Lesson 21 Flashcards
excitation
action potentials in motor nerve fiber lead to action potentials in the muscle fiber
excitation-contracting couping
events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them for contraction
contraction
the step in which the muscle fiber develops tension and may shorten
relaxation
when stimulation ends, a muscle fiber relaxes and returns to its resting length
what molecule helps muscle return to their resting length?
titin
rigor mortis
hardening of muscles and stiffening of the body beginning 3-4 hours after death
what causes rigor mortis?
muscle relaxation requires ATP, and since the cell is dead it cannot produce more ATP to break the cross bridge
tension produced by muscle fibers depends on: (3)
- the number of pivoting cross-bridges that are formed
- the fiber’s resting length at the time of stimulation
- the frequency of stimulation of the muscle
length-tension relationship
the amount of tension generated by a muscle depends on how stretched or shortened it was before it was stimulated
If overly shortened before stimulated, contraction is _____
weak; thick filaments butt up against Z discs, some thin filaments overlap
if too stretched before stimulated, contraction is _____
weak; minimal overlap between thick and thin filaments results in minimal cross-bridge formation
muscle tone
the nervous system maintains partial contraction to ensure that resting muscles are near optimum resting length
twitch
a single neural stimulation produces a single contraction
threshold
minimum voltage that causes a muscle twitch
increasing the frequency of stimulus delivery increases _____ _____
tension output
muscle’s _____ _____ influences cross-bridge formation - affects the spacing between thick and thin filaments
hydration level
warmer muscles’ enzymes work _____
quicker
treppe
a stair-step increase in twitch tension; repeated stimulations immediately after the relaxation phase
what is treppe stimulus frequency?
less than 50/second
what is treppe caused by?
gradual increase in Ca2+ concentration in the sarcoplasm, the pumps aren’t fast enough to get ALL of the previously released Ca2+
wave summation
increasing tension or summation of twitches; repeated stimulations before the end of the relaxation phase
what is the stimulus frequency of wave summation?
greater than 50/second
what do higher frequency stimuli produce?
temporal (wave) summation
temporal (wave) summation
each new twitch “rides piggyback” on the previous one, generating higher tension
incomplete tetanus
only partial relaxation between stimuli, resulting in fluttering
complete (fused) tetanus
unnaturally high stimulus frequencies cause a steady contraction
Clostridium tetani
the bacterium that produces the toxin that causes tetanus
what does the tetanus toxin do?
caused over activity of skeletal muscle motor neurons by blocking inhibitory interneurons in the spinal cord
motor units
muscle fibers controlled by single motor neuron
stimulating the nerve with higher voltages produces _____ contactions
stronger; higher voltages excite more nerve fibers which stimulate more motor units to contract
recruitment
multiple motor unit (MMU) summation
- process of bringing more motor units into play with stronger stimuli
size principle
weak stimuli recruits small units, while strong stimuli recruit small and large units for powerful movements
isometric contraction
contraction without a change in length
isotonic contraction
contraction with a change in length but no change in tension
other forces involved during muscle relaxation: (3)
- elastic forces
- opposing muscle contractions
- gravity
