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Questions and Answers
What type of muscle is classified as non-striated?
What type of muscle is classified as non-striated?
Which of the following functions is NOT associated with skeletal muscle?
Which of the following functions is NOT associated with skeletal muscle?
How much of the body weight is comprised of skeletal muscle?
How much of the body weight is comprised of skeletal muscle?
Which type of muscle is classified as involuntary?
Which type of muscle is classified as involuntary?
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What is the primary function of cardiac muscle?
What is the primary function of cardiac muscle?
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What primarily composes a motor unit?
What primarily composes a motor unit?
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Which type of muscle fiber is characterized as slow-oxidative?
Which type of muscle fiber is characterized as slow-oxidative?
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How does muscle strength increase during activation of motor units?
How does muscle strength increase during activation of motor units?
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What is a result of strength training on muscle fiber?
What is a result of strength training on muscle fiber?
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Which statement best describes oxidative fibers?
Which statement best describes oxidative fibers?
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What effect does endurance training generally have on muscle fibers?
What effect does endurance training generally have on muscle fibers?
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What regulates skeletal muscle tone?
What regulates skeletal muscle tone?
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What best describes fast-glycolytic fibers?
What best describes fast-glycolytic fibers?
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What characterizes incomplete tetanus?
What characterizes incomplete tetanus?
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Which factor contributes to the staircase effect (Treppe)?
Which factor contributes to the staircase effect (Treppe)?
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What happens during complete tetanus?
What happens during complete tetanus?
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What does the length-tension relationship indicate?
What does the length-tension relationship indicate?
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How is contracture characterized?
How is contracture characterized?
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What is a key feature of spatial summation?
What is a key feature of spatial summation?
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What occurs in a short sarcomere during contraction?
What occurs in a short sarcomere during contraction?
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Which phenomenon describes contraction strength increasing with repeated stimuli of the same intensity?
Which phenomenon describes contraction strength increasing with repeated stimuli of the same intensity?
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What is the primary storage site for Ca2+ in muscle cells?
What is the primary storage site for Ca2+ in muscle cells?
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What is the structure formed by 1 T-tubule and 2 terminal cisternae?
What is the structure formed by 1 T-tubule and 2 terminal cisternae?
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During muscle contraction, which area appears light due to the lack of overlap between actin and myosin?
During muscle contraction, which area appears light due to the lack of overlap between actin and myosin?
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Which protein filament is primarily involved in muscle contraction?
Which protein filament is primarily involved in muscle contraction?
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What is the primary role of the myosin head in muscle contraction?
What is the primary role of the myosin head in muscle contraction?
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What is located at the Z-line in a muscle sarcomere?
What is located at the Z-line in a muscle sarcomere?
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What happens to the I-band during muscle contraction?
What happens to the I-band during muscle contraction?
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Which protein component of the thin filament serves as a binding site for myosin heads?
Which protein component of the thin filament serves as a binding site for myosin heads?
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What measures muscle response or electrical activity in response to nerve stimulation?
What measures muscle response or electrical activity in response to nerve stimulation?
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What primarily causes muscular fatigue?
What primarily causes muscular fatigue?
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What type of skeletal muscle responds well to repetitive stimulation without becoming fatigued and is involved in maintaining posture?
What type of skeletal muscle responds well to repetitive stimulation without becoming fatigued and is involved in maintaining posture?
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What is a neuronal factor contributing to muscle fatigue?
What is a neuronal factor contributing to muscle fatigue?
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What happens to fatigue if adequate recovery time does not occur?
What happens to fatigue if adequate recovery time does not occur?
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Study Notes
Muscle
- Soft tissue found in most animals
- Composed of cells (muscle cells) and connective tissue
- Comprise ~45% of body weight
- Function to produce force and motion
Types of Muscles
-
Morphology (histology)
- Striated muscle: skeletal muscle, cardiac muscle
- Non-striated muscle: smooth muscle
-
Innervation
- Voluntary muscle: skeletal muscle
- Involuntary muscle: smooth muscle, cardiac muscle
General Functions of Muscles
- Energy converter, transducer
- Muscle contraction: chemical energy ➡️ mechanical and heat energy
- Skeletal muscle: movement, locomotion, body heat control
- Smooth muscle: control internal diameter of blood vessels and bronchi ➡️ resistance control ➡️ blood and air flow regulation
- Cardiac muscle: generates blood pressure ➡️ energy for blood flow
Skeletal Muscle
- Striated muscle
- About 40% of body weight, approximately 400 skeletal muscles in the body
- Innervated by the central nervous system, effector for supporting and moving skeleton
Structure of Skeletal Muscle
- Myofibril: densely packed parallel units within muscle fiber
- Sarcomere: functional unit of muscle contraction, extends from Z-line to Z-line
- Sarcolemma: muscle cell membrane
- T-tubule: invaginations of the sarcolemma, carry action potentials into muscle fiber
- Lateral sac (terminal cisternae): an inflated area adjacent to the T-tubule, stores Ca2+
- Triad: 1 T-tubule and adjacent 2 terminal cisterni
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Myofilament: contractile protein, components of myofibril:
- Thick filament: Myosin
- Thin filament: Actin
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Striation:
-
A-band: corresponds to the length of myosin filament, can be subdivided into:
- H-zone: area where myosin is not overlapped with actin
- M-line: attachment site for thick filaments
- I-band: corresponds to the length of actin filament not overlapped with myosin, shortened during contraction
- Z-line (A-disk): actin attachment site, centerline of I-band
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A-band: corresponds to the length of myosin filament, can be subdivided into:
Contractile Proteins
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Myosin Filament:
- Polymer of about 200 myosin molecules
-
Myosin head: bumps of about 20nm with:
- Actin-binding site: forms actin-myosin cross-bridge
- Enzymatic site: ATPase activity
- Myosin neck: acts as a hinge, utilizes ATP energy
-
Actin Filament:
- Comprised of 3 proteins: actin, tropomyosin, troponin:
- Actin (G-actin): globular monomer, connected in a row to form two spiral chains (F-actin)
- Cross-bridge binding site: located in the furrow between actin chains, covered by tropomyosin in resting state
- Tropomyosin: filamentous protein that blocks myosin binding sites on actin
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Troponin: complex of 3 proteins:
- TnT: binds to tropomyosin
- TnC: binds to Ca2+
- TnI: inhibits actin-myosin interaction
- Comprised of 3 proteins: actin, tropomyosin, troponin:
Sliding Filament Theory
-
Description:
- Myosin heads bind to actin, forming cross-bridges
- Myosin heads pull actin filaments towards the M-line
- Sarcomere shortens, muscle contracts
- Power stroke requires ATP hydrolysis
- Requires Ca2+ released from the sarcoplasmic reticulum
-
Steps:
- Resting State: Myosin head is cocked, bound to ATP, but not to actin
- Ca2+ Binding: Ca2+ binds to troponin, causing tropomyosin to shift, exposing myosin binding sites on actin
- Cross-bridge Formation: Myosin head binds to actin
- Power Stroke: Myosin head pivots, pulling actin filament toward the M-line, releasing ADP and Pi
- ATP Binding: ATP binds to myosin head, causing it to detach from actin
- Myosin Reactivation: ATP is hydrolyzed, myosin head returns to cocked position
Muscle Contraction
-
Action Potential:
- Nerve impulse triggers release of acetylcholine at the neuromuscular junction
- Acetylcholine binds to receptors on the sarcolemma, generating an action potential
- Action potential travels down T-tubules, reaching the sarcoplasmic reticulum
- Sarcoplasmic reticulum releases Ca2+ into sarcoplasm
-
Relaxation:
- Acetylcholinesterase breaks down acetylcholine, ending the action potential
- Ca2+ is actively pumped back into the sarcoplasmic reticulum
- Tropomyosin blocks myosin binding sites on actin, preventing cross-bridge formation
- Muscle fiber relaxes
Types of Muscle Contractions
-
Twitch: single, brief contraction caused by a single action potential
- Latent Period: time between stimulation and contraction, Ca2+ release and cross-bridge formation
- Contraction Phase: time during which the muscle shortens, cross-bridge cycling
- Relaxation Phase: time during which the muscle returns to its resting length, Ca2+ reuptake
-
Summation: repeated stimulation before muscle can fully relax, leading to greater tension
- Incomplete Tetanus: partial dissipation of elastic tension between subsequent stimuli
- Complete Tetanus: no time for dissipation of elastic tension between rapidly recurring stimuli
- Tetanus: sustained contraction with greater force than twitch, caused by repeated stimulations
- Staircase Effect (Treppe): increased contraction strength with repeated stimuli of the same intensity, due to increased Ca2+ availability and heat accumulation
-
Contracture: persistent contraction, reversible, not propagated
- Rigor Mortis: stiffness of skeletal muscles after death, due to depletion of ATP and lack of Ca2+ reuptake
Length-Tension Relationship
- Magnitude of maximum tension depends on the length of the muscle before contraction
- Optimal Length: produces maximum tension due to optimal actin-myosin overlap
- Short Sarcomere: little tension due to lack of room for actin filaments to slide
- Long Sarcomere: little tension due to limited actin-myosin overlap
Control of Muscular Strength
- Motor Unit: motor neuron and all skeletal muscle fibers innervated by its axon terminals, including the neuromuscular junctions
-
Size of Motor Unit: innervation ratio, dictates the number of muscle fibers a single motor neuron controls
- Extraocular Eye Muscle: 1:5
- General Muscle: 1:500
- Muscle Strength: increases as a large number of motor units are activated (Spatial Summation)
- Precision: smaller motor units enable more precise control
Energy for Muscle Contraction
- ATP: immediate source of energy for muscle contraction, but quickly depleted
- Creatine Phosphate: stored compound that can be used to regenerate ATP quickly
- Oxidative Phosphorylation: uses oxygen to generate ATP, provides energy for sustained muscle contraction
- Glycolysis: breaks down glucose to generate ATP, provides energy for short bursts of activity
Types of Skeletal Muscle Fibers
- Classified by shortening velocity (fast, slow) and metabolic pathways for ATP generation (oxidative, glycolytic)
- Slow-Oxidative Fiber (Type I): red muscle fiber, slow contraction speed, high fatigue resistance, relies on oxidative metabolism
- Fast-Oxidative Fiber (Type IIa): red muscle fiber, fast contraction speed, relatively high fatigue resistance, relies on both oxidative and glycolytic metabolism
- Fast-Glycolytic Fiber (Type IIb): white muscle fiber, fast contraction speed, low fatigue resistance, relies primarily on glycolytic metabolism
Exercise Effect
-
Strength Training:
- Hypertrophy: increase in muscle fiber size due to increased contractile protein content
- Increased Anaerobic Glycolytic Enzyme Content: improves short bursts of intense activity
-
Endurance Training:
- Increased Capillary Vessel Number: improves blood flow and oxygen delivery
- Increased Mitochondrial Enzyme Content: enhances aerobic metabolism and fatigue resistance
- No change in the type of muscle fiber
Skeletal Muscle Tone
- Muscle Tension: due to nerve excitement from the spinal cord, controlled by muscle spindle (sensory receptor that monitors muscle length) and descending regulation from the brain stem
- Maintains Posture: slight, continuous tension even at rest
Electromyography (EMG)
- Measures muscle response or electrical activity in response to nerve stimulation
- Increased Muscular Activity: during muscle contraction
- Decreased Muscular Activity: in cases of neuronal injury and muscular atrophy
- Used for: diagnosing muscle disorders, monitoring muscle activity, and providing feedback in rehabilitation
Muscle Fatigue
- Inability to maintain muscle tension at a certain level, accompanied by muscle discomfort and pain
-
Muscular Factors:
- Depletion of energy sources (ATP, creatine phosphate)
- Accumulation of inorganic phosphate and H+
- Inappropriate blood supply
-
Neuronal Factors:
- Defects in release or generation of acetylcholine at the neuromuscular junction
- Neuromuscular fatigue: reduced ability of nerve to stimulate muscle
Recovery from Fatigue
- Rest: allows for replenishment of energy sources, removal of waste products, and restoration of normal function
- Inadequate Recovery Time: leads to faster fatigue reoccurrence
Distribution of Muscle Fiber Types
- Slow-Oxidative (Type I): postural muscles, require sustained contraction
- Fast-Oxidative (Type IIa): walking and running, fast and repetitive contractions
- Fast-Glycolytic (Type IIb): sprinting, jumping, short bursts of intense activity
- Most skeletal muscles contain a mixture of fiber types, allowing for a range of movements and activities
References:
- Refer to your physiology textbook and other relevant sources for more detailed information
Note:
- Remember to study the information presented in the text and consult your instructors for further guidance on the topic.
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Description
Test your knowledge on the structure and function of different types of muscles, including skeletal, cardiac, and smooth muscles. This quiz covers muscle morphology, innervation, and general functions of muscles within the body. Perfect for biology students and enthusiasts!
