Cerebral Cortex Flashcards
What is MS?
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 the main symptoms of MS?
Blurred vision, fatigue, difficulty walking, numbness or tingling (paraesthesia) in different parts of the body, muscle stiffness and spasms
What is an 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 fast response is M wave. Takes around 8 ms.
How are M waves recorded?
electromyography (EMG)
What is H reflex?
Stimulus causes activation of sensory fibres. The action potentials can travel along the 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. Takes around 30 ms.
What is an 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. 30 ms, not a reflex.
Define orthodromic and antidromic
Orthodromic - travelling in the normal direction in a nerve fibre
Antidromic - travelling in the opposite direction to that normal in a nerve fibre
What is a motor evoked potential?
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.
How is cortical stimulation created?
Transcranial magnetic stimulation (TMS)
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 can be calculated using the formula: (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.
What is central motor conduction time (CMCT)?
TMCT - PMCT
How does MS affect TMCT and PMCT?
TMCT determined from brain stimulation - will be delayed. Longer than usual MEP latency. Problem could be in UMN or LMN.
PMCT determined from peripheral nerve stimulation. F wave latency will be normal as no issue with LMN. PMCT normal.
