Physio Ex Reviewer PDF

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Spans 2 joints and attach to skeletons thru o

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Composed of hundreds to thousands of o

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Tendons attach to periosteum of a bone Muscle fibers produce

When isolated and placed on a o

Possible to generate muscle contractions 

o

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An in vitro experiments producing in vivo function

o

Motor neuron and

o

Muscle fibers it innervates

Junction NMJ

Location where axon terminal of neuron meets specialized region of muscle fiber plasma membrane Motor End Plate (MEP)  specialized region

End – Plate Potential o

Events in NMJ leads to this

o

Triggers a series of events that results in contraction

o

Entire process called

Action Potential o

Motor neuron triggers release of Acetylcholine (Ach) from its terminal 

o

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Intersect at Neuromuscular

Neuromuscular Junction 

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Controlled electrical stimulation

Consists of:

o

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also known as

Ach diffused onto sarcolemma (muscle fiber plasma membrane) and binds to receptors in MEP

Use of electrical pulses instead of Ach in expt.

Muscle Twitch o

Single electrical stimulus will result in this

o

The mechanical response to a single action potential

o

Has 3 phases 

Latent Period 

Time that elapses between generation of Action Potential (AP) and start of contraction

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No force is generated

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Release of Calcium from Sarcoplasm reticulum occurs in Contraction o

Chemical changes occur intracellularly

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Contraction Phase 

Starts at end of latent period and ends in peak of muscle tension

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Myofilaments utilize cross-bridge cycle

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Muscle develops tension

Relaxation Phase 

From peak tension till end of muscle contraction

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Contraction ends and muscle returns to normal resting state

Equipments used: 1.

Skeletal Muscle of Frog

2. Electrical Stimulator a. Delivers voltage via electrodes on muscles 3. Mounting stand a. Includes force transducer b. Measures amount of force/tension in muscle 4. Oscilloscope a. Displays stimulated muscle twitch and amount of active, passive and total force by muscle Things to note while doing Physio Ex Expt 2 activity 1 Pre – lab Quiz 1.

Skeletal muscles are connected to bones by Tendons

2. Skeletal muscles are composed of thousands of cells called Fibers 3. Motor Unit refers to 1 motor Neuron and all the Skeletal muscle fibers it innervates 4. Motor Neuron and Muscle intersect at the Neuromuscular Junction 5. A twitch is 1 contractile response to a single action potential Predict Question: Will changes to stimulus voltage alter the duration of the latent period? What occurs during the latent period of these isometric contractions? -

All the steps of excitation – contraction coupling occur

Skeletal Muscle -

Produces

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Number of active motor units at a given moment o

 (aka muscle force) when nervous/electrical stimulation is applied

Reflected by force generated by whole muscle

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Strong Muscle Contraction = Many Motor Units activated

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Weak muscle Contraction = few motor units activated (but each unit still reaches its maximal tension)

Motor Unit Recruitment -

Increasing number of active motor units we can produce a steady increase in muscle force this is called Motor Unit Recruitment

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As in literal na nagrerecruit ka ng motor unit para dumami chz

Muscle Twitch -

A single stimulated contraction

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Regardless of number of motor units activated, still considered 1 stimulated contraction

In this activity you will: -

Isometric/fixed - length contraction of an isolated skeletal muscle

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Involves indirect stimulation by electrode

Threshold Voltage -

Smallest stimulus required to induce AP

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Stimulus Voltage o

As stimulus voltage to muscle increases beyond threshold voltage, amount of force produced by whole muscle increases

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Maximal tension o

Occurs when all muscle fibers have been activated by a strong stimulus (the maximal voltage)

Pre-lab Quiz: 1.

Skeletal muscle fibers are innervated/stimulated by motor neurons

2. A single action potential propagating down a motor axon results in a single action potential and a single contractile event in the muscle fibers it innervates 3. In resting skeletal muscle, Calcium is stored in the sarcoplasmic reticulum 4. During latent period for isometric contraction the cellular events involved in excitation – contraction coupling occur Stop And Think Question: What do you see in the active force display when the stimulus voltage is set to 0.0, and why does this observation make sense? -

0.00 g there was no activation of skeletal muscle fibers by the stimulus

Maximal voltage -

Amount of stimulus required to successfully recruit all muscle fibers into developing active force

Why was maximal voltage observed in the expt? -

At maximal voltage, all muscle fibers in muscle are depolarized all develop active force (that is they were all successfully recruited)

Treppe -

Progressive increase in force generated when a muscle is stimulated in succession

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Results in muscle twitches following one another closely o

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With each successive twitch peaking slightly higher than the one before

Also known as staircase effect (because of step-like increase) o

First few twitches, successive twitches produce more force than previous twitch 

As long as muscle is able to fully relax between stimuli

Skeletal muscle stimulated repeatedly -

Twitches may overlap producing a strong muscle contraction

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Phenomenon known as o

Wave summation occurs when muscle fibers that are developing tensions are stimulated before fibers relax

o

Achieved by increasing stimulus frequency or rate of stimulus delivery to muscle

o

Occurs because muscle fibers are partially contracted when subsequent stimuli are delivered

Pre-lab quiz 1.

During a single twitch of a skeletal muscle, maximal force is never achieved

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

Yes, the second twitch generated more muscle force

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This demonstrates treppe

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Despite the treppe there is a limit to the increase

Increasing Stimulus Frequency -

Results in increase in force produced by whole muscle

Plateau -

State known as

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Happens when stimuli continue to be applied frequently to a muscle over a prolonged period of time

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The maximum possible muscle force from each stimulus will reach this

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Stimuli applied with greater frequency

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Twitches begin to fuse so that the peaks of each twitch become indistinguishable from one another

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When stimulus reaches a value beyond which no further increases in force are generated by muscle

Stimulus frequency refers to the rate that stimulating voltage pulses are applied to an isolated whole skeletal muscle In a state of unfused tetanus, muscle tension increases and decreases Maximal tetanic tension is when the stimulus frequency reaches a value beyond which no further increases in force are generated by the muscle Fused tetanus develops at greater stimulus frequency *Maximal tetanic tension develops with high stimulation frequencies Post – Lab: 1.

The term tetanus refers to sustained muscle tension due to very frequent stimuli

2. Maximal Tetanic tension is when the stimulus frequency reaches a value beyond which no further increases in force are generated by the muscle

Maximal Tetanic Tension -

When stimulus frequency reaches a value beyond which no further increase in force is generated by the muscle

Fatigue -

Refers to decline in skeletal muscle’s ability to maintain a constant level of force/tension after prolonged repetitive stimulation

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Causes of fatigue (thought to be involved) o

Accumulation of lactic acid

o

ADP and P in muscles from exercise

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Failure of a muscle fiber to produce tension because of previous contractile activity

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Decline in muscle’s ability to maintain a constant force of contraction after prolonged, repetitive stimulation

Rest Periods -

Alter onset of fatigue in skeletal muscle

Intracellular concentrations of ADP and P decline during rest period Post-Lab 1.

During cross bridge cycling in skeletal muscle force is creased by the Power Stroke of Myosin Heads

2. The term tetanus refers to sustained muscle tension due to repetitive stimuli 3. Decline in muscle’s ability to maintain a constant level of force or tension after prolonged repetitive stimulation is called fatigue 4. During fatigue a numer of active cross bridges begin to decline although the rate of stimulus delivery remains constant 5. If an intervening rest period is imposed on skeletal muscle the development of fatigue will be delayed

Skeletal Muscle Contractions: -

Either: o

Isometric Contraction 

When a muscle attempts to move a load that is equal to the force generated by the muscle

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Isometric means same length

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Accomplished experimentally by keeping both ends of the muscle in a fixed position while electrically stimulating the muscle

o

Isotonic Contraction

Resting Length -

Length of muscle before stimulation

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Factor in determining the amount of force that a muscle can develop when stimulated

Passive force -

Generated by stretching the muscle

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Results from elastic recoil of tissue itself

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Caused by protein titin o

Titin acts as molecular bungee cord

Active Force -

Generated when myosin thick filaments bind to actin thin filaments o

Engages the cross bridge cycle and ATP hydrolysis

Skeletal Muscle -

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2 force properties o

Passive force when it is stretched

o

Active force when stimulated

Total Force o

Sum of passive and active forces

Isometric Length – Tension Relationship -

Used to understand optimum resting length in max force production

Pre-lab 1.

During an isometric contraction the skeletal muscle is generating force but remains at a fixed length

2. Active force is determined by the amount of myosin bound to actin

3. The Isometric length-tension curve indicates 3 forces the: a. Total force b. Active force c. Passive force 4. Passive force in skeletal muscle is largely caused by the protein titin Post – Lab 1.

The muscle is contracting isometrically when a skeletal muscle is stimulated and generates force but remains at a fixed length

2. Titin is responsible for passive force 3. Active force stimulated through a range of muscle lengths will utilize ATP hydrolysis to drive the cross bridge cycle 4. Maximal active tension will be produced in a skeletal muscle fiber when the fiber is at its resting length

Isotonic Contraction -

Skeletal muscle length changes

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Load moves a measurable distance

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Isotonic Concentric Contraction

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o

Happens when the muscle length shorts as the load moves

o

Happens when muscle generates a force greater than the load attached to the muscle’s end

There is a Latent Period in this contraction o

There is a rise in muscle tension but no movement of weight

o

After muscle tension exceeds the weight of the load an isotonic concentric contraction begins

o

Latent period gets longer as the weight of the load gets larger

o

Building muscle force exceeds load, muscle shortens, weight moves

Relaxation Phase o

Force of contraction will decrease as the muscle twitch begins in the relaxation phase

o

Load will return to its original position

Isotonic Twitch -

Not all-or-nothing

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Load is increased, muscle must generate more force to move it

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Latent period will get longer because it will take more time for the force to generate by the muscle

Muscle Shortening Velocity -

Speed of contraction

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Depends on the load that the muscle is attempting to move

Maximal Shortening Velocity -

Attained with minimal load attached to the muscle

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The heavier the load, the slower the muscle twitch

Isotonic Muscle Contraction Experiment -

One end of the muscle remains free

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Unlike isometric contraction (both ends are held at a fixed position)

Pre-Lab Quiz 1.

During isotonic concentric contraction the force generated by the muscle is greater than the weight of the attached load

2. During isotonic concentric contraction the latent period increases with heavier loads 3. During latent period for isotonic concentric contraction cross bridges cycle and when muscle tension exceeds the load, muscle shortening occurs 4. Muscle shortening velocity is constant regardless of load 5. The length of muscle changes in isotonic contraction Post – Lab Quiz 1.

Fastest Muscle Shortening velocity = lightest load

2. Longest Latent Period of Muscle Contraction = Heaviest Load 3. Muscle Contraction move the greatest distance = Lightest load 4. Longest duration of muscle contraction = Lightest Load 5. Isotonic contraction of a muscle is one in which the length of the muscle changes 6.In lifting a heavy load the muscle shortening velocity is decreased in comparison with lighter loads