Module 3: The Muscle System

Question 1

What is the primary function of skeletal muscle?

Answer 1

Mobility, movement, heat production

Question 2

What are the two components of skeletal muscle?

Answer 2

Contractile part (muscle) and non-contractile part (tendon)

Question 3

What are the protein filaments that form the contractile part of skeletal muscles?

Answer 3

Thin filaments (actin) and thick filaments (myosin).

Question 4

What is the role of calcium ions in muscle contraction?

Answer 4

It binds to troponin, causing a change in tropomyosin’s position and allowing myosin heads to bind to actin filaments.

Question 5

What is the Sliding Filament theory?

Answer 5

Myosin heads attach to actin filaments, forming cross-bridges. Using ATP, myosin heads pivot and pull actin filaments toward the sarcomere center. This causes the actin filaments to slide over myosin, shortening the sarcomere. As sarcomeres shorten, the entire muscle fiber shortens, resulting in muscle contraction. The process repeats as long as ATP and calcium are available, driving continuous contraction.

Question 6

What is a sarcomere?

Answer 6

The structural and functional unit of a myofibril in striated muscle, extending from one Z line to the next. It is responsible for muscle fiber shortening, which leads to muscle contraction.

Question 7

What is the M line?

Answer 7

The central line of the sarcomere, located in the H zone.

Question 8

What is the Z line?

Answer 8

Marks the boundary of one sarcomere and the beginning of the next. It anchors actin filaments and helps maintain the structural organization of the sarcomere.

Question 9

What are myofibrils?

Answer 9

Long, thread-like structures within muscle fibers that contain sarcomeres and are responsible for muscle contraction.

Question 10

What is a muscle fiber?

Answer 10

A long, cylindrical muscle cell containing multiple myofibrils. It is multinucleated, surrounded by the sarcolemma (plasma membrane), and contains sarcoplasm.

Question 11

What is a fascicle?

Answer 11

A bundle of muscle fibers (cells) surrounded by the perimysium.

Question 12

Name and describe the different sheaths in the skeletal muscle.

Answer 12

Endomysium: Surrounds individual muscle fibers.
Perimysium: Surrounds bundles of muscle fibers (fascicles).
Epimysium: Surrounds the entire muscle.

All sheaths are made of dense irregular connective tissue.

Question 13

What is the difference between force and strength?

Answer 13

Force: The amount of tension or exertion produced by a muscle at a specific moment (a snapshot of muscle exertion).
Strength: The overall capacity of a muscle to generate force (a measure of a muscle’s ability to exert force over time).

Question 14

What is muscle work?

Answer 14

The effort a muscle exerts during contraction

Muscle Work = Muscle Force × Muscle Length Change

Question 15

What is a concentric contraction? Give an example.

Answer 15

The muscle shortens while generating force. If the muscle lengthens too quickly, it produces less force because cross-bridges can’t form fast enough.
Example: Bicep curl (lifting the weight).

Question 16

What is an eccentric contraction? Give an example.

Answer 16

The muscle lengthens while generating force. The faster the muscle lengthens, the more force it can produce, up to a limit. Beyond that, the muscle struggles to control the movement, and force decreases.
Example: Lowering the weight during a bicep curl.

Question 17

What is an isometric contraction? Give an example.

Answer 17

The muscle generates force without changing its length. The force produced equals the force required to hold the load steady, with no muscle movement.
Example: Holding a book while reading (the muscle keeps the book in place without changing length).

Question 18

What is a motor unit?

Answer 18

A functional unit of skeletal muscle, consisting of a motor neuron and the muscle fibers it innervates.

Question 19

What are the two ways muscles control force?

Answer 19

Recruiting more motor units (Size Principle)
Increasing the frequency of motor unit stimulation (Frequency of Recruitment / Summation)

Question 20

What is the Size Principle for Muscle Force Control?

Answer 20

Smaller, low-threshold motor units are recruited first for low-intensity tasks; larger motor units are activated as force demands increase

Question 21

How does increasing stimulation frequency increase force?

Answer 21

Force increases through temporal summation, where repeated stimuli build on prior contractions, amplifying force production.

Question 22

What is the length-tension relationship of a muscle?

Answer 22

A muscle’s ability to produce force depends on its length. The muscle generates the most force when it is at its optimal length—neither too stretched nor too contracted. If the muscle is too stretched or too contracted, fewer cross-bridges form, reducing force production.

Question 23

Describe passive tension.

Answer 23

The tension generated in a muscle when it is stretched without active contraction, primarily due to the elastic properties of the muscle tissue.

Question 24

Define muscle power.

Answer 24

How fast a muscle does work.

Calculation: Force of the Muscle Contraction x How Quickly it Contracts.

Isometric Contraction: Power is 0 because the muscle isn’t changing length.

Concentric Contraction: Power is positive because the muscle shortens and generates force.

Eccentric Contraction: Power is negative because the muscle lengthens while generating force.

Question 25

Define muscle force.

Answer 25

A muscle’s ability to create movement by pulling or pushing. The amount of tension produced by a muscle when contracting.

Question 26

Define muscle endurance.

Answer 26

A muscle’s ability to sustain repeated contractions over time without fatigue. Depends on the muscle’s ability to use oxygen to make energy.

Type I Muscle Fibers are good at using oxygen and are resistant to fatigue. Muscles with more Type I fibers can work longer before getting tired.

Question 27

Define muscle fatigue.

Answer 27

Inability of a muscle to sustain force

The muscle doesn’t respond well to stimuli,
The muscle runs out of energy,
Metabolic waste builds up in the muscle,
Even if the brain signals the muscle to contract, it cannot because its too fatigued.

Question 28

Give two reasons why it is important to measure strength.

Answer 28

1) Assess physical ability to evaluate a person’s overall muscle function and ability to perform daily activities.
2) Track progress monitors changes in strength over time due to training, recovery, or rehabilitation.

Question 29

Describe the Oxford Grading Scale of Muscle Strength.

Answer 29

Measures muscle strength and function on a scale of 0-5, to assist diagnosing and track progress

0: No movement at all
1: A flicker of movement
2: Full range of movement without gravity resistance
3: Full range of movement against gravity
4: Full range of movement against gravity and resistance
5: Full range of movement with maximal resistance

Question 30

What is the overload principle of muscle strengthening?

Answer 30

To increase muscle strength, the muscles must be subjected to greater loads than they are accustomed to, leading to adaptation and growth.

Question 31

Which physiological process must occur for muscle strength to increase?

Answer 31

Muscle hypertrophy, an increase in the size of muscle fibers, must occur for muscle strength to increase.

Question 32

What are the principles of strength training?

Answer 32

Specificity, progressive, overload, reversibility

Question 33

What are the main differences between strength and endurance training?

Answer 33

Strength Training:
Goal: Increase muscle strength.
Focus: Improves the muscle’s ability to exert force.
Parameters: Involves high resistance with fewer repetitions. The training is often shorter in duration but more intense.
Target: Often works more Type II (fast-twitch) muscle fibers.
Examples: Weightlifting, resistance exercises.

Endurance Training:
Goal: Improve muscle endurance.
Focus: Enhances the muscle’s ability to sustain activity over time.
Parameters: Involves low resistance with higher repetitions and longer duration. Training is less intense but more prolonged.
Target: Often works more Type I (slow-twitch) muscle fibers.
Examples: Running, cycling, long-distance swimming.