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29 Cards in this Set

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Muscle is classified into which 3 different types?
Skeletal, smooth or cardiac
What is the difference between the classifications of muscles?
Skeletal muscle is primarily voluntary movement while smooth and cardiac muscle have to do with various systems (ie respiratory, GI)
What does skeletal muscle look like?
It is made of individual muscle fibers with each fiber being a single cell. There are no synctial bridges. Cross striations are a defining characteristic.
The thousands of fibrils in each skeletal muscle contain these contractile proteins:
Myosin, Actin, Tropomysin, and Troponin.
What is sarcoplasm?
A matrix inside the skeletal muscle where the myofibrils are suspended.
What does the sarcoplasm contain?
It contains mitochondria, enzymes, potassium ions, and an extensive endoplasmic reticulum known as the sarcoplasmic reticulum.
What is sarcolemma?
It the cell membrane of muscle fiber.
What is hypertrophy?
It is the synthesis of new myofibrils.
What is hyperplasia?
It is the formation of new cells--skeletal muscle is limited in the formation of new cells
What is excitation-contraction coupling?
It is the process by which depolarization of the sarcolemma and propagation of action potential initiates skeletal muscle contraction.
What are the steps of excitation-contraction coupling?
1. Motor neurons produce action potentials in fibers
2. Action potential is tranmitted into skeletal muscle by transverse (T) tubules
3. Opening of sarcoplasmic calcium channels which release calcium from sarcoplasmic reticulum to vicinity of myofibrils
4. Calcium ions bind to troponin thus abolishing inhibitory effect of troponin on myosin and actin interactions
5. Head of myosin molecule links to actin molecule (cross-bridging), producing movement of myosin on actin which is repeated serially to produce contraction.
6. sarcoplasmic reticulum begins to reaccumulate calcium by active transport (calcium pump)
7. Once the calcium concentration in sarcoplasm has been lowered sufficiently cross-bridging ceases and muscle relaxes
When action potentials go down T-tubules which receptors undergo conformational changes that result in opening of sarcoplasmic calcium channels?
dihydropyridine receptors
What is the other name for sarcoplasmic calcium channels?
Ryanodine receptors
What does failure in the calcium ion pump result in?
Sustained skeletal muscle contraction and marked increases in heat production---> MALIGNANT HYPERTHERMIA!!
What is responsible for malignant hyperthermia?
The ryanodine receptor is on chromosome 19 and a mutation in this gene is believed to make people more susceptible.
What happens in muscles during rigor mortis?
ATP depletion and failure of the calcium ion transport mechanism leading to permanent cross-bridging bwtween myosin and actin. The muscles remain rigid for 15-25 hours after death or until the muscle proteins are destroyed by autolysis from lysosomal enzymes.
What is the neuromuscular junction?
Site at which presynaptic motor nerve endings meet the postsynaptic membranes of skeletal muscles (motor end plates)
What is the synaptic cleft?
It is the space between the nerve ending and the sacrolemma and is filled with extracellular fluid.
Where is acetylcholine synthesized and stored?
It is synthesized in the cytoplasm of the nerve terminal and stored in synaptic vesicles.
How is an action potential transmitted to the muscle?
A nerve impulse arriving at nerve ending causes the release of 60 vesicles with each containing an estimated 10,000 molecules of acetylcholine.
What is the threshold potential at which skeletal fibers are stimulated to contract?
50 mv
What is the duration of action in skeletal muscle? in cardiac muscle?
<5ms, ~200ms
How do nondepolarizing neuromuscular-blocking drugs prevent muscle movement?
They compete with acetylcholine at the alpha subunits of nicotinic acetylcholine receptors and prevent permeability of skeletal muscle membranes-->endplate potential doesn't occur and neuromuscular transmission is prevented.
Describe how skeletal muscles are innervated.
Skeletal muscles are innervated by large myleniated alpha motor neurons that originate from cell bodies in ventral horns of spinal cord. The nerve axon exits via the ventral root and reaches the muscle through a mixed peripheral nerve. Motor nerves branch in the skeletal muscle with each nerve terminal innervating a single muscle cell.
What is the motor unit and what does it consist of?
A motor unit is the functional contractile unit. It consists of the motor nerve and of all the muscle fibers innervated by that nerve.
What is an electromyogram?
It is a recording from skin electrodes of the electrical current that spreads from skeletal muscles to skin during simultaneous contraction of numerous skeletal muscle fibers.
How is smooth muscle different from skeletal muscle?
no striation, no T-tubules, have caveoli; stimulation in absence of extrinsic innervation; sensitive to local hormones and tissue factors; spontaneous contractions as a single unit; lack troponin; do not atrophy on denervation
How does smooth muscle contract?
Calcium-calmodulin complex activates the enzyme necessary for phosphorylation of myosin, myosin has ATPase activity, and actin slides on myosin to produce contraction
Descibe the smooth muscle neuromuscular junction.
Nerve fibers branch diffusely on top of a sheet of smooth muscle fibers without making actual contact--acetycholine and norepinephrine are secreted into the interstitial fluid space