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Questions and Answers
The muscular system has three types of muscle tissue.
True
Skeletal muscle fibers contract partially when stimulated.
False
Small motor units are composed of fast-twitch white fibers.
False
The sliding filament mechanism explains how muscle fibers contract.
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Red muscle fibers are typically associated with fast and explosive movements.
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Motor units within a muscle can consist of both red and white fibers.
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The nervous system controls muscle contraction through electrical impulses.
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Normal muscle length has no relation to muscle tone.
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The microanatomy of a muscle fiber is primarily composed of adipose tissue.
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Therapeutic exercises are not part of physical therapist interventions.
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Study Notes
Functions of the Muscular System
- Movement, posture, heat production, fluid movement, and support
Three Types of Muscle Tissue
-
Skeletal Muscle: Voluntary, striated (striped pattern), attached to bones by tendons
- Responsible for body movement, posture maintenance
-
Smooth Muscle: Involuntary, non-striated (no striped pattern)
- Found in various organs like the stomach, bladder, blood vessels
- Responsible for functions like digestion, blood pressure regulation
-
Cardiac Muscle: Involuntary, striated (striped pattern), found only in the heart
- Responsible for heart contractions, pumping blood throughout the body
Myofascial Unit
- Includes the muscle fibers and their connective tissues (fascia)
Microanatomy of a Muscle Fiber
- Sarcolemma: Cell membrane surrounding a muscle fiber
- Sarcoplasm: Cytoplasm of a muscle fiber containing organelles and the protein myoglobin
- Myofibrils: Specialized organelles within a muscle fiber that contain the contractile proteins actin and myosin
Sliding Filament Mechanism
- Muscle contraction occurs by the sliding of the thin filaments (actin) over the thick filaments (myosin)
- Actin: Thin filament, contains binding sites for myosin
- Myosin: Thick filament, has a head region that binds to actin and pulls it toward the center of the sarcomere
- ATP: Energy source required for the myosin heads to detach from actin and reattach, continuing the sliding process
- Calcium: Activates the sliding filament mechanism by binding to troponin, which moves tropomyosin away from the active sites on actin, allowing myosin to bind
Nervous System Control of Muscle Contraction
- Motor Neuron: A nerve cell that transmits impulses from the brain or spinal cord to muscle fibers
- Synapse: The junction between a motor neuron and a muscle fiber
- Neurotransmitter: A chemical released by the motor neuron at the synapse, acetylcholine, which stimulates the muscle fiber to contract
Motor Unit
- A motor neuron and all the muscle fibers it innervates
- Size of a motor unit can vary, affecting the precision and power of a muscle
All or None Response Law
- A muscle fiber will contract completely if it receives an electrical impulse, otherwise, it will remain relaxed
Red and White Muscle Fibers
-
Red Fibers (Slow-twitch):
- Fatigue-resistant, rely on oxygen for energy
- Used for endurance activities
-
White Fibers (Fast-twitch):
- Fatigue quickly, rely on anaerobic metabolism
- Used for short bursts of power and speed
- Motor units are composed of homogeneous fibers, either all red or all white
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Description
Explore the essential functions of the muscular system, including movement, posture, and heat production. Learn about the three types of muscle tissue: skeletal, smooth, and cardiac, along with the microanatomy of a muscle fiber. This quiz will test your knowledge about the structure and function of muscles in the human body.
