Flashcards in A&P Chapter 11 Muscle Physiology Deck (85):
What does the Length-Tension relationship state?
That the amount of Force or Tension a muscle can generate is related to how contracted or stretched it was PRIOR to stimulation.
Length and Tension affect what?
How much contraction can occur.
What is OPTIMAL RESTING LENGTH? What is the result?
The thin filaments are just overlapping with ALL the myosin heads.
The result is the maximal contraction.
What happens when the thin filaments overlap the thick filaments too much and are butting up against the Z-Disc?
There is no room for additional sarcomere shortening and a WEAK contraction is produced.
When the muscle is overly stretched and only a SMALL part of the thin filament overlaps the thick filaments what happens?
The myosin heads can't grab onto the thin filaments and a WEAK contraction or no contraction is produced.
What is Muscle Tone?
The certain degree of contraction a muscle exhibits even at rest.
What causes Muscle Tone?
Partial contraction as a result of a spinal reflex in the MUSCLE SPINDALS (stretch receptors) buried within the muscle tissue.
What is important about Muscle Tone?
It allows the sarcomeres of the muscle fibers to remain at their optimal length which allows for the maximal contraction.
Muscle tone is also important for posture, balance and joint stability.
Describe how a stretch receptor and a motor neuron work together, why do they do this?
A stretch receptor (Muscle Spindal) senses how stretched a muscle is, if it is out of the OPTIMUM RESTING LENGTH then it sends a signal to the spinal column which inturn activated a motor neuron to stimulate the muscle thus shortening the Sarcomeres and bringing the muscle back to the OPTIMAL RESTING LENGTH.
This occurs so that when you need your muscles to produce a movement they are able to do so efficently.
What is Threshold when reffering to muscle physiology?
The sufficiently strong stimulus that can trigger the contraction of the muscle fibers in a motor unit.
A single impulse may not be strong enough to trigger contraction, it may require REPEATED or STRONGER nerve impulses to reach threshold.
Remember that repeating nerve impulses rapidly will cause a greater and greater contraction due to the amount of Ca2+ ions that stay in the Sarcoplasm between impulses.
What is the LATENT PERIOD?
The period of time between initial stimulus and the beginning of muscle contraction, this is only a few milliseconds.
All the things that have to happen before the shortening of the Sarcomere can occur take place in the LATENT PERIOD.
What is a MUSCLE TWITCH?
The cycle of contraction and relaxation.
There are four parts: Time of initial stimulus, Latent Period, The Contraction Phase and the Relaxation Phase.
What happens during the CONTRACTION phase of a Muscle Twitch?
The Sarcomere shortens causing the muscle fiber to shorten causing a muscle contraction.
This phase is short because the Sarcoplasmic Reticulum rapidly reabsorbs the Ca2+ from the Sarcoplasm.
This is the phase where the muscle generates tension and force.
What happens during the RELAXATION phase of a Muscle Twitch?
Ca2+ ions are reabsorbed by the Sarcoplasmic Reticulum and as a result the Troponin changes conformation back to it's original state causing Tropomyosin to cover the ACTIVE SITES on Actin which prevents CROSS BRIDGES from being formed.
The thin filaments slide BACK over the thick filaments and the Sarcomere lengthens resulting in muscle fibers lengthening and the muscle relaxes.
ELECTRICAL STIMULATION of the muscle fiber is reffered to as what? What does it mean?
It means that once the motor end plate is stimulated and a voltage change occurs that by design the entire sarcolemma becomes stimulated and thus the entire cell.
What are the factors that affect Muscle Contraction strength?
Strength of Stimulation (Nerve Impulse or Voltage)
Degree of Stretch before Stimulation
Temperature (Warm Enhances, Extremes Inhibit)
Muscle pH (Low pH inhibits contraction-decreases myosin action)
Hydration (Proper hydration of a cell is required for organization of myofibrils)
What does the Sarcomere look like with the strongest contraction?
The Sarcomere is at it's shortest with more interaction between actin and myosin heads.
What does the Sarcomere look like during a weak contraction?
It only shortens part way before relaxing, not enough myosin heads pulling on actin to completely shorten the sarcomere.
What is a NERVE?
A bundle of AXONS from MANY neurons, larger nerves contain axons from more neurons.
What is a Neuron?
One Individual Neural Cell
Explain the Strength of Stimulation effect on muscle contraction.
An increase in stimulation STRENGTH causes more Axons within the motor nerve to be stimulated.
Once THRESHOLD is reached a contraction will occur; The greater number of axons stimulated=greater nerve impulse=greater number of motor units stimulated resulting in a STRONGER REACTION.
This is the basis behind RECRUITMENT, the more motor units involved the stronger the contraction.
Once all fibers are contracting maximally ADDITIONAL STIMULATION WILL NOT INCREASE MUSCLE CONTRACTION.
With an individual Muscle Twitch what happens to the Ca2+ ions between stimuli?
All the Ca2+ ions are REABSORBED back into the Sarcoplasmic Reticulum.
Explain how the Frequency of Stimulation affects muscle contraction.
Repeated, rapid stimulation causes Ca2+ ion levels to increase in the Sarcoplasm of the Muscle Fiber. This results in a stronger muscle fiber contraction because MORE active sites on Actin are exposed to myosin heads.
What is the TREPPE EFFECT?
Rapid stimulation of a muscle fiber prevents all of the Ca2+ ions from being reabsorbed by the Sarcoplasmic Reticulum, Ca2+ accumulates resulting in stronger contraction.
Why is some heat helpful for muscle contractions? And infact makes them more efficient?
As a muscle warms up the Myosin ATPase enzyme works more efficiently breaking down ATP into ADP, P, and Energy.
What is INCOMPLETE TETANUS?
When stimulation of a muscle fiber is so rapis that one muscle contraction begins before the previous one ends resulting in overlapping contractions. This is a faster frequency than what is required for the Treppe Effect.
What happens to the muscle fiber with INCOMPLETE TETANUS?
Successive nerve impulses stimulate a partially contracted muslce fiber resulting in a STRONGER contraction.
What happens if the stimulation rate rises above what is needed for Incomplete Tetanus?
COMPLETE TETANUS will occur, this is a sustained, continuous contraction which almost NEVER happens in the human body.
What are the two types of muscle contractions?
Isometric and Isotonic Contractions
When lifting an object explain how the muscle goes through Isometric and Isotonic contractions.
When you begin to lift an object muscle tension begins to build, this is the ISOMETRIC Phase where the muscle is NOT getting shorter. It isn't until the muscle tension exceeds the load of the object does the muscle begin to shorten. At the moment the muscle begins to shorten an ISOTONIC contraction begins.
Define Isometric Contraction
Muscle contracts and develops tension but DOES NOT SHORTEN in length, it remains a constant length.
Define Isotonic Contraction
The muscle contracts, develops tension and may EITHER lengthen or shorten depending on the force of contraction.
Where is ACTIVE TRANSPORT required when referring to Ca2+ ions in a muscle cell during relaxation?
Active Transport is required to push the Ca2+ ions BACK into the Sarcoplasmic Reticulum during the Relaxation Phase, remember this takes ATP.
What are the two ways Muscles can generate ATP? What determines which method the body will use?
Aerobic Respiration and Anaerobic Fermentation
The Availability of Oxygen is what determines what method the body will use.
Where is ATP required in the contraction/relaxation of a muscle?
1. Maintenance of a polarized NERVE and MUSCLE Cells, remember the Na+/K+ ATPase pump.
2. Contraction of the Myofilaments, the racheting of the myosin heads.
3. The relaxation of myofilaments by removing Ca2+ from the Sarcoplasm via Active Transport back into the Sarcoplasmic Reticulum.
What does Aerobic respiration involve?
The OXIDATION of Glucose or Fatty Acids
What is the bodies #1 preferred source of glucose?
What are the options the body can use to sythesize ATP with Aerobic Respiration?
Glucose (Preferrably from Carbs), Fatty Acids, Amino Acids and Proteins
What is the waste product of Aerobic Respiration? How do we get rid of it?
We get rid of CO2 by exhaling.
What is the KEY step in Aerobic Respiration called?
The KREBS CYCLE (The Citric Acid Cycle)
What happens to Glucose and Fatty Acids before they enter the Krebs Cycle?
They are converted into ACETYL CoA
Define the KREBS CYCLE
A complex serioes of biochemical reactions that uses ACETYL CoA to generate a SMALL amount of actual ATP and a larger amount of intermediates (Reduced Energy Carriers) to sythesize even more ATP later.
What is the process that turns the Reduced Energy Carriers formed in the KREBS CYCLE to ATP called?
How many molecules of ATP are produced from ONE molecule of Glucose during Aerobic Respiration?
What is ANAEROBIC FERMENTATION?
The process of creating ATP only used when oxygen is NOT available in sufficient quantities.
How many molecules of ATP are produced for every one molecule of glucose using ANEROBIC FERMENTATION?
What is the waste product of ANEROBIC FERMENTATION? What are the problems associated with it?
Lactic Acid, it's very toxic and much more difficult to remove than CO2.
Lactic Acid also LOWERS the pH level of the muscle which causes enzymes not to work as well which inhibits the formation of CROSS BRIDGES between myosin heads and actin active sites.
What is Immediate Energy? When do we need it?
Immediate energy is energy produced from a few different sources at the beginning of physical exercise when we can't supply the muscles with enough oxygen to keep up with ATP demand from simply breathing.
We need it during the breif period during the beginning of exercise when the cardiovascular system and repirator systems have not reacted to supply the muscles with needed oxygen for ATP production with Aerobic Respiration.
What sources do we get ATP from during the use of Immediate Energy? List them in order.
We use stored Oxygen from MYOGLOBIN in muscle cells first to produce a SMALL amount of ATP, this is a VERY short term solution.
Then we get most of the rest of our immediate energy ATP from the activities of MYOKINASE and CREATINE KINASE.
The PHOSPHAGEN SYSTEM uses what to produce ATP?
Myokinase and Creatine Kinase
What does Myokinase do to make ATP?
It takes one Phosphate group from one ADP (Making it AMP) and puts it on another ADP to create ATP
Kinase does what?
Adds a phosphate group to anything.
What does Creatine Kinase do to make ATP?
Creatine Kinase takes the phosphate group from CREATINE MONOPHOSPHATE and addis it to ADP to create ATP.
Creatine Monophosphate is a popular athletic supplement.
What is ATP broken down to make energy?
Describe Short-Term Energy
After we uses up our immediate energy (obtained via myokinase and creatine kinase) our muscles shift to Anaerobic Fermentation.
This system can supply muscles with enough ATP for 20-40 seconds of max effort.
Produces small amounts of ATP per Glucose molecule and produces Lactic Acid which inhibit muscle contraction.
Describe Long-Term Energy
Eventually our breathing and cardiovascular function catch up and can supply enough oxygen to support Aerobic Respiration.
It's much more efficient at producing ATP (36 ATP's per Glucose) and produces a waste product that is easy to get rid of (CO2)
Important for endurance athletes.
Why do people take Creatine Monophosphate as a supplement? What is good about it? What is Bad? How much can your body use in a day?
People take Creatine Monophosphate so they can increase the amount of Creatine Monophosphate in their muscles which will lead to increased ATP availability. Creatine Monophosphate donates its phosphate through Creatine Kinase to ADP to make a molecule of ATP.
It's not so great because it also attracts water causeing muscles to swell which makes muscles larger but not stronger. People tend to take too much which is excreated by kidneys which can be hard on them.
You can only use 2-5g/day.
What is the only way to increase muscle strength?
To work out and use muscles. use promotes an increase in muscle protein mass and you get more thin and thick filaments as a result.
What is FATIGUE?
The progressive weakening of a muscle from prolonged, strenuous use resulting in a loss of muscle fiber contracility.
What are the causes of Physiological FATIGUE?
1. Insufficient energy sources.
2. Lactic Acid Build Up
3. Hyperpolarization of a muscle and nerve cells
4. Insufficient ACh stores
Explain why Insufficient energy sources results in FATIGUE
Without ATP your muscles cannot function. Without a way to produce ATP your muscles cannot function.
You need Acetyl CoA for the Kreb's cycles to make ATP.
Muscles contain lots of Glycogen which can be depleted during long strenuous exercise resulting in less ATP.
You need to maintain polarized muscle and nerve cells using ATP to keep the Na+/K+ ATPase pump going.
Without ATP the crossbridges cannot be formed with the myosin heads, and ratcheting cannot occur.
Why does Lactic Acid build up lead to FATIGUE?
It lowers the muscle cell pH resulting in inefficient protein and enzyme function producing a WEAK contraction.
What is HYPERPOLARIZATION of a muscle or nerve cell?
When the positive charge outside the cell becomes so great it is difficult to overcome it.
How does a cell become HYPERPOLARIZED?
Rapid or prolonged contraction results in K+ to accumulate outside the cell which then rases the overall positive charge making it more and more difficult to get enough of Na+ molecules into the cell to overcome the positive charge outside.
This makes it VERY difficult to overcome the large POSITIVE charge outside resulting in HYPERKALEMIA.
How does insufficient ACh stores result in FATIGUE?
If repeated prolonged contraction causes the synaptic bulb to run out of ACh then no action potential can be created at the motor end plate. Without an action potential the Ca2+ ions cannot be released from the Sarcoplasm and the muscle cannot contract.
What is JUNCTIONAL FATIGUE?
When the rapid prolonged contraction of a muscle causes ACh in the synaptic bulb to be depleted then an Action potential cannot be created at the motor end plate resulting in a loss of muscle contraction and funtion.
What are the two things that preventing FATIGUE is dependent on?
Oxygen Intake and Energy Stores
What is oxygen debt?
The need to replenish the bodies oxygen supplies after exercise.
What is oxygen needed for after exercise?
Replenishing O2 Stores, O2 bound to Myoglobin, Replenish O2 in dissolved blood, tissue fluids and hemoglobin.
Need O2 to regenerate substrates used by Myokinase and Creatine Kinase, O2 is used to form ADP and Creatine Monophosphate.
Oxidation of Lactic Acid, Helps replinish glycogen stores turning lactic acid into something useful.
What are the 2 main categories of skeletal muscle fibers?
Slow Twitch and Fast Twitch
All muscles contain some of both fibers, they differ in function and metabolic needs.
ALL OF THE FIBERS FROM A GIVEN MOTOR UNIT CONTAIN ONLY FAST OR SLOW TWITCH FIBERS!!
Describe Slow Twitch Muscle Fibers
Exhibit a twich cycle of about 100msec/twitch.
Posses LOTS of Mitochondria, myoglobin (more stored O2) and are well supplied with blood vessels.
Well suited for aerobic respiration, very resistant to physiological fatigue.
Muscles with alot of slow twitch fibers have a dark red appearance. RED MEAT
Describe Fast Twitch Muscle Fibers
They have a twitch rate of about 7.5msec/twitch.
They have less mitochondria, less myoglobin and fewer blood vessels. This gives them a lighter color (WHITE MEAT)
They have more components for ANAEROBIC FERMENTATION and the PHOSPHAGEN SYSTEM. This makes them good at producing a quick forceful contraction for a short period of time.
They are more susceptible to physiological fatigue. They have a larger Sarcoplasmic reticulum and so they can release and abosorb more Ca2+ ions for more rapid and forceful contractions.
Reliance on anaerobic fermentations produces alot of lactic acid.
Describe Cardiac Muscle
Striated like Skeletal Muscle but only ONE Nucleus.
Cardiac muscle is involuntary.
Intercalated discs and mechanical junctions allow one cardiac muscle cell to stimulate it's neighbors and remain tightly connected unlike skeletal muscle.
Cardiomyocytes don't necessarily need nervous system input.
Stimulation of special cells trigger contraction of muscles cells throughout the heart via intercalated discs which are a combination of DESMOSOMES AND GAP JUNCTIONS.
Cardiac cell twitches are VERY slow compared to skeletal muscle (250msec/twitch).
Relies almost exclusively on aerobic respiration, very resistant to fatigue. Lots of myoglobin, mitochondria and glycogen stores.
Describe Smooth Muscle
Tapered cells with NO STRIATIONS.
Smooth muscle is involuntary.
Cells do contain Thick and Thin Filaments but they are arranged in such a way that no striations are seen.
Thick and Thin filaments attach to plasma membrane via a complex internal cytoskeleton and protein masses called DENSE BODIES.
Thin filaments attach to dense bodies and sytoskeleton instead of Z-Discs.
They still need Ca2+ for contraction like all muscle but the Ca2+ ions come from the extracellular fluid NOT FROM THE SACROPLASMIC RETICULUM.
Ca2+ions flow into the cell for contraction and is pumped out during relaxation.
What are DENSE BODIES?
They are protein masses that thin filaments connect to in Smooth Muscle cells.
What can cause Smooth Muscle to contract?
A variety of things or conditions such as the presence of Hormones, CO2 Levels, Changes in pH, the degree of stretch and other factors.
Any one of these factors can cause Ca2+ channels to open allowing Ca2+ into the cell causing a contraction.
What are the 2 main types of smooth muscle?
Multiunit and Single Unit
Describe the differences betwen Multiunit Smooth muscle cells and Single Unit Smooth Muscle cells.
Multiunit requires innervation from the autonomic nervous system. Nerve fibers innervate many smooth muscle cells creating a motor unit like skeletal muscle.
Single unit cells communicate via gap junctions. A nearby nerve fiber releases ACh near one cell and the stimulation is passed to other connected cells kind of like Cardiac muscle cells.
What is PHOSPHORYLATION?
Adding a phosphate group to a protein.
What is CALMODULIN?
A unique protein found in smooth muscle cells.
It binds Ca2+ and activates an enzyme that transfers a phosphate group from ATP to the myosin head.
Explain how Smooth muscle uses 2 ATP instead of 1 ATP like in Skeletal Muscle fibers?
One ATP is needed for MYOSINKINASE to add a Phosphate group to the Myosin head. The head binds to actin and uses a Second ATP to ratchet.
What enzyme is needed for smooth muscle contraction? What activates it?
Myosinkinase, When Calmodulin binds to Ca2+ it activates Myosinkinase.
Explain how the Smooth Muscle cell contracts
Calmodulin binds to Ca2+ ions and activates Myosinkinase which uses an ATP to put a phophate group on the Myosin head. The head uses another ATP to ratchet.
The ratcheting pulls on the thin actin filaments connected to the DENSE BODIES which then causes the cell to contract.
Why is a smooth muscle twitch VERY slow?
The pumping of the Ca2+ into and out of the cell occurs much more slowly with out a SR.
Ratcheting of smooth muscle myosin requires more steps and uses more ATP.
Phosphorylation/dephosphorylation of Myosin is slow.