muscle tissue - 2/20 quiz LEC
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| Muscle Tissue Functions (3) | Movement, Posture, Heat Production
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| Skeletal Muscle Tissue type is | Connective Tissue (Fibrous)
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| CT types found in skeletal tissue (3) | Epimysium, Perimysium, Endomysium
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| Epimysium, Perimysium, Endomysium combine to form | tendon that combines with periosteum of bone
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| Epimysium | surrounds entire muscle
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| Perimysium | surrounds muscle fiber bundles
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| Endomysium | surrounds each muscle fiber
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| the merging of the tendon and periosteum of bone is | strong bond, slow to heal
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| muscle cells are called | muscle fibers (myofibers)
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| within each muscle cell we have (5) | sarcolemma, sarcoplasm, sarcoplasmic reticulum, transverse tubules (T tubules), myofibrils
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| sarcolemma | cell membrane
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| sarcoplasm | cytoplasm
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| sarcoplasmic reticulum | smooth ER with dilaetd sacs called terminal cristernae which contain calcium ions
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| transverse tubules (T tubules) | extensions of the sarcolemma that run perpendicular to the sarcolemma
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| myofibrils | small fibers within the myofiber
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| each myofibril consists of | a series of repeating sarcomeres, the basic unit of contraction
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| sarcomeres | the basic unit of contraction
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| sarcomeres run from | Z line to Z line
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| Sarcomeres consist of | alternating A (dark) and I (light) bands
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| In the center of the A band | is a slightly lighter H zone
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| when the muscle (sarcomere) contracts (4) | 1. the Z lines come closer 2. the I band gets smaller 3. the H zone disappears 4. the A band remains the same
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| the I band components must slide over the A band components | Sliding Filament Theory
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| thin filaments | extend from the Z lines. Make up the I band and A band, which is exclusive of the H zone
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| Thin filaments are made up of | Proteins: Actin, Tropomyosin, Troponin
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| Actin | globular proteins that possess a myosin binding site
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| Tropomyosin | strands that cover the myosin binding site on the actin
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| Troponin | located at regular intervals on the tropomyosin
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| Thick Filaments | make up the A band
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| Thick filaments are made up of | myosin: club-shaped protein
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| Thick filaments possess a | cross-bridge (head)
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| cross-bridge (head) consist of | an actin-binding site and an ATP binding site
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| During contraction, a nerve impulse causes | synaptic vesicles in the motor axon end bulbs to release acetylcholine by exocytosis
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| During contraction, the impulse does not simply "jump" from neuron to muscle. What happens? | ACh diffuses across the synaptic cleft within the NMJ and initiates an impulse that spreads over the surface of the sarcolemma.
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| the impulse enters the T tubule and | stimulates the sarcoplasmic reticulum to open channels to release calcium ions from storage into the sarcoplasm
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| calcium ions combine with | the tropinin which changes shape. This causes the troponin-tropomysoin complex to move, thus exposing the myosin binding sites on the actin
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| the cross bridge is energized with | energy from an ATP
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| the actin binding site combines with | the myosin binding site
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| the cross bridge then uses its energy to | Powerstroke: bend the bridge which pulls the actin along (sliding filament)
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| the sliding draws the z lines | closer together thus shortening the sarcomere and the muscle
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| ATP binds with the | ATP binding site thus breaking the bridge and energizing the bridge for another power stroke
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| once the impulses stop, | calcium ions are actively transported back to the sarcoplasmic reticulum.
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| To relax the muscle | It takes ATP
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| The (high or low?) calcium ion concentration in the sarcoplasm allows | low. the tropomyosin/troponin complex to cover the myosin binding sites. Myosin cross bridges seperate from the actin.
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| sarcomeres return to their resting lengths | and the muscle relaxes
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| Neuromuscular Junction (NMJ) | the joining of a nerve cell (neuron) and a muscle cell. No physical contact. Only one per muscle.
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| Motor end plate | region of the sarcolemma adjacent to the neuron terminal
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| the neuron terminal contains | vesicles filled with neurotransmitter
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| the motor end plate contains | many neurotransmitter receptors
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| the space between the neuron and the muscle fiber | cleft
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| a nerve impulse causes | calcium ions channels to open allowing calcium to enter the axon. This somehow causes the vesicles to fuse with the neuronal membrane releasing the neurotransmitter, ACh, into the cleft
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| ACh combines with | the receptor sites and alters the membrane's permeability to Na and K ions (ie generates an impulse on the muscle membrane)
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| ACh in inactivated by the | sarcolemma protein, no acetylcholinesterase (AChE). As a result, ACh no longer affects the NMJ
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| curare | drug that acts as competitive inhibitor with acetylcholine
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| botulinum toxin | a toxin from a bacterium that prevents the release of ACh
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| Myasthenia gravis | an autoimmune disease that destroys the muscle Ach receptors. Causes muscle weakness, not life threatening
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| autoimmune disease | diseases whereby we produce antibodies that attack our own tissues
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| idiopathic | unknown cause
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| motor unit | the motor neuron and all the muscle fibers it stimulates
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| motor unit range | 10 (precision) to 2000 (gross) fibers per unit
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| ALL-OR-Nothing Principle | When a muscle fiber* contracts, it contracts all-the-way given the same starting point. (gun trigger)
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| all muscle fibers of a given unit will | contract all the way
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| recruitment | increasing the number of active motor units. Brain does this. Thus, more muscle strength of contraction
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| muscle tone | minimum number of motor units that are always active. Enough to make the muscle tense, but not enough to produce movement. more active=more active units
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| 100 motor units and 50 fibers/unit = | 5000 fibers/muscle
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| flacid | cut the *NMJ
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| twitch | single muscle response to a single stimulus
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| twitch consists of (3) | latent period, period of contraction, period of relaxation
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| tetanus | a sustained contraction in response to frequent stimuli
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| refractory period | a period of time following a stimulus whereby the muscle fiber loses its excitability and connot respond to another stimulus. refuses to respond
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| wave summation | occurs when a stimulus is applies AFTER the refractory period but the muscle has not completely relaxed. The second wave adds on to the first. different starting points.
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| incomplete tetanus | a sustained contraction in response to high frequency stimuli but with attempts at relaxation. These are out everyday activities
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| complete tetanus | a sustained contraction (with no relaxation) in response to a very high frequency of stimulation. Perhaps seen when lifting an elephant.
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| isotonic contraction | Movement: muscle shortening with little increase in tension. Increases strength
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| isometric contraction | No Movement: minimal shortening with great increase in tension. 2 sets muscle contractions. increases size
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| how does length influence strength of a contraction | muscle fibers contract minimally when at optimal length, attained when muscle is slightly stretched. stregth of contraction reflects degree of overlap of the thick and thin filaments. over-stratching produces a decrease in the strength of a contraction
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| muscle fibers do NOT | undergo mitosis. Only size of the CELL gets larger or smaller
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| Atrophy | decrease in individual muscle cell size
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| Hypertrophy | increase in individual muscle cell size
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| immediate energy source for a contraction | ATP
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| ATP energy time for exercise | 5-6 seconds
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| after 15 seconds | glycolysis kicks in
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| 5-15 seconds | Phosphocreatine (PC): high energy molecule that replenishes ATP stores
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| ADP + PC ---> | ATP + C
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| Oxygen debt | build up of lactic acid - need O2 to get rid of pyruvic acid
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| Glycolysy (anaerobic provides | 2 ATP molecules/glucose..
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| The Krebs Cycle (aerobic) provides | 36 ATPs/glucose. But it is limited by the availability of oxygen and NAD+
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| during intense exercise,Krebs cycle | cant keep up
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| krebs cycle limitation is overcome by | catabolizing many molecules of glucose by glycolysis (anaerobic)
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| pyruvic acid begins to build up and is converted to | lactic acid (pain, fatigue)
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| lactic acid is disposed of by | the taking in of additional oxygen after exercise (heavy breathing). This build up of acid creates oxygen debt. Heavy breathing after exercuse pays back the debt.
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