Muscle Cells and Related Sturctures Flashcards
Structure of a Sarcolemma
T tubules and sarcoplasmic reticulum
T tubules invaginate toward the SR cisternae
form triads
Slide filament mechanism: all the steps
a) AP arrives at synapse terminal
b) calcium channels bring in Ca2+, cause vesicle fusion
c) neurotransmitter release into synapse
d) AcC binds to ligand gated channel
e) end plate depolarization
f) action potential occurs down sarcolemma
g) AP carries down t Tubule
h) AP causes conformation change in DHP receptors
i) DHP causes conformation change in Ryanodine ion channels
j) ryanodine receptors release calcium from SR
k) calcium binds to troponin
l) tropomyosin allows actin to bind to myosin
m) power stroke
n) calcium uptake carriers in SR and sarcolemma pump Ca out of cell
Where are the t tubules in relation to the actin and myosin
they invaginate the sarcolemma at the I-A band, form “triads” with cisternae
two per sarcomere
DHP
dihydropyridine receptors
voltage sensitive l type calcium channels arranged in quadruplets
located on the sarcolemma t tubules
cause a conformational change in the ryanodine receptors
a minute amount of calcium flows intot the cytosol via these channels
RyRs
Ca+2 release channels
open in response to conformation change in DHP receptors
How do muscle cells return calcium once it has been released by RyR from the SR?
atp dependent pumps
calsequestrin: monitors and maintains optimal calcium concentration gradient
SERCA
Sarcoplasmic Reticulum Calcium ATPase
Sarcomere Lengths (Maximum tension to Maximum Extension)
SR max tension between (1.6-2.2)micrometers
“Resting” length is 2 mic.m
beyond 2.2 there’s no tension, and below 1.6 mic.m there’s no tension
ATP in skeletal muscle: where and why
ATP used for powerstroke
ATP used for pumping calcium back into SR
ATP used for Na/K pump
Concentration of calcium in muscle fibers
4 mmol, enough for 1-2 sec contractions
energy sources in skeletal muscles
a. phosphocreatine (reconstitutes ATP), rapid release, sustains 5-8 second contractions
b. glycolysis, sustains up to 1 minute contractions
c. Oxidative metabolism, 95% of energy needs met for long term contraction
Isometric contraction
increase in tension but not in length
Isotonic contraction
eccentric and concentric
eccentric occurs when the muscle lengthens
concentric occurs when the muscle shortens
White vs Red fibers
Categorized based on endurance
White is fast, contains less mitochondria, myoglobin, and relies on mainly anaerobic respiration (lactic acid/pyruvate build up), and lots of ATPase
Red is slower, has more mitochondria, aerobically based, has more myoglobin, smaller concentration of ATPase
Myofibers
cannot be increased after birth
myofibrils CAN be increased, so mass can be increased but not number
Lost muscle will be replaced by
scar tissue (fibrous connective tissue
Myofiber type
dark fibers (myofiber) (soleus) light fibers (myofibers) (gastrocnemius
the “motor unit” consists of the
a single nerve cell may innervate from a few to several hundred myofibers
a) motorunit consists of the myofibers and the neuron
all or none
Summation
electrical events occur faster than mechanical events
additional “spike” ca cause MORE calcium to add to a previous cycle, total Ca2+ increases, causing increased muscle tension
the spikes are additive (sum)
Tetany
no relaxation between “spikes” of calcium influx, muscle remains at maximum contraction
Machines transmit forces from one place to another. What are the forces involved? By what means?
Force applied TO the machine (in force)
Force applied FROM the machine (out force)
the system of levers muscle and bones create
Architecture of the Lever
Distance between point of force on the lever arm and fulcrum (joint or pivot) is the “in lever arm”
distance from the lever to the out force is the out lever arm
Mi = FiLi
M = moment; F = force; L = lever arm
Mo=FoLo
At equilibrium, the muscle lever equation reads
FiLi=FoLo
Which muscle activates the lever system?
biceps
Classification of levers is based on
the position of the fulcrum to the in force/out force
Types of levers
1st class: fulcrum is in the middle
a. in force equals out force move in opposite
directions
2nd class: resistence (out-force) is in the middle
a. fulcrum = ball of the foot if you elevated yourself using your toes
b. both in and out forces are on the same side of the
fulcrum
3rd class: effort (in force) is in the middle
(lifting a weight in the palm of your hand)
