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Anatomy of Skeletal muscle
Every muscle is supplied by one nerve that stimulates it to contract. One artery supplies each muscle with oxygenated blood and several veins to remove waste products.
Each muscle fascicle is made of a group of ____. Each muscle fiber is a long cylindrical cell with multiple nuclei.
The muscle fibers/cells are covered by a plasma membrane called____. The nuclei are located just beneath the _____. The muscle fiber contains all the usual cell organelles and is especially rich in mitochondria.
Like other cells, the sarcolemma has a characteristic ________ due to the unequal distribution of positive and negative charges across the membrane. Sudden change in the ____ is the first step that leads to contraction.
The sarcoplasm contains ____ which are granules that store glycogen. ______ provides ATP for the muscle cell.
Sarcoplasm also contains ____ which is a protein that carries oxygen which is essential for the muscle cell metabolism.
Each muscle fiber is made of a bundle of densely packed, rod-liked contractile units called _____ which extend the entire length of the muscle fiber.
Alternating _____ of dark A bands and light I bands on the myofibrils give the muscle its striated appearance.
Sarcoplasmic reticulum (SR)
____ is a network of connected tubules that completely surround each myofibril. They run parallel to the myofibrils under the sarcolemma.
Transverse tubules (T tubules)
____ are tiny pockets of the sarcolemma that extend into the muscle cell. These ____ are filled with extracellular fluid and they extend deep into the sarcoplasma at right angles to the cell surface.
On either side of the T tubules, the SR distends to form small sacs that store calcium called _____.
Never impulses reach the sarcolemma, and are conducted through the sarcolemma down the T tubules. This will trigger calcium release from the terminal cisternae of the SR into the muscle cell interior. These electrical impulses or ____ are the triggers for muscle contraction.
The myofibrils are made of contractile units called ___ that are lined end to end. ____ are the actual contractile units of the muscle responsible for shorting during contraction.
Within each sarcomere, there are two types of thread like ____ which are arranged in alternating layers, partially overlapping in some areas.
Thick filaments made of a contractile protein called ___ extend the length of the A band, thus giving the dark appearance.
Thin filaments made of a different contractile protein called ____ extends across the I band giving the lighter appearance. They are anchored to the Z discs on either side.
Each _____ present in the thick filaments is made of a tail and 2 globular heads. The heads attach to the thin filaments contraction forming cross bridges.
The ___ is a globular protein that contains a myosin-binding site. The two subunits besides actin are troponin and tropomyosin.
In the relaxed muscle, ____ is a protein strand that acts to hide the myosin-binding site on actin.
For muscle contraction to occur, the level of ____ in the muscle fiber must increase so that ____ will bind to troponin. Troponin will pull on tropomyosin which will move and expose the binding sites on actin, thus making it possible for actin to bind to myosin.
Myosin heads will attach to the actin forming ____ and will pull on the thin filament causing it to slide inwards. The myosin heads detach from one actin molecule and attach to the next in a ratcheting manner thus pulling both thin filaments on either side closer together towards the M line which leads to shorting of the sarcomere.
A motor unit consists of a ____ and all muscle fibers it activates. Each muscle is supplied by one ____.
This nerve in the spinal cord as neuron cell bodies and the long axons leave the spinal cord and branch into a munber of ______ which form junctions with the sarcolemma and with individual muscle fibers. These juncions are called neuro-muscular junctions.
Control of skeletal muscle activity. This is the area where the nerve comes in contact with the muscle fiber.
_____ (synaptic terminal) with synaptic vesicles containing the neuro transmitter acetylcholine (ACh)
Motor end plate
______ of the muscle which is a specialized part of the sarcolemma containing acetylcholine receptors.
A very narrow space between both the axonal endings and motor end plate is called the _____.
When a _____ (action potential) reaches the end of an axon a the neuro-muscular junction, calcium channels will open and calcium enters the axon.
____ will cause release of acetylcholine from the vesicles. Acetylcholine will transverse the cleft and bind with its ____ on the motor end plate in the sarcolemma. When acetylcholine binds with its receptor it opens Na+ channels and Na+ will rush into the sarcoplasm. This will trigger an action potential.
An _____ is an electrical current created by movement of ions across the muscle membrane. It spreads down the whole length of the sarcolemma and also travels inward along the T tubules.
Once generated, the actin potential is propagated down the sarcolemma. It will reach T tubules and trigger Ca++ release from terminal cisternae. Ca++ will bind to tropnin and expose actin. Myosin heads will form cross bridges with actin causing sliding filament mechanism and muscle contraction.
The synaptic cleft and sarcolemma also contain molecules of an enzyme called _____. This enzyme is reponsible for breaking down acetylcholine. Some of the acetylcholine is picked up by the synaptic vesicles and it stored to be re-used on the next stimulus. Ca++ is removed by the SR and it stored again in the cisternae. Actin and myosin will detach and the muscle fiber will relax and return to its original length.
It is the graphic tracing of the contraction of muscle fibers in response to a single threshold action potential. It has three distinct phases: Latent period, period of contraction and period of relaxation.
First few milliseconds following the stimulus. The muscle action potential travels along the sarcolemma and Ca++ is released from the SR. No contraction but there is increase in muscle tension.
Period of relaxation
Ca++ is reabsorbed into the SR. Cross bridges detach and muscle returns to its original length.
____ differs from one type of muscle to another, the difference being the length of time it takes to complete these stages. Small brisk muscles involved in blinking the eye take a much time than a large muscle in the calf because of the different metabolic needs of each muscle.
A single action potential in a motor neuron will result in a single breif contraction of the muscle fibers called ____. Each ____ is a brief event because of the rapid breakdown of acetylcholine.
If a second stimulus reaches the muscle before it has time to completely relax, the second contraction will be stronger and is called _____.
Very rapid stimulation will lead to sustained contraction without relaxation, a condition known as ____. It is due to the buildup of Ca++ released from the SR due to repeated rapid stimuli.
____ is a phenomenon of gradual increase in the strength of muscular contraction following rapid repeated stimulation, also called the staircase phenomenon. If the number of stimuli of the same intensity are sent to a muscle, the muscle will show successive increase in strength of contractions. This is the basis for the importance of warming up before the game.
At rest all body muscles are not flaccid (flabby), but they exhibit a degree of tension or tautness known as _____. This keeps muscles firm and enables for examples the neck muscles to keep the head upright.
____ is due to the constant release of a small amount of acetylcholine by neurons in the brain and spinal cord which will cause the muscles to be slightly contracted. These contractions will cause the muscle to stay firm, but are not strong enough to cause actual movement.
Hypertonia, spastic paralysis
Increase in muscle tone is called ____ where there is muscle spasm or rigidity. It may lead to ____.
The bacterium Clostridium tetani causes a disease called ___ which is characterized by muscle spasm due to the toxin produced by the bacteria.
____ is increase in muscle mass due to exercise or various muscle diseases. The hypertrophied muscle will appear enlarged due to the increase in the bulk of myofibrils. Thick and thin filaments increase in number.
____ is the reverse of hypertrophy. It is defined as decrease in muscle mass due to decrease in the bulk of myofibrils and number of myofilaments. Most often ____ is a consequence of lack of use of muscle as in cases of paralysis.
Lead to change in muscle length such as flexing the elbow to pull or lift a chair.
Does not lead to change in length of muscle, but there is increase in tension. These contractions are important in maintaining upright posture and supporting objects in a fixed position such as holding a book steady using an outstretched arm.
ATP is the source of energy for cross bridge movements and detchment. After ATP is utilized, it needs to be regenerated for muscle contraction to resume. ATP--> ADP + Pi
Hemoglobin and myoglobin
Both _____ are oxygen-binding proteins. They bind oxygen when it is plentiful and release it when it is scarce.
If the muscle uses up ATP faster than its ability to be regenerated, muscle fatigue will occur. Other causes of fatigue are lactic acid accumulation, depletion of CP, and lack of oxygen.
Prime movers (agonists)
Provide the major force for a certain movement. E.g. the biceps flexes the elbow and the rectus abdominus flexes the trunk.
Oppose the agonists, such as the triceps which extends the elbow and the erector spinae which resumes the erect position. ____ are usually located on the opposite side of an agonist. _____ can be prime movers in their own right.
Work together with prime movers to add force to the movement such as hamstring muscles which all help in knee flexion and the quadricepts group respnsible for knee extension.
The interaction of ADP with ______. ______ is a molecule produced by the liver and kidneys, and is stored in muscle. During rest the excess ATP in muscle cells is used to synthesize ______.
____ stores become replenished during rest. This pathway is the first to be used during strenuous exercise and it provides energy for a very short time (15 sec.) One molecule of ATP is produced from each _____ molecule.
In the absence of oxygen, glucose delievered to the muscle by the arteries will be broken down by a series of reactions first into pyruvic acid and then lactic acid.
____ is carried by the blood to the liver where it is converted to glucose and is returned to the muscle to be used again. In this process 2 ATP molecules are released which provides energy for 30-60 sec.
Glycolysis, aerobic respiration
In the presence of enough oxygen, glucose will undergo ____ into pyruvic acid, and the latter will enter the mitochondria to complete its breakdown by several metabolic processes collectively known as _____ to yeild 36 molecules of ATP. This provides energy for several hours.
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