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Ch. 12 Muscle Physiology

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What do muscle generate?
Motion, force, and heat.
What are the 3 types of muscle?
Skeletal, cardiac, and smooth.
Which muscles are striated?
Skeletal and Cardiac.
Skeletal muscles are controlled by
Somatic motor neurons. Voluntary.
Cardiac and smooth muscles are controlled by
Autonomic innervation, paracrines, and hormones. Some are autorhythmic and contract spontaneously.
Skeletal muscles are always attached to the bone by tendons.
Falso; usually attached be tendons but not always.
Origin
End of the muscle attached CLOSEST to the trunk or to the stationary bone.
Insertion
End of the muscle that is the more distal or mobile attachment.
Flexors
Brings bones closer together
Extensors
Moves bones away from each other.
What are flexor-extensor pairs examples of?
Antagonistic muscle groups.
A skeletal muscle is a collection of
muscle fibers; large cells with MANY nuclei.
T-tubules
Allows action potentials to move rapidly into the interior of the fiber and release calcium from the sarcoplasmic reticulum.
Why is the sarcoplasmic reticulum also known as a modified endoplasmic reticulum?
Unlike the normal function of ER, it has the ability to store and release calcium.
Myofibrils
Intracellular bundles of contractile and elastic proteins.
What are thick filaments made of?
Myosin.
What are thin filaments mostly made of?
Actin.
What holds thick and thin filaments?
Titin and nebulin.
What is created between the binding of myosin and actin?
Crossbridges between thick and thin filaments.
Sarcomere
The smallest functional unit of muscle tissue.
One sarcomere is composed of
Two Z discs and the filaments between them.
A sarcomere is divided into
I Bands- THIN filaments only.
A Band- Runs the LENGTH of a THICK filament.
H Zone- Occupies THICK filaments only
What does the M Line and the Z discs represent?
The attachment sites for myosin and actin.
Muscle tension
The force created by a contracting muscle.
Load
A weight or force that opposes contraction of a muscle.
Sliding filament theory of contraction
As a direct result from CROSSBRIDGE movement, during contraction overlapping thick and thin filaments slide past each other in an energy dependent manner.
What does myosin convert energy from?
ATP into motion.
Power stroke
Myosin releases Pi and the myosin head group attached to the actin filament tilts backwards, pulling the thick filament to overlap further with the thin filament. Energy from ATP is used and ADP is released.
Rigor state
When contraction cycle ends, myosin is tightly bound to actin.
When does the sarcoplasmic reticulum use Ca2+?
During relaxation.
Excitation-contraction coupling
A somatic motor neuron releases Ach which initiates a skeletal muscle action potential that leads to contraction.
Excitation
The chemical and electrical events that triggers the mechanical events in a muscle fiber.
Twitch
A single contraction-relaxation cycle.
Latent period
"Brief." The time between the end of the muscle action potential and the beginning of muscle tension development represents the time required for Ca2+ release and binding to troponin.
Muscle Fatigue
A condition in which a muscle is no longer able to generate or sustain the expected power output.
What is one of the causes of muscle fatigue?
Depletion of glycogen storage.
How are skeletal muscle fibers classified?
By the basis of their speed of contraction and resistance to fatigue: Fast-twitch glycolytic fibers, fast-twitch oxidative-glycolytic fibers, and slow-twitch oxidative fibers.
What type of skeletal muscle fiber are most resistant to fatigue?
Oxidative fibers.
Myoglobin
An oxygen-binding pigment that transfers oxygen to the interior of the muscle fiber.
How is the tension of a skeletal muscle contraction determined?
By the length of the sarcomeres before contraction begins.
Tetanus
A state of maximal contraction.
motor unit
Composed of a group of muscle fibers and the somatic motor neuron that controls them. The number of fibers vary in one motor unit but are all the same fiber type.
Recruitment
By the addition of motor neurons, the force of contraction within a skeletal muscle can be increased.
What does summation in a single muscle fiber mean?
Fiber increases force and frequency of contraction.
Isotonic contraction
Creates force and moves a load.
Isometric contraction
Creates force without moving a load.
Concentric actions
Shortening contractions.
Eccentric actions
Lengthening contractions
Why do isometric contractions occur?
Series elastic elements allow the fibers to maintain constant length even though the sarcomeres are shortening and creating tension.
How does the body uses its bones?
As levers and joints as fulcrums. This system maximizes distance and speed but also requires muscles to do more work.
When is contraction fastest?
When the load on the muscle is zero. Speed depends on muscle fiber type and load.
Although smooth muscle is slower than skeletal muscle, smooth muscle can...
Sustain contractions longer without fatiguing.
Single-unit smooth muscle
Contracts as a single unit when depolarizations pass from cell to cell through gap junctions.
Multi-unit smooth muscle
Individual muscle fibers are stimulated independently.
What happens during smooth muscle relaxation?
Ca2+ is pumped out of the cytosol and myosin light chains are dephosphorylated by MYOSIN PHOSPHATASE.
What happens during smooth muscle contraction?
Ca2+ enters the cell through Ca2+ channels in the cell membrane. Additional Ca2+ is released from the sarcoplasmic reticulum.
Myogenic contraction
Stretches open Ca2+ channels of membrane.
What are forms of unstable membrane potentials in smooth muscle?
Slow wave or Pacemaker potentials.
Rising phase of smooth muscle
Due to Ca2+ entry rather than Na+ entry.
Pharmacomechanical coupling
Ca2+ entry causes smooth muscle contraction without a significant change in membrane potential.
What is smooth muscle controlled by?
Sympathetic and parasympathetic neurons and a variety of chemical signals.