Biology Muscle Fibers Quiz

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Questions and Answers

What determines the number of pivoting cross bridges in a muscle fiber during contraction?

The size of the muscle fiber

The speed of muscle fiber contraction

The degree of overlap between thick and thin filaments (correct)

The type of motor unit activated

What is the purpose of muscle tone?

To maintain posture and readiness for action (correct)

To allow for rapid muscle contractions

To increase the overall size of muscle fibers

To assist in muscle recovery after fatigue

Which of the following correctly differentiates between isometric and isotonic contractions?

Both types of contractions are identical in function and result.

Isometric contractions lengthen the muscle, while isotonic keep it the same length.

Isometric contractions produce tension without changing muscle length, whereas isotonic contractions involve muscle length change. (correct)

Isometric contractions shorten the muscle, while isotonic do not.

What primarily causes muscle fatigue?

Accumulation of lactic acid and depletion of energy sources Signup and view all the answers

How is the relative size of a motor unit related to muscle control?

Smaller motor units allow for greater fine control. Signup and view all the answers

What is the primary factor that determines the tension produced during a twitch in muscle fibers?

Timing and frequency of stimulation Signup and view all the answers

Which phase of a twitch involves the propagation of the action potential and the release of calcium ions from the sarcoplasmic reticulum?

Latent period Signup and view all the answers

How can muscle tension be increased beyond a single twitch?

By increasing the frequency of stimulation Signup and view all the answers

Which statement correctly describes a motor unit?

It consists of the motor neuron and all the muscle fibers it innervates Signup and view all the answers

What primarily affects the length-tension relationships in muscle fibers?

The initial length of the muscle fiber at rest Signup and view all the answers

What maintains high calcium concentration during sustained muscle contraction?

Frequent action potentials preventing calcium reuptake Signup and view all the answers

What is NOT a factor that influences muscle tension production?

Variability in muscle fiber types within a motor unit Signup and view all the answers

What is the result of sustained muscle contraction without adequate relaxation?

Increased fatigue and muscle soreness Signup and view all the answers

What is the primary function of muscle spindles found within regular contractile muscle fibers?

To monitor the degree of stretching in a muscle Signup and view all the answers

What type of muscle fiber changes does training typically induce?

Alterations in muscle fiber composition or size Signup and view all the answers

Which type of cells are primarily responsible for repairing injured skeletal muscle?

Satellite cells Signup and view all the answers

What is a characteristic of the majority of mature skeletal muscle fiber nuclei?

They are amitotic Signup and view all the answers

What factors influence the precise changes in muscle fibers due to training?

Type of training and intensity Signup and view all the answers

What type of contraction occurs when muscle tension exceeds the load while the muscle shortens?

Concentric contraction Signup and view all the answers

What role do antagonists play in muscle movement?

Control and modulate the action of agonists Signup and view all the answers

How does recruitment of motor units occur during muscle contractions?

From smallest to largest motor units Signup and view all the answers

What is true about isometric contractions?

Muscle length remains unchanged due to equal tension and load Signup and view all the answers

During sustained contractions, what role do motor units play?

They alternate activation to allow recovery Signup and view all the answers

What type of contraction is identified when muscle length decreases while maintaining constant tension?

Concentric contraction Signup and view all the answers

Which muscle group assists the agonists by minimizing unwanted movement during contraction?

Synergists Signup and view all the answers

How does heightened muscle tone affect voluntary contractions?

It allows for faster recruitment of motor units Signup and view all the answers

What defines eccentric contractions?

Tension is less than the external load while lengthening Signup and view all the answers

Which statement about muscle fibers in motor units is correct?

They alternate activation to ensure balanced tension in tendons Signup and view all the answers

What primary role does ATP play in muscle contraction?

It provides energy for the release of myosin heads from actin. Signup and view all the answers

Which process contributes to the immediate energy supply for muscles during contraction?

Creatine phosphate breakdown Signup and view all the answers

What is the net gain of ATP from glycolytic catabolism?

2 ATP Signup and view all the answers

What happens to pyruvic acid when there is insufficient oxygen during intense exercise?

It is converted into lactic acid. Signup and view all the answers

How does lactic acid accumulation affect muscle fibers?

It alters pH and can lead to fatigue. Signup and view all the answers

What is the primary source of oxygen for muscle tissues during aerobic respiration?

Bloodstream diffusion and myoglobin Signup and view all the answers

Which of the following contributes to muscle fatigue?

Buildup of lactic acid and ADP Signup and view all the answers

What does Excess Postexercise Oxygen Consumption (EPOC) refer to?

Increased oxygen intake after exercise to restore homeostasis. Signup and view all the answers

What factors can affect the time it takes for the body to recover after exercise?

Intensity of the activity and hydration levels. Signup and view all the answers

Which mechanism does not occur simultaneously to generate ATP in muscle cells?

Photosynthesis Signup and view all the answers

Study Notes

Tension Generation in Muscle Fibers

The amount of tension produced by a single muscle fiber can vary.
The number pivoting cross-bridges is determined by:
- Degree of overlap between thick and thin filaments when contraction begins
- Frequency of stimulation by the motor neuron
Greatest tension is produced within a narrow range of sarcomere lengths.
A twitch is a single stimulus-contraction-relaxation sequence in a muscle fiber.
A twitch has three phases:
- Latent Period: Time for action potential to:
  - Propagate across sarcolemma
  - Release Ca++ from SR
- Contraction Period: Repeated cross-bridge cycles generate tension.
- Relaxation Period: Calcium ion levels reduced in cytosol by SR pumps; tension diminishes.
Tension produced during a twitch varies due to:
- Timing and frequency of stimulation.
- Length of fiber at rest.
- Type of muscle fiber.
Wave summation increases tension with more frequent stimulation.
Calcium levels remain high, allowing contraction to continue.
Action potentials are so frequent that the SR cannot pump the Ca++ back.
Increased tension can be achieved through repeated stimulation.

Tension Production in Skeletal Muscles

Tension is determined by:
- Total number of muscle fibers stimulated.
- Total tension produced by the individual muscle fibers.
Motor neurons innervate a subset of muscle fibers.
Motor unit: A motor neuron controls all the muscle fibers within it.
- Size varies significantly
  - Single motor neuron controlling a few muscle fibers provides precise control.
  - Single motor neuron controlling thousands of muscle fibers provides less precise control.
All muscle fibers within a motor unit are the same type.
Motor units are intermingled throughout the muscle.
Muscle tone is the resting tension caused by some motor units always being active.
- Higher tone accelerates recruitment during voluntary contractions.
- Makes skeletal muscles more defined.
- Increases resting metabolic rate.
Recruitment increases the number of active motor units starting with the smallest to the largest.
During sustained contractions, motor units are activated on a rotating basis to allow for rest and recovery.

Types of Muscle Contractions

Isotonic Contractions: tension is constant, but muscle length changes:
- Concentric Contractions: muscle shortens, force generated is greater than external force.
- Eccentric Contractions: muscle lengthens, external force is greater than force generated by the muscle.
Isometric Contractions: Muscle length remains unchanged because tension does not exceed the load.

Functional Groups of Muscles

Agonists (Prime Movers): Primary force for movement.
Antagonists: In contrast to agonist; provide control.
Synergists: Provide supplemental force, minimize unwanted movement, stabilize joints.
Fixators: Stabilizing force that anchors bone; provides movement efficiency and prevents injury.

Muscle Metabolism

Skeletal muscle requires ATP for:
- Na+/K+ pumps to maintain ion gradients.
- Release myosin heads from actin active sites.
- Pump calcium back into the sarcoplasmic reticulum.
Muscles cannot get ATP from the blood or other tissues.
ATP present in muscle cells is only sufficient for a few seconds of contraction.
ATP for contraction comes from three mechanisms that can occur simultaneously:
- Creatine Phosphate (CP): Provides energy for about 15 seconds.
  - Resting muscle fibers produce more ATP than needed.
  - Excess ATP is used to synthesize CP.
  - CP can transfer P to ADP to generate new ATP.
- Glycolytic Catabolism: Anaerobic process that occurs in the cytosol.
  - Glucose from the bloodstream and glycogen are broken down into pyruvic acid.
  - Pyruvic acid is converted to lactic acid if not enough oxygen is present.
  - Rapid production of lactic acid can lead to muscle fatigue.
- Oxidative Catabolism: Aerobic process that occurs in the mitochondria.
  - Pyruvic acid from glycolysis undergoes reactions to produce ATP, CO2, water, and heat.
  - Slower process than glycolysis, but yields 30+ ATP.
  - Oxygen comes from the blood and myoglobin.

Muscle Fatigue

Inability to maintain a given level of intensity during activity.
Factors that contribute to fatigue:
- Central Fatigue: Feeling of tiredness; wanting to stop activity.
- Depletion of Metabolites: Glucose, glycogen and creatine phosphate.
- Decreased Oxygen Availability.
- Buildup of Lactic Acid, ADP and Other Chemicals.
- Environmental Conditions: Excessive heat leading to electrolyte imbalances.

Muscle Recovery Period

Time taken for the body and muscles to return to the pre-exercise state.
Can take minutes to days depending on intensity.
Requires:
- Heat dissipation
- Restoration of intra- and extracellular ion concentrations.
- Correction of blood pH.
EPOC (Excess Postexercise Oxygen Consumption): Increased oxygen intake compared to resting levels.

Types of Muscle Fibers

Classified based on:
- Speed of contraction
- Primary method of ATP generation (oxidative vs.glycolytic)
Type I (Slow Oxidative Fibers): Slow contraction speeds, high oxidative capacity.
Type IIa (Fast Oxidative-Glycolytic Fibers): Fast contraction speeds, intermediate oxidative capacity.
Type IIb (Fast Glycolytic Fibers): Fast contraction speeds, high glycolytic capacity.

Changes Due to Physical Training

Muscle fibers can change in response to training, but not in number.
Endurance Training: Focuses on increasing oxidative capacity and mitochondrial density in fibers.
Resistance Training: Focuses on increasing size and strength of muscle fibers.

Muscle Spindles and Golgi Tendon Organs

Muscle Spindles: Sensory structures that monitor the degree of stretching in a muscle.
Golgi Tendon organs: Sensory structures located in tendons that monitor the degree of tension generated by the muscle.

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Description

Test your knowledge on tension generation in muscle fibers, including the phases of a twitch and factors influencing tension production. Understand the relationship between sarcomere length, frequency of stimulation, and the types of muscle fibers involved. This quiz will cover essential concepts related to muscle contraction and physiology.