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Questions and Answers
What characteristic distinguishes the appearance of smooth muscle fibers?
What characteristic distinguishes the appearance of smooth muscle fibers?
How do dense bodies function in smooth muscle fibers?
How do dense bodies function in smooth muscle fibers?
What type of contraction does smooth muscle exhibit compared to striated muscle?
What type of contraction does smooth muscle exhibit compared to striated muscle?
Where does the calcium necessary for smooth muscle contraction primarily come from?
Where does the calcium necessary for smooth muscle contraction primarily come from?
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What is the structural arrangement of thick and thin filaments in smooth muscle?
What is the structural arrangement of thick and thin filaments in smooth muscle?
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What distinguishes multi-unit smooth muscle from single-unit smooth muscle?
What distinguishes multi-unit smooth muscle from single-unit smooth muscle?
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What happens to smooth muscle fibers during contraction?
What happens to smooth muscle fibers during contraction?
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What role does the slow movement of calcium play in smooth muscle function?
What role does the slow movement of calcium play in smooth muscle function?
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What defines isometric contraction in muscle activity?
What defines isometric contraction in muscle activity?
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Which type of cardiac muscle cell is responsible for mechanical pumping action?
Which type of cardiac muscle cell is responsible for mechanical pumping action?
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What is the primary role of autorhythmic cells in cardiac muscle?
What is the primary role of autorhythmic cells in cardiac muscle?
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Which physiological property of cardiac muscle refers to its ability to spontaneously generate electrical impulses?
Which physiological property of cardiac muscle refers to its ability to spontaneously generate electrical impulses?
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What is the effect of sympathetic stimulation on the pacemaker cells of the heart?
What is the effect of sympathetic stimulation on the pacemaker cells of the heart?
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How does smooth muscle differ from other types of muscle regarding its structural appearance?
How does smooth muscle differ from other types of muscle regarding its structural appearance?
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Which of the following is NOT a characteristic of cardiac muscle properties?
Which of the following is NOT a characteristic of cardiac muscle properties?
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What is the muscle type characterized by smaller fibers and resistance to fatigue?
What is the muscle type characterized by smaller fibers and resistance to fatigue?
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Which type of cardiac muscle contracts weakly due to containing few contractile fibrils?
Which type of cardiac muscle contracts weakly due to containing few contractile fibrils?
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What characteristic distinguishes cardiac muscle fibers from skeletal muscle fibers?
What characteristic distinguishes cardiac muscle fibers from skeletal muscle fibers?
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What is the primary functional unit of cardiac muscle called?
What is the primary functional unit of cardiac muscle called?
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Which of the following statements about the sarcoplasmic reticulum in cardiac muscle is correct?
Which of the following statements about the sarcoplasmic reticulum in cardiac muscle is correct?
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What role do gap junctions at the intercalated discs of cardiac muscle play?
What role do gap junctions at the intercalated discs of cardiac muscle play?
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Which channel type is specialized in cardiac muscle sarcolemma compared to skeletal muscle?
Which channel type is specialized in cardiac muscle sarcolemma compared to skeletal muscle?
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Which type of muscle allows for greater shortening and lengthening due to not being anchored at the ends?
Which type of muscle allows for greater shortening and lengthening due to not being anchored at the ends?
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What does the term 'syncytium' refer to in the context of cardiac muscle?
What does the term 'syncytium' refer to in the context of cardiac muscle?
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Study Notes
Muscular System Overview
- The muscular system is a complex system composed of three main types of muscle: skeletal, smooth, and cardiac.
- Cardiac muscle is specifically for the heart.
Learning Outcomes
- Students will be able to understand the structure, function, and inner workings of cardiac and smooth muscle.
- Students will be able to differentiate among skeletal, smooth, and cardiac muscle
Cardiac Muscle: Contractile Mechanism
- The heart is made up of three major types of cardiac muscle: Atrial, Ventricular, and Specialized Excitatory & Conductive Muscle.
- Atrial and Ventricular muscle contract similarly to skeletal muscle, but the contraction duration is longer.
- Specialized excitatory and conductive muscle fibers contract more weakly due to fewer contractile fibrils.
Cardiac Muscle Fibers
- Cardiac muscle fibers are striated in appearance.
- The functional unit is a sarcomere.
- Fibers branch and connect at intercalated discs.
- Intercalated discs contain gap junctions.
- Nuclei are centrally located.
- The sarcoplasmic reticulum is less abundant in comparison to skeletal muscle, but more dense than smooth muscle.
- Sarcolemma has ion channels, including voltage-gated Ca2+ channels, which aren't found in skeletal muscle.
- Fibers are not anchored at ends, facilitating sarcomere shortening and lengthening.
Cardiac Muscle: Intercalated Discs
- Cell membranes of intercalated discs fuse to form "communicating junctions" (gap junctions).
- Gap junctions allow free ion diffusion.
- Ions move easily through the longitudinal axes of cardiac muscle fibers, enabling easy action potential transmission from one cardiac cell to the next.
- This interconnectedness creates a syncytium, allowing the action potential to spread throughout all heart muscle cells.
Cardiac Muscle Contraction
- Cardiac muscle contraction is described as isometric (occurs without significant shortening) or isotonic (occurs without significant change in force).
- Intercalated discs form functional syncytia.
- Two types of membrane junctions within these discs: desmosomes and gap junctions.
Cardiac Muscle Cells
- The heart beats rhythmically due to action potentials generated within the heart itself (autorhythmicity).
- Two types of cardiac muscle cells:
- Contractile cells: make up 99% of cardiac muscle and do the pumping work.
- Autorhythmic cells: do not contract but are specialized to initiate and conduct action potentials for working cells' contraction.
Cardiac Muscle Properties
- Automaticity: ability to spontaneously generate an electrical impulse.
- Excitability: ability to respond to an electrical impulse.
- Conductivity: ability to transmit the electrical impulse to other cardiac cells.
- Contractility: ability to contract after an electrical impulse.
- Rhythmicity: ability to send electrical impulses in a regular manner.
Smooth Muscle
- Smooth muscle is a primitive type of muscle compared to skeletal and cardiac muscle.
- Smooth muscle lacks striations and sarcomeres.
- It is highly resistant to fatigue, and its cross-sectional area strength is comparable to skeletal muscle.
- Smooth muscle fibers are smaller, involuntary, and have tapered ends and a centrally positioned nucleus.
- Sarcoplasm contains more thin than thick filaments with dense bodies similar to Z-disks anchoring the thin filaments.
Smooth Muscle Contraction
- Sliding filament mechanism involves thick and thin filaments
- No troponin complex.
- Actin and myosin pull on the dense bodies attached to the sarcolemma.
- Contraction causes lengthwise shortening and bulges in the fiber.
- Shortening is a corkscrew-like twisting of the fiber helix.
Types of Smooth Muscle
- Single-unit smooth muscle: large aggregates of cells acting as a single unit. Found in hollow organs and blood vessels.
- Multi-unit smooth muscle: individual cells with a single nerve connection, found in specific areas like the iris and arrector pili muscles.
Smooth Muscle Contractile Mechanism
- Smooth muscle contraction begins slower and lasts longer compared to striated muscle.
- Contractions can extend for hours or days.
- They can shorten and stretch significantly more.
- Initiation is triggered by Ca2+ influx.
- Calcium movement is slow, owing to the sparse sarcoplasmic reticulum and lack of T-tubules.
Smooth Muscle Stimulation
- Smooth muscle responds to nerve impulses, hormones, and mechanical stimulation.
- Key hormones influencing smooth muscle include norepinephrine, epinephrine, acetylcholine, angiotensin II, oxytocin, vasopressin, serotonin, and histamine.
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Description
This quiz explores the intricacies of the muscular system, focusing particularly on the types of muscles: skeletal, smooth, and cardiac. Students will learn to identify and differentiate between these muscle types and understand the functions of cardiac muscle fibers.
