Lab 8 Flashcards
Muscle Fiber
Single muscle cell, comprised of many myofibrils, multiple nuclei, surrounded by a sarcolemma
Myofibril
Long, rod-shaped organelles that fill sarcoplasm, contain the sarcomeres and the light/dark bands
Sarcomere
The smallest contractile unit of muscle
Go from the middle of one I band (z disc) to the middle of the next I band.
So from Z disc to Z disc
Consists of actin, tropomyosin, troponin, myosin, titin
Myofilament
Threadlike structures that make up myofibrils, composed primarily of actin and myosin
Thick filament
Myosin, each thick filament is surrounded by 6 thin filaments
Thin filament
Actin, each thin filament is surrounded by 3 thick filaments
Actin is what gets pulled in and shortens the sarcomere
T Tubule
Located between the A and I band. Run deep into the muscle fiber between Terminal cisterns of the SR. Ca2+ storage
Triad
Regions where SR terminal cisterns border a T tubule on each side.
Endomysium
Surrounds each muscle fiber, subdividing the fascicles
Perimysium
Connective tissue surrounding each muscle fascicle
Epimysium
Dense connective tissue covering the entire muscle
Tendon
All 3 sheaths converge to form cordlike attachment to bone or other muscles
Provide durability and conserve space, provide a route of entry/exit for nerves and blood vessels
Aponeurosis
All 3 sheaths converge to a sheet like attachment to bones or other muscles.
Provide durability and conserve space, provide a route of entry/exit for nerves and blood vessels
Tropomyosin
Blocks the myosin binding site on the actin, moved by Troponin
Troponin
Reacts to calcium and moves tropomyosin off binding site to allow myosin to bind
Break down of the Structure of skeletal muscle
I band: light band, Z disc in middle
A band: Dark band, contains the H zone and M line
3 connective tissue sheaths covering muscle at various layers
Neuromuscular junction
Where the motor neuron axon connects with a muscle fiber, one motor neuron can innervate more than one muscle fiber. Motor neuron releases ACh
Entry of Na+ into muscle cell through ACh receptor channel initiates muscle action potential
Excitation-contraction coupling
The conversion of electrical stimulus to movement.
The AP releasing ACh in motor neuron, ACh binds to receptors in end plate which causes depolarization, change in potential triggers contraction
Electrical stimulus
Substitute for ACh, triggers a muscle twitch
Muscle Twitch
The mechanical response to a single action potential
Composed of 3 phases: Latent, contraction, relaxation
Latent period
Period of time that elapses between the generation of AP and the start of muscle contraction. Chemical changes occur in preparation for contraction. Length does not change with increase in stimulus.
Contraction phase
Starts at end of latent period, ends when muscle tension peaks.
Relaxation phase
Period of time from peak tension until the end of muscle contraction
How do different intensities of electrical stim affect twitch
As you increase voltage the peak tension increases until you reach a max tension value, then increasing voltage will not increase tension anymore.
End plate potential
The graded depolarization in the skeletal muscle fiber that is elicited in response to one action potential from the motor neuron
What is released when there is an action potential in a motor neuron
Acetylcholine
What is the motor unit
A neuron and all the muscle fibers it stimulates, stronger muscle contraction means more motor units are recruited
Motor unit recruitment
Increasing the number of active motor units produces a steady increase in muscle force.
Increasing tension affect on motor unit recruitment
A larger contraction implies more motor units are activated.
Weak contraction implies fewer motor units are activated but each motor unit develops its maximal tension regardless.
Maximal voltage
When all the muscle fibers have been activated, maximal tension/contraction occurs
Threshold Stimulus
Smallest stimulus required to induce action potential in a muscles sarcolemma
Wave summation
When muscle fibers that are developing tension are stimulated again before the fibers have relaxed.
Treppe
Progressive increase in force when a muscle is stimulated in succession, each successive twitch peaks slightly higher than the previous. The muscle must fully relax between the stimuli
How does increasing stimulus frequency affect force generation
The faster the stimuli occur the larger the force, the stimuli are summed together to create a greater affect
Unfused tetanus
When stimulus are applied frequently over a prolonger period the maximum possible muscle will reach a plateau
Fused tetanus
Once plateau is reached, if stimuli are applied with an even greater frequency the twitches will fuse to where peaks and valleys are indistinguishable
Maximal tetanic contraction
When the stimulus frequency reaches a value beyond which no further increases in force are generated by the muscle
Causes of fatigue
Accumulations of lactic acid, ADP, Pi
Fatigue
Decline of muscle’s ability to maintain a constant level of force after prolonged repetitive stimulation
OR
Failure of a muscle fiber to produce tension because of a previous contractile activity.
Rest period affect on fatigue
Rest period will delay the onset of fatigue
Rest allows for Lactic acid, ADP, and Pi concentrations to decrease it will delay fatigue and allow for maintaining maximum force.
Isometric contraction
Muscle stays at a fixed length, the load attempted to move is equal in weight to the force generated by the muscle.
Isotonic contraction
Skeletal muscle length changes, so the load moves a measurable distance
If muscle is shortening it’s isotonic concentric contraction (muscle generates a force greater than the load)
Latent period gets longer as load increases
Active force (know graph)
Generated when myosin thick filaments bind to actin thin filaments engaging the cross bridge cycle and ATP hydrolysis
Passive force (Know graph)
Generated by the stretching of a muscle and results from the elastic recoil of the tissue, caused by titin which acts as molecular bungee cord
Why is there a dip in the force graph
At 80 mm the active force has decreased but the passive force has not increased to a significant value
Length tension relationship
Describes the amount of tension that is produced by a muscle as a feature of its length. The longer the muscle the larger the force. Peak tension is when sarcomeres are at their resting length because this provides optimum alignment between actin and myosin
Load velocity relationship
The greater the load the smaller the shortening velocity (slower)
Lighter load also means longer contraction duration
Can you label all the diagrams?
Prove it. Now.
Latent period of isotonic contraction
cross bridges cycle and, when muscle tension exceeds the load, muscle shortening occurs.
