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2/20 quiz LEC

muscle tissue - 2/20 quiz LEC

Muscle Tissue Functions (3) Movement, Posture, Heat Production
Skeletal Muscle Tissue type is Connective Tissue (Fibrous)
CT types found in skeletal tissue (3) Epimysium, Perimysium, Endomysium
Epimysium, Perimysium, Endomysium combine to form tendon that combines with periosteum of bone
Epimysium surrounds entire muscle
Perimysium surrounds muscle fiber bundles
Endomysium surrounds each muscle fiber
the merging of the tendon and periosteum of bone is strong bond, slow to heal
muscle cells are called muscle fibers (myofibers)
within each muscle cell we have (5) sarcolemma, sarcoplasm, sarcoplasmic reticulum, transverse tubules (T tubules), myofibrils
sarcolemma cell membrane
sarcoplasm cytoplasm
sarcoplasmic reticulum smooth ER with dilaetd sacs called terminal cristernae which contain calcium ions
transverse tubules (T tubules) extensions of the sarcolemma that run perpendicular to the sarcolemma
myofibrils small fibers within the myofiber
each myofibril consists of a series of repeating sarcomeres, the basic unit of contraction
sarcomeres the basic unit of contraction
sarcomeres run from Z line to Z line
Sarcomeres consist of alternating A (dark) and I (light) bands
In the center of the A band is a slightly lighter H zone
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
the I band components must slide over the A band components Sliding Filament Theory
thin filaments extend from the Z lines. Make up the I band and A band, which is exclusive of the H zone
Thin filaments are made up of Proteins: Actin, Tropomyosin, Troponin
Actin globular proteins that possess a myosin binding site
Tropomyosin strands that cover the myosin binding site on the actin
Troponin located at regular intervals on the tropomyosin
Thick Filaments make up the A band
Thick filaments are made up of myosin: club-shaped protein
Thick filaments possess a cross-bridge (head)
cross-bridge (head) consist of an actin-binding site and an ATP binding site
During contraction, a nerve impulse causes synaptic vesicles in the motor axon end bulbs to release acetylcholine by exocytosis
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.
the impulse enters the T tubule and stimulates the sarcoplasmic reticulum to open channels to release calcium ions from storage into the sarcoplasm
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
the cross bridge is energized with energy from an ATP
the actin binding site combines with the myosin binding site
the cross bridge then uses its energy to Powerstroke: bend the bridge which pulls the actin along (sliding filament)
the sliding draws the z lines closer together thus shortening the sarcomere and the muscle
ATP binds with the ATP binding site thus breaking the bridge and energizing the bridge for another power stroke
once the impulses stop, calcium ions are actively transported back to the sarcoplasmic reticulum.
To relax the muscle It takes ATP
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.
sarcomeres return to their resting lengths and the muscle relaxes
Neuromuscular Junction (NMJ) the joining of a nerve cell (neuron) and a muscle cell. No physical contact. Only one per muscle.
Motor end plate region of the sarcolemma adjacent to the neuron terminal
the neuron terminal contains vesicles filled with neurotransmitter
the motor end plate contains many neurotransmitter receptors
the space between the neuron and the muscle fiber cleft
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
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)
ACh in inactivated by the sarcolemma protein, no acetylcholinesterase (AChE). As a result, ACh no longer affects the NMJ
curare drug that acts as competitive inhibitor with acetylcholine
botulinum toxin a toxin from a bacterium that prevents the release of ACh
Myasthenia gravis an autoimmune disease that destroys the muscle Ach receptors. Causes muscle weakness, not life threatening
autoimmune disease diseases whereby we produce antibodies that attack our own tissues
idiopathic unknown cause
motor unit the motor neuron and all the muscle fibers it stimulates
motor unit range 10 (precision) to 2000 (gross) fibers per unit
ALL-OR-Nothing Principle When a muscle fiber* contracts, it contracts all-the-way given the same starting point. (gun trigger)
all muscle fibers of a given unit will contract all the way
recruitment increasing the number of active motor units. Brain does this. Thus, more muscle strength of contraction
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
100 motor units and 50 fibers/unit = 5000 fibers/muscle
flacid cut the *NMJ
twitch single muscle response to a single stimulus
twitch consists of (3) latent period, period of contraction, period of relaxation
tetanus a sustained contraction in response to frequent stimuli
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
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.
incomplete tetanus a sustained contraction in response to high frequency stimuli but with attempts at relaxation. These are out everyday activities
complete tetanus a sustained contraction (with no relaxation) in response to a very high frequency of stimulation. Perhaps seen when lifting an elephant.
isotonic contraction Movement: muscle shortening with little increase in tension. Increases strength
isometric contraction No Movement: minimal shortening with great increase in tension. 2 sets muscle contractions. increases size
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
muscle fibers do NOT undergo mitosis. Only size of the CELL gets larger or smaller
Atrophy decrease in individual muscle cell size
Hypertrophy increase in individual muscle cell size
immediate energy source for a contraction ATP
ATP energy time for exercise 5-6 seconds
after 15 seconds glycolysis kicks in
5-15 seconds Phosphocreatine (PC): high energy molecule that replenishes ATP stores
ADP + PC ---> ATP + C
Oxygen debt build up of lactic acid - need O2 to get rid of pyruvic acid
Glycolysy (anaerobic provides 2 ATP molecules/glucose..
The Krebs Cycle (aerobic) provides 36 ATPs/glucose. But it is limited by the availability of oxygen and NAD+
during intense exercise,Krebs cycle cant keep up
krebs cycle limitation is overcome by catabolizing many molecules of glucose by glycolysis (anaerobic)
pyruvic acid begins to build up and is converted to lactic acid (pain, fatigue)
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.
Created by: la66