Multiple Sclerosis Flashcards
What is MS
An autoimmune disease which results in the destruction of myelin sheath from neurons in the CNS
Symptoms
Fatigue,blurred vision,muscle spasms,feeling dizzy and off balance
How can brain and nerve stimulation confirm the central nature of MS
MRI: helps visualize lesions in the brain and spinal chord that indicate MS, the presence of thee supports diagnosis of and confirms central involvement of disease
Evoked potentials: these tests measure the electrical activity in the brain in response to stimuli. Delayed responses indicate disruption to CNS pathways
TMS:non invasive technique that asses functional integrity of neural pathways in the brain. Can reveal disruptions in motor pathways supporting diagnosis of MS
M wave
electrical signal leading to muscle twitch caused by stimulation of peripheral nerve motor axons
For orthodomic motor activation providing info about nerve to muscle stimulation. Noted as fasted time 8ms
F wave
twitch resulting from large stimulus causing antidromic activation of motor axons (i.e. opposite way to normal)
Observing antidromic stimulation and assess integrity of the entire nervous pathway for example peripheral root damage
Not a reflex
These travel along the motor nerve to spinal cord which activates lower motor neurons to be activated. Causes twitch
H wave
reflex activation of the muscle elicited by a stimulus strong enough to feel (sensory neurons activated)
Occur after 30ms as do h reflexes which are significant for orthodomic sensory activation
Action potentials from spinal cord activate lower motor neuron in spine which travel to motor neuron in muscle causing twitch
Which is faster
M is faster than H
Antidromic vs orthodomic
antidromic = travelling opposite way to usual in a nerve fibre, orthodromic = normal way
what is an MEP?
motor evoked potential → activation of upper motor neurons e.g. by TMS causes action potentials to travel along the entire motor pathway causing muscle contraction
what is TMCT?
total motor conduction time → time for signal to travel from brain to muscle (MEP latency)
what is PMCT?
peripheral motor conduction time → time from spinal cord to muscle along motor axon
formula for PMCT?
M-wave latency + F-wave latency - 1) / 2
M = muscle → partly to spinal cord. F = rest of way to spinal cord → turn around (hence - 1) → lower motor → muscle
what is CMCT and its formula?
central motor conduction time (brain to spinal cord) → TMCT – PMCT
effect of MS on these?
Brain stimulation-TMCT slower (longer MEP latency),
Peripheral nerve stimulation-F wave unaffected (PMCT normal)
