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arrives at a synaptic knob and causes calcium channels to open, which allows the calcium ions to enter the synaptic knob
entry into the synaptic knob triggers exocytosis of synaptic vesicles, which release acetylcholine into the synaptic cleft
diffuses across the synaptic cleft and binds to receptors on the motor end plate, which causes them to change shape
open and sodium ions enter the muscle fiber while potassium ions leave the muscle fiber
in the sarcoplasmic reticulum open and calcium ions diffuse into the sarcoplasm within one millisecond
shifts to a new position, which exposes the myosin-binding sites on the actin filament so cross-bridges can form
the thin filaments slide inward past the thick myosin filaments and cause a sarcomere to shorten; neither thin nor thick filaments change their length
attaches to an ATP-binding site on a myosin head and gets split by myosin ATPase, which energizes the myosin head
the myosin head swivels toward the center of the sarcomere, which draws the thin filament past the thick filaments and generates this
second ATP molecule
attaches to the ATP-binding site on the myosin head, which allows it to detach from the actin filament
when nerve signals no longer arrive at the neuromuscular junction, teh synaptic knob stops releasing acetylcholine
brekas acetylcholine molecules into fragments, which get absorbed into synaptic knob
are actively transported out of sarcoplasm and back into the sarcoplasmic reticulum using ATP energy, where they bind to the protein calsequestrin
of calcium ions from troponin molecules and the troponin-tropomyosin complex moves back into its original position, blocking the myosin-binding sites on the actin strand
calcium ions leak into the sarcoplasm and bind to toponin molecules, which initiates cross-bridge formatino and triggors rigor mortis within three-four hours
since ATP can't be synthesized by dead people, myosin cross bridges can't detach from actin molecules until myofilaments break down
of a muscle contraction depends on the length of the sarcomeres within a muscle fiber before the muscle contraction begins
develops when the resting length of the sarcomere is optimal due to degree of overlap between thick and thin filaments
there is little overlap between the thick filaments and the thin filaments and few cross bridges can form, so muscle tension falls to zero
there is too much overlap between teh thick filaments and the thin filaments; the thck filaments crumpe as they get cmopressed against the z disc, so muscle tension falls to zero
the principles that govern the contraction of a single muscle fiber also govern the contraction of a whole muscle
will stimulate an individual muscle fiber to contract with less than maximum force, so the total tension produces depends on the frequency of stimulation of the fiber
in motor unit are dispersed and not clustered together, muscle contraction will be weak over a wide are rather than localized
a biref contraction of all the muscle fibers in a motor unit in response to a single stimulus form a motor neuron
obeys an "all-or-nothing" law when electrically excited; either contracts to its maximum extend or doesn't contract at all
is a time interval between the application of a threshold stimulus and the beginnign of the twitch contraction
calcium ions are released from teh sarcoplasmic reticulum into the sarcoplasm which allows cross bridges to form
is a time interval when peak muscle tension gets produced (can last up to 100 milliseconds)
is a time interval when muscle tension decreases (can last up to 100 milliseconds)
calcium ions are actively transported out of the sarcoplasm back into the sarcoplasmic reticulum
varies strength of the twitch contraction
state of hydration of the muscle that affects cross bridge formation
are usually insufficient to do any useful work, but stronger twitches can be produced by increasing the voltage of the stimulus
higher voltages excite more nerve fibers in motor nerve causing more motor units to contract (multiple motor unit summation)
healthy muscle contraction
relatively smooth and varies in strength according to the demands placed upon it
below 10 stimuli per second
identical twitches will be produced for each stimulus and the msucle will fully recover between twitches
between 10 and 20 stimuli per second
the muscle fully recovers between twitches, each twitch can develop more tension than the preceding twitch because of treppe (staircase)
calcium ions should be more available because sarcoplasmic reticulum doesn't have time to completely reabsorb them
the difference between teh resting rate of oxygen consumption adn the elevated rate of oxygen consumption following exercise; "it must be repaid"
can be reconverted to pyruvic acid or converted back into glucose, which gets stored as glycogen in the liver
have many mitochondria, a high myoglobin content, an extensive capillary network, and are adapted for aerobic respiration
have fewer mitochondria, a lower myoglobin content, and fewer capillaries than red fibers; adapted for anaerobic respiration
contain many mitochondria, large amount of myoglobin, and many blood capillaries (red fibers)
contain fewer mitochondria, less myoglobin, and relatively fewer blood capillaries (white fibers)
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