A&P Chapter 11 Muscle Physiology Flashcards
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?
“all-or-none”
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)
Stimulation Frequency
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.