Muscle Flashcards
what causes skeletal muscle excitation
neuromuscular somatic synaptic transmission
T/F cardiac muscle doesn’t require an outside stimulus
true, pacemaker cells will depolarize on their own, gap junctions allow for the AP to travel, and the ANS modulates the response
what causes smooth muscle excitation
either electric coupling or autonomic stimulation
what position is the myosin cross bridge in relation to actin at rest
at a 90 degree angle and not touching
what happens to actin and myosin during activation
myosin binds to actin
what happens when myosin binds to actin
ADP and P are released, allowing the myosin head to move from a 90 to 45 deg angle to actin
how does the myosin head uncouple from actin? how does it return to its resting state
ATP binds with myosin to release the actin filament, then ATP is hydrolyzed to return myosin to resting state
describe the entire process of cross bridge cycling
- myosin is at rest at right angles to actin, bound to ADP and P
- myosin binds to actin at binding sites, releasing ADP and P
- unbound myosin heads change confirmation and shift to a 45 in relation to actin
- ATP binds with myosin to uncouple it from actin
- ATP is hydrolyzed into ADP and P to return the head to a 90 deg rest position
what is the normal concentraion of calcium in the cytoplasm?
where is the majority of calcium stored
0
in the sacroplasmic reticulum
what is the function of Ca in excitation-contraction coupling
it links excitation with coupling by binding to troponin to move tropomyosin off myosin binding sites, allowing for activation
what is a T tubule? what is the function?
extensions of the cell membrane from one muscle cell to another
they allow for rapid activation of L type calcium channels and propogate depolarization to surrounding cells
what is the “triad” of cell structures that participate in propogation of action potentials between muscle cells
the sarcoplasmic reticulum of two cells sandwiching a T tuble
what is the difference in excitation-contraction coupling between skeletal and cardiac muscle cells
muscle cells use mechanical coupling between calcium release channels an on the SR and L type calcium channels on the T tubule
in cardiac cells L type calcium channels on the T tubule secrete calcium, which activates calcium release channels
describe the process of calcium release through mechanical coupling in skeletal muscle
- skeletal muscle is stimulated by AcH release from a neuron
- skeletal muscle depolarizes, opening L type calcium gated channels on the T tubule
- L type channels physically bind to calcium release channels on the SR
- calcium release channels release calcium into the T tubule to bind with troponin allow myosin cross bridges to form
how is the process of calcium release into t tubules different for cardiac muscle?
what is the alternative?
there is no mechanical binding
calcium for L type calcium channels binds to the calcium release channels, stimulating ion current
how is calcium removed from the cytoplasm?
Na-Ca pump and Ca pump remove calcium from the cell
Ca sequestering pump pumps Ca into the SR where it bound to calreticulin and calsequestrin
what happens to muscle cell when calcium is removed from the cytoplasm
with no calcium to bind troponin, tropomyosin will cover the cross bridge sides and block myosin attachments
isometric contraction
a contraction with myosin-actin cross bridge cycling, sarcomere shortening, but no movement
isotonic contraction
a muscle contraction where there is myosin actin cross bridging and sacromere shortening that results in shortening of the muscle fibers
what are the three phases of an isometric twitch
latent, contraction, relaxation
what is happening during the latent phase of an isometric twitch
there has been a stimulus received by the muscle but no calcium release until the end of the latent phase
what is happening during the contraction phase of an isometric twtich
calcium that has been release by the SR binds to tropomyosin, allowing for cross bridge cycling
what is happening during the relaxation phase of an isometric twitch
calcium is being pumped out of the cytoplasm to slow down cross bridge cycling
summation
when successive depolarization events converge on a muscle cell, causing the release of more calcium and a stronger contraction
unfused tetanus
when summation produces an average constant tension between contractions
fused tetanus
when summation by repeated stimuli causes a max tension curve with no individual contractions
elasticity
the force a subtance produces that resists change in shape
compliance
the abilty for an object to change shape
relate elasticity and compliance to a real world object
a rubber band is compliant because it will stretch, and elastic because it will produce force to counteract stretching force and return it to its original shape
contractile component of muscle
cellular components that generate force (sarcomeres)
series elastic component
the non-contractile parts of a cell and the tendons which produce force against stretch
what regulates the maximum amount of force a sarcomere can generate
the amount of contact between actin and myosin
described the amount of force produced by these situations
- actin myosin overlapping
- actin myosin in contact with no H band
- actin myosin in contact with an H band
- actin myosin with some heads exposed
- no contact of the myosin heads
- less force because some of the cross bridge sites are covered by the adjecent actin filament
- maximum number of cross bridges = max force
- max force because there are no exposed myosin heads
- less force because of fewer binding sites are accessible
- no force because there are no binding sites accessible
what happens to active force as length increases? passive force?
active force decreases, passive force increases
what three factors influence force generated by individual muscle fibers
- frequency of stimulation
- fiber diameter
- changes in fiber length
how does stimulation frequency effect contraction strength
more frequent stimulus can result in summation of contractions
how does fiber diameter effect force generation?
a larger fiber has a larger length constant and will conduct an AP further, allowing for the recruitment of other parallel fibers
how does changing fiber length effect contraction strength
increasing the fiber lengh will stretch the sarcomeres, which can allow for more or less contract between the sarcomeres depending on the start position
motor unit
a neuron and all the muscle fiber it innervates
recruitment
the stimulation of multiple muscle fibers through a stronger stimulus
threshold
the lowest stimulus that will produce a contraction
maximal stimulus
the lowest stimulus that will produce maximal force production
if motor unit 1 requires a 5 V stimulus, unit 2 a 10, and unit 3 a 15 V stimulus, how much will it take to stimulate all the motor units
15V
T/F graded stimulus can activate individual fibers of a motor unit
false, motor units are all or none
what are the three periods of an isotonic twitch
latent, plateau, and relaxiation
what is happening in the latent phase of an isotonic contraction
muscle is developing tension without moving
what is happening in the plateau phase of an isotonic contraction
there is no more tension being produced because the load is moving by shortening muscle fibers
what is happening in the relaxation phase of an isotonic contraction
tension declines to zero
what would happen if there were no plateau in an isometric contraction
there would be no shortening of sarcomeres greater than the elasticity of the tendons, so no movement would take place (isometric)
describe the load-velocity curve
higher loads produce more force but less velocity, therefore less power
loads that are too low produce high speed but don’t generate much force, there for less power
around what percent of maximum is power the highest
35%
