Cortical organisation and function tutorial- Multiple Sclerosis Flashcards
What is MS?
MS is an autoimmune disorder which results in the loss of myelin from neurons of the central nervous system, i.e. the brain and spinal cord.
What are some of the main symptoms of MS?
Blurred vision, fatigue, difficulty walking, numbness or tingling (paraesthesia) in different parts of the body, muscle stiffness and spasms
Peripheral nerve stimulation - basics
What is M-wave
An electrical stimulus of an appropriate intensity to a peripheral nerve can activate sensory and motor axons.
The activation of the motor axons can cause action potentials to travel along the nerve to cause muscle contraction, a twitch. This can be recorded with electromyography (EMG).
This fast response is called the M (motor)-wave.
What is an H-reflex (wave)
An electrical stimulus of an appropriate intensity to a peripheral nerve can activate sensory and motor axons.
The action potentials can travel along the sensory nerve to the spinal cord. These can then cause the lower motor neurons in the spinal cord to become activated. Action potentials in the motor axons can travel along the motor neuron to the muscle where they cause muscle contraction, a twitch. This is a reflex activation of the muscle.
This later response is called the H-reflex
What is F-wave?
A large electrical stimulus can cause activation of the motor axons to conduct antidromically
These action potentials travel along the motor nerve to the spinal cord (i.e. in the opposite way to normal). These can then cause the lower motor neurons in the spinal cord to become activated. Action potentials in the motor axons can travel along the motor neuron to the muscle where they cause muscle contraction, a twitch.
This later response is called the F-wave, as it was first demonstrated in the foot. It is not a reflex.
What does orthodromic and antidromic mean?
Orthodromic - travelling in the normal direction in a nerve fibre
Antidromic - travelling in the opposite direction to that normal in a nerve fibre
What happens on cortical motor stimulation by transcranial magnetic stimulation
The activation of the upper motor neurons causes action potentials to travel along the entire motor pathway (upper and lower motor neurons) to cause muscle contraction. This EMG response is known as a motor evoked potential (MEP).
What is total motor conduction time?
time from brain to muscle (MEP latency
What is peripheral motor conduction time?
time from spinal cord to muscle along motor axon
How is PMCT calculated?
PMCT = (M latency + F latency-1) /2
The -1 is the estimated time for the action potentials arriving at the lower motor neuron cell body to turn around
How is central motor conduction time calculated?
TMCT - PMCT
How do we know that the problem in MS lies in the CNS?
