Skeletal Muscle Structure and Function
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Questions and Answers

Which of the following muscle types are involuntary?

  • Skeletal
  • Cardiac (correct)
  • Smooth (correct)
  • All of the above

What is a myofibril?

Myofibrils are composed of thick and thin filaments and are the basic functional unit of a muscle fiber.

What is a sarcomere?

The basic functional unit of a myofibril, and the contractile unit of muscle. It contains myosin and actin.

What is the role of tropomyosin in the structure of actin?

<p>Tropomyosin twists around actin and attaches to both actin and troponin at regular intervals.</p> Signup and view all the answers

What is the role of troponin?

<p>Troponin attaches to both actin and tropomyosin, and contains the binding site for calcium.</p> Signup and view all the answers

What is an alpha motor neuron?

<p>An alpha motor neuron is a nerve that connects and innervates with skeletal muscle fibers, causing muscle contraction.</p> Signup and view all the answers

What is the role of calcium in muscle contraction?

<p>Calcium binds to troponin, causing a conformational change in tropomyosin and exposing the active binding site on actin, allowing myosin heads to bind to actin.</p> Signup and view all the answers

The ______ of the myosin head causes it to shift and pull the actin toward the center of the sarcomere.

<p>tilting</p> Signup and view all the answers

What is the primary energy source for the body?

<p>Glucose.</p> Signup and view all the answers

What is the role of ATP in muscle contraction?

<p>ATP provides the energy required for the muscle contraction. It is also used to pump calcium back into the sarcoplasmic reticulum after contraction, allowing the muscle to relax.</p> Signup and view all the answers

What is ATPase?

<p>ATPase is an enzyme located on the myosin head that breaks down ATP to yield ADP and inorganic phosphate, releasing energy that powers the power stroke of the myosin head.</p> Signup and view all the answers

Which of the following muscle fiber types is responsible for slow, sustained movements, such as jogging and swimming?

<p>Type I (A)</p> Signup and view all the answers

Which of the following muscle fiber types is responsible for fast, powerful movements, such as sprinting and jumping?

<p>Type IIb (A)</p> Signup and view all the answers

The optimal sarcomere length for muscle contraction is when the thin and thick filaments are maximally overlapped.

<p>True (A)</p> Signup and view all the answers

What happens when sarcomeres are stretched beyond their optimal length?

<p>Less force is generated, as there is less overlap between actin and myosin, resulting in fewer cross-bridge interactions.</p> Signup and view all the answers

Which of the following is the primary energy source during prolonged exercise?

<p>Fat (A)</p> Signup and view all the answers

What is the role of enzymes in energy production?

<p>Enzymes speed up chemical reactions by lowering the activation energy required for the reaction to occur, but they do not start or control the rate of the reaction.</p> Signup and view all the answers

What is a rate-limiting enzyme?

<p>A rate-limiting enzyme is an enzyme that controls the rate of a metabolic pathway. It is usually found at the beginning of the pathway and is regulated by negative feedback.</p> Signup and view all the answers

What are the three main energy systems used by the body?

<p>The three main energy systems are the ATP-PCr system, glycolysis, and oxidative phosphorylation.</p> Signup and view all the answers

What is the ATP-PCr system and how much ATP does it produce?

<p>The ATP-PCr system is the fastest energy system and produces 1 ATP molecule. It is the primary source of energy for activities lasting less than 15 seconds.</p> Signup and view all the answers

What is glycolysis and how much ATP does it produce?

<p>Glycolysis is the breakdown of glucose to pyruvate. It produces 2 ATP molecules from glucose and 3 ATP molecules from glycogen. It is the primary source of energy for activities lasting 2-3 minutes.</p> Signup and view all the answers

What is oxidative phosphorylation, where does it take place, and how much ATP does it produce?

<p>Oxidative phosphorylation is the process of producing ATP by utilizing oxygen. It takes place in the mitochondria and produces 32 ATP molecules from glucose and 33 ATP molecules from glycogen. It is the primary source of energy for sustained aerobic exercise.</p> Signup and view all the answers

What is the electron transport chain, and where does it take place?

<p>The electron transport chain is a series of protein complexes located in the inner mitochondrial membrane. It is responsible for creating a concentration gradient of hydrogen ions, ultimately leading to the production of ATP.</p> Signup and view all the answers

What are the major players in the oxidative phosphorylation system?

<p>The major players in oxidative phosphorylation are NADH, FADH2, protein complexes, and ATP synthase.</p> Signup and view all the answers

What is beta oxidation and why is it important?

<p>Beta oxidation is a process that breaks down fatty acids into acetyl-CoA, a molecule that can be used in the Krebs cycle to produce energy. It is an important source of energy, particularly during prolonged, low-intensity exercise.</p> Signup and view all the answers

What are the four phases of beta oxidation?

<p>Beta oxidation involves four phases: 1. fatty acid activation, 2. fatty acid transport into the mitochondria, 3. the beta oxidation cycle itself, and 4. the production of acetyl-CoA.</p> Signup and view all the answers

The oxidation of protein is a primary energy source during exercise.

<p>False (B)</p> Signup and view all the answers

What is the crossover concept, and what are the key crossover points during exercise?

<p>The crossover concept describes the shift in primary energy source from fat to carbohydrates during exercise. The crossover point is usually at about 60% of maximal oxygen uptake for fat, and above 75% for carbohydrates.</p> Signup and view all the answers

What are the two main divisions of the peripheral nervous system?

<p>The two main divisions of the peripheral nervous system are the sensory division and the motor division.</p> Signup and view all the answers

What are the five steps of sensory-motor integration?

<p>The five steps include: 1) stimulus, 2) sensory neuron activation, 3) CNS processing, 4) motor neuron activation, and 5) muscle contraction.</p> Signup and view all the answers

What are the main functions of the endocrine system?

<p>The endocrine system is primarily responsible for regulating metabolism, maintaining homeostasis, and controlling growth and development.</p> Signup and view all the answers

What are steroid hormones, and where are they produced?

<p>Steroid hormones are lipid-soluble hormones produced by the adrenal cortex, ovaries, testes, and placenta.</p> Signup and view all the answers

What are non-steroid hormones, and how do they work?

<p>Non-steroid hormones are water-soluble and cannot pass through cell membranes. They bind to receptors on the cell membrane, triggering a series of events that lead to cellular changes.</p> Signup and view all the answers

What is the difference between downregulation and upregulation of hormone receptors?

<p>Downregulation refers to a decrease in the number of hormone receptors on a cell, while upregulation refers to an increase in the number of hormone receptors. These processes are regulated by the body to maintain appropriate hormone levels and cellular responses.</p> Signup and view all the answers

What is the role of growth hormone during exercise?

<p>Growth hormone stimulates protein and muscle growth, and it also accelerates fat metabolism, which can help to increase exercise intensity.</p> Signup and view all the answers

What are the main functions of the thyroid gland?

<p>The thyroid gland produces the hormones T3 and T4, which play a crucial role in regulating metabolism, influencing protein synthesis, carbohydrate utilization, and overall energy expenditure.</p> Signup and view all the answers

What are the main functions of the adrenal medulla?

<p>The adrenal medulla produces catecholamines (epinephrine and norepinephrine) and corticosteroids (cortisol). Catecholamines are involved in the 'fight-or-flight' response to stress, increasing heart rate and blood pressure, while cortisol helps regulate blood sugar levels and promotes protein breakdown.</p> Signup and view all the answers

What are the two main hormones produced by the pancreas, and what are their roles in regulating blood sugar?

<p>The pancreas produces insulin and glucagon. Insulin lowers blood sugar levels by promoting glucose uptake into cells, while glucagon raises blood sugar levels by stimulating the breakdown of glycogen and the production of glucose by the liver.</p> Signup and view all the answers

What are the two main methods for measuring energy expenditure?

<p>The two main methods for measuring energy expenditure are direct calorimetry and indirect calorimetry.</p> Signup and view all the answers

What is the respiratory exchange ratio (RER)?

<p>The respiratory exchange ratio (RER) is the ratio of carbon dioxide produced to oxygen consumed. It is used to determine the primary fuel source being utilized during exercise.</p> Signup and view all the answers

What is basal metabolic rate (BMR)?

<p>Basal metabolic rate (BMR) is the minimum amount of energy required to keep the body functioning at rest. It is typically measured under specific conditions, such as after a 12-hour fast and in a thermoneutral environment.</p> Signup and view all the answers

What is resting metabolic rate (RMR)?

<p>Resting metabolic rate (RMR) is similar to BMR but is a more practical measure, as it does not require strict fasting or a thermoneutral environment. It is often used to estimate daily energy expenditure.</p> Signup and view all the answers

What is VO2max?

<p>VO2max is the maximum amount of oxygen that the body can utilize during maximal exercise. It is a crucial indicator of aerobic fitness.</p> Signup and view all the answers

What is lactate threshold?

<p>Lactate threshold is the point during exercise where the accumulation of lactate in the blood begins to increase significantly. It is often used as a measure of anaerobic threshold, as it signifies the point at which the body starts to rely more heavily on anaerobic metabolism.</p> Signup and view all the answers

Fatigue is a decrease in muscular performance that is accompanied by sensations of tiredness and inability to maintain required power output.

<p>True (A)</p> Signup and view all the answers

What are the major causes of fatigue?

<p>Fatigue can be caused by a variety of factors, including inadequate energy delivery, accumulation of metabolic by-products, impaired muscle fiber contractile mechanisms, and alterations in neural control of muscle contraction.</p> Signup and view all the answers

Flashcards

Voluntary Muscle Type

Skeletal muscle; controlled consciously.

Involuntary Muscle Types

Cardiac and smooth muscle; controlled unconsciously.

Myofibril

Long, thread-like structures within a muscle fiber, composed of filaments.

Sarcomere

Basic contractile unit of a myofibril; contains actin and myosin.

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Myosin

Thick filament with globular heads, responsible for binding to actin.

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Actin

Thin filament with binding sites for myosin heads; includes troponin and tropomyosin.

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Troponin

Protein that binds to actin and tropomyosin; role in muscle contraction.

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Tropomyosin

Protein that wraps around actin, covering myosin binding sites at rest.

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Alpha Motor Neuron

Neuron that innervates skeletal muscle fibers, causing contraction.

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Excitation-Contraction Coupling (EC-Coupling)

Process linking electrical stimulation to muscle contraction.

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Calcium's Role

Binds to troponin, exposing myosin-binding sites on actin for contraction.

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Sliding Filament Theory

Myosin heads bind, tilt, detach from actin, and reattach to initiate contraction, sliding filaments and shortening sarcomere.

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ATP's Role

Supplies energy for muscle contraction and relaxation; for myosin head binding, detaching to actin, and pumping calcium.

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ATPase

Enzyme on myosin head, hydrolyzes ATP to provide energy for power stroke.

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Type I Muscle Fiber

Slow-twitch, fatigue-resistant fibers; used for endurance activities.

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Type II Muscle Fiber

Fast-twitch, fatigue-prone fibers; used for short, intense bursts of activity.

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Length-Tension Relationship

Optimal sarcomere length maximizes cross-bridge interactions, leading to maximum force generation.

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Carbohydrates

Primary energy source for muscles and brain, stored as glycogen.

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Fat

Secondary energy source during prolonged low-intensity exercise.

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Protein

Energy source utilized less frequently during exercise compared to carbs and fats.

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Mass Action Effect

Cells preferentially utilize the most abundant substrate available.

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Rate-Limiting Enzyme

Enzyme early in a metabolic pathway that controls the overall speed of the reaction.

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ATP-PCr System

Anaerobic energy system; provides rapid energy for short bursts of activity (1-15 sec).

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Glycolysis

Anaerobic energy system that breaks down glucose to produce ATP in the absence of oxygen (2-3 min).

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Resting Membrane Potential

Electrical charge difference between the inside and outside of a cell at rest.

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Depolarization

Inside of a cell becomes less negative.

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Hyperpolarization

Inside of a cell becomes more negative.

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Study Notes

Skeletal Muscle Structure and Function

  • Skeletal muscle is voluntary
  • Cardiac and smooth muscle are involuntary
  • Myofibrils are composed of thick and thin filaments (actin and myosin)
  • Sarcomere is the basic functional unit of a myofibril
  • Myosin has globular heads that bind to actin
  • Actin is twisted with tropomyosin and troponin
  • Troponin binding sites are covered by tropomyosin at rest
  • Calcium binding to troponin uncovers the binding sites, allowing myosin heads to bind
  • The sliding filament theory describes the shortening of sarcomeres during contraction
  • Myosin heads bind to actin, cause a shape change(power stroke) pulling the actin, and detach to repeat the cycle
  • ATP is required for all steps of muscle contraction and relaxation
  • ATPase splits ATP to provide energy for the power stroke
  • Muscle fiber types (Type I and Type II) differ in speed of contraction, oxidative capacity, and recruitment patterns

Muscle Fiber Contraction

  • Alpha motor neurons connect and innervate skeletal muscle fibers, triggering contraction.
  • Excitation-Contraction Coupling (EC-Coupling) describes the process following motor neuron activation that leads to muscle contraction.
    • Action potential travels down T-tubules
    • Calcium is released from sarcoplasmic reticulum (SR)
    • Calcium binds to troponin causing tropomyosin to move, exposing myosin binding sites
  • The steps are: Action potential -> acetylcholine release -> depolarization -> calcium release from SR -> binds to troponin -> tropomyosin moves -> actin-myosin binding -> power stroke -> calcium re-uptake -> relaxation

Muscle Fiber Types

  • Type I (slow-twitch) fibers are recruited first during low-intensity exercise, have high oxidative capacity for endurance activities
  • Type II (fast-twitch) fibers are more powerful and are recruited during high-intensity exercise, higher glycolytic capacity

Energy for Muscle Contraction

  • ATP is the primary energy source for muscle contraction
  • ATP is broken down to ADP and inorganic phosphate, releasing energy for the power stroke.
  • Several ATP cycles are typically needed for each myosin head.
  • ATP is also needed to pump calcium back into SR for relaxation.

Fuel for Exercise

  • Carbohydrates: Primary energy source (glucose) for high-intensity exercise; muscle and liver glycogen are used.
  • Fats: Important during prolonged low-intensity exercise, sources are free fatty acids and glycerol.
  • Proteins: Provides a limited amount of energy during exercise; amino acids.

Basic Energy Systems

  • ATP-PCr system: Anaerobic; provides energy for short-duration, high-intensity activities (3-15 seconds)
  • Glycolysis: Anaerobic; rapid breakdown of glucose or glycogen (2-3 minutes)
  • Oxidative system: Aerobic; major energy source for prolonged exercise, utilizing carbohydrates or fats.

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Description

Explore the intricacies of skeletal muscle structure and its functional role in voluntary movement. This quiz covers essential concepts such as the sliding filament theory, muscle contraction mechanisms, and differences in muscle fiber types. Test your knowledge on myofibrils, sarcomeres, and the role of ATP in muscle contraction.

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