Tutorial 1 Mechanichal Changes in Skeletal Muscle

Tutorial 1

PREPERED BY :Dr. Radwa Ali MehannaDr. Eman Magdy

SUPERVISION BY : Dr/Samar El ghotny

physiology department

Definition Of Simple Muscle Twitch

A single brief contraction followed by a relaxation of a skeletal muscle due to application of a single adequate stimulus.

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Recording apparatusMuscle

SO We Need

Electrical stimulus

-As nature -No permanent damage-Easy for application

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-As human-cheap

Stimulus Frog

Recording apparatus : The apparatus which is commonly

used in the routine laboratory experiments on the muscle and nerve consists of :

1. Stimulation set ( delivers electrical stimulus for the muscle nerve preparation ) .

2. kymograph .

3. Myograph .

Stimulation set :

1. source of galvanic current .

2. Induction coil .

3. Connecting wires.

4. Simple key .

5. Two stimulating electrodes .

Myograph

Fall 2000Jenna Hellack

Frog Dissection

OBJECTIVE: TO RECORD SIMPLE MUSCLE TWICH (SMT)

LEARNING OBJECTIVES: By the end of this experiment student should know: How to pith the frog. How to prepare nerve and muscle for further

procedure. How to record a graph of simple muscle twitch.

TO PITH THE FROG  REQUIREMENTS:

Frog and dissecting instruments. THEORY: Before using any animal for

experimental purposes it should be made unconscious.

To produce unconsciousness there are two methods:

Anesthesia:

The unconsciousness may be produced by using any anesthetic agent which may be used orally, intravenously or by inhalation of chloroform or ether, etc. but it is very costly and carries its own risk.

Pithing: The unconsciousness may be produced by destroying the brain and spinal cord that is the CNS. This prevents the frog from perceiving any pain (the frog is clinically dead).

Pithed Frog

PREPARATION OF NERVE AND MUSCLE OF FROG OBJECTIVE:The student should be able to :•Prepare gastrocnemius sciatic preparation.•Explain the effects on nerve and muscle if not placed in Ringer's Solution.

REQUIREMENTS:Frog, dissecting instruments, Ringer's solution, beaker, thread, dissecting board, glass rod, Common pin.PRINCIPLE: The principle of this experiment is to obtain a separate independent muscle along with its nerve supply so that: It may be stimulated and various effects observed

PROCEDURE: Lay the pithed frog on the frog board.

Cut the skin transversely all around the trunk and remove the skin from the two hind Limbs.

Open the abdominal cavity, remove the viscera, a white, shining nerve may be seen emerging from the last 3 vertebrae.

Give a transverse cut just over the last 3 vertebrae and cut the two hind limbs into two pieces by giving a longitudinal cut very carefully so that the nerve is not damaged.

Remove all the muscles of the thigh completely and also cut the femur just near the knee joint so that a small portion of femur remains attached with the knee joint.

The sciatic nerve is completely exposed and only a portion of the last 3 vertebrae remain attached with sciatic nerve.

Free the sciatic nerve from surrounding tissue

Expose the nerve in the thigh where it lies deep between the large thigh muscles

Now separate the muscle with the help of a glass rod, tie a thread at Achilles tendon and cut it about 1 cm away from the knot.

Now cut the tibia just near the knee joint so that a small portion of it remains attached with the knee joint.

This is Nerve Muscle Preparation or Gastrocnemious Sciatic Preparation.

Gastrocnemius m with its nerve sciatic nerve

What is the meaning of after loaded muscle and freeloaded muscle?

To understand the meaning of free loaded and after loaded muscle we must return to the myograph ,a part of the recording apparatus .

The myograph board has a metalic projection which carries a lever .

The lever has two arms :

a. Horizontal arm to which is fitted a pointer with a writing point at its end

b.Vertical arm to which is attached a thread ligated in the tendon of the muscle ,when the preparation is mounted on the myograph .

Horizontal arm

the lever is also provided with a screw called after loading screw . This screw can be moved up and down to make the muscle free loaded or after loaded .

After loaded muscle

If the weight ( lever) attached to the tendon of a muscle is supported by the after loading screw during relaxation and does not pull the muscle except when the muscle start to shorten

i.e the muscle carries no weight at the start of contraction ( unstretched)

The muscle is loaded after start of contraction

Free loaded muscle When the load (weight of the lever) pulls

the muscle during relaxation and increases its length i.e Muscle is stretched ( this is done by opening the after loading screw)

Free loaded muscle is capable of giving stronger contraction provided that the weight does not over stretch the muscle

Freeloaded and afterloaded muscle

Tension varies with the starting length of the sacromere

Method Of Stimulation

Direct stimulation Indirect stimulation

Direct stimulation of the muscle

Stimulation of the nerve which supply the muscle

Which is better ?

Direct stimulation Indirect stimulation

Supply to all muscle fiberSame as nature of our body

Recording Of Simple Muscle Twitch

Phases of SMTLatent phase : the time that passes between

the application of the stimulus to start of contraction

Contraction phase :the period which the muscle shorten in length

Relaxation phase : the period during the muscle restores its initial length

Duration of the SMT

Total twitch time(TTT) = ,1 sec

Latent phase : ,01 sec

Contraction phase : ,04 sec

Relaxation phase : ,05 sec

Causes Of Latent Phase

1- Action potential in the nerve

2- Chemical transmission

3- Action potential in the muscle

1

2

3

Chemical Transmission

Types Of Contraction

Same tension Muscle

shortening Work is done Energy ¼ work

& ¾ lost as heat

Tension Increase Same Length No Work Is Done Energy Lost as

Heat

Isometric ContractionIsotonic Contraction

Isotonic and Isometric Contractions

Factor Affecting SMT

1- Warming

2- Cooling

3- Fatigue

Warming warm saline (physiological

saline of frog ,69% Nacl) 30-38C.

Duration decrease , amplitude increase.

Mechnism :↑ metabolic chemical reaction & ↓viscosity of the muscle

Over heating produce irreversible coagulation of its protein ( heat rigor)

warming

SMT

Cooling Cold saline (physiological

saline of frog ,69% Nacl) 0-4C.

Duration increase , amplitude decrease

Mechnism :↓ metabolic chemical reaction & ↑viscosity of the muscle

Excessive cooling or freezing lead to loss of vitality &irritability

SMT

COOLING

Fatigue By Repeated successive stimulation . Duration increase , amplitude decrease. Mechanism : depletion of energy stores &

accumulation of metabolites as lactic acid The first site of fatigue motor end plate

SMT

fatigue

Motor End Plate

Multiple Stimulation

The effect of applying multiple successive stimuli to a muscle depends upon the frequency of these stimuli ( duration between them),which can be either:

Low frequent stimuli Moderate frequent stimuli High frequent stimuli

Low Frequent Stimulation

In which each stimulus fall after the complete muscle relaxation of the previous stimulus.

So it results in the production of successive simple muscle twitches ( contraction then relaxation) which are called Separate Twitches

Moderate frequent stimuli

In which each stimulus fall during muscle relaxation of the previous stimulus

So it results in the production of successive contractions each followed by incomplete relaxation which are called Clonus or

Incomplete Tetanus

Clonus or Incomplete Tetanus

Stimulus applied Stimulus applied

Muscle fiber was not able to relax so tension increased

High frequent stimuli In which each stimulus fall during muscle

contraction of the previous stimulus. So it results in the production of successive

contractions ( contraction on top of contraction ) which is called Complete Tetanus

When action potentials come VERY RAPIDLY muscle fiber CANNOT relax result in contraction on top of contraction . i.e sustained contraction

StimuliComplete Tetanus

Fig. 7.10

Treppe or staircase phenomenon This phenomenon states that with

successive stimulation the force of contraction increases although the intensity is constant

It occurs due to successive stimulation of the muscle whatever is the frequency of stimulation

Causes of treppe phenomenon In low frequent stimuli: It is due to increased heat production

Heat

Muscle viscosity which acts as resistance to contraction

In Moderate frequent stimuli: It is due to increased heat production Accumulation of Ca++ ions

As the stimulus reach the muscle while relaxing ( ie relaxation is not complete) the Ca2+ is not completely pumped back to SR

So the stimulus adds Ca2+ to the already present from the previous twitch and so on

More ca2+ increase force of contraction

Treppe in Moderate frequent stimuli

In High frequent stimuli: It is due to increased heat production Accumulation of Ca++ ions Possibility of falling of the stimulus in the

supra normal phase of excitability

Excitability Of Skeletal Muscle Excitability

Ability to receive and respond to a stimulus

Relation between excitability and

mechanical changes

Tetanus never occurs in the cardiac muscle

Factors Affecting Clonus Warming Cooling Fatigue

Warming

Muscle warming coverts the clonus into separate twitches as:Warming accelerates the chemical reactions ,thus all phases of the muscle twitch are shortened The stimulus will fall at the end of relaxation instead of falling during relaxation

Cooling

Muscle cooling coverts the clonus into tetanus:cooling decelerates the chemical reactions ,thus all phases of the muscle twitch are prolonged The stimulus will fall during contraction instead of falling during relaxation

Fatigue

Prolonged stimulation of a muscle leads to muscle fatigue. It is due to:

Depletion of ATP, glycogen & creatine phosphate ( energy stores)

Accumulation of metabolites (lactic acid) and increased acidity.

Fatigue

Tetanus fatigue