Chapter 7. Q/A Review The human body contains _________ types of muscles. Three.
Types of Muscles
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Transcript of Types of Muscles
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Types of Muscles
Smooth Involuntary muscle; controlled unconsciously In the walls of blood vessels and internal organsCardiac Controls itself with help from nervous and
endocrine systems
Only in the heartSkeletal Voluntary muscle; controlled consciously Over 600 throughout the body
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SKELETAL MUSCLE STRUCTURE
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KEY POINTS An individual muscle cell is called a
muscle fiber.
A muscle fiber is enclosed by a plasma membrane called the sarcolemma.
The cytoplasm of a muscle fiber is called a sarcoplasm.
Within the sarcoplasm, the T tubules allow transport of substances throughout the muscle fiber and the sarcoplasmic reticulum stores calcium.
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AN ACTIN FILAMENT
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The Myofibril
Myofibrils are made up of sarcomeres, the smallest functional units of a muscle.
A sarcomere is composed of filaments of two proteins, myosin and actin, which are responsible for muscle contraction.
Myosin is a thick filament with a globular head at one end.
An actin filament—composed of actin, tropomyosin, and troponin—is attached to a Z disk.
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Events Leading to Muscle Fiber Action
1. A motor neuron releases acetylcholine (ACh).
2. ACh binds to receptors on the sarcolemma.
3. The action potential triggers release of Ca2+.
4. The Ca2+ binds to troponin on the actin filament, and the troponin pulls tropomyosin off the active sites, allowing myosin heads to attach to the actin filament.
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The Sliding Filament Theory
When myosin cross-bridges are activated, they bind strongly with actin, resulting in a change in the cross-bridge.
The change in the cross-bridge causes the myosin head to tilt toward the arm of the cross-bridge and drag the actin and myosin filaments in opposite directions.
The tilt of the myosin head is known as a power stroke.
The pulling of the actin filament past the myosin results in muscle shortening and generation of muscle force.
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Changes in Membrane Potential
Depolarization—inside of cell becomes less negative relative to outside (> –70 mV)
Hyperpolarization—inside of cell becomes more negative relative to outside (< –70 mV)
Graded potentials—localized changes in membrane potential (either depolarization or hyperpolarization)
Action potentials—rapid, substantial depolarization of the membrane (–70 mV to +30 mV to –70 mV all in 1 ms)
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JUNCTION
THE NEUROMUSCULAR JUNCTION
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Fiber Types
• Type I • Type IIa• Type IIb• Type of Muscular Contractions –
– Concentric, Eccentric– Isometric, Isotonic, Isokinetic
• Origin – ProximalInsertion – Distal
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Muscle and Joint Nerve Endings
Proprioceptors
Joint kinesthetic receptors in joint capsules sense the position and movement of joints.
Muscle spindles sense how much a muscle is stretched and angle of stretch
Golgi tendon organs detect the tension of a muscle on its tendon, providing information about the strength of muscle contraction.
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Chapter 2
• Factors affecting Strength– Amount of Neuromuscular Stimulation– Hypertrophy of Sarcomere– Age (Sarcopenia)– Sex– Angle of Pennation– Prestretching