Module 3: The Muscle System Flashcards
What is the primary function of skeletal muscle?
Mobility, movement, heat production
What are the two components of skeletal muscle?
Contractile part (muscle) and non-contractile part (tendon)
What are the protein filaments that form the contractile part of skeletal muscles?
Thin (actin) and Thick (myosin) filaments
What is the role of calcium ions on muscle contraction?
Binding to troponin, which causes a change in the configuration of tropomyosin, allowing myosin heads to bind to actin filaments.
What is the “sliding filament theory”?
Myosin heads attach to the actin filaments, forming cross-bridges.
Using ATP, myosin heads pivot and pull actin filaments toward the center of the sarcomere.
Actin filaments slide over the myosin filaments, resulting in the shortening of the sarcomere.
As sarcomeres shorten, the entire muscle fiber shortens, producing muscle contraction.
The process repeats if ATP and calcium are available, driving the continuous contraction of the muscle.
What is a sarcomere?
The structural and functional unit of a myofibril in striated muscle. It extends from one Z line to another Z line. Responsible for the shortening of muscle fibers leading to muscle contraction.
What is the M line?
The central line of the sarcomere, in the H zone.
What is the Z line?
The boundary of one sarcomere and the beginning of the next. Anchors actin and maintains the structural organization of the sarcomere
What are myofibrils?
Long, thread-like structures within muscle fibers that contain the contractile elements (sarcomeres) and are responsible for muscle contraction
What is a muscle fiber?
A long, cylindrical muscle cell containing multiple myofibrils. Multinucleated. Surrounded by sarcolemma (plasma membrane) and contains sarcoplasm.
What is a fascicle?
A bundle of muscle fibers (cells) surrounded by perimysium.
Name and describe the different sheaths in the skeletal muscle.
Endomysium – surrounds individual muscle fibers
Perimysium – surrounds bundles of fascicles
Epimysium – surrounds whole muscle
All are made of dense irregular connective tissue
What is the difference between force and strength?
Force (the picture): The amount of exertion or tension produced by a muscle at a given moment (a snapshot of muscle exertion at a particular moment)
Strength (the video): The overall capacity of a muscle to generate force (a comprehensive measure of a muscle’s ability to exert force)
What is muscle work?
The effort a muscle exerts during contraction
Muscle Work = Muscle Force × Muscle Length Change
What is a concentric contraction? Give an example of an activity.
The muscle shortens while generating force.
The muscle produces less force if it lengthens too quickly because cross bridges cannot form fast enough.
Bicep curl.
What is an eccentric contraction? Give an example of an activity.
The muscle lengthens while generating force.
As the muscle lengthens faster, it produces more force up to a limit. Beyond that limit, the muscle can’t control the movement well, and the force decreases.
Lowering from bicep curl
What is an isometric contraction? Give an example of an activity.
Occurs when a muscle generates force without changing its length. The force produced by the muscle is equal to the force required to hold the load steady. There is no movement of the muscle.
Holding a book while reading, the muscle exerts force to keep the book in place without changing its length
What is a motor unit?
A functional unit of skeletal muscle formed by the muscle’s fibers and the motor neuron that innervates the fibers
What are the two ways by which the muscle controls force?
1) Recruiting more motor units (Size Principle)
2) Increasing the frequency of stimulation of the motor units (Frequency of Recruitment/Summation)
Describe the Size Principle for Control of Muscle Force.
Smaller motor units (with lower threshold) are recruited first for low-intensity activities, while larger motor units are recruited as the force requirement increases.
Describe how force is increased by increasing the Frequency of Stimulation.
Force is increased by increasing the frequency of stimulation through temporal summation, where subsequent stimuli build on the previous contraction, leading to greater force production.
Define the length-tension relationship of a muscle.
A muscle’s ability to produce force depends on its length. When a muscle is at its optimal length—neither too stretched nor too contracted—it generates the most force. If the muscle is too stretched or too contracted, fewer cross-bridges form, reducing the muscle’s force output.
Describe passive tension.
The tension generated in a muscle when it is stretched without active contraction, primarily due to the elastic properties of the muscle tissue.
Define muscle power.
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.
Define muscle force.
A muscle’s ability to create movement by pulling or pushing. The amount of tension produced by a muscle when contracting.
Define muscle endurance.
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.
Define muscle fatigue.
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.
Give two reasons why it is important to measure strength.
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.
Describe the Oxford Grading Scale of Muscle Strength.
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
What is the overload principle of muscle strengthening?
To increase muscle strength, the muscles must be subjected to greater loads than they are accustomed to, leading to adaptation and growth.
Which physiological process must occur for muscle strength to increase?
Muscle hypertrophy, an increase in the size of muscle fibers, must occur for muscle strength to increase.
What are the principles of strength training?
Specificity, progressive, overload, reversibility
What are the main differences between strength and endurance training?
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.
