skeletal muscle tissue
voluntary, striated, movement
cardiac muscle tissue
only in heart, propels blood, striated, involuntary
smooth muscle tissue
propels fluids and other substances, nonstriated, involuntary
ability to receive and respond to a stimulus
ability to shorten forcibly when adequately stimulated
ability to be stretched or extended
ability to recoil and resume its resting length after being stretched
Four Important Muscle Functions:
produce movement, maintain body posture and position, stabilizing joints, generating heat
overcoat of dense irregular connective tissue that surrounds the whole muscle
surrounds each fasicle (groups of muscle fibers)
surrounds each individual muscle fiber
where muscle connects to moveable bone
where muscle connects to immovable bone
epimysium of muscle connects directly to the periosteum of bone or perichondrium of cartilage
muscle sheath forms a tendon or aponeurosis that anchors the muscle to the connective tissue of bone or cartilage, or the fascia of other muscles
plasma membrane of muscle
cytoplasm of muscle cell; contains unusually large amounts of glycosomes and myoglobin
granules of stored glycogen that provide glucose during periods of muscle cell activity
red pigment that stores oxygen
rodlike contractile elements that occupy most of the muscle volume (80%); composed of sarcomeres arranged end to end (appear banded); thousands per myofiber
contractile unit, composed of myofilaments made up of contractile proteins
contain myosin and extend the entire length of the A band
contain actin and extend across the I band and partway into the A band
coin shaped sheet composed largely of the protein alpha-actinin, anchors thin filaments
Desmin (intermediate) filaments
extend from the Z disc and connect each myofibril to the next
act as motor to generate the tension developed by contracting muscle cells; formed when globular heads of thick filaments link to thin filaments
spirals around actin core and stiffens/stabilizes it; lines up beside actin to block myosin-receptor sites
three parts: TnI: inhibitory and binds to actin; TnT: binds to tropomyosin and helps position it on actin (to block the myosin receptor sites); and TnC: binds to calcium ions
What are the three types of filaments?
Thin: actin, troponin, tropopmyosin; Thick: myosin; Elastic: Titin
links thin filaments to the integral proteins of sarcolemma (which in turn are anchored to extracellular matrix)
elaborate smooth endoplasmic reticulum; interconnecting tubules surround each myofibril; most of these tubules run longitudinally along myofibril communicating at the H zone: MAJOR ROLE is to regulate intracellular levels of ionic calcium; stores calcium and releases it on demand when muscle fiber is stimulate to contract
form larger, perpendicular cross channels at the A band-I band junctions and always occur in pairs
runs length of thick filament
end of A band, where thin filaments are
where the sarcolemma of the muscle cell protrudes deep into the cell interior; increase muscle fiber's surface area; each T Tubule runs between the paired terminal cisternae, forming triads; conduct impulses to deepest regions of the muscle cell and every sarcomere (which signal for the release of calcium from the adjacent terminal cisternae); can be thought of as a rapid telegraph system that ensures that every myofibril in the muscle fiber contracts at virtually the same time
successive groupings of the: terminal cisternae, T Tubule then Terminal Cisternae again
Contraction is not shortening:
activation of myosin's cross bridges, which are force generating sites
sliding filament model of contraction
during contraction, thin filaments slide past the thick ones so that actin and myosin filaments overlap to a greater degree
only one within each muscle fiber; this is what the branches off the axon is called; include axon endings, synaptic cleft, junctional folds
space between axon terminal and muscle fiber, and is filled with gel like extracellular substance rich in glycoproteins and collagen fibers; where the impulse passes through from the axon to the myofiber; contains acetylcholinesterase, which breaks down ACh
small membranous sacs containing acetylcholine, or ACh
trough like part of the muscle fiber's sarcolemma that is highly folded to provide a large surface area for the millions of ACh receptors
Three steps of generation of action potential:
1) local depolarization and generation of an end plate potential; 2) generation and propagation of the action potential; 3) repolarization
sarcolemma is restored to original polarized state; note that repolarization only restores the electrical conditions of the cell; the ATP dependent Na+ K+ pump restores ionic conditions of resting state, but hundreds of action potentials can occur before ionic imbalances interfere with contractile activity
sequence of events by which transmission of an action potential along the sarcolemma leads to the sliding of myofilaments; occur during latent period, between action potential initiation and the beginning of contraction
What are the three components of the neuromuscular junction?
synaptic cleft, axon terminal, junctional folds of sarcolemma
What is the initial trigger for muscle contraction? The final?
Depolarization of the sarcolemma; certain concentration of calcium ions in the cytosol
the force exerted by a contracting muscle on an object
the opposing force exerted on the muscle by the weight of the object to be moved
motor neuron and all the muscle fibers it supplies; when a motor neuron fires (transmits an action potential), all the muscle fibers it innervates contract; stimulation of a single motor unit causes a weak contraction throughout the entire muscle
response of a motor unit to a single action potential of its motor neuron
relaxed muscles are always contracted somewhat; due to spinal reflexes that activate first one group of motor units then another in response to activation of stretch receptors in the muscles; keeps muscles firm, healthy and ready to respond to stimulation, and helps stabilize joints and maintain posture
latent period of twitch contraction
when muscle tension is starting, but you can't see it; during excitation contraction coupling
period of contraction of twitch contraction
when cross bridges are active, from onset to peak
period of relaxation of twitch contraction
initiated by reentry of calcium ions into sarcoplasmic reticulum; also, muscles contract faster than they relax!
partial relaxation, frequent stimulation after refractory period but before relaxation
stimulus frequency increases until maximal tension is reached; doesn't happen often, for example when someone displays superhuman strength and lifts a car off a friend
muscle length changes and moves the load
two types of isotonic contractions
concentric: muscle shortens; eccentric: muscle lengthens
tension builds up but no shortening or lengthening of the muscle; muscles contract isometrically when they hold joints, maintain posture, etc
the length of time a muscle can continue to contract using aerobic pathways
the point at which muscle metabolism converts to anaerobic glycolysis
state of physiological inability to contract even though the muscle still may be receiving stimuli; due to a problem in excitation contraction coupling, rare cases due to problems at neuromuscular junction; ATP use > ATP production; excessive accumulation of lactic acid; K disrupts the Na/K pump
total lack of ATP that results in states of continuous contraction because the cross bridges are unable to detach (writer's cramp, rigor mortis!)
extra amount of oxygen that the body must take in for these restorative processes
What 4 factors affect the force of muscle contraction?
number of muscle fibers stimulated; frequency of stimulation; relative size of fibers being stimulated; degree of muscle stretch
What are the requirements for "resting state"?
oxygen reserves must be replenished; lactic acid must be converted into pyruvic acid, glycogen or glucose; glycogen stores must be replaced; ATP reserve must be resynthesized; creatine phosphate reserve must be re synthesized
slow oxidative fibers:
slow contraction (because myosin ATPases are slow); depends on oxygen; located in areas of oxygen; aerobic respiration; can last awhile/resistant to fatigue/for endurance activities; RED
fast oxidative fibers:
fast contraction (because myosin ATPases are fast); located in areas of oxygen; aerobic respiration; moderately fatigue resistant; RED to PINK
fast glycolytic fibers:
fast contraction (because myosin ATPases are fast); anaerobic glycolysis!!; located in areas of no oxygen; prone to fatigue; WHITE
3 factors that influence velocity of contraction?
muscle fiber type; load; number of motor units contracting
the alternating contraction and relaxation of opposing longitudinal and circular layers of smooth muscle tissue that mixes substances in the lumen and squeezes them through the organ's passageway
bulbous swellings of the nerves in the smooth muscles; release neurotransmitters into synaptic clefts
pouchlike infoldings that sequester bits of extracellular fluid containing a high concentration of calcium ions close to the membrane; consequently, when calcium channels in the caveolae open, calcium influx occurs rapidly
How does smooth muscle differ from skeletal muscle? 4 ways
thick filaments are fewer but have myosin heads along their entire length; no troponin complex in thin filaments; thick and thin filaments arranged diagonally; intermediate filament dense body network
what regulates smooth muscle contraction?
nerves, hormones, local chemical changes
What are special features of smooth muscle contraction?
response to stretch; length and tension changes; hyperplasia
allows a hollow organ to fill or expand slowly to accommodate a greater volume without promoting strong contractions that would expel its contents
cells dividing to increase numbers; for example, when a woman gets pregnant, high levels of estrogen stimulate uterine hyperplasia to accommodate growing fetus
Which cell structure releases calcium?
Binding of the neurotransmitter to receptors on the motor endplate opens channels that let which ion enter the cell and cause depolarization?
The binding of what to the myosin head puts the cross bridge in its high-energy conformation?
What is the cause of rigor mortis?
depletion of ATP
What molecule must be removed in order to rebuild ADP into ATP?
A water molecule
The muscles of the eye need to make precise small motor movements. What size are the motor units in the eye?
What will happen to a muscle if the motor neuron is cut?
the muscle will become flaccid
An increase in the strength of the stimulus will cause an increase in tension development caused by:
recruitment of more motor units
The shortest phase of a muscle twitch, usually lasting less than 5 milliseconds, is called the
Sarcomeres lengthen during which phase/period of muscle twitch?
hen a single stimulus is applied to a muscle, a curve of the tension developed (muscle twitch) can be generated. If the same strength stimulus is applied to the muscle again (after complete relaxation), how will the size of the second curve be altered?
the height of the curve will be equal to that of the first curve
During the initial phase of muscle contraction, each successive stimulus produces a slightly stronger contraction because of increased muscle warming and efficiency of enzymes. This stage is called:
With rapid, multiple stimulations, the contraction-relaxation cycles are shorter but there still is some degree of relaxation. What is this stage called?
If a muscle is applied to a load that exceeds the muscle's maximum tension
the muscle length will not change during contraction
is duchenne muscular dystrophy more common in females than in males?
The space between the neuron and the muscle is the
The term that means a continued mild or partial contraction of an entire muscle is muscle
autoimmune disease of acetylcholine receptors?
muscle contraction as result of repeated continual stimulation; part of tetanus; eventually contraction gets to certain strength
partial relaxation; frequent stimulation after refractory period but before relaxation
no relaxation of muscle; stimulus frequency = relaxation period
occurs when muscle is undergoing tetanal contraction; second stimulus applied before complete relaxation; second contraction is stronger than original
aids in the growth of tissues