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Questions and Answers
What characterizes the contraction in which muscle length changes while tension remains stable?
What characterizes the contraction in which muscle length changes while tension remains stable?
Which type of muscle contraction occurs when muscle fibers shorten while generating force?
Which type of muscle contraction occurs when muscle fibers shorten while generating force?
What is the primary role of acetylcholinesterase (AChE) in the neuromuscular junction?
What is the primary role of acetylcholinesterase (AChE) in the neuromuscular junction?
Which factor affects the amount of tension produced by a skeletal muscle?
Which factor affects the amount of tension produced by a skeletal muscle?
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What primarily dictates the number of muscle fibers that are stimulated during muscle activation?
What primarily dictates the number of muscle fibers that are stimulated during muscle activation?
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In which condition would you expect eccentric contractions to occur?
In which condition would you expect eccentric contractions to occur?
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Which term describes the unit consisting of a motor neuron and all the muscle fibers it innervates?
Which term describes the unit consisting of a motor neuron and all the muscle fibers it innervates?
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What is the result of the influx of Na+ into the muscle fiber sarcoplasm?
What is the result of the influx of Na+ into the muscle fiber sarcoplasm?
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What characterizes concentric muscle contraction?
What characterizes concentric muscle contraction?
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What happens during an eccentric contraction?
What happens during an eccentric contraction?
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Which physiological change occurs during muscle hypertrophy?
Which physiological change occurs during muscle hypertrophy?
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What is the main outcome of muscular atrophy?
What is the main outcome of muscular atrophy?
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Which type of muscle contraction involves muscle length remaining constant while tension is maintained?
Which type of muscle contraction involves muscle length remaining constant while tension is maintained?
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What describes the primary consequence of muscular dystrophy?
What describes the primary consequence of muscular dystrophy?
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What is the role of the origin in muscle activation?
What is the role of the origin in muscle activation?
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Which of the following statements about polio is accurate?
Which of the following statements about polio is accurate?
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Which statement accurately describes the characteristics of cardiac muscle tissue?
Which statement accurately describes the characteristics of cardiac muscle tissue?
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Which type of muscle contraction involves the muscle lengthening while generating force?
Which type of muscle contraction involves the muscle lengthening while generating force?
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What role does the sarcoplasmic reticulum play in muscle contraction?
What role does the sarcoplasmic reticulum play in muscle contraction?
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Which muscle fiber type is primarily responsible for rapid, powerful contractions but fatigues quickly?
Which muscle fiber type is primarily responsible for rapid, powerful contractions but fatigues quickly?
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How do transverse tubules contribute to muscle contraction?
How do transverse tubules contribute to muscle contraction?
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What is a primary characteristic of isometric contractions?
What is a primary characteristic of isometric contractions?
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In the context of muscle disorders, what does myopathy refer to?
In the context of muscle disorders, what does myopathy refer to?
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Which statement about skeletal muscle fibers is NOT true?
Which statement about skeletal muscle fibers is NOT true?
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During muscle activation, which structure's change in charge initiates contraction?
During muscle activation, which structure's change in charge initiates contraction?
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Which type of connective tissue surrounds the entire muscle and separates it from adjacent tissues?
Which type of connective tissue surrounds the entire muscle and separates it from adjacent tissues?
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Study Notes
Skeletal Muscle Tissue
- Skeletal muscle tissue is a type of muscle tissue that comprises ~700 muscles.
- Two divisions of skeletal muscle tissue exist: axial and appendicular.
- Axial muscles support and position the axial skeleton.
- Appendicular muscles support, move, and brace the limbs.
- Functions of skeletal muscle tissue include producing body movement, maintaining posture and body position, supporting soft tissues, guarding body entrances/exits, maintaining body temperature, and storing nutrients.
Muscular System Functions
- Muscle tendons move and pull bones.
- Muscles stabilize joints.
- Muscle tissues surround, support and shield internal structures.
- Sphincters encircle openings and regulate swallowing, defecation, and urination.
- Muscle contraction generates heat.
- Muscle proteins break down, releasing amino acids for glucose synthesis or energy.
Muscle Tissue
- Skeletal muscle tissue is mostly made up of skeletal muscle tissue.
- It includes connective tissue, nerves, and blood vessels.
- Skeletal muscle fibers are attached directly or indirectly to bones.
- Three types of muscle tissue exist: skeletal, cardiac, and smooth.
Comparison of Muscle Tissues
- Skeletal muscle tissue is voluntary, multinucleated, and has long, cylindrical cells with striations.
- Cardiac muscle tissue is involuntary, uninucleated, and has branching cells with striations.
- Smooth muscle tissue is involuntary, uninucleated, and has fusiform cells (tapered).
Skeletal Muscle
- Skeletal muscle is an organ.
- At each end, connective tissues fuse to form tendons or aponeuroses.
- Tendons attach muscle to bones, while aponeuroses are broad sheets attaching to bones.
- Muscle contractions pull on the tendons or aponeuroses that pull on and move the bones.
Building a Muscle
- Skeletal muscle fibers contain myofibrils—bundles of protein filaments.
- Endomysium is thin areolar connective tissue surrounding each skeletal muscle fiber, including collagen & elastic fibers, blood vessels, and nerves.
- Epimysium is a dense sheath of collagen that surrounds a muscle to separate it from other tissues and organs. It connects to deep fascia.
- Muscle fascicles are bundles of muscle fibers enclosed by perimysium.
Inside a Skeletal Muscle Fiber
- Sarcolemma is the plasma membrane surrounding a muscle cell.
- Sarcoplasm is the cytoplasm inside a muscle cell.
- Myofibrils are cylindrical structures inside muscle fibers running along the length of the fiber with a striated arrangement.
- Mitochondria are present along myofibrils.
- Nuclei are located on the cell's edge.
Transverse Tubules (T-tubules)
- T-tubules are continuous with the sarcolemma.
- They extend into the sarcoplasm forming passageways through the muscle fibers, encircling the sarcomeres.
- This allows events at the cell surface to penetrate to the interior of the muscle cell.
Sarcoplasmic Reticulum (SR)
- The sarcoplasmic reticulum is similar to smooth endoplasmic reticulum in other cells.
- It contacts the T-tubules.
- It surrounds each muscle cell and stores calcium ions.
- Calcium ions play a major role in muscle contraction.
Myofilaments
- Myofilaments are bundles of protein filaments located inside myofibrils.
- Thin filaments are mostly composed of actin.
- Thick filaments are mostly composed of myosin.
- The arrangement of these filaments creates striations.
Sliding Filament Theory
- Sarcomeres are repeating functional units of skeletal muscle fibers containing overlapping thick and thin filaments.
- ~10,000 sarcomeres make up a myofibril, each about 2 µm in resting length.
- Z lines are junctions of adjacent sarcomeres, I bands are lighter bands with only thin filaments, A bands are dark/dense regions containing thick filaments, zone of overlap is the region where thick and thin filaments overlap, M lines are the center of A bands where adjacent thick filaments connect, and H bands are the region on each side of the M line with only thick filaments.
- When muscles contract, thin filaments slide over thick filaments.
- H and I bands get smaller; zones of overlap get larger; Z lines move closer together, but A bandwidth remains unchanged.
- Myofibrils, and therefore the muscle fibers shorten during contraction.
Sliding Filament Theory of Muscle Contraction
- A nerve signal travels to the muscle causing contraction (electrical signal).
- The signal travels through the transverse tubules.
- Calcium is released.
- Myosin and actin bind.
- Z-lines move closer, and the sarcomere shortens.
- Causing the muscle to shorten.
Excitable Membranes
- Electrical charges differ across cell membranes because cells unequally distribute charged ions across their membranes, with the inside of the cell slightly more negative.
- These charges are measured in millivolts (mV).
- Nuerons’ resting potential is −70 mV, and skeletal muscle fibers’ resting potential is −85 mV.
- Cytosol and extracellular fluid have different chemical compositions.
- Membranes are selectively permeable.
- Ion pumps maintain the concentration gradient. More Na+ outside (ECF) and more K+ inside (cytosol). In the ECF, there is more Cl−, but not much diffuses across the membrane.
Movement of Sodium and Potassium
- Integral transmembrane proteins act as channels.
- The sodium-potassium pump exports three sodium ions (Na+) and imports two potassium ions (K+).
- Uneven distribution maintains resting membrane potential.
5 Steps in an Action Potential
- A small increase in membrane permeability to Na+ moves the membrane potential in a positive direction to threshold (−55 mV).
- Rush of positive Na+ ions into the cell depolarizes the cell membrane.
- Voltage-gated Na+ channels close, voltage-gated K+ channels open, and K+ leaves, cell repolarization begins.
- Voltage-gated K+ channels begin closing.
- Membrane potential stabilizes at resting level.
Action Potential Propagation
- Neurons and skeletal muscle fibers have excitable membranes.
- Action potentials (APs) propagate along the plasma membrane.
- APs are generated in less than 2 ms.
- APs travel in only one direction due to the refractory period.
- This rapid communication allows for fast transmission of signals.
Neuromuscular Junction (NMJ)
- Location where motor neurons control skeletal muscle fibers.
- One NMJ per muscle fiber; multiple muscle fibers can be controlled by one neuron.
Neuron
- Nervous tissue comprising the neuron.
- Components include cell body, dendrites, axon, and axon terminals.
Neuromuscular Junction - Components
- Axon terminal (synaptic terminal) of motor neuron: has vesicles with acetylcholine (ACh), a neurotransmitter.
- Motor end plate: portion of muscle fiber that receives the nerve signal; contains ACh receptors able to bind ACh; junctional folds increase the number of ACh receptors.
- Synaptic cleft: space between the axon terminal and motor end plate; contains acetylcholinesterase (AChE) that breaks down ACh.
Neuromuscular Junction - Activities
- Action potential arrives at motor neuron axon terminal, causing ACh vesicles to fuse with the neuron plasma membrane, releasing ACh into the synaptic cleft via exocytosis.
- ACh diffuses across the synaptic cleft, binds to ACh receptors on the motor end plate, changing sarcolemma Na+ permeability and allowing Na+ to enter the muscle fiber sarcoplasm.
- Na+ influx generates action potential in sarcolemma.
- ACh diffuses away or breaks down by AChE, and ACh receptors close.
- Action potential moves down T-tubules between terminal cisternae of sarcoplasmic reticulum (SR), changing Ca2+ permeability of SR.
- SR releases stored Ca2+ into sarcoplasm starting the contraction.
Muscle Tension and Contraction
- Tension produced by a skeletal muscle is determined by the amount of tension produced by each muscle fiber, and the number of stimulated muscle fibers (determined by stimulation frequency).
- A motor unit is a motor neuron and all the muscle fibers it innervates; one motor neuron can control multiple muscle fibers.
Muscle Contraction
- Non-resting contractions occur in pairs.
- Isotonic contractions include concentric and eccentric contractions, characterized by whether the muscle shortens or lengthens.
- Isometric contractions are those in which muscle length stays the same.
Muscle Activity
- Origin: where the fixed end of a skeletal muscle attaches.
- Insertion: where the movable end of a skeletal muscle attaches.
- Action: specific movement produced by a skeletal muscle.
Muscle Disorders
- Atrophy occurs with decreased muscle stimulation, use, normal aging, or nerve damage.
- Hypertrophy is muscle enlargement due to high stress (ex: weight lifting).
- Muscular dystrophy is a group of inherited diseases.
- Diseases such as polio, tetanus, botulism, and myasthenia gravis also cause muscle dysfunction and weakness.
- Rigor mortis is generalized muscle contraction shortly after death, caused by the depletion of ATP, preventing the myosin cross-bridges from detaching from the active sites.
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Description
Explore the fascinating world of skeletal muscle tissue in this quiz. Learn about the major divisions, functions, and structures that support body movement and posture. Test your knowledge on how muscles interact with bones and their role in maintaining overall health.
