Cerebral Cortex Tutorial

Question 1

What is MS?

Answer 1

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

Question 2

What are the main symptoms of MS?

Answer 2

1. Blurred vision
2. fatigue
3. difficulty walking
4. numbness or tingling (paraesthesia) in different parts of the body
5. muscle stiffness
6. spasms

Question 3

What can an electrical stimulus of an appropriate intensity to a peripheral nerve activate?

Answer 3

sensory and motor axons

Question 4

What does activation of the motor axons cause?

Answer 4

action potentials to travel along the nerve to cause muscle contraction, a twitch

Question 5

How is this recorded?

Answer 5

with electromyography (EMG)

Question 6

What is the fast response called?

Answer 6

M (motor)-wave

Question 7

What type of activation is an M wave?

Answer 7

purely motor activation from stimulus

Question 8

What is an M and H wave in relation to each other?

Answer 8

1. Response direct activation of motor axons
2. Then delay as sensory axons send signal back to spinal cord which activate motor neurone, then motor neurone impulse sent back down nerve to muscle causing second response H wave

Question 9

What type of activation is a H wave?

Answer 9

sensory and the motor axon activation

Question 10

Can the same stimulus cause activation of the sensory axons (subject feels stimulus)?

Answer 10

Yes

Question 11

Describe a reflex action

Answer 11

1. The action potentials can travel along the nerve to the spinal cord
2. These can then cause the lower motor neurons in the spinal cord to become activated
3. Action potentials in the motor axons can travel along the motor neuron to the muscle where they cause muscle contraction, a twitch
4. This is a reflex activation of the muscle

Question 12

What can a large electrical stimulus cause?

Answer 12

activation of the motor axons to conduct antidromically

Question 13

What is the process of these action potentials?

Answer 13

1. These action potentials travel along the motor nerve to the spinal cord (i.e. in the opposite way to normal)
2. These can then cause the lower motor neurons in the spinal cord to become activated
3. Action potentials in the motor axons can travel along the motor neuron to the muscle where they cause muscle contraction, a twitch

Question 14

Is the later response, F wave a reflex?

Answer 14

No

Question 15

Why is a F wave different?

Answer 15

1. Travel to spinal cord rather than muscle initially
2. Then action potentials turn around in motor neurone cell body in spinal cord and travel back down in normal way towards the muscle and generate a late response

Question 16

What is the difference between F and H wave?

Answer 16

F wave and H wave muscle responses but brought about by different mechanisms, H reflex is sensory and then motor and F wave is motor and motor

Question 17

What is orthodromic peripheral nerve stimulation? What is it for sensory and motor?

Answer 17

travelling in the normal direction in a nerve fibre: orthodromic for sensory is periphery to spinal cord and for motor is spinal cord to muscle

Question 18

What is antidromic peripheral nerve stimulation?

Answer 18

travelling in the opposite direction to that normal in a nerve fibre

Question 19

What happens if stimulus is turned high?

Answer 19

then get F wave, dependent on stimulus intensity on nerve

Question 20

What happens if its low intensity?

Answer 20

only sensory neurones which cause reflex activation and H wave

Question 21

What happens if you turn up the intensity?

Answer 21

1. If turn up, sensory and motor neurone conduct in normal way (orthodromic)
2. If high then antidromic

Question 22

How do you have cortical motor stimulation?

Answer 22

using transcranial magnetic stimulation (TMS)

Question 23

What does the activation of the upper motor neurons cause?

Answer 23

action potentials to travel along the entire motor pathway (upper and lower motor neurons) to cause muscle contraction

Question 24

What is this EMG response?

Answer 24

known as a motor evoked potential (MEP)

Question 25

What is Total motor conduction time (TMCT)?

Answer 25

time from brain to muscle (MEP latency)

Question 26

What is Peripheral motor conduction time (PMCT)?

Answer 26

time from spinal cord to muscle along motor axon can be calculated using the formula

Question 27

What formula is used for PMCT?

Answer 27

PMCT = (M latency + F latency-1) /2

Question 28

Why is their a -1?

Answer 28

is the estimated time for the action potentials arriving at the lower motor neuron cell body to turn around

Question 29

How do you calculate Central motor conduction time (CMCT)?

Answer 29

TMCT - PMCT

Question 30

What is the effect of MS of these?

Answer 30

1. Brain stimulation - longer than usual MEP latency
2. Problem along upper motor neurons, lower motor neurons or both – we don’t know!
3. Total motor conduction time - delayed
4. Peripheral nerve stimulation – normal F wave latency
5. No issue with lower motor neurons.
6. Peripheral motor conduction time - normal
7. Problem is in CNS!