Lecture Quiz 5 Flashcards
Give a brief overview of muscular contraction from a cellular perspective
thin filaments slide past the thick filaments
overlap of myofilaments increases
sarcomere shortens
What are the 7 steps of muscular contraction? No description needed
stimulation by neuron action potential calcium release activation of actin myosin forms cross-bridges with actin cross bridge detachment relaxation
What happens during stimulation by neuron in muscle contraction?
nerve impulse causes the release of Ach into the synaptic cleft
Ach binds to receptors on sarcolemma
ligand-gated channels open
Na+ allowed to enter muscle fiber down the concentration gradient
What happens during the action potential stage in muscle contraction?
inflow of Na+ depolarizes membrane, giving it positive charge
depolarization spreads in all direction
action potential generated, membrane excited
action potential reaches t tubules
What happens during the calcium release in muscle contraction?
membrane depolarization in the t tubule causes Ca2+ release from sarcoplasmic reticulum into sarcoplasm
What happens during the activation of actin in muscle contraction?
Ca2+ binds to troponin
tropomyosin moves, exposing binding center on actin
active centers now open for interaction with myosin
What happens when myosin forms cross bridges with actin?
the cross bridge moves, pulling the two filaments past each other
ADP is released
What happens during the cross-bridge detachment stage of muscle contraction?
ATP molecule binds to myosin head
bond is broken between actin and myosin
myosin head moves into a cocked position
What happens during the muscle relaxation stage of muscle contraction?
depolarization of the sarcolemma passes
Ca-pumps return Ca2+ to sarcoplasmic reticulum
troponin makes actin unavailable
muscle stops contracting
elastic component of the cell recoils and pulls myofilaments into original position
What is the rule of thumb for excitability in a muscle cell?
only the contractile component is excitable
elastic component is inert
What happens to the sarcomere when the muscle contracts? Use descriptive parts of sarcomere
length of myofilaments does not change
Z lines brought closer together
I-bands and H-zones shorten and disappear
A-bands move closer together but do not change in length
What happens when ATP is converted to ADP?
ATP -> ADP + phosphate + energy
How is ATP used in muscle contraction?
breaks the cross-bridges
energizes the ion pumps
How is ATP replenished during muscle contraction?
phosphorylation by creatinine phosphate
glycolysis
Describe aerobic glycolysis
occurs in the mitochondria
O2 is required
produces CO2 and 30-36 ATP molecules
glucose + O2 -> CO2 + H2O + 30-36 ATP
Describe anaerobic glycolysis
occurs in the cytoplasm no O2 needed yields little ATP produces lactic acid this is the cause of pain after exercise glucose -> 2 lactic acid + 2 ATP
How much ATP is utilized for muscle contraction?
40%
the rest is lost in the form of heat through sweating and radiation from the skin
When does muscle use anaerobic glycolysis?
when exercise demands exceed the ability of muscle metabolism to keep up with ATP demand
Describe fast glycolytic fibers
large white fibers contain little myoglobin and few mitochondria generation of ATP mostly anaerobic capable of strong, fast contractions fatigue easily
Describe slow oxidative fibers
small red fibers
contain a lot of myoglobin and mitochondria
ATP is mostly generated aerobically
very fatigue resistant but contract slowly
Describe fast oxidative fibers
medium-size pink fibers containing many mitochondria and a moderate amount of myoglobin
capable of both anaerobic and aerobic glycolysis
moderately fatigue-resistant
What type of twitch fibers do certain muscles contain?
Muscles have all three types of muscle fibers
training can change the predominant fiber type in muscles
What type of muscle fibers would you want for certain physical activities?
endurance running - slow oxidative
sprints - fast-oxidative
power lifting - fast glycolytic
How does hypertrophy occurs?
only if the muscle develops at least 75% of its maximum tension
only a few minutes several times a week is needed
What happens during hypertrophy of muscles?
during the first few weeks of conditioning, the muscle compensates by involving more motor units
finally, inserton of myosin and actin begins, resulting in larger, more powerful muscles
How do anabolic steroids affect humans?
promotes muscular hypertrophy similar to testosterone damage kidney and heart causes aggressiveness females - sterility, facial hair, breast and uterine atrophy males - baldness, atrophy of testes
What happens during atrophy?
decrease in cell size
results when muscle is not stimulated and does not contract
ex: leg in cast, astronauts in space
describe a motor unit
a single motor neuron and all the muscle fibers it innervates
small motor units exhibit fine control
size and number of motor units being stimulated determines the strength of the muscular contraction
What are the three stages of a muscle twitch?
latent period
contraction period
relaxation period
What happens during the latent period of a muscle twitch?
excitation of the muscle fiber occurs
calcium ions are released from the sarcoplasmic reticulum into the cytoplasm
What happens during the contraction period of a muscle twitch?
cross bridges are formed between the thick and thin filaments
sarcomere shortens
generated force is transferred to the elastic components
What happens during the relaxation period of a muscle twitch?
calcium ions are removed from the cytoplasm
cross bridges disappear
elastic components pull the sarcomere back to its original configuration
What happens during the refractory period of a muscle twitch and where is the only place this is present?
the time when muscle cannot be excited and contract
only significant in cardiac muscle
What happens during treppe contractions?
motor unit responds more forcefully to repeated stimuli
after a few twitches, muscle reaches its maximum performance
“warm up”
What happens during wave summation contractions?
if a second stimulus is applied while the effects of the first stimulus are still present, then the second twitch adds to the remaining force of the first twitch
What happens during tetanus contractions of muscle twitch?
as frequency of the stimuli increase, the individual twitches fuse to form a smooth, sustained contraction
this is the normal physiological response of a muscle
What happens during incomplete and complete tetanus contractions?
incomplete - muscle partially relaxes between the stimuli
complete - no relaxation is observed between stimuli
What happens during fatigue of muscle contractions?
after multiple stimulations, the force of the contraction diminished
motor unit is said to be undergoing fatigue
muscle fibers have depleted their fuel (carbohydrates and ATP)
What happens during fatigue of muscle contractions under anaerobic conditions?
the produced lactic acid drops pH which interferes with protein function
What is junctional fatigue of muscle contraction?
caused by depletion of Ach in the synapse
What is isometric contraction?
muscle contracts, but does not shorten
What is isotonic contraction?
concentric - muscle contracts and shortens
eccentric - muscle contracts and increases in length
What are the three types of muscle groups in contraction and what are their roles?
prime mover - muscle that causes a movement
synergist - muscle that assists the prime mover
antagonist - opposing muscle that stretches
What are the components of a lever system?
sulcrum - fixed point, typically the joint. moving
lever - rod that moves at the fulcrum
resistance - the load against which the muscle works
effort - the tension force the muscle develops
When does muscle contraction happen from a lever perspective?
when the force (effort) is greater than the load (resistance)
Describe a first class lever system
the fulcrum is between the effort and the resistance
most efficient type of lever system
rare in the body
Describe the second class lever system
fulcrum is at one end of the lever and the force is at the other end with the load in the middle
rare in the human body
Describe the third class lever system
effort is applied between the fulcrum and the resistance
least mechanically efficient
most prominent type of lever in human body
