 11

what’s a nissl body

Answer 11

clump of ER

Question 12

what happens to chances of recovery if endoneurium is intact

Answer 12

good chance of recovery

Question 13

what are the 4 steps for pn injury repair

Answer 13

1. proximal axon sprouts
2. axon sprouts find way to endoneurium tube schwann cells
3. tube guides axonal growth
4. complete recovery if possible

Question 14

what can happen without proper innervation

Answer 14

muscles can atrophy

Question 15

what happens when end of damaged nerve cells aren’t aligned

Answer 15

no repair
tangled axons form neuroma/glioma

Question 16

what are overall factors that affect nerve repair outcomes

Answer 16

type of injury
restoring contact with target muscle in periphery
proximal vs distal injury
age

Question 17

what is a motor unit

Answer 17

basic unit of motor function
a motor neuron + group of muscle fibres it innervates

Question 18

significance of motor unit

Answer 18

depends on dexterity of mvm + mass body part to be moved
smaller units recruited first, then larger units as muscle force increases

Question 19

what are the 3 disease targets of the motor unit

Answer 19

cell body (MN disease), can affect CNS + PNS
axon: peripheral neuropathies
nmj: myasthenia gravis, botulism

Question 20

what are the symptoms of peripheral neuropathy

Answer 20

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)

Question 21

demyelinating vs axonal peripheral neuropathy classifications

Answer 21

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

Question 22

what is acute neuropathy - guillain-barre syndrome

Answer 22

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

Question 23

pathogenesis of guillain barre syndrome

Answer 23

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

Question 24

describe chronic neuropathy - diabetic peripheral neuropathy

Answer 24

• capillary damage = compromised vasculature
• nerves dont get nutrient supply
• impaired transmission of sensory input
• loss sensation + circulation => increased risk infection

Question 25

what are the 2 categories of disease at NMJ

Answer 25

block ntsm action (myasthenia gravis)
block ntsm release (botulism)

Question 26

describe myasthenia gravis

Answer 26

• 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

Question 27

describe botulism

Answer 27

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