Lecture 31

Question 1

Length tension relationship:

Answer 1

At the level of the sarcomere the maximum active force (tension developed) is dependent on the degree of actin and myosin overlap`

Question 2

At optimal length:

Answer 2

greatest tension produced due to maximum number of cross-bridges foremd

Question 3

Decrease length:

Answer 3

reduces tension due to extensive overlap

Question 4

No tension can form when:

Answer 4

Thick filaments meet Z lines are sarcomeres cannot shorten.

Question 5

Reduced size of zone of overlap means:

Answer 5

fewer cross bridges formed and reduced tension

Question 6

Zero zone of overlap results in:

Answer 6

zero tension due to no interactions between thick and thin filaments

Question 7

Excitation-contraction coupling Part 1(the neuromuscular junction) step 1

Answer 7

-ACh is released into the neuromuscular junction, an AP travels down the motor neuron. Ca2+ enters the axon terminal. Vesicles containing ACh fuse with the terminal membrane, releasing ACh into the neuromuscular junction

Question 8

Excitation-contraction coupling Part 1 step 2

Answer 8

Activation of ACh receptors:

• After step 1, ligand gated ion channels open.
• Opening of these channels allows movement of predominantly Na+ into the muscle cell making it less negative (end plate potential)
• The effects of ACh are short lasting as the enzyme ACh esterase rapidly breaks down ACh

Question 9

Excitation-contraction coupling Part 1 step 3:

Answer 9

If sufficient ligand gated channels are opened the end plate potential reaches threshold.

• Voltage gated Na+ cahnnels open and an action potential is triggered
• The action potential is then propagated along the sarcolemma into the T tubule system

Question 10

An action potential in skeletal muscle (5 steps)

Answer 10

1. Small increase in Na+ permeability
2. Na+ channels open. Na+ rushes in. Cell is depolarized.
3. Na+ channels close. K+ channels open. Cell begins repolarization.
4. K+ channels begin closing.
5. Membrane potential stabilizes at resting level. Concentrations of Na+ and K+ are restored.

Question 11

Excitation-contraction coupling Part 2 (calcium coupling) step 4

Answer 11

-Calcium is released from the SR. Ca2+ channels in the SR open. Ca2+ is then released into the cytosol

Question 12

Excitation-contraction coupling Part 2 (calcium coupling) step 5

Answer 12

When Ca2+ concentrations reach a critical threshold the myosin binding sites on the actin filament are exposed allowing the cross-bridge cycle to occur.

Question 13

Excitation-contraction coupling Part 2 (calcium coupling) step 6

Answer 13

-Contraction ends when Ca2+ levels fall

• Ca2+ is pumped back to SR via Ca2+-ATPase pumps
• Troponin moves back covering the myosin binding site
• The muscle twitch is complete

Question 14

Creatine phosphate:

Answer 14

• For brief periods creatine phosphate can act as an ATP ‘store’
• Anaerobic

Question 15

Anaerobic glycolysis:

Answer 15

fast but inefficient

Question 16

Aerobic glycolysis

Answer 16

Efficient but slow

Question 17

Type 1 fibre:

Answer 17

slow oxidative, Slow ATPase rate, small diameter, aerobic, ‘slow twitch’

Question 18

Type 2B fibre: fast glycolytic

Answer 18

Fast, high, anaerobic glycolysis, ‘fast twitch’

Question 19

Type 2A fibre:

Answer 19

Fast, aerobic, ‘fast twitch’

Question 20

Regulation force is dependent on:

Answer 20

-Rate of simulation of individual motor units, the number of motor units recruited

Question 21

Rate of stimulation:

Answer 21

Single twitch, a single stimulus is delivered.

-Low of stimulation –> unfused (incomplete) tetanus

Question 22

Increased frequency=

Answer 22

temporal summation. At high frequencies, there is no relaxation at all between stimuli.