Simple muscle curve(twitch)

Introduction A single brief electrical shock of adequate strength applied to the nerve of a skeletal muscle gives rise to a brief contraction of the muscle followed by relaxation, this response is called as simple muscle twitch and the contraction recorded on a moving kymograph is called as a simple muscle curve

Requirements Nerve muscle preparation

Sherringtons drum

Lucas muscle trough

Du-Bois Raymond induction coil

connectionsPulley combination:1:4 fast gearDrum in circuit

Procedure Mount the nerve muscle preparation in the afterloaded condition

Adjust the strength of stimulus(maximum break without make)

Adjust writing lever tangentially touching it lightlyWith primary key closed and short circuiting key open, set the drum into motion and obtain baseline by setting drum into speed

Stimulate the nerve with single stimulus and record the muscle contraction

Stop the drum and without changing anything record the point of stimulus after making contact of strikers with the contact foil. Similarly ,mark the point of beginning of contraction, point of maximum contraction and point of relaxation

With the help of tuning fork take the Time tracing.

Measure latent period ,contraction period and relaxation period.

SMCA- Point of stimulusB- Beginning of contractionC- Peak of contractionD- End of relaxation

DiscussionLatent period (LP): interval between point of stimulus and point of beginning of contraction Causes :True latent period of the nerve Conduction time along the nerve Delay at myoneural junctionLatent period for excitation-contraction couplingInstrumental inertia

Contraction period(CP): interval between point of beginning of contraction to point of maximum contraction

Relaxation period(RP): interval between point of maximum contraction to point of relaxation.

Shatter curve(physiological curve) : Cause-inertia of instrument and elasticity of muscle total duration of simple muscle curve LP + CP + RP 0.01+0.04+0.05 0.1sec.

Questions 1 Define latent period and enumerate its causesAns: latent period: it can be defined as an interval between the point of stimulus and point of beginning of contraction. The causes of latent period are:true latent period of the nerve conduction time along the nerve delay at myoneural junctionlatent period for excitation-contraction couplinginstrumental inertia

2. What is excitation-contraction coupling?Ans: excitation-contraction coupling con be defined as mechanism (S) by which an action potential (excitation) of muscle fibres produces contraction

3. what are the factors responsible for relaxation?Ans: the factors responsible for the relaxation are: i ) removal of ca++ from the sarcoplasm into sarcoplasmic reticulum which is an active process ii) load acting on the muscle

4 define rheobase, utilization time and chronaxie.Ans: rheobase: strength of current just sufficient to excite a tissue when applied for indefinite period of time is called rheobaseUtilization time: the minimum time required to elicit a response is known as utilization timeChronaxie : the minimum time required to excite a tissue when the current strength used is twice the rheobase is called chronaxie.

5 define isotonic and isometric contraction.Ans isotonic contraction: contraction of muscle is said to be isotonic when the tension generated in the muscle remains constant throughout the contraction phase.Isometric contraction : contraction of muscle is said to be isometric when the length of muscle remains constant throughout the contraction phase

DETERMINATION OF CONDUCTION VELOCITY of NERVE impulse

Principle :

The Velocity of Nerve Conduction is determined by dividing the distance between the two points of stimulation with the difference in the latent period of both the recordings.

Requirements Nerve muscle preparation

Sherringtons drum

Lucas muscle trough

Du-Bois Raymond induction coil

Procedure

Mount the nerve muscle preparation in the afterloaded condition

Adjust the strength of stimulus(maximum break without make)

Record the simple muscle curve by stimulating the nerve at vertebral end (V curve)and mark the point of stimulus and point of contraction

Without changing point of stimulus, strength of stimulus and baseline record another simple muscle curve by stimulating muscular end(M curve) & mark the point of contraction.

Take time tracing with the help of tuning fork.

Measure the distance between the points of stimulation(vertebral and muscular end) on the nerve in meters

Note the difference between the latent periods in seconds of the two SMCs.Calculate Conduction velocity in met/sec

= Distance travelled in meters Difference in latent periods in seconds

Observation :

Precautions

Point of stimulus should be same.Distance between the points should be accurately measured .Difference in the latent periods should be accurately measured .

Discussion Conduction Velocity of nerve depends onDiameter of nerveMyelination TemperatureConducting media in which nerve is placed

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