Skeletal Muscle Contraction Flashcards
What is the epimysium?
connective tissue surrounding the entire muscle
What is the muscle made up of?
multiple fascicles.
What is the perimysium?
tissue surrounding multiple fascicles.
what is the endomysium?
tissue surrounding each myofiber
what is the sarcolemma?
cell membrane of muscle fiber
what is a myofiber?
muscle cell; an indivudali multinucleated muscle cell
what is the myofibril?
a chain of sarcomeres within a myofiber; it contains actin and myosin necessary for a muscle contraction.
What is a myofilament?
actin and myosin filaments that make up a sarcomere.
What are T-tubues
invaginations of the sarcolemma that lie close to cisternae of the sarcolasmic reticulum.
What does the sarcoplasmic reticulum do?
regulates calcium storage and reuptake; important for muscle contraction.
What does the sarcomere lie inbetween?
two Z-disks.
Where are the Z discs, and what do they do?
at the end of the sarcomere; they anchor the actin filaments.
What are I bands composed of?
actin; their width changes during contraction.
What are A bands composed of?
myosin and actin; they do not change during contraction
What are H bands composed of?
myosin; the width changes during contaction.
What does Titin do?
holds actin and myosin in place and acts as a framework. It is springy and allows for contraction of the sarcomere.
What enters a nerve fiber’s terminal buttons after an action potential has been fired?
calcium
What neurotransmitter does the nerve fiber release?
acetylcholine
What kind of sodium channels are opened when Ach binds?
ligand-gated
What kind of channels are open once sodium enters through the ligand-gated channel?
voltage-gated
What do DHP channels on T-tubules interact with once an action potential has been initiated on the sarcolemma?
ryanodine receptors
What are ryanodine receptors sensitive to?
calcium
Where are ryanodine receptors located?
sarcoplasmic reticulum membrane
What is released after the opening of ryanodine receptors on the SR membrane?
calcium
What do calcium ions from the SR bind to?
troponin
What is deactivated (and allows binding of actin to myosin) once calcium binds to troponin?
tropomyosin
What molecule do the ATPase heads of myosin use before binding to actin?
ATP
What does myosin have to use to break away from actin?
ATP
When does contraction stop?
When ATP-dependent calcium pumps moves calcium ions back into the sarcoplasmic reticulum.
What is DHP?
Dihydropyridine receptor; it is on the membrane of the sarcolemma (T-tubules) and changes conformation of ryanopyridine if an action potential is initiated.
What is SERCA?
ATP dependent pump that moves calcium back into the SR
What is calsequestrin?
molecule in the SR that maintains optimum calcium concentration gradients.
When does a sarcomere have the least tension?
When the actin filaments do not overlap.
When does a sarcomere have the most tension?
When the actin filaments either touch or overlap all of the cross bridges.
Does velocity increase or decrease with the amount of contraction?
decrease
When is ATP required for muscle contraction?
pumping calcium ions into SR, maintaining Na/K concentration after action potentials, binding/release of myosin heads from actin filaments.
What is phosphocreatine?
a molecule that contains a high-energy phosphate; it releases it to make ATP for 5 - 8 seconds of contraction.
How long can glycolysis sustain muscle contractions?
1 minute
What metabolic pathway provides the most energy needed for long-term contraction?
oxidative metabolism
What are isometric contractions?
Increase in tension, but not length
What are isotonic contractions?
Change in muscle length. Is either eccentric or concentric.
What is an eccentric contraction?
isotonic contraction in which the muscle length lengthens
What is an concentric contraction?
isotonic contraction in which the muscle length shortens
What are characteristics of fast, white fibers?
are muscles that react rapidly; they have fast twitch fibers, few mitocondria, high levels of ATPase, and use anaerobic respiration
What are characteristics of slow, red fibers?
are muscles that contract slowly, but have endurance. They have high mitochondria and myoglobin and small ATPase; they use aerobic respiration.
What muscle component can be increased after birth?
myofibrils; lost muscle tissue is replaced by scar tissue.
Which muscle is composed predominantly of dark fibers?
soleus
Which muscle is composed predominantly of light fibers?
gastrocnemius
What is a motor unit?
a single nerve cell (neuron) that innervates myofibers. When a neuron fires, all the myofibers in the motor unit contract.
What is summation?
Addition of individual twitch contractions to the increase the overall intensity of a muscle contraction. It increases muscle tension and adds to the effects of the previous spikes.
How is summation caused?
When electrical event soccur before the previous calcium ions enter the SER again; the amount of Ca ions ourside the SER increases.
What is tetany?
When a muscle rmains at maximal contraction from summation; little ability to use the muscle for a perio dof time.
