BIO 201 Exam 3 V3 | BIO 201 A&P |
StraighterLine | Q&A with Rationale (BIO
201 Exam 3)
1. Which of the following connective tissue layers surrounds an individual muscle fiber?
A. Endomysium
B. Perimysium
C. Epimysium
D. Fascia
Answer: A
Rationale: The endomysium is a thin layer of areolar connective tissue that ensheaths each
individual muscle cell. This layer helps insulate the electrical activity of the fiber and
provides space for capillaries and nerve fibers. In contrast, the perimysium surrounds
bundles of fibers called fascicles, and the epimysium surrounds the entire muscle.
2. In a sarcomere, the region that contains only thin filaments is known as the:
A. A band
B. H zone
C. I band
D. M line
,Answer: C
Rationale: The I band is the light region of the sarcomere that consists strictly of thin
(actin) filaments. During muscle contraction, the width of the I band decreases as the actin
filaments slide toward the center. The Z disc is located in the middle of each I band and
serves as the boundary for the sarcomere.
3. What is the primary role of calcium ions in the sliding filament model of contraction?
A. To bind to tropomyosin and expose myosin-binding sites
B. To provide energy for the power stroke of the myosin head
C. To activate the sodium-potassium pump on the sarcolemma
D. To bind to troponin, causing a conformational change in tropomyosin
Answer: D
Rationale: Calcium ions bind specifically to troponin, which is part of the regulatory
protein complex on the thin filament. This binding causes troponin to change shape,
effectively pulling tropomyosin away from the active sites on actin. Once these sites are
exposed, myosin heads can attach and initiate the contraction cycle.
4. The enzyme responsible for breaking down acetylcholine in the synaptic cleft is:
A. Monoamine oxidase
B. ATPase
C. Acetylcholinesterase
, D. Creatine kinase
Answer: C
Rationale: Acetylcholinesterase is essential for terminating the signal at the
neuromuscular junction by hydrolyzing acetylcholine into choline and acetate. This rapid
degradation prevents continuous stimulation of the muscle fiber in the absence of a new
nerve impulse. Without this enzyme, the muscle would remain in a state of unwanted
tetanic contraction.
5. A motor unit is defined as:
A. A single muscle fiber and all the neurons that innervate it
B. All the muscles in a specific functional group
C. A single motor neuron and all the muscle fibers it innervates
D. The set of all motor neurons in a single spinal nerve
Answer: C
Rationale: A motor unit represents the smallest functional unit of muscle contraction
under the control of the nervous system. When the motor neuron fires an action potential,
all fibers within that specific unit contract simultaneously. Small motor units are used for
fine motor control, while large motor units provide powerful movements.
6. During the latent period of a muscle twitch, which of the following events occurs?
A. The sarcolemma depolarizes and calcium is released from the sarcoplasmic reticulum
StraighterLine | Q&A with Rationale (BIO
201 Exam 3)
1. Which of the following connective tissue layers surrounds an individual muscle fiber?
A. Endomysium
B. Perimysium
C. Epimysium
D. Fascia
Answer: A
Rationale: The endomysium is a thin layer of areolar connective tissue that ensheaths each
individual muscle cell. This layer helps insulate the electrical activity of the fiber and
provides space for capillaries and nerve fibers. In contrast, the perimysium surrounds
bundles of fibers called fascicles, and the epimysium surrounds the entire muscle.
2. In a sarcomere, the region that contains only thin filaments is known as the:
A. A band
B. H zone
C. I band
D. M line
,Answer: C
Rationale: The I band is the light region of the sarcomere that consists strictly of thin
(actin) filaments. During muscle contraction, the width of the I band decreases as the actin
filaments slide toward the center. The Z disc is located in the middle of each I band and
serves as the boundary for the sarcomere.
3. What is the primary role of calcium ions in the sliding filament model of contraction?
A. To bind to tropomyosin and expose myosin-binding sites
B. To provide energy for the power stroke of the myosin head
C. To activate the sodium-potassium pump on the sarcolemma
D. To bind to troponin, causing a conformational change in tropomyosin
Answer: D
Rationale: Calcium ions bind specifically to troponin, which is part of the regulatory
protein complex on the thin filament. This binding causes troponin to change shape,
effectively pulling tropomyosin away from the active sites on actin. Once these sites are
exposed, myosin heads can attach and initiate the contraction cycle.
4. The enzyme responsible for breaking down acetylcholine in the synaptic cleft is:
A. Monoamine oxidase
B. ATPase
C. Acetylcholinesterase
, D. Creatine kinase
Answer: C
Rationale: Acetylcholinesterase is essential for terminating the signal at the
neuromuscular junction by hydrolyzing acetylcholine into choline and acetate. This rapid
degradation prevents continuous stimulation of the muscle fiber in the absence of a new
nerve impulse. Without this enzyme, the muscle would remain in a state of unwanted
tetanic contraction.
5. A motor unit is defined as:
A. A single muscle fiber and all the neurons that innervate it
B. All the muscles in a specific functional group
C. A single motor neuron and all the muscle fibers it innervates
D. The set of all motor neurons in a single spinal nerve
Answer: C
Rationale: A motor unit represents the smallest functional unit of muscle contraction
under the control of the nervous system. When the motor neuron fires an action potential,
all fibers within that specific unit contract simultaneously. Small motor units are used for
fine motor control, while large motor units provide powerful movements.
6. During the latent period of a muscle twitch, which of the following events occurs?
A. The sarcolemma depolarizes and calcium is released from the sarcoplasmic reticulum
