Module 4: Lecture 4

Question 1

what is used to power the cross bridge cycle?

Answer 1

the free energy that is released from splitting ATP

Question 2

how does cross-bridge cycling initiate?

Answer 2

all comes down to the calcium signal from the action potential

Question 3

what splits the ATP for cross-bridge cycling?

Answer 3

myosin ATPase head
- which then they energize after the split in order to form cross-bridges

Question 4

when ATP is split on the myosin head, what happens to its products immediately?

Answer 4

nothing, they remain attached to the myosin

Question 5

when is the inorganic phosphate going to be released from the myosin ATPase head?

Answer 5

during the power stroke

Question 6

when is the ADP going to be released from the myosin ATPase head?

Answer 6

after the power stroke

Question 7

when does the myosin head detach from the actin?

Answer 7

when a new/fresh ATP molecule binds to the myosin head/ATPase active sites

Question 8

why after someone passes, they get a very stiffening of all their skeletal muscles?

Answer 8

no more ATP production to detach the myosin head from actin
- CALLED RIGOR MORTIS/COMPLEX
- cross-bridge has formed and its undergone a power stroke
- ADP and Pi have left and it will remain in this state

Question 9

what is responsible for ensuring the cyclical cross bridge process?

Answer 9

the hydrolysis of ATP

Question 10

what is the end goal of an action potential?

Answer 10

to get calcium in the cytosol to increase

Question 11

what is the latent period?

Answer 11

the time it takes for an action potential to travel along the muscle fiber, enter the t-tubule, causes the release of calcium
- all of those processes

• the time from when the action potential is first initiated in the muscle fiber to the onset of actual mechanical tension

Question 12

about how long is mechanical activity?

Answer 12

about 100ms (varies widely)
- much longer than an action potential which lasts 1-2 msec

Question 13

what is a muscle twitch?

Answer 13

the whole process of contraction as well as the relaxation

Question 14

what is the smallest activation signal an individual fiber can receive?

Answer 14

the action potential

Question 15

what is a single action potential in a single muscle fibre?

Answer 15

very brief and weak contraction
- it is a muscle twitch

Question 16

can a twitch have a real effect at the level of the entire muscle and the body?

Answer 16

a twitch is too weak and too short to have a real effect at the level of the entire muscle and the body

Question 17

why can we vary the force developed by our muscles?

Answer 17

because muscle fibres cooperate to produce muscle contractions for variable strength

Question 18

what are the two mechanisms of how our central nervous system controls how much force our skeletal muscles use?

Answer 18

1. by changing the number of fibres contracting (recruited) within the muscle
2. by affecting the tension developed by each contracting fibre (ie. activation rate)

Question 19

do we control our individual muscle fibres?

Answer 19

no. we control out motor units

Question 20

what is a motor unit?

Answer 20

one motor neuron + all the myofibres it innervates (different size depending on muscle types)

Question 21

what is motor unit recruitment?

Answer 21

all muscle fibres within a motor unit are activated when a motor unit is recruited

Question 22

what is the neuromuscular junction?

Answer 22

upon reaching a muscle, the axon makes several divisions/branches, and each branch will form one connection with one fibre

Question 23

what happens anytime you activate your motor unit (motor neurons fires an action potential)?

Answer 23

every single one of the fibres that the motor unit innervates, will generate an action potential and they will generate force

Question 24

when are the number of fibres contracting changed?

Answer 24

whenever a motor unit is recruited

Question 25

does your nervous system control individual fibres?

Answer 25

no, it activates individual motor units and then all of the fibres within that motor unit get activated whenever they start producing force