Muscles: The Neuromuscular Junction Part 2

Question 1

1. What is ach release dependent on

Answer 1

depending depolarisation of the presynaptic membrane of the motor neurone

Question 2

2. What does depolarisation of the presynaptic membrane result in

Answer 2

results in Ca2+ ion influx via voltage-dependent Ca2+ channels

Question 3

3.What do the Ca2+ ions promote in the presynaptic neurone

Answer 3

fusion of the vesicles with the presynaptic membrane

Question 4

What does activation of nAChRs by Ach lead to

Answer 4

leads to depolarisation of muscle fibre membrane

Question 5

5. How many molecules of Ach per nAChR

Answer 5

2 molecules per receptor

Question 6

6. What does the release of a single vesicle of Ach result in

Answer 6

miniature end plate potential

Question 7

7. What does the release of several Ach vesicles result in

Answer 7

when a end plate potential (EPP)

Question 8

8. When would a single Ach vesicle be released

Answer 8

at rest

Question 9

9. When would several ACh vesicles be released

Answer 9

when the motor neurone is activated

Question 10

1. Skeletal muscles are composed of many what?

Answer 10

many fascicles of muscle fibres

Question 11

2. What is each individual muscle fibre formed by and what is the term for this

Answer 11

syncytium

Question 12

what does syncytium mean

Answer 12

a fibre that is multi nucleated

Question 13

What are the 2 classes a muscle fibre can be categorised in in relation to speed of contraction?

Answer 13

1. fast contracting
2. slow contracting

Question 14

5. What is the speed of muscle contract dependant on?

Answer 14

the kinetics of ATPase activity in the myosin

Question 15

What are the 3 classes a muscle fibre can be categorised in relation to its metabolism

Answer 15

• oxidative
• glycolytic
• Oxidative-glycolytic

Question 16

7. What is each muscle fibre packed full with

Answer 16

myofibrils

Question 17

8. What does muscle contraction require

Answer 17

nerves input from alpha neurones in the spinal cord

Question 18

What do the thick and thin protein filaments in myofibrils interact to produce?

Answer 18

shortening of the muscle fibre and thus contraction of the whole muscle

Question 19

1. Where is the M line

Answer 19

middle of the myosin filament

Question 20

2. What does Z line to Z line show?

Answer 20

shows where each sarcomere starts and stops

Question 21

3. What does the H band section show?

Answer 21

where there is myosin filament but no actin is present

Question 22

4. What does the I band section show

Answer 22

I band is where there is actin but no myosin present

Question 23

what does the A band section go from

Answer 23

A band goes from one end of myosin filament to the other side

Question 24

1. In the sliding filament mechanism, what are 3 things that are observed

Answer 24

• sarcomere shortening
• thick filaments are stationary; thin are dragged over thick
• length of the filaments do not change