KINES 314 EXAM 1 QUESTIONS AND
ANSWERS
What are the roles of the components in the contraction of a skeletal muscle fiber? -
Correct Answers -1. Nerve impulse arrives at neuromuscular junction, Action Potential
from motor neuron causes release of acetylcholine into synaptic cleft, then it binds to
receptors on the motor end plate, producing an end plate potential that depolarizes the
muscle cell, this depolarization is conducted down the transverse (T) tubules, resulting
in the release of calcium from the sarcoplasmic reticulum.
2. The calcium diffuses into the muscle and binds to troponin on the actin molecule.
This causes a position change in tropomyosin so that the active sites on the actin are
uncoverd. This permits binding of a myosin cross bridge on the actin molecule. This
cross bridge binding initiates the release of energy stored within the myosin molecule,
where the inorganic phosphate is released from the myosin head. THe power stroke
causes the filaments to slide and ADP is released, which produces movement and
muscle shortening. A new ATP attaches to the myosin crossbridge and ATPase breaks
down the ATP attached to the myosin crossbridge providing energy necessary for
positioning the myosin crossbridge for reattachment to another active site on the actin
molecule (It's original orientation).
What happens to intracellular calcium? - Correct Answers -In Force vs. Calcium
concentration in muscle cell [Ca2+]
First relaxed, then eventually with a little more Calcium, get huge increase in force.
Cooperativity: Calcium binding to troponin C which in turn makes it easier for each next
calcium to bind, which is why get huge increase in force for little more calcium. Once
process gets going, takes off on its own. Because saturate all binding sites on troponin
C.
Higher action potential frequency, means calcium channels are held open longer.
What do you look for as difference in time for rate of tension development? - Correct
Answers -Rate that calcium is being released can affect this, cross bridge development
from calcium either being faster or more plentiful causes cross bridges to form.
What affects twitch amplitude? - Correct Answers -Amount of cross bridges, more cross
bridges, more force, due to more cross bridges available, or higher sensitivity within
them, or due to faster or more available calcium.
What affects the rate of relaxation? - Correct Answers -Calcium has to be released back
into Sarcoplasmic Reticulum. Longer the time to relaxation, the slower the calcium is
released back. Tropomyosin changes configuration after calcium leaves.
, Could be slower to relaxation if rate of cycling of crossbridges is slower.
What is a Tetanus Muscle contraction? - Correct Answers -Multiple stacked muscle
contractions, to the point that there are so many action potentials sent that it is a
continuous twitch. So there is no removal of calcium. SR is trying to get calcium back,
but action potential is continually pulling the calcium back into the muscle.
So in a twitch, not releasing all of calcium. So basically calcium release channel is just
held open. A lot more calcium available to muscle but wasn't time to have it, so since
action potential keep calcium channel open, then get continuous inflow of calcium
increasing force with no decrease. Called summation.
How does summation affect force? (Force vs. frequency) - Correct Answers -First
relaxed, then eventually with a little more Calcium, get huge increase in force.
Calcium binding to troponin C which in turn makes it easier for each next calcium to
bind, which is why get huge increase in force for little more calcium. Once process gets
going, takes off on its own. Because saturate all binding sites on troponin C.
What is the ultimate factor limiting force output in a muscle? - Correct Answers -Number
of active crossbridges is ultimate limiting factor, any intervention to change force output
affects the crossbridges.
What is limiting factor for how quickly a muscle can shorten? - Correct Answers -
Crossbridge turnover rate, cycling rate.
What affects the rate of crossbridge turnover? - Correct Answers -Rate at which they
hydrolyze ATP. Myosin ATPase rate. Rate at which myosin can bind and split ATP.
What is the length-tension relationship for skeletal muscles? And why is this the case at
the cellular level? - Correct Answers -Less force at long or very short lengths, more
force at medium lengths of joint angle.
Could predict length where no overlap between thin (actin) and thick (myosin) filaments,
so no force could be created.
Then found where optimal overlap is between thick and thin filaments. Optimal ability to
form crossbridges.
Length where they will bump into each other was next to be found.
Proved that filaments sliding past each other create force.
Intact muscles never get to the extremes, where you wouldn't get force output.
How is the amount of force controlled, considering moving at same velocity between
different weights being lifted? - Correct Answers -1. Action Potential frequency
2. Increase number of motor units recruited (recruitment). Number of muscle fibers
activated.
Fewest number of muscle fibers can activate is six, since from spinal cord comes 3
neurons to motor nerve which splits into two at muscle fibers. Has to do with where
ANSWERS
What are the roles of the components in the contraction of a skeletal muscle fiber? -
Correct Answers -1. Nerve impulse arrives at neuromuscular junction, Action Potential
from motor neuron causes release of acetylcholine into synaptic cleft, then it binds to
receptors on the motor end plate, producing an end plate potential that depolarizes the
muscle cell, this depolarization is conducted down the transverse (T) tubules, resulting
in the release of calcium from the sarcoplasmic reticulum.
2. The calcium diffuses into the muscle and binds to troponin on the actin molecule.
This causes a position change in tropomyosin so that the active sites on the actin are
uncoverd. This permits binding of a myosin cross bridge on the actin molecule. This
cross bridge binding initiates the release of energy stored within the myosin molecule,
where the inorganic phosphate is released from the myosin head. THe power stroke
causes the filaments to slide and ADP is released, which produces movement and
muscle shortening. A new ATP attaches to the myosin crossbridge and ATPase breaks
down the ATP attached to the myosin crossbridge providing energy necessary for
positioning the myosin crossbridge for reattachment to another active site on the actin
molecule (It's original orientation).
What happens to intracellular calcium? - Correct Answers -In Force vs. Calcium
concentration in muscle cell [Ca2+]
First relaxed, then eventually with a little more Calcium, get huge increase in force.
Cooperativity: Calcium binding to troponin C which in turn makes it easier for each next
calcium to bind, which is why get huge increase in force for little more calcium. Once
process gets going, takes off on its own. Because saturate all binding sites on troponin
C.
Higher action potential frequency, means calcium channels are held open longer.
What do you look for as difference in time for rate of tension development? - Correct
Answers -Rate that calcium is being released can affect this, cross bridge development
from calcium either being faster or more plentiful causes cross bridges to form.
What affects twitch amplitude? - Correct Answers -Amount of cross bridges, more cross
bridges, more force, due to more cross bridges available, or higher sensitivity within
them, or due to faster or more available calcium.
What affects the rate of relaxation? - Correct Answers -Calcium has to be released back
into Sarcoplasmic Reticulum. Longer the time to relaxation, the slower the calcium is
released back. Tropomyosin changes configuration after calcium leaves.
, Could be slower to relaxation if rate of cycling of crossbridges is slower.
What is a Tetanus Muscle contraction? - Correct Answers -Multiple stacked muscle
contractions, to the point that there are so many action potentials sent that it is a
continuous twitch. So there is no removal of calcium. SR is trying to get calcium back,
but action potential is continually pulling the calcium back into the muscle.
So in a twitch, not releasing all of calcium. So basically calcium release channel is just
held open. A lot more calcium available to muscle but wasn't time to have it, so since
action potential keep calcium channel open, then get continuous inflow of calcium
increasing force with no decrease. Called summation.
How does summation affect force? (Force vs. frequency) - Correct Answers -First
relaxed, then eventually with a little more Calcium, get huge increase in force.
Calcium binding to troponin C which in turn makes it easier for each next calcium to
bind, which is why get huge increase in force for little more calcium. Once process gets
going, takes off on its own. Because saturate all binding sites on troponin C.
What is the ultimate factor limiting force output in a muscle? - Correct Answers -Number
of active crossbridges is ultimate limiting factor, any intervention to change force output
affects the crossbridges.
What is limiting factor for how quickly a muscle can shorten? - Correct Answers -
Crossbridge turnover rate, cycling rate.
What affects the rate of crossbridge turnover? - Correct Answers -Rate at which they
hydrolyze ATP. Myosin ATPase rate. Rate at which myosin can bind and split ATP.
What is the length-tension relationship for skeletal muscles? And why is this the case at
the cellular level? - Correct Answers -Less force at long or very short lengths, more
force at medium lengths of joint angle.
Could predict length where no overlap between thin (actin) and thick (myosin) filaments,
so no force could be created.
Then found where optimal overlap is between thick and thin filaments. Optimal ability to
form crossbridges.
Length where they will bump into each other was next to be found.
Proved that filaments sliding past each other create force.
Intact muscles never get to the extremes, where you wouldn't get force output.
How is the amount of force controlled, considering moving at same velocity between
different weights being lifted? - Correct Answers -1. Action Potential frequency
2. Increase number of motor units recruited (recruitment). Number of muscle fibers
activated.
Fewest number of muscle fibers can activate is six, since from spinal cord comes 3
neurons to motor nerve which splits into two at muscle fibers. Has to do with where
