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Ashley Weiss
Chapter 9 / 10 quiz
1. The thick filament which contain myosin are located in the H zone, M line and part of the A zone which is what is used for muscle contraction. The thin filaments consist of two strands of actin subunits twisted into a helix plus to types of regulatory proteins; troponin and tropomyosin. The sarcomere is the contractile unit, which is composed of myofilaments which also contain the A band, I band, H zone, Z disk and M line. Myofibrils are rod like contractile elements that occupy most if the muscle cell volume. Composed of saromeres arranged end to end they appear banded. The muscle fiber which is composed of many microfibrils is enclosed in endomysium and under that is the sarcolemma which houses the nuclei. Tendons connect muscles to their bony origins and insertions. Aponeuroses are layers of flat connective tissue (fascia) separating muscles from each other. The SR contain mitochondria and glycogen granules stored in the sarcoplasm which are involved in producing the energy for contraction. The fascicle is composed of many muscle fibers and is enclosed in the perimysium; the muscle is composed of many fascicles and is enclosed in the epimysium. The tubules of the sarcoplasmic reticulum have sac like terminal cisterns and the T tubules run between those. Spots that contain a t tubule and 2 terminal cisterns are called a triad. An action potential is carried down the sarcolemma to the neuromuscular junction . There are very many ion channels located on the sarcolemma which is has junctional folds in the motor end plate to allow for more ion channels. The action potential arrives at the axon terminal of the motor neuron allowing the ACh to fuse through the synaptic vessels and open the chemically gated channels. Fast glycolytic fibers fatigue rapidly, while slow oxidative fibers are highly resistant to fatigue. Muscles that need to be active continuously, such as weight-supporting postural muscles, contain a higher percentage of fatigue-resistant slow oxidative muscle fibers.
2. The axons of the nerve cells of the spinal cord branch and attach to each muscle fiber forming a neuromuscular junction. An action potential passes down the nerve. When an action potential reaches the axon terminal of a motor neuron at the endplate potential, vesicles carrying neurotransmitters mostly acetylcholine are exocytosed and the contents are diffused into the neuromuscular junction. These neurotransmitters bind to receptors on the postsynaptic membrane and lead to its depolarization. The nerve releases Ca+ that results in the release of Acetylcholine (ACh). ACh binds with the sarcolemma. Muscle Fiber Action Potential ACh binds with receptors and opens the voltage gated Na+ ion channels. Na + rushes in and the sarcolemma depolarizes. The regional depolarization spreads rapidly. The voltage gated K+ channels open and the region repolarizes immediately after the action potential passes the membrane permeability changes again. Na+ channels close and the K+ channels open. K+ rushes out of the cell and the cell is repolarized. Ca++ is stored in the sarcoplasmic reticulum. Depolarization releases the Ca++. The Ca++ clears the actin binding sites. During muscle contraction the thin actin filaments slide over the thick myosin filament. When Calcium is present the blocked active site of the actin clears. Myosin head attaches to actin. (High energy ADP + P configuration) Power stroke is when the myosin head pivots pulling the actin filament toward the center. The cross bridge detaches when a new ATP binds with the myosin. Cocking of the myosin head occurs when ATP becomes ADP + P. Another cross bridge can form. The end result is a shortening of the sarcomere. The distance between the Z discs shortens, the H zone disappears, the dark A band increases because the actin and myosin overlap more and the light I band shortens. Ca++ is removed from the cytoplasm and tropomysin blocks the actin site.
3. Acetylcholine at the neuromuscular junction is broken down by acetylcholinesterase, and this terminates the stream of action potentials along the muscle fiber surface. The sarcoplasmic reticulum ceases to release calcium ions, and immediately starts to requester all the calcium ions that have been released through the calcium pumps. In the absence of calcium ions, a change in the configuration of troponin and tropomyosin then blocks the action of the myosin molecule heads, and contraction ceases
4. A motor unit consists od one motor neuron and all the muscle fibers it innervates or supplies. Recruitment of motor neurons controlling skeletal muscle fibers is orderly and follows the size principal which is small fibers are recruited first, then medium then the largest for last. A muscle twitch is a single jerky contraction that is not the typical way a muscle reacts. A Wave summation is generated by increasing the frequency of the stimulus. As the rate of stimulation increases, contractions sum up, ultimately producing tetanus and generating more force. Isotonic contractions result in movement occurring at the joint and a change in the length of muscles (the force remains constant). Isometric contractions result in increases in muscle tension, but no lengthening or shortening of the muscle occurs. ATP is generated by breaking down glucose obtained from the blood stored in the muscle. Muscle fatigue os a state of inability to contract even though the muscle still may be receiving stimuli.
1. prime mover - a muscle that acts directly to bring about a desired movement.
Agonist - a contracting muscle whose contraction is opposed by another muscle
Antagonist - any muscle that opposes the action of another.
Synergist – a muscle that increases the action of another
Fixator - a muscle that acts as a stabilizer of one part of the body during movement of another part

2. The origin is the attachment site that doesn't move during contraction, while the insertion is the attachment site that does move when the muscle contracts. The particular movement is a direct result of the muscle attachment.
3. Action they perform in Anatomical Position, Shape of muscle, Origin and Insertion, Location, Relative Size, Direction of Fibers, number of Origins.
4. There are circular, which are shaped liked a circle, convergent which converge to a single tendon of insertion. Parallel which runs parallel to the long axis of the muscle. Fusiform which are spindle shaped and pennate which are short and attach to a central tendon.
5. First class lever the fulcrum is in the middle and the load and effort are on either side. The examples are a scissors and the head, raising the head off the chest. A second class lever the fulcrum is all the way on one side and the load is in the middle with the effort on the opposite side. Examples would be a wheel barrow and standing on your tip toe. A third class lever is where the effort is in the middle and the load and fulcrum are on the ends. Examples would be tweezers and flexing the forearm.

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