10. 4 - 10.7 Flashcards
resting membrane potential for skeletal muscle
NEGATIVE 85 mV (-85 mV)
excitable membranes
permit rapid communication between different parts of a cell
types of excitable membranes
depolarization
hyperpolarization
repolarization
depolarization
membrane potential becomes less negative due to influx of sodium ions
hyperpolarization
the membrane potential becomes more negative due to outflow of potassium ions
repolarization
return to the resting membrane potential after depolorization
neuromuscualar junction (NMJ)
the synapse between a motor neuron and a skeletal muscle fiber
axon (synaptic) terminal
expanded end of the axons of the motor neuron
motor end plate
folded membrane of the skeletal muscle fiber at the NMJ
synaptic cleft
narrow space between the axon terminal and the motor end plate
neurotransmitter
chemical released from the axon terminal into the synaptic cleft
neurotransmitter at the NMJ is
acetylcholine (ACh)
excitation-contraction coupling
link between the generation of an action potential in the sarcolemma and the start of muscle contraction
steps of excitation-contraction coupling (5)
contraction cycle
series of molecular events that enable muscle contraction
contraction cycles involved the formation of
cross bridges: myosin heads bind to the active sites on actin
power stroke
the myosin head uses energy from ATP to pivot and pull on active towards the M line
steps that initiate a muscle contraction
-ACh released
-action potential reaches T tubule
-sarcoplasmic reticulum releases stored calcium ions
-active sites exposed and cross bridges form
- contraction cycle begins
steps that end a muscle contraction
-ACh is broken down
- SR reabsorbs calcium ions
-active sites covered and cross bridge formation ends
- contraction ends
- muscle relaxation occurs
rigor mortis
muscle stiffens after death resulting from a muscles being locked in a contracted position
tension
pull force generated by the muscle when it contracts
length tension relationship
tension produced by a muscle fiber relates to the length of the sarcomeres
twitch
a single stimulus contraction relaxation sequence
myogram
graph showing tension development in muscle fibers
phases of a twitch
latent period
contraction phase
relaxation phase
latent period
the time it takes from the stimulation to move across the sarcolemma and for the SR to release calcium ions
contraction phase
tension increases as the muscle fiber is forming cross bridges and the myosin heads do power strokes
relaxation phase
tension decreases as cytosolic calcium ion levels decrease, myosin binding sites on actin are covered by tropomyosin, and cross bridges detach
treppe
an increase in peak tension caused by repeated stimulations which happen after the end of each relaxation phase
wave summation
increasing tension due to successive stimuli that arrive before the relaxation phase has been completed
tetanus
maximum tension
incomplete tetanus
the muscle produces near maximum tension due to rapid cycles of contraction and very brief incomplete relaxation
complete tetanus
the muscle is in continuous contraction due to high stimulation frequency which eliminates the relaxation phase
motor unit
a motor neuron and all the muscle fibers it controls
fasciculation
involuntary muscle twitch which is caused by the synchronous contraction of one motor unit
recruitment
increase in muscle tension due to the increase of active motor units
motor unit summation
“relay” approach in which some motor units are contracting, and some are resting and recovering
muscle tone
the resting tension of a skeletal muscle
types of muscle contractions
isotonic and isometric
isotonic contractions
causes the skeletal muscle to change length
isotonic concentric contraction
muscle tension exceeds the load (resistance) and the muscle shortens
isotonic eccentric contraction
peak muscle tension is less than the load and the muscle elongates due to gravity or the contraction of another muscle
isometric contractions
the skeletal muscle develops tension, but does not change length
how does atp transfer energy
atp transfers energy (in the form of a phosphate) to create creatine phosphate (CP)
- catalyzed by the enzyme creatine kinase
atp is generated by
glycolysis and aerobic metabolism
glycolysis
anaerobic metabolism that breaks down glucose to pyruvate in the cytosol
aerobic metabolism
oxygen dependent process in which mitochondria use organic substrates (ex: pyruvate) to produce atp
recovery period
the time required for muscles to return to pre-exertion conditions
oxygen debt/excess postexercise oxygen consumption
the amount of oxygen required to restore normal pre-exertion conditions
