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Questions and Answers
Which characteristic of muscle tissue refers to its ability to generate an action potential in response to a stimulus?
Which characteristic of muscle tissue refers to its ability to generate an action potential in response to a stimulus?
What term describes the ability of muscle cells to shorten forcefully?
What term describes the ability of muscle cells to shorten forcefully?
Automaticity, one of the specific electro-physiologic properties of myocardial cells, refers to which capability?
Automaticity, one of the specific electro-physiologic properties of myocardial cells, refers to which capability?
The phase of the cardiac muscle action potential characterized by rapid depolarization due to Na⁺ influx is known as?
The phase of the cardiac muscle action potential characterized by rapid depolarization due to Na⁺ influx is known as?
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In cardiac muscle physiology, changing the strength of contraction is referred to as?
In cardiac muscle physiology, changing the strength of contraction is referred to as?
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What does extensibility allow muscle tissues to do?
What does extensibility allow muscle tissues to do?
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Which phase of cardiac muscle action potential involves the opening of K⁺ channels and begins the repolarization process?
Which phase of cardiac muscle action potential involves the opening of K⁺ channels and begins the repolarization process?
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Which property of cardiac muscle cells allows for the rhythmic pumping action of the heart?
Which property of cardiac muscle cells allows for the rhythmic pumping action of the heart?
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What causes the plateau phase in cardiac muscle action potential?
What causes the plateau phase in cardiac muscle action potential?
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Which phase of the cardiac action potential is characterized by the closure of L-type Ca2+ channels?
Which phase of the cardiac action potential is characterized by the closure of L-type Ca2+ channels?
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What is the primary reason for the slower rate of repolarization compared to depolarization in cardiac muscle?
What is the primary reason for the slower rate of repolarization compared to depolarization in cardiac muscle?
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Which component of cardiac action potential is involved in restoring ionic gradients?
Which component of cardiac action potential is involved in restoring ionic gradients?
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During which periods does the relative refractory period (RRP) occur?
During which periods does the relative refractory period (RRP) occur?
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What is the role of the potassium efflux during the repolarization phase?
What is the role of the potassium efflux during the repolarization phase?
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What phenomenon prevents tetany in cardiac muscle?
What phenomenon prevents tetany in cardiac muscle?
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In smooth muscle, what property allows it to adapt to changes in length without altering tension?
In smooth muscle, what property allows it to adapt to changes in length without altering tension?
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Study Notes
Excitable Tissues II: Cardiac and Smooth Muscle
- Learning Outcomes: Students should be able to describe the physiological properties of cardiac and smooth muscles, the concept of excitation-contraction coupling, and the molecular basis of smooth muscle contraction.
Classifications
- Location: Skeletal muscle, cardiac muscle, smooth muscle
- Microscopic Appearance: Striated muscle, smooth muscle
- Activity: Voluntary muscle, involuntary muscle
Muscle Types: Location
- Skeletal muscle: Shown in diagram
- Cardiac muscle: Shown in diagram
- Smooth muscle: Shown in diagram
Muscle Types: Microscopic Appearances
- Skeletal muscle: Shown in diagram
- Smooth muscle: Shown in diagram
- Cardiac muscle: Shown in diagram
Muscle Fiber Details
- Skeletal muscle fibers: Striated, under voluntary control, and many nuclei
- Smooth muscle fibers: Spindle-shaped, under involuntary control, one central nucleus
- Cardiac muscle fibers: Striated, under involuntary control, one or two central nuclei
Terminologies
- Protoplasm - sarcoplasm
- Mitochondria - sarcosome
- Plasmalema - sarcolemma
- 1 contractile unit - sarcomere
- Endoplasmic reticulum - sarcoplasmic reticulum
Skeletal Muscle
- Shape: Cylindrical
- Features: Striations, multiple peripheral nuclei, voluntary
- Attachment: Bone, skin, joint capsule, eyeball, sphincter
Cardiac Muscle
- Fibers: Branching, anastomose with neighboring fibers, one or two central nuclei, striations
- Intercalated discs: Specialized junctions maintaining cell-to-cell cohesion (fascia adherentes, macula adherentes, junctional gap)
- Involuntary
Smooth Muscle
- Shape: Spindle-shaped
- Features: No striations, single central nucleus, involuntary
- Location: Gastrointestinal tract, respiratory tract, genitourinary tract, blood vessels, arrector pili muscle, eye (iris, ciliary body)
Properties of Muscle Tissue
- Contractility: Ability to shorten forcefully.
- Excitability: Ability to generate an action potential.
- Extensibility: Ability to stretch or extend.
- Elasticity: Ability to return to original length.
- All muscle tissues share these characteristics
Myocardial Cell Properties
- Automaticity - ability to spontaneously generate action potentials
- Excitability
- Conductivity - ability to transmit action potentials
- Contractility - ability to contract
- Rhythmicity - ability to contract in a regular pattern
- Refractoriness - period of time during which a cell cannot be excited
Characteristics of Cardiac Muscle Cells
-
Autonomic nervous system: Affects cardiac pumping by changing:
- Rate of contraction (Chronotropism)
- Strength of contraction (Inotropism)
- Increasing rate of electrical conduction is often inotropic and chronotropic.
Cardiac Muscle Ventricle Action Potential Phases
- Phase 0 (Depolarization): Rapid depolarization due to fast Na⁺ influx.
- Phase 1 (Early Rapid Repolarization): Repolarization begins as Na⁺ channels close and K⁺ channels open.
- Phase 2 (Plateau): Plateau occurs due to slow long-lasting L-type Ca²⁺ channels.
- Phase 3 (Repolarization): L-type Ca²⁺ channels close, K⁺ efflux causes repolarization.
- Phase 4: Na+/K+ pump restores ionic gradients; slow loss of positive charge.
Cardiac Muscle's Slower Repolarization
- Slow opening of K⁺ channels
- Plateau due to slow long-lasting L-type Ca²⁺ channels
- Depolarization via high-speed Purkinje system; repolarization is slower, cell to cell conduction outside the Purkinje system
Myocardial Cell Structure
- Sarcomere: Contractile unit similar to skeletal muscle. Thin and thick filaments slide to create shortening.
- Intercalated Disks: End of cells; maintain cell-to-cell cohesion
- Gap Junctions: Located at intercalated disks; low resistance paths for rapid electrical spread of action potentials.
Myocardial Cell Additional Details
- Mitochondria: More numerous in cardiac muscle than skeletal muscle
- T-tubules: Continuous with cell membrane, invaginate the cells at Z lines, crucial for signal transmission. Well developed in ventricles; dyads with sarcoplasmic reticulum.
- Sarcoplasmic Reticulum: Stores and releases Ca²⁺ for excitation-contraction coupling.
Excitation-Contraction Coupling in Skeletal Muscle
- Action potentials in the muscle cell membrane initiate depolarization of T-tubules.
- T-tubule depolarization triggers Ca²⁺ release channels in the sarcoplasmic reticulum (SR) releasing Ca²⁺ into the intracellular fluid, increasing intracellular [Ca²⁺].
Steps in Cardiac Muscle Excitation-Contraction Coupling
- Action potential spreads into T tubules
- Plateau causes increased Ca²⁺ conductance and entry from extracellular fluid
- Ca²⁺ triggers Ca²⁺ release from the SR (Ca²⁺-induced Ca²⁺ release).
- Ca²⁺ binds to troponin C and tropomyosin moves, initiating actin-myosin binding.
- Filaments slide, producing contraction.
- Relaxation occurs when Ca²⁺ is reaccumulated by the SR via active Ca²⁺-ATPase pump.
Smooth Muscle
- Characteristics: Plasticity (stress relaxation), fatigue resistance (uses less ATP), and involuntary
- Types of Smooth Muscle: Multi-unit, unitary (single-unit), and vascular
Smooth Muscle Excitation-Contraction Coupling
- No troponin; Ca²⁺ regulates myosin.
- Depolarization opens voltage-gated and ligand-gated Ca²⁺ channels; intracellular Ca²⁺ increases.
- Intracellular Ca²⁺ binds to calmodulin, activating myosin light-chain kinase.
- Phosphorylation of myosin light chains allows interactions with actin.
- Decreasing intracellular Ca²⁺ produces relaxation.
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Description
This quiz assesses your understanding of the physiological properties of cardiac and smooth muscles, including excitation-contraction coupling and the molecular basis of smooth muscle contraction. Dive into the characteristics of different muscle types and their appearances.
