AnatomyL written assignment

equipment used (the effect of stimuli frequency on skeletal muscle contraction lab)

-an intact, viable skeletal muscle dissected off the leg of a frog -an electrical stimulator- delivers the desired amount and duration of stimulating voltage to the muscle via electrodes resting on the muscle -a mounting stand- includes a force transducer to measure the amount of force, or tension, developed by the muscle -an oscilloscope- displays the stimulated muscle twitch and the amount of active, passive, and total force developed by the muscle

skeletal muscle contraction (the skeletal muscle length-tension relationship lab)

-contractions are either isometric or isotonic -when a muscle attempts to move a load that is equal to the force generated by the muscle, the muscle contracts isometrically

equipment used (The muscle twitch and the latent period lab)

-intact, viable skeletal muscle dissected off the leg of a frog -electrical stimulator-delivers the desired amount and duration of stimulating voltage to the muscle via electrodes resting on the muscle -mounting stand- includes a force transducer to measure the amount of force, or tension, developed by the muscle -oscilloscope- displays the stimulated muscle twitch and the amount of active, passive, and total force devloped by the muscle

what we did

-stimulating excitation-contraction coupling -used electrical impulses, rather than acetylcholine to trigger action potentials -pulses were administered by an electrical simulator that can set a precise voltage, frequency, and duration of shock desired -when applied to muscle that has been surgically removed from an animal, a single electrical stimulus will result in a muscle twitch

The skeletal Muscle Length-Tension relationship lab

-this activity allows you to set and hold constant the length of the isolated skeletal muscle and subsequently stimulate it with individual maximal voltage stimuli

Wave summation

-when a skeletal muscle is stimulated repeatedly, such that the stimuli arrive one after another within a short period of time, muscle twitches can overlap with each other and result in stronger muscle contraction than a stand-alone twitch. -this phenomenon is known as wave summation -occurs when when muscle fibers that are developing tension are stimulated again before the fibers have relaxed -****achieved by increasing stimulus frequency(the rate of stimulus delivery to muscle)**** -occurs because the muscle fibers are already in a partially contracted state when subsequent stimuli are delivered

What skeletal muscle lengths generated passive force? (Provide a range.)

80-100 mm muscle lengths.

Based on the unique arrangement of myosin and actin in skeletal muscle sarcomeres, explain why active force varies with changes in the muscle's resting length.

Active force depends on the rate of combine between actin and myosin. If the resting length of the muscle is shortened, there are more actin bound to myosin which increases the active force.

As the resting length of the muscle is changed, what will happen to the amount of total force the muscle generates during the stimulated twitch?

An increase in muscle length will increase total force.

Does the force generated by the muscle change with each additional stimulus?

As the stimulus frequency increased, the muscle tension generated by each successive stimulus also increased, and a limiting maximum value was observed.

As the stimulus frequency increases, what will happen to the muscle force generated with each successive stimulus? Will there be a limit to this response?

As the stimulus frequency increases, the muscle force generated by each successive stimulus will increase. There will be a limit to this increase.

As the stimulus frequency increases further, what will happen to the muscle tension and twitch appearance with each successive stimulus? Will there be a limit to this response?

As the stimulus frequency increases, the muscle tension generated by each successive stimulus will increase. There will be a limit to this increase.

Indicate what type of force was developed by the isolated skeletal muscle in this activity at the following stimulus frequencies: at 50 stimuli/sec, at 140 stimuli/sec, and above 146 stimuli/sec.

At 50 stimuli/sec, the force generated is in a state called unfused tetanus, the muscle tension increase and decrease at different values At 140 stimuli/sec, the force generated is in a state called complete (fused) tetanus, the muscle tension are not wavering anymore. At above 146 stimuli/sec, the force generated is in a state called maximal tetanic tension which means it is highest value.

Note the dip in total force at a muscle length of 90 mm. Why does this occur?

At this muscle length, active force has decreased in value and passive force has not yet increased to a significant value.

the graded depolarization in the skeletal muscle fiber that is elicited in response to one action potential from the motor neuron is called___________

EPP (end-plate potential)

compare and contrast frequency-dependent wave summation with motor unit recruitment (previously observed by increasing the stimulus voltage). How are they similar? How was each achieved in the experiment? Explain how each is achieved in vivo.

Frequency-dependent wave summation is dependent on stimulation by the nervous system. The number of motor fibers that available influence the motor recruitment.

How does the trace at 130 stimuli/sec compare with the trace at 50 stimuli/sec?

Fused tetanus develops at this greater stimulus frequency.

If you were curling a 7-kg dumbbell, when would your bicep muscles be contracting isometrically?

In situation when the bicep muscles fix its length.

How did the frequency of stimulation affect the amount of force generated by the isolated skeletal muscle when the frequency of stimulation was increased such that the muscle twitches did not fully relax between subsequent stimuli? Are these results called treppe or wave summation? How well did the results compare with your prediction?

In time that the stimulation frequency was increased to the situation in which muscle relaxation did not occur, the amount of force increased with each stimulus. When muscle twitches overlap and stimuli occurs one after another in a short amount of time, the muscle contraction is higher if a single stand alone contraction had occurred. This is known as wave summation.

Describe how increasing the stimulus frequency affected the force developed by the isolated whole skeletal muscle in this activity. How well did the results compare with your prediction?

Increasing stimulus frequency increases muscle tension generated by each successive force and it had limit, as predicted.

How do the traces with 146-150 stimuli per second compare with the trace at 130 stimuli per second?

Maximal tetanic tension develops with these very high stimulation frequencies.

What is the key variable in an isometric contraction of a skeletal muscle?

Muscle length because in isometric contraction, the muscle length does not change.

Which of the following distinguishes a state of unfused tetanus from a state of complete (fused) tetanus?

Muscle tension increases and decreases between different values for an unfused tetanus.

Which of the following distinguishes a state of unfused tetanus from a state of complete (fused) tetanus?

Muscle tension increases and decreases during a state of unfused tetanus.

To achieve an active force of 5.2 g, did you have to increase the stimulus voltage above 8.5 volts? If not, how did you achieve an active force of 5.2 g? How well did the results compare with your prediction?

My prediction was wrong. I did not increase the stimulus voltage, but just increase the rate of stimulus.

everything below is

The Effect of Stimulus Frequency on Skeletal muscle contraction

A sufficiently strong electrical stimulus applied to an isolated, mounted skeletal muscle induces the development of muscle force, or muscle tension. Which of the following statements concerning this observation is true?

The electrical stimulus mimics acetylcholine release at a neuromuscular junction

Beyond what stimulus frequency is there no further increase in the peak force? What is the muscle tension called at this frequency?

This muscle tension is called maximal tetanic tension.

this experiment you observed the effect of stimulating the isolated skeletal muscle multiple times in a short period with complete relaxation between the stimuli. Describe the force of contraction with each subsequent stimulus. Are these results called treppe or wave summation?

When stimulating the isolated skeletal muscle multiple times in a short period with complete relaxation between, each force between each stimulus increased slightly in step like form to a max peak. This is Treppe.

Is the total muscle force generated by the higher frequency stimulation greater than the force generated in previous stimulations?

Yes, it is greater than the previous stimulations.

Was there any change in the force generated by the muscle during the second stimulated twitch?

Yes, the second twitch generated more muscle force.

isometric length-tension relationship

a graph relating the 3 forces generated to the fixed length of the muscle will automatically be plotted after you stimulate the muscle -in muscle psychology this graph is known as ... -the results of this stimulation can be applied to human muscles to understand how optimum resting length will result in maximum force production

skeletal muscle twitch

a mechanical(one contractile) response to a single action potential -has 3 phases: latent period, the contraction phase, and relaxation phase -single twitch of skeletal muscle= maximal force is never achieved

an action potential in a motor neuron triggers the release of what neurotransmitter?

acetylcholine

is determined by the amount of myosin bound to actin.

active force

end-plate potential

an action potential in a motor neuron triggers the release of acetylcholine from its terminal. Acetylcholine then diffuses onto the muscle fiber's plasma membrane (sarcolemma) and binds to receptors in the motor end plate, initiating change in ion permeability that results in a graded depolarization of the muscle plasma membrane (the end-potential). The end-plate potential triggers a series of events that results in the contraction of a muscle cell. (whole process is called excitation-contraction)

what happens when you increase the stimulus voltage to an isolated skeletal muscle(up to a maximum value)

an increase of force produced by the whole muscle -the experimental result is analogous to motor unit recruitment in the body, importantly this result relies on being able to increase the single stimulus intensity in the experiment.

Which of the following is not one of the ways that the body can increase the force produced by a skeletal muscle?

application of higher voltages to the whole muscle

motor unit

consists of a motor neuron and all the muscle fibers it innervates

Which of the following correctly matches the twitch phase with its definition?

contraction phase= the time between the end of the latent period and peak muscle tension

role of acetylcholine

diffuses onto the muscle fiber's plasma membrane (sarcolemma) and binds to receptors in the motor end plate and make electric potential

The muscle twitch and the latent period

everything below

What happens to the amount of total force the muscle generates during the stimulated twitch? How well did the results compare with your prediction?

force is changed by the starting resting length of the muscle. If muscle is lengthened past its resting length, the passive force is increased. If the muscle is shortened to its resting length, the active force increases.

passive force(the skeletal muscle length-tension relationship lab)

generated by stretching the muscle and results from the elastic recoil of the tissue itself. -largely caused by the protein titin, which acts as a molecular bungee cord.

active force(the skeletal muscle length-tension relationship lab)

generated when myosin thick filaments bind to actin thin filaments thus engaging the cross bridge cycle and ATP hydrolysis

skeletal muscle(the skeletal muscle length-tension relationship lab)

has two properties: exerts passive force when it is stretched (like a rubber band exerts passive force) and active force when it is stimulated

Which of the following is not a phase of a skeletal muscle twitch?

hyper-polarization phase

complete (fused) tetanus (tetanus in isolated skeletal muscle)

if stimuli are applied with even greater frequency the twitches will begin to fuse so that the peaks and valleys of each twitch become indistinguishable from one another -this state is known as complete tetanus

unfused tetanus (tetanus in isolated muscle)

if stimuli continue to be applied frequently to a muscle over a prolonged period of time, the maximum possible muscle force from each stimulus will eventually reach a plateau- a state known as unfused tetanus

Wave summation increases the force produced in the muscle. Another way to increase the force produced by a muscle is to

increase the number of activated motor units

electrical stimulus

makes the muscle contract -if electrical stimuli are applied to a skeletal muscle in quick succession, the overlapping twitches generated more force with each successive stimulus -if stimuli continue to be applied frequently to a muscle over a prolonged period of time, the maximum possible muscle force from each stimulus will eventually reach a plateau- a state known as unfused tetanus

When the stimulus frequency reaches a value beyond which no further increases in force are generated by the muscle, the muscle has reached its

maximal tetanic tension

sarcolemma

muscle fiber's plasma membrane

The force that results from muscles being stretched is

passive force

relaxation phase

period of time from peak tension until the end of the muscle contraction

latent period

period of time that elapses between the generation of an action potential in a muscle cell and the start of muscle contraction. -no force is generated in latent period -chemical changes(including the release of calcium from the sarcoplasmic reticulum) occur intracellularly in preparation for contraction. -all the steps of excitation-contraction coupling occur

treppe

progressive increase in force generated when a muscle is stimulated in succession such that muscle twitches follow one another closely with each successive twitch peaking slightly higher than the one before -this step-like increase in force is why treppe is also known as *****the staircase effect**** -for the first few twitches each successive twitch produces slightly more force than the previous twitch as long as the muscle is allowed to fully relax between stimuli and the stimuli are delivered relatively close together.

stimulus frequency

rate of stimulus delivery to the muscle. -rate of stimulating voltage pulses are applied to an isolated whole skeletal muscle -increasing stimulus frequency to an isolated skeletal muscle results in an increase in force produced by the whole muscle.

equipment

same

equipment

same except for mounting stand: -includes a force transducer to measure the amount of force or tension developed by the muscle -a gearing system that allows the hook through the muscle's lower tendon to be moved up or down thus altering the fixed length of the muscle

skeletal muscle fiber

single muscle cell that consist skeletal muscle(individual skeletal muscle cell)

tendons

skeletal muscles are connected to bones by tendons

at the threshold stimulus do sodium ions start to move into or out of the cell to bring about the membrane depolarization?

sodium ions move into the cell during the threshold stimulus to make the membrane depolarize

motor end plate

specialized region of the muscle fiber's plasma membrane(sarcolemma) meets with axon terminal of the neuron

contraction phase

starts at the end of the latent period and ends when muscle tension peaks

stimulus intensity

strength of stimulus

total force(the skeletal muscle length-tension relationship lab)

sum of passive and active forces

tetanus

sustained muscle tension due to very frequent stimuli.

When you generate the isometric length-tension curve, which of the following forces will not be indicated on your screen?

tetanic force

Maximal active tension will be produced in a skeletal muscle fiber when

the fiber is at its resting length

what happens when a muscle first contracts

the force is able to produce less than the force is able to produce with subsequent stimulations within a relatively short time span

does the duration of the latent period change with different stimulus voltages?

the latent period remained the same no matter what

resting length

the length of the muscle before stimulation -resting length is an important factor in determining the amount of force that a muscle can develop when stimulated

When a skeletal muscle is stimulated and generates force but remains at a fixed length

the muscle is contracting isometrically

isometric contraction(the skeletal muscle length-tension relationship lab)

the muscle stays at a fixed length (isometric means same length) ex: when you stand in a doorway and push on the doorframe. -the load that you are attempting to move (the doorframe) can easily equal the force generated by your muscles, so your muscles do not shorten even though they are actively contracting -accomplished experimentally by keeping both ends of the muscle in a fixed position while electrically stimulating the muscle

excitation-contraction coupling in skeletal muscle fibers

the neuromuscular junction leads to end-plate potential and the end-plate potential triggers a . process that results in the contraction of the muscle

Passive force in skeletal muscle is largely caused by

the protein titin

During an isometric contraction

the skeletal muscle is generating force, but it remains at a fixed length

Which if the following is not depicted in a typical skeletal muscle isometric length-tension curve?

time

Which protein is mostly responsible for the development of passive force in a muscle?

titin

When a muscle receives a stimulus frequency that causes non-overlapping twitches to follow each other closely in time such that the peak tension of each twitch rises in a stepwise fashion up to a plateau value, the result is known as

treppe

What begins to happen at around 80 msec?

unfused tetanus develops

In this experiment the isolated skeletal muscle was repetitively stimulated such that individual twitches overlapped with each other and resulted in a stronger muscle contraction than a standalone twitch. This phenomenon is known as

wave summation

When a skeletal muscle is repetitively stimulated, twitches can overlap each other and result in a stronger muscle contraction than a stand-alone twitch. This phenomenon is known as

wave summation

maximal tetanic tension (tetanus in isolated skeletal muscle)

when the stimulus frequency reaches a value beyond which no . further increases in force are generated by the muscle, the muscle has read maximal tetanic tension

neuromuscular junction

where the motor neuron and a muscle fiber intersect -location where the axon terminal of the neuron meets a specialized region(motor end plate)of the muscle fiber's plasma membrane -events that occur here lead to end-plate potential

In skeletal muscle, active force stimulated through a range of muscle lengths

will utilize ATP hydrolysis to drive the cross bridge cycle.

In order to produce sustained muscle contractions with an active force value of 5.2 grams, do you think you will need to increase the stimulus voltage?

yes