5.1 Neuromuscular junctions

Question 1

when does the muscle contract?

Answer 1

when it receives a nerve impulse

Question 2

1. where is a nerve impulse conducted?

Answer 2

along the motor neurone

Question 3

2. when a nerve impulse reaches the neuromuscular junction what does it stimulate to open?

Answer 3

voltage gated Ca2+ channels

Question 4

2. as the Ca2+ floods in to the synaptic knob what does it cause?

Answer 4

the vesicles to fuse with the membrane

Question 5

2. as the vesicles fuse with the membrane, what does it release and by what process?

Answer 5

releases acetylcholine by exocytosis

Question 6

3. what does the acetylcholine now do?

Answer 6

diffuses across the cleft and binds with receptor molecules on the post synaptic membrane

Question 7

what is another term for the post synaptic membrane on a motor neurone?

Answer 7

sarcolemma

Question 8

4. as the acetylcholine binds what does it cause to open?

Answer 8

chemical gated sodium ion channels

Question 9

4. the opening of the sodium channels makes the membrane more permeable to what?

Answer 9

sodium

Question 10

4. as sodium flood into the sarcolemma what happens to the membrane?

Answer 10

depolarizes, initiating action potential

Question 11

5. acetylcholine is broken down by what?

Answer 11

acetylcholinesterase

Question 12

5. what is acetylcholine broken down into?

Answer 12

choline and ethanoic acid

Question 13

5. what does the breakdown of acetylcholine prevent?

Answer 13

muscle being overstimulated

Question 14

6. where does depolarization spread?

Answer 14

through the t tubules

Question 15

6. what are the t tubules in contact with?

Answer 15

the sarcoplasmic reticulum

Question 16

6. what does the sarcoplasmic reticulum contain?

Answer 16

stored Ca2+

Question 17

7. action potentials stimulate what to open?

Answer 17

Ca2+ channels

Question 18

7. as channels open what does the Ca2+ do?

Answer 18

diffuses down the concentration gradient flooding the sarcoplasm with Ca2+

Question 19

8. as the Ca2+ floods into the sarcoplasm what does it cause?

Answer 19

muscle contraction

Question 20

(sliding filament theory)

1. nerve impulses stimulate the release of what?

Answer 20

Ca2+ from the sarcoplasmic reticulum

Question 21

(sliding filament theory)

2. Ca2+ attach to what?

Answer 21

the troponin molecule

Question 22

(sliding filament theory)

3. what happens to the troponin when bound to Ca2+ and what effect does this have?

Answer 22

changes shape pulling tropomyosin upwards exposing myosin binding site

Question 23

(sliding filament theory)

4. what does the bulbous head of the myosin filament do?

Answer 23

attaches to the exposed binding site forming a cross bridge

Question 24

(sliding filament theory)

5. what is activated when the head attaches to the binding site? and what does this do?

Answer 24

Myosin ATPase

ATP is hydrolysed this releases enough energy for the angle of the head to change

Question 25

(sliding filament theory)

6. where does the actin filament slide?

Answer 25

closer to the centre of the sarcomere

Question 26

(sliding filament theory)

7. what attaches to the myosin head?

Answer 26

a new ATP

Question 27

(sliding filament theory)

8. what does the myosin head leave and what does the actin do?

Answer 27

myosin head leaves binding site

Actin filament moves back to original position