Muscles Flashcards
sarcomere
basic unit of a muscle fiber, defined by the area between two Z-discs, containing thick and thin filaments
myofilament
protein filaments in muscle fibers; thick filaments (myosin) and thin filaments (actin) that facilitate contraction
cross-bridge
the connection formed when a myosin head binds to an actin filament during muscle contraction
excitation-contraction coupling
the process that links electrical stimulation of a muscle to its contraction, involving calcium release and interaction between actin and myosin
3 types of muscle
skeletal, cardiac, smooth
which muscles are voluntary
skeletal muscle
involuntary muscle
cardiac and smooth muscle
striated muscle
skeletal and cardiac muscle
unstriated muscle
smooth muscle
what type of muscle cell is a muscle fiber
multinucleated
thin filaments
a two-strand actin helix + the filamentous protein tropomyosin + the troponin complex
actin
a protein found in all muscle tissues, creates smaller filaments
thick filmanets
hundreds of indentical myosin proteins
myosin
a protein found in all muscle tissue, creates large filaments
what do the head regions of myosin contain
actin and atp-binding sites
what happens to sarcomeres during muscle contraction
they shorten; thin filaments actively slide along the thick filaments
what do cross-bridges convert
chemical energy into mechanical energy
where does the cross-bridge cycle start
binding site
what are the stages of the cross-bridge cycle
- release - binding of ATP causes myosin to detach from actin
- binding - hydrolysis of ATP causes myosin head to extend and attach to actin
- power stroke - release of phosphate promotes myosin head rotation
how does rigor mortis occur
without ATP, myosin binds irreversibly to actin causing stiffening of muscles
what mineral is myosin movement dependent on
calcium
when Ca is low
tropomyosin blocks the myosin binding sites on actin, muscles relaxed
when Ca is high
troponin pulls tropomyosin out of the way, allowing cross bridges to form
excitation-contraction coupling
muscle fibers contract when a postsynaptic end plate potential at the neuromuscular junction causes a propagated AP in the fiber sarcolemma
what type of tubules conduct action potentials into cell interior
transverse
what molecules are involved in excitation-contraction coupling
voltage sensitive DHPR and RyR
Ca pumps
Calsequestrin
what is a twitch
a single AP leading to a momentary flood of Ca inside cell, allows cross bridges to form, develops tension (last 5 - 20x longer than action potential)
temporal summation
addition of tension due to repeated and rapid stimulation, can result in max tension
how many muscle fibers are innervated by one motor neuron
one
how to increase muscle tension
- increasing AP frequency (temporal summation)
- recruiting more motor units
- recruiting higher intensity contraction fibers
force-velocity relationship
as load increases, velocity of shortening decreases
reason for inverse relationship between load and velocity
cross bridge cycling takes time, when slowed more myosin heads can act at same time leading to greater force potential
force transducer
measures tension generated by the muscle fiber when stimulated to contract
FG fiber ATP production
glycolysis
SO fiber ATP production
oxidative phosphorylation
is rate of Ca uptake by SR higher in FG or SO
FG
roles of ATP
cross bridge cycling, regulating intracellular Ca levels, maintaining nerve membrane potential
what type of movement demands less ATP
high force, low speed
what would let an athlete win in a 50 m spring
more FG fibers (unsustained)
what would let an athlete win a marathon
more SO fibers (sustained)
glycolysis
glucose is broken down into pyruvate, producing energy in the form of ATP in absence or presence of oxygen
oxidative phosphorylation
takes place in mitochondria, energy from nutrients is used to produce ATP via electron transport chain and oxygen is final electron acceptor
creatine phosphate
high energy molecule stored in muscles that quickly donates a phosphate group to ADP to regenerate ATP during short bursts of high intensity activity
how is burst energy ATP made available so quickly
creatine phosphate system and anaerobic glycolysis
how does sustained energy have an uninterupted supply of ATP
aerobic respiration and fatty acid oxidation
what determines the rate at which a muscle can work
ATP production rate
2 definining features of ATP
not transported between cells, not stored
what did the mouse experiment demonstratae
mice mutants with full Creatine kinase activity had higher burst activity performance than those with no CK activity, showing that the ability of muscle to perform burst activity is proportional to CK activity
what does high-intensity and short term activity produce
lactic acid (indicator of fatigue)
what causes fatigue in sustained exercise
inadequate muscle glucose
muscle fatigue results from (3 answers)
depletion of energy reserves (ATP, glycogen), ion disturbances, and pH imbalance
how can you recover from muscle fatigue
replenishing energy stores (using Cori cycle)
reestablishing ion balance (gradients, Ca stores, pH)
where does ATP have to come from to recover muscle (recovery metabolism)
aerobic pathways
EPOC
Excess post-exercise oxygen recovery
why is there an o2 deficit at beginning of exercise
demand of O2 > supply of O2
what is the repayment phase
exercise has stopped but oxygen remains high to restore the bodys energy balance
what do superfast muscles do
contract synchronously at rates that would put regular muscles into tetanus
what is tetanus
sustained contraction with no relaxation
what conditions allow superfast muscles to work
- short Ca transients (rapid cycling between SR and cytoplasm)
- quick cross-bridge cycling (force generation extremely fast)
what does flight require
continuous aerobic high power output at high contraction frequencies
adaptations to flying
increasing muscle temperature, skeletal adaptations, increasing mitochondria inner membrane for more ATP production
synchronous flight muscles
connect to the wing, one set of muscles raises the wing (elevator muscle) and another lowers them (depressor muscle)
what animals have synchronous flight muscles
vertebrates and some insects
asynchronous flight muscles
connected to the whole body, vertical muscles contract to make body vertically compressed, longitudinal muscles contract to shorten the body
oppositional muscles
when one stretches the other contracts
effect of oppositional muscles on Ca
as muscle stretches, Ca increases, triggering contraction
AP and contraction relation in asynch flight
single AP initiates series of contractions , frequency of contr is not synched w frequency of AP
space distribution in asynch flight muscles
less space for SR and mitochondria, more space for myofibrils
what type of muscle is internalized to retain heat in tuna
red muscle
what type of muscle is red muscle
slow oxidative muscle, packed with ATP
regional heterothermy
parts of the fish are kept warmer than surrounding environment, improving the efficiency of muscles
rete mirabile
structure that retains heat in muscle and prevents loss of heat to gill
heater organs
specialized eye muscles that keep brain/eye temp stable and warmer than surrounding water
what is the carotid rete
collects heat generated by the heater muscle
differences between skeletal muscle cells and heater organ muscle cells
increase in mitochondria content (increased ATP production)
increased SR content (increase storage and release of Ca)
proliferation of T-tubules (increase release of Ca into cell)
no contractile apparatus
what is responsible for storing and releasing Ca
SR and T tubule
