Lecture 04 Skeletal Muscle Flashcards
what sarcomeric band does not undergo a change in length during the contraction of a skeletal muscle?
A Band
What refers to a chain of sarcomeres?
Myofibril
Dihydropyridine (DHP) channels are part of what structure?
T tubules
Ryanodine-sensitive calcium ion release channels are part of what structure?
Sarcoplasmic reticulum
Which of the following events occurs first during the transmission of a signal from an alpha motor neuron to a skeletal muscle fiber? End-plate Depolarization Calcium Ion Influx into Axon Terminal Exocytosis of synaptic vesicles Sarcolemma action potential
Calcium Ion Influx into Axon Terminal
Which of the following represents the factor by which the concentration of calcium ion increases in the cytosol after release from the sarcoplasmic reticulum 10 50 100 1000
100
Which of the following maintains an optimum calcium concentration gradient to facilitate return of calcium to SR Calsequestrin SERCA DHP Ryanodine
Calsequestrin
Fast twitch fibers have what characteristics?
More fatigable than slow twitch fibers
Which of the following represents an example of an eccentric contraction?
- The triceps muscle during the throwing of a ball
- The triceps muscle while raising the body from the floor during a push-up
- The triceps muscle while lowering the body to the floor during a push-up
- The biceps muscle while raising the body during a pull up
3
What is epimysium
Connective tissue surrounding entire muscle
What is a muscle?
Made up of multiple fascicles
What is perimysium?
Connective tissue surrounding individual fascicle
What is a fascicle
A bundle of myofibers
What is endomysium
Delicate connective tissue around each myofiber
What is sarcolemma
The plasmalemma or cell membrane of a muscle fiber
What is myofiber
Individual multinucleated muscle cell
What is myofibril
A chain of sarcomeres within a myfiber
What is myofilament
Actin and myosin filaments that make up a sarcomere
What creates a triad?
Two cisternae with t tubule in between
What is a T-tubule?
Invaginations of sarcolemma
What are the four sections of sarcomeres?
Z lines, I bands, A bands, and H bands
What is a Z disc?
Anchor actin filaments and are loacted at each end of a sarcomere
What are I bands?
Composed entirely of actin and the width changes during contraction
What are A bands?
Composed of actin and myosin and width does not change during contraction
What are H bands?
Composed of entirely myosin and width changes during contractions
When sarcomeres are aligned what pattern is produced?
Banding pattern characteristic of striated muscle. Bands are lined up
Where is the nucleus in a muscle fiber?
Nucleus pushed to the outside of the of the sarcomeres
What steps happen in the synaptic cleft and terminal end of nerve fiber?
- Arrival of action potential at terminal end of nerve fiber
- Opening of voltage-gated calcium channels on nerve fiber ending. Ca diffuse into the terminal
- Neurotransmitter (Ach) are released from synaptic vesicles into synaptic cleft (exocytosis) and diffuses
- 2 Ach attach to ligand-gated sodium channels of the sarcolemma
What happens once the ligand-gated sodium channels of the sarcolemma open?
- There is a sodium ion influx that causes End - plate Depolarization and thus opens voltage-gated sodium channels (Sarcolemma action potential)
- Voltage-gated channels on T tubules (DHP) interact with ryanodine receptors on the SR membrane
- Opeing of ryanodine - releases calcium
- Increase Calcium ion in cytosol activates the sliding filament mechanism
What is DHP?
Dihydropyridine receptors that are voltage sensitive. L - type calcium channels arranged in quadruplets. Causes conformation change in the ryanodine receptors
What happens once calcium is released into the cytosol?
Calcium binds to troponin C on the actin filament.
Troponin then conforms and cause tropomyosin to expose active sites on actin
Myosin heads bind to actin active sites
What activates the myosin head?
ATP bound to the myosin hydrolyzed to ADP and inorganic phosphate. Energy liberated from the hydrolysis of ATP activates the myosin forcing it to the cock position.
What are the cross bridge steps?
- Activated myosin head binds to actin forming a cross bridge
- Inorganic phosphate is released and the bond between actin and myosin becomes stronger
- ADP is released and the activated myosin head power strokes.
- When another ATP binds to myosin head, the link between myosin and actin weakens and the myosin detaches
When will the myosin sliding stop?
As long as the active sites are exposed the process will repeat. When Calcium ions are actively transported back into the Sarcoplasmic reticulum causing the troponin to return to original shape allowing tropomyosin to glide over and cover myosin binding sites on actin
Between what bands are the T tubules located?
Between the A-I interface. Because of that they can have cisterni on each side of the t tubules and become triads.
Once ryanodine channels open where does the Ca ions flow out of?
Out of the sarcoplamic reticulum
When does the ryanodine channels close?
When the sarcolemma repolarizes
What does calsequestrin do?
Binds the Ca within the sarcoplasmic reticulum so that when the ATP calcium pumps are uptaking Ca they are not working so hard. Controls the concentration of free calcium with in the SR.
The calcium pump on in the SR is what type of transport?
Active transport
What are ryanodine receptors?
(RyRs) calcium release channels that are located on the cisternae. Open in response to conformational change in DHP receptors
What is SERCA?
Sarcoplasmic reticulum calcium ATPase - Uses ATP to pump calcium back into the SR
Why is there no tension when the sarcomere is fully stretched out?
Because there is no interaction between the myosin and actin when fully stretched out
When is tension maximum in a sarcomere?
When there is interaction between actin and myosin. And actin filament has overlapped all the cross bridges.
At what point is no more tension possible?
Max point occurs when acting filaments touch
What happens when actin filaments overlap?
Tension drops toward 0 because no more sliding can occur
True or False
When our bodies are at rest on a couch our muscles are 100% relaxed
No. There is some tension in all of our muscle. Keeps us sitting.
What is muscle tone?
Keep muscles in a slightly contracted state. Allows us to be ready to have a muscle contraction when needed
Where is ATP required for muscle contraction?
Sliding filament mechanism, pumping Ca ions from sarcoplasm into SR, pumping Na and K ions through the sarcolemma to reestablish resting potential
What is the concentration of ATP in muscle fiber?
4mmol which is enough to maintain contraction for 1-2 seconds
How does phosphocreatine restore ATP?
Phosphocreatine can release energy rapidly to ATP. Add phosphates back to ATP. Provides enough energy for 5-8 seconds of contraction when phosphocreatine is used with ATP
What are three methods of rephosphorylation of ATP?
Phosphocreatine, Glycolysis, oxidative metabolism
How does Glycolysis rephosphorylize ATP?
Can produce ATP and sustain contraction for 1 minute but there is a build up of pyruvic acid and which is converted to lactic acid.
What rephosphorylizes ATP the best for long-term contractions?
Oxidative metabolism: provides more than 95% of all energy needed for long-term contraction
Electron transport chain and kreb’s cycle in the mitochondrion provides a lot of ATP
What are two main types of muscle contractions?
Isometric and isotonic
What is isometric muscle contraction?
Occurs when there is an increase in tension but not in length. Achieved by pushing on wall and muscle length remains the same but tension builds up
What is isotonic muscle contraction?
When muscle length changes
What are the two types of isotonic contractions?
Eccentric: Muscle gets longer : Force is greater than tension
Concentric: muscle gets shorter : Force is less than the tension
What are the two types of myofibers?
Dark, slow fibers (red)
Light, Fast fibers (white)
What are fast muscle fibers?
They are fibers that contract rapidly but have less endurance. Fewer mitochondria, little myoglobin, use anaerobic respiration primarily. Larger concentration of ATPase
What are slow fibers?
Red fibers that contract more slowly but have more endurance. They have more mitochondria, use aerobic respiration, have more myoglobin, and have smaller concentration of ATPase
True or False
In adulthood, one cane increase the number of myofibers?
False. Mass of myofiber can increase by increasing myoFRIBRILS
What happens if there is a lost of muscle tissue?
It will be replaced by scar tissue. Fibrous connective tissue
What muscle is predominantly composed of dark fibers in mammals?
Soleus
What muscle is predominantly composed of light fibers?
Gastrocnemius
What is a motor unit?
Neuron and the myofibers it innervates
What does the all - or - none really refer to?
A motor unit
What is summation?
Electrical events occur faster than mechanical events
How does summation work in skeletal muscle fibers?
Before the Ca returns to the SR the remaining Ca causes another action potential. Continued cycling between myosin and actin which increases the muscle tension. Each additional spike adds to the effects of the previous spikes
What is tetany?
If the frequency of spikes is fast enough, there is no time for relaxation between spikes and the muscle remains at maximal contraction.
How does the bone-muscle system often transmit forces?
Levers
Bone is the lever. The joint is the pivot/fulcrum
What is an example of a First - class lever system? Explain the first - class lever system
Fulcrum is in the middle and raising chin using the sternocleidomastoids or similar muscles. In-force and out-force move in opposite directions
What is a second-class lever system? Give an example
Resistance (out-force) is in the middle. Example is raising the body on the ball of the foot. Fulcrum= ball of foot. Both in and out forces are on the same side of the fulcrum
What is a third - class lever system? Give an example
Effort (in-force) is in the middle. Lifting a weight in the palm of your hand. Both in and out forces are on the same side of the fulcrum. And both forces move in same direction
Where do machines transmit forces?
From one place to another
What two forces involve machines?
Force applied to the machine (in-force (Fi) or effort)
Force derived from the machine (out-force (Fo) or resistance)
The force times it lever arm is a moment. Functional lever must have at least two moments. What are the two equations?
Mi=FiLi
Mo=FoLo
Equilibrium = FiLi = FoLo
Is our bicep elbow lever system designed for weight or speed?
Speed.
