Muscle Contraction: Types and Characteristics
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Questions and Answers

Which characteristic distinguishes skeletal muscle from both cardiac and smooth muscle?

  • Involuntary movements
  • Single nucleus per cell
  • Attachment to the skeleton (correct)
  • Presence of striations

What is the correct order, from thickest to thinnest, of the connective tissue layers surrounding muscle?

  • Epimysium, Perimysium, Endomysium (correct)
  • Epimysium, Endomysium, Perimysium
  • Perimysium, Endomysium, Epimysium
  • Endomysium, Perimysium, Epimysium

During an eccentric contraction, what happens to the muscle's length and tension?

  • Muscle shortens; tension remains constant
  • Muscle lengthens; tension decreases
  • Muscle lengthens; tension is maintained (correct)
  • Muscle shortens; tension increases

During muscle contraction, what is the role of calcium?

<p>Binds to troponin, causing a conformational change (B)</p> Signup and view all the answers

Which type of muscle contraction involves no change in muscle length?

<p>Isometric (D)</p> Signup and view all the answers

If a muscle is described as shortening while generating force against resistance, what type of contraction is occurring?

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

What structural protein is primarily responsible for anchoring the myosin filaments and maintaining their alignment within the sarcomere?

<p>Titin (D)</p> Signup and view all the answers

What happens to the length of the actin filaments during muscle contraction?

<p>They slide, but their length remains constant (B)</p> Signup and view all the answers

How does the mitochondrial content typically differ between Type 1 and Type 2 muscle fibers?

<p>Type 1 fibers generally have higher mitochondrial content, supporting their oxidative metabolism. (C)</p> Signup and view all the answers

During sustained, low-intensity exercise, which metabolic characteristic is most utilized by Type 1 muscle fibers?

<p>Efficient ATP production through oxidative phosphorylation. (C)</p> Signup and view all the answers

What is the key characteristic that distinguishes hybrid muscle fibers from pure Type 1 or Type 2 fibers?

<p>Hybrid fibers exhibit a mix of Type 1 and Type 2 characteristics, without fully adopting either profile. (B)</p> Signup and view all the answers

A weightlifter is performing short bursts of very high-intensity exercises. Which energy system is primarily utilized, and which type of muscle fibers are most recruited?

<p>Glycolysis; Type 2 fibers (B)</p> Signup and view all the answers

How is the usage of each muscle affected based on the mitochondrial density?

<p>Muscles with higher mitochondrial density rely less on anaerobic pathways. (B)</p> Signup and view all the answers

Which metabolic adaptation is most likely to delay the onset of fatigue in Type II muscle fibers?

<p>Decreasing the reliance on glycogen for ATP production. (C)</p> Signup and view all the answers

What best explains the primary mechanism by which lactic acid contributes to muscle fatigue?

<p>It interferes with calcium ion dynamics and pH balance. (A)</p> Signup and view all the answers

Which training adaptation would be most effective in increasing the endurance capacity of Type II muscle fibers?

<p>Enhancing the muscle fiber's ability to utilize glucose. (D)</p> Signup and view all the answers

What cellular change would be MOST effective for delaying fatigue in Type II muscle fibers?

<p>Developing a greater mitochondrial content. (B)</p> Signup and view all the answers

Under what conditions can muscle fibers change permanently from one type to another?

<p>With consistent and specific strength training regimens. (B)</p> Signup and view all the answers

What is the primary role of tropomyosin in muscle contraction?

<p>To block the myosin-binding sites on actin molecules in a resting muscle. (D)</p> Signup and view all the answers

Which event directly triggers the conformational change in troponin that initiates muscle contraction?

<p>The release of calcium ions from the sarcoplasmic reticulum. (C)</p> Signup and view all the answers

During muscle contraction, what causes the sarcomere to shorten?

<p>The sliding of actin filaments over myosin filaments. (C)</p> Signup and view all the answers

Where does the energy required for muscle contraction directly come from?

<p>Hydrolysis of ATP. (C)</p> Signup and view all the answers

In excitation-contraction coupling, what is the role of acetylcholine?

<p>To transmit the action potential from the motor neuron to the muscle cell. (D)</p> Signup and view all the answers

What is the primary function of T-tubules in muscle cells?

<p>To transmit action potentials throughout the muscle cell. (D)</p> Signup and view all the answers

What type of receptor does acetylcholine bind to on the muscle cell membrane to initiate excitation-contraction coupling?

<p>Nicotinic acetylcholine receptors. (B)</p> Signup and view all the answers

Which receptor is directly stimulated by acetylcholine (ACh) at the neuromuscular junction?

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

What is the role of the sarcoplasmic reticulum (SR) in muscle contraction?

<p>To store and release calcium ions. (C)</p> Signup and view all the answers

What is the correct sequence of events in muscle contraction following the arrival of an action potential at the neuromuscular junction?

<p>Acetylcholine release → Action potential in muscle fiber → Calcium release → Myosin binding to actin. (B)</p> Signup and view all the answers

How does the sliding filament theory explain muscle contraction?

<p>Thin filaments slide past thick filaments, causing the sarcomere to shorten. (B)</p> Signup and view all the answers

What prevents the detachment of myosin from actin after death, leading to rigor mortis?

<p>Depletion of ATP. (A)</p> Signup and view all the answers

Which of the following events directly leads to the exposure of myosin-binding sites on actin?

<p>The binding of calcium to troponin. (A)</p> Signup and view all the answers

How does the action potential initiated at the sarcolemma reach the myofibrils located deep within the muscle fiber?

<p>Via the transverse tubules (T-tubules). (C)</p> Signup and view all the answers

What is the direct role of the ryanodine receptor in muscle contraction?

<p>To release calcium from the sarcoplasmic reticulum. (A)</p> Signup and view all the answers

What is the sequence of events that leads to muscle contraction after an action potential reaches the muscle cell?

<p>Action potential → T-tubules → Ryanodine receptor → Calcium release → Troponin binding (A)</p> Signup and view all the answers

During glycolysis, what is the net production of ATP if the process starts with glycogen rather than glucose?

<p>Three ATP molecules, due to the direct conversion of glucose-1-phosphate to glucose-6-phosphate. (C)</p> Signup and view all the answers

How does decreased calcium availability within the sarcoplasmic reticulum (SR) affect muscle contraction?

<p>It reduces the amount of calcium available to bind to troponin, weakening muscle contractions. (D)</p> Signup and view all the answers

Under aerobic conditions, what is the primary fate of pyruvate produced during glycolysis?

<p>Transport into the mitochondria for further oxidation. (A)</p> Signup and view all the answers

A muscle cell is undergoing intense anaerobic exercise. Which of the following best describes the likely metabolic state?

<p>Increased pyruvate conversion to lactate, decreased calcium release from the SR. (B)</p> Signup and view all the answers

Which statement correctly describes the relationship between glycolysis and the citric acid cycle (also known as the Krebs cycle)?

<p>Glycolysis produces pyruvate, which is then converted into acetyl-CoA to fuel the citric acid cycle. (D)</p> Signup and view all the answers

Flashcards

Cardiac Muscle

Muscle type found in the heart and characterized by rhythmic contractions.

Smooth Muscle

Muscle type found in the walls of internal organs like the stomach and intestines.

Skeletal Muscle

Muscle type attached to bones, providing movement via leverage.

Epimysium

Thickest connective tissue layer surrounding the entire muscle.

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Perimysium

Connective tissue layer surrounding a fascicle (muscle bundle).

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Endomysium

Thinnest connective tissue layer surrounding individual muscle fibers.

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Isometric Contraction

Muscle contraction with no length change.

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Isotonic Contraction

Muscle contraction where length changes.

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Type II muscle fiber

Muscle fiber with less glycogen content.

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Type I muscle fiber

Muscle fiber type with more mitochondria.

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Type II fibers

Glycolytic enzymes are related to this muscle fiber type.

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Type I motor unit

A motor unit that primarily consists of Type I muscle fibers.

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Hybrid Fibers

Muscle fibers that can take on characteristics of both Type I and Type II fibers.

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T-Tubules

Invaginations of the sarcolemma that transmit action potentials throughout the muscle cell.

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Nicotinic Receptor

A receptor on the muscle cell membrane that binds acetylcholine (Ach).

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Sarcoplasmic Reticulum (SR)

Stores and releases calcium ions (Ca2+) to trigger muscle contraction.

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DHP Receptor

A receptor in the T-tubules that is sensitive to voltage changes.

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Ryanodine Receptor

Located on the sarcoplasmic reticulum, it releases calcium into the sarcoplasm.

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ATP's Role: Unbinding

Myosin detaches from actin, allowing muscle relaxation.

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Rigor Mortis

Muscle stiffness after death due to the lack of ATP.

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Troponin's Action

Moves tropomyosin away from actin binding sites.

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Troponin & Tropomyosin

Troponin and tropomyosin regulate muscle contraction by controlling myosin's access to actin binding sites.

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Sliding Filament Theory

Actin filaments slide over myosin filaments, shortening the sarcomere and causing muscle contraction.

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Calcium's Role in Contraction

Calcium binds to troponin, causing a conformational change that exposes the actin binding sites for myosin.

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Muscle Relaxation

After contraction, myosin unbinds from actin, muscles relax, and sarcomeres lengthen.

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Energy Source for Muscles

Energy for muscle contraction comes from nutrients stored in the body, such as fat.

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Excitation-Contraction Coupling

Excitation-contraction coupling is the process where an action potential in a muscle cell leads to muscle contraction.

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Acetylcholine's Role

Acetylcholine is a neurotransmitter released by motor neurons that binds to nicotinic receptors on muscle cells.

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Receptor Binding & Action Potential

The binding of acetylcholine to receptors triggers an action potential in the skeletal muscle cell.

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Fatigue

A decline in muscle force and power over time.

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Type 2 Fibers & Fatigue

Muscle fibers with high susceptibility to fatigue due to their reliance on glycogen.

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Type 2 Fibers & Glucose

Muscle fibers primarily utilizing glucose to produce ATP.

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Fiber Type Conversion

Type 2 muscle fibers can shift their characteristics with strength training.

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Lactic Acid & Fatigue

The accumulation of lactic acid, calcium and hydrogen ions which can cause fatigue.

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Glycogen & Calcium

Glycogen breakdown leads to less calcium being released from the sarcoplasmic reticulum (SR).

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Calcium & Muscle Contraction

In the absence of sufficient calcium, troponin's reduced binding prevents tropomyosin from moving, inhibiting myosin from binding to actin.

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Glycolysis

Glycolysis is the process and its enzymes converts glucose into pyruvate.

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Pyruvate's Destination

Pyruvate must go into the mitochondria for aerobic metabolism.

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Pyruvate to Citrate

Pyruvate becomes Citrate (Citric Acid Cycle).

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Study Notes

  • There are three types of muscle: cardiac, smooth, and skeletal.
  • Cardiac and smooth muscles share similarities in their contractions.
  • Skeletal muscles attach to the skeleton through the lever system.
  • Skeletal muscles provides more than one movement.

Muscle Structure

  • Connective tissues include the epimysium, perimysium, and endomysium.
  • Epimysium is connective tissue.
  • Perimysium surrounds the fascicle and is connective tissue which creates muscle bundles
  • Endomysium is connective tissue.
  • Muscles, tendons and bones are involved in physical movement.
  • A muscle contains muscle bundles.
  • Muscle bundles are made up of muscle fibers.
  • Muscle fibers (cells) contain myofibrils.
  • Myofibrils are made up of sarcomeres.

Sarcomere Structure

  • Sarcomeres are the basic contractile units of muscle fibers and are what make up Myofibrils
  • Z lines define the boundaries of a sarcomere.
  • Actin and myosin are the proteins that make up the sarcomere.
  • Titin is a protein found in the sarcomere.

Types of Contractions:

  • Isometric contractions have no movement with contraction.
  • Isotonic contractions have the same force with muscle shortening.
  • Concentric contractions have the muscle shortening.
  • Eccentric contractions are when the muscle lengthens against resistance.
  • Muscle striations are created by actin and myosin.

Troponin and Tropomyosin

  • Troponin and tropomyosin are key proteins in muscle contraction.
  • Tropomyosin prevents actin from binding to myosin
  • When calcium binds to troponin, it causes a conformational change.
  • This change moves tropomyosin away from the actin binding site.
  • The exposure of the binding site allows myosin to bind to actin.

Sliding Filament

  • The sliding filament theory explains how muscles contract.
  • Actin slides over myosin during muscle contraction.
  • ATP is split into ADP and inorganic phosphate (Pi).
  • This action energizes the myosin head.
  • The myosin head then attaches to actin, forming a cross-bridge.
  • Inorganic phosphate is released.
  • The release initiates the power stroke, where the myosin head pivots.
  • The actin filament slides toward the M line, and ADP is released.
  • A new ATP molecule attaches to the myosin head.
  • The link between myosin and actin weakens.
  • The cross-bridge detaches.
  • The myosin then rebinds to actin, and contraction restarts.

Excitation-Contraction Coupling

  • Action potentials from motor neurons stimulate muscle contraction.
  • Acetylcholine is the neurotransmitter involved at the neuromuscular junction.
  • Neurotransmitter acetylcholine binds to receptors in the skeletal muscle cell
  • Receptors trigger another action potential.
  • T-tubules transmit action potentials throughout the entire muscle cell, stimulating it
  • The sarcoplasmic reticulum (SR) contains calcium, which is needed for muscle contraction
  • Action potentials trigger the release of calcium from the SR.
  • Calcium binds to troponin, initiating the sliding filament mechanism.
  • Calcium concentration degraded so Calcium returns back into the body

ATP and Muscle Contraction

  • ATP is needed for myosin to unbind from actin.
  • Rigor mortis occurs after death due to the lack of ATP.
  • This causes muscles to stiffen due to myosin remaining bound to actin.

Motor Units

  • A motor unit consists of an alpha motor neuron and all the muscle fibers it stimulates.
  • Muscle length and tension are related.
  • There is an optimal resting length for muscle to generate maximum tension.

Muscle Fiber Types

  • Muscle fiber types differ is contractile characteristics.
  • Muscle fiber types differ is structural characteristics.
  • Muscle fiber types differ is enzymatic characteristics.
  • Muscle fiber types differ is energy substrate.
  • Muscle fiber recruitment follows the size principle.
  • Smaller Type I muscle fibers are recruited before larger Type II fibers.
  • Humans can use speed quickly with a mix of fiber types.
  • Muscle length and tension can be monitored with applications.
  • A muscle unit is either type 1 or type 2, and can't contain both.
  • People typically have more of one fiber type genetically.
  • Fiber types determine muscle characteristics.
  • Type I fibers are fatigue-resistant and rely on aerobic metabolism
  • Type II fibers are more powerful but fatigue quickly.

Type I Fibers

  • Type 1 fibers (Breast & wing-Type 1) are tasty beccause of ↑ fat content

Type 2 Fibers

  • Legs-Type 2. less fat content.
  • Fiber type can influence athletic performance.
  • Fibers can use a combination of both type 1 and 2 characteristics
  • Developing more mitochondria content is training
  • Hybrid fibers can somewhat convert
  • Lactid acid acts as a buffer in mitochondria.
  • Type II fibers primarily use glycolysis to make ATP.
  • Build up of Ca2+ + H builds
  • SR calcium coming out, less Ca2+ binding to troponin, tropomyosin is now in way, myosin can't bind to actin.

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Explore the distinctions between skeletal, cardiac, and smooth muscle tissue. Understand eccentric and isometric contractions along with the role of calcium. Also, understand the difference between Type 1 and Type 2 muscle fibers.

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