1) What is responsible for the varying muscle tension when the muscle starts at different lengths?

A) The length of the muscle determines the rate at which Ca2+ is pumped back into the SR (sarcoplasmic reticulum).

B) The length of the muscle determines the number of cross-bridges that can be formed between myosin and actin.

C) The length of the muscle determines how many myosin binding sites on actin filaments are obstructed by tropomyosin.

D) The length of the muscle determines the amount of Ca2+ that diffuses out of the SR (sracoplasmic reticulum).

E) The length of the muscle determines the affinity of Ca2+ for binding sites on troponin.

2) A motor unit contains only one type of muscle fiber. Different muscle fiber types will fatigue at different rates. If you want to achieve a maximal muscle contraction, you need to recruit the motor units with the fastest fatigue rate last. 

Identify the order (first to last) that motor unit types are recruited to achieve a maximal contraction.
a) fast-twitch glycolytic muscle fibers
b) fast-twitch oxidative-glycolytic muscle fibers
c) slow-twitch oxidative muscle fibers

3) Spatial summation involves the recruitment of multiple motor units. Which of the following best describes a motor unit?

1) A motor unit refers only to the active muscle fibers.

2) A motor unit is a single muscle fiber and all the motor neurons that innervate it.

3) A motor unit is a single motor neuron plus all the muscle fibers that it innervates.

4) A motor unit is the sarcomere of the muscle fiber.

5) A motor unit consists of all the motor neurons in a motor nerve and the muscle fibers that they innervate.

4) Joel was at the gym working out. He performed 10 repetitions lifting a 10-kg weight and 10 repetitions lifting a 5-kg weight. Which set of repetitions took a longer time?

A) Repetitions with the 5-kg weight took a longer time.

B) There are 10 repetitions with each weight so the time would be the same regardless of the weight.

C) Repetitions with the 10-kg weight took a longer time.

5) In the experiments, you stimulated the muscle with electrodes. In reality, there are no electrodes to contract our skeletal muscle. Stimulating muscle with electrodes in the experiments is analogous to which event in regular skeletal muscle contraction?

A) Achetylcholinesterase breaking down ACh in the synaptic cleft

B) Achetylcholine binding to its receptor at the neuro-muscular junction

C) Ca2+ ions entering the motor neuron to release neurotransmitter

D) Ca2+ ions leaving the sarcoplasmic reticulum to bind to troponin

E) Myosin binding to actin during crossbridge cycling

6) PEX-02-General. In the gym, you are attempting to squat a heavy weight, which requires almost 100% effort for you. Describe and explain the 3 factors that allow skeletal muscle to generate maximum tension.