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Which characteristic of skeletal muscle tissue refers to its ability to respond to nervous system stimulation?
What is one of the primary functions of skeletal muscles?
Which property allows skeletal muscle to stretch without damage?
What is the role of conductive properties in skeletal muscle tissues?
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Which of the following best describes the contractile capability of skeletal muscle tissue?
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Which protein is involved in forming the thick filaments of muscle fibers?
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What is the function of tropomyosin in muscle fibers?
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Which of the following proteins binds to calcium ions in the muscle contraction process?
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Where are actin proteins primarily located in a muscle cell?
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Which of the following statements is true regarding ATPase activity in muscle contraction?
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What is the primary role of satellite cells in muscle tissue?
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Which structure surrounds each myofibril and acts as a storage site for calcium ions?
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What type of channels are primarily responsible for the depolarization of the sarcolemma during an action potential?
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Which pumps are essential for maintaining the resting membrane potential in muscle cells?
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What is the primary function of voltage gated Ca+2 channels in muscle fibers?
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What is the primary composition of the structure that acts as a conduit for action potentials deep into the muscle fiber?
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Which channel is primarily located in the sarcoplasmic reticulum membrane and crucial for muscle relaxation?
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What structure forms rings around myofibrils to support their function during contraction?
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Which protein covers the myosin binding sites on actin filaments in a noncontracting muscle?
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What is the primary structural component of thick filaments in muscle fibers?
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What is the term for the structural unit formed by overlapping thick and thin filaments?
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What occurs to the H zone during maximal muscle contraction?
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What is found at the center of the H zone where thick filaments attach?
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What type of protein is connectin classified as?
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In the sarcomere, which band appears light under a microscope?
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Which of the following describes the state of muscle fibers during relaxation?
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What is the primary role of troponin in muscle contraction?
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What happens to the muscle fiber when it contracts fully?
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How are myofilaments organized within a myofibril?
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Which structural component anchors thin filaments at both ends of a sarcomere?
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What is the effect of maximal muscle contraction on the overall appearance of a sarcomere?
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What is the resting membrane potential primarily dependent on?
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What type of filament is primarily responsible for muscle contraction?
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What describes a motor unit?
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What maintains the gradients of Na+ and K+ across the plasma membrane?
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How does K+ behave in relation to its concentration gradient?
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What is meant by 'muscle tone'?
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Which ions contribute to establishing the resting membrane potential?
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What occurs to the charge of the inside of the cell as Na+ enters?
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Why does K+ reach equilibrium in its movement across the membrane?
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What is the effect of fewer Na+ leak channels in a cell?
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What happens when some motor units are stimulated randomly?
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What term describes the energy difference across the plasma membrane when the cell is at rest?
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Which factor negatively influences K+ movement out of the cell?
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How do electrical gradients influence the movement of Na+?
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Study Notes
Muscle Tissue
- Muscle tissue is found almost everywhere in the body and makes up 40-50% of the weight of an adult.
- Functions of muscular tissue include bending joints, pumping blood, propelling food through the digestive tract, and regulating air flow in the lungs.
- The muscular system contains approximately 700 skeletal muscles.
- Functions of the skeletal muscles include body movement, posture maintenance, protection and support, storage and movement of materials, and heat production.
Characteristics of Skeletal Muscle Tissue
- Excitability: Ability to respond to nervous system stimulation due to the resting membrane potential (RMP), allowing the muscle to be stimulated by nerve impulses.
- Conductivity: The ability to propagate an electrical change (action potential) along the plasma membrane, due to the presence of voltage-gated channels.
- Contractility: Ability to shorten and generate tension, due to contractile proteins within muscle cells, allowing the pulling of bones of the skeleton.
- Extensibility: Ability to lengthen, due to partial overlap of actin and myosin filaments, as seen in the extension of the triceps brachii when flexing the elbow joint.
- Elasticity: Ability to return to its original length after being stretched or contracted.
Microscopic Anatomy of Skeletal Muscle Tissue
- Sarcoplasm: Cytoplasm of a muscle fiber, containing organelles.
- Multiple Nuclei: Muscle fibers are multinucleated, with nuclei located along the periphery of the fiber, due to fusion of myoblasts during development.
- Sarcolemma: Plasma membrane of a muscle fiber, surrounding the muscle fiber and containing transverse tubules (T-tubules).
- Transverse Tubules (T-tubules): Invaginations of the sarcolemma that extend into the muscle fiber, allowing for rapid conduction of action potentials from the sarcolemma to the sarcoplasmic reticulum.
- Sarcoplasmic Reticulum: Specialized endoplasmic reticulum of muscle fibers, surrounding each myofibril and storing calcium ions (Ca2+) which are essential for muscle contraction.
- Terminal Cisternae: Enlarged sacs of the sarcoplasmic reticulum that lie close to T-tubules, releasing Ca2+ into the sarcoplasm when stimulated by an action potential.
Myofibrils
- Long, cylindrical structures that extend the length of the muscle fiber and make up 80% of its volume.
- Composed of numerous myofilaments.
Myofilaments
- Bundles of protein filaments that are arranged in repeating units called sarcomeres.
- There are two types of myofilaments: thick filaments and thin filaments.
Thick Filaments
- Composed of bundles of myosin protein molecules.
- Each myosin protein has two intertwined strands, each with a globular head and an elongated tail.
- Tails point towards the center of the thick filament, while heads point towards the edges.
- The heads have binding sites for actin (thin filaments) and a site where ATP attaches and is split.
Thin Filaments
- Composed of two strands of actin protein twisted around each other.
- Many small spherical molecules of globular actin connect to form a fibrous strand of filamentous actin.
- Globular actin has myosin binding sites where myosin heads attach during contraction.
- Tropomyosin is a twisted string-like protein that covers small bands of the actin strands, covering myosin binding sites in a non-contracting muscle.
- Troponin is a globular protein attached to tropomyosin, containing a binding site for Ca2+.
- Together, tropomyosin and troponin form the troponin-tropomyosin complex.
Organization of Myofilaments: Sarcomere
- Sarcomeres are the repeating units of myofilaments.
- The number of sarcomeres varies with the length of the myofibril.
- Each sarcomere is composed of overlapping thick and thin filaments and is delineated at both ends by Z discs.
- Z Discs: Specialized proteins that are perpendicular to myofilaments and act as anchors for thin filaments.
Sarcomere: Overlapping Filaments
- I Bands: Regions containing only thin filaments that extend from both directions of the Z disc.
- I bands are bisected by the Z disc, appear light under a microscope, and disappear during maximal muscle contraction.
- A Band: The central region of the sarcomere, containing the entire thick filament and partially overlapping thin filaments.
- A bands appear dark under a microscope.
- H Zone: Central portion of the A band where only thick filaments are present; no thin filament overlap.
- The H zone disappears during maximal muscle contraction.
- M Line: A protein meshwork structure at the center of the H zone that serves an attachment site for thick filaments.
Sarcomere: Contractility, Extensibility, Elasticity
- Sliding Filament Theory: Explains how muscle contraction occurs.
- Contraction: During muscle contraction, the thin filaments slide past the thick filaments, pulling the Z discs closer together, making the sarcomere shorter and the H zone and I band disappear.
- Extensibility: The ability of the sarcomere to lengthen, facilitated by the elasticity of the sarcomere, and relies on partial overlap of the actin and myosin filaments.
- Elasticity: Ability of the sarcomere to return to its original length after being stretched or contracted, enabled by proteins such as connectin, which acts as a spring-like structure, producing passive tension during contraction and releasing that tension during relaxation.### Resting Membrane Potential
- Plasma membrane establishes and maintains an electrochemical gradient - the resting membrane potential
- Membrane potential is the potential energy of the charge difference
- Resting membrane potential (RMP) is the potential when a cell is at rest
- It is essential for muscle and nerve cell function
Electro-Chemical Gradients
- Potassium (K+) moves down its steep concentration gradient through leak channels from cytosol to interstitial fluid.
- Negatively charged proteins remain inside the cell.
- The electrochemical gradient creates a force that repels the movement of K+ out of the cell and attracts it inward
- Equilibrium is reached when the two forces become equal.
- Sodium (Na+) diffuses into cells from interstitial fluid to cytosol.
- Na+ enters through Na+ leak channels.
- Na+ is pulled by the electrical gradient, and fewer leak channels prevent as much Na+ from entering the cytosol as K+ leaves.
- This makes the inside of the cell relatively more positive.
Na+/K+ pump
- The Na+/K+ pump maintains K+ and Na+ gradients following their diffusion.
- Na+ is pumped out of the cell and K+ is pumped in.
- They move in opposite directions, against their concentration gradients.
Innervation of Skeletal Muscle Fibers
- A motor unit is a single motor neuron and all the muscle fibers it controls.
- The number of fibers a neuron innervates varies.
- Small motor units have fewer muscle fibers than large motor units.
- There is an inverse relationship between the size of a motor unit and the degree of control.
- Muscle fibers are dispersed throughout most of a muscle, and they produce a weak contraction over a wide area.
- Muscle tone is the resting tension in a muscle.
- It is generated by involuntary nervous stimulation of muscle.
- Some motor units are stimulated randomly at any time.
- Muscle tone doesn't produce strong enough contraction for movement, but it helps to stabilize tendons and joints.
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Description
Explore the fascinating world of muscle tissue, its functions, and characteristics. This quiz covers the importance of muscular tissue in the body, including skeletal muscle functions and key properties such as excitability, conductivity, and contractility.
