Chapter 10: The Motor System: Motor Neurons

Chapter 10: The Motor System: Motor Neurons

Complete Chapter Questions With Answers

Sample Questions Are Posted Below

1. Which one of the following proteins is NOT involved in the active process of muscle contraction?
2. Myosin
3. Actin
4. Tropomyosin
5. Troponin
6. Titin

ANS: E

Rationale: Binding of Ca²⁺ with troponin causes tropomyosin to move, exposing active sites on actin for myosin to bind. When the heads of myosin swivel, the sarcomere actively contracts. Titin is a structural protein, not involved in active contraction.

2. Continuous prolonged immobilization of skeletal muscle in a shortened position results in which of the following?
3. Increased muscle tone from hyperactive reflexes
4. Contracture from loss of sarcomeres
5. Increased tensile strength from the addition of titin
6. Both A and B
7. A, B, and C

ANS: B

Rationale: When skeletal muscle is continually immobilized for a prolonged time, the muscle physiologically adjusts to the shortened position by losing sarcomeres from the ends of myofibrils. This length adjustment enables the shortened muscle to contract optimally at the shortened length.

3. Which one of the following produces weak actin-myosin bonding?
4. Active muscle contraction
5. Muscle immobility
6. Physiologic contracture
7. Active contraction in lengthened muscles
8. Reflexive muscle contraction

ANS: B

Rationale: When skeletal muscle is at rest, a small number of myosin crossbridges bind to actin but the crossbridge heads do not swivel. The longer muscle is immobile, the greater the number of actin-myosin weak bonds and the greater the muscle resistance to stretch. The hamstring stiffness upon standing after prolonged sitting is due to weak actin-myosin bonds.

4. What is the purpose of alpha-gamma coactivation?
5. Prevents simultaneous activation of fast twitch and slow twitch muscles.
6. Coordinates reciprocal reflex innervation.
7. Coordinates the actions of the basal ganglia and cerebellum.
8. Maintain muscle spindle sensitivity when extrafusal muscle fibers contract.
9. Prevents contraction of an antagonist muscle when the agonist is contracting.

ANS: D

Rationale: To maintain muscle spindle sensitivity when the extrafusal muscle fibers contract, when alpha motor neurons fire gamma motor neurons to the spindle in the same muscle also fire. The gamma signals cause the ends of the intrafusal muscle fibers to contract, maintaining the stretch of the central region of intrafusal fibers when the extrafusal muscle fibers actively contract.