NMJ And Muscle Contraction

Question 1

What is a motor unit?

Answer 1

A single motor neurone and all the muscle fibres that it stimulates

Question 2

What are MEPPs?

Answer 2

Miniature end plate potential
At rest when individual vesicles get released
Shows that a vesicle has a discrete amount of acetylcholine

Question 3

Name 3 NMJ disorders

Answer 3

Lambert Eaton myasthenia syndrome = autoimmune, antibodies against VGCC (lung cancer)
Botulism = Ach cannot exocytose as calcium cannot Exeter pre synaptic
Myasthenia gravis = autoimmune, antibodies against nicotinic receptor

Question 4

Describe the structure on a muscle

Answer 4

Muscle fibres and endomysium form fascicles
Each fascicle surrounded by perimysium
Muscle = fascicles, blood vessel, nerves surrounded by exomysium

Question 5

Describe parts of the sarcomere

Answer 5

Z lines = lines of actin
A band = myosin and actin = DARK
I band = actin only = LIGHT
H zone = only myosin

Question 6

Describe skeletal muscle contraction

Answer 6

AP along t tubules
Dihydropiridine receptor open and touch ryanodine receptors in sarcoplasmic reticulum
Calcium binds to troponin and moves tropomyosin
Myosin heads bind to actin

Question 7

What happens to the parts of the sarcomere during contraction?

Answer 7

A band remains the same

H zone and I band gets smaller

Question 8

What are the 2 ways to take an EMG?

Answer 8

Extracellularly recording = both electrode are outside the muscle fibre and EMF recorded

Intrecellularly recording = one electrode in muscle and one outside, measure emf

Question 9

Define:
Twitch
Summation
Tetany

Answer 9

Twitch- basic response
Summation - stimulus is applied before the muscle relaxes and both add up
Tetany = frequency of stimulus increases, sustain contraction

Question 10

What diagnostic techniques can we use?

Answer 10

EMG = AP in skeletal muscle fibre
ECG = AP in cardiac muscle
EEG = AP from brain
CT scan = good for strokes as blood shows up really well
MRI = good for tumours as soft tissue sows up well
Lumbar puncture = meningitis

Question 11

How many muscle fibres can one nerve stimulate?

Answer 11

Many

But each muscle fibres stimulated by a nerve is not stimulated by another nerve as well

Question 12

How big is a myofibril?

Answer 12

1-2 micrometers in diameter

Question 13

What is a characteristic of myasthenia gravis?

Answer 13

Muscle weakness in the face

Question 14

What is the classic action potential shape on an EMG externally?

Answer 14

Small triangle up and then a small triangle down

Internally = like a normal action potential

Question 15

what is an artefact?

Answer 15

An interference between stimulating equipment and measuring equipment