Nerve And Muscle 1

Spring 2007 Practical

Stimulus

Threshold: It is the minimal stimulus that can cause an action potential if applied for a specific time.

Types of Stimuli: PhysicalChemicalMechanicalElectrical (why is it the best?)

Preparation Used

Frog Gastrocnemius Sciatic Preparation

Preparation Used

Kymograph

Simple Muscle Twitch

Definition: The skeletal muscle contractile response to a single stimulus of sufficient strength and duration is called the simple muscle twitch.

Components: Latent Period Contraction Phase Relaxation Phase

Simple Muscle Twitch

Simple Muscle Twitch

Simple Muscle Twitch

Latent Period (0.01sec):1. propagation of the impulse through the

nerve2. its transmission in the motor end plates3. spread of action potential in the muscle

Contraction Phase (0.04sec) Relaxation Phase (0.05sec)

Effect of Temperature

Effect of Temperature

Warming the muscle decreases the latent, contraction and relaxations periods and increase the amplitude of contraction. This is because it increases enzymatic reaction in the muscle, increases the metabolism (ATP delivery) and decreases the viscosity.

The maximum temperature after which there is no further increase in amplitude of contraction is 45°C.

The effect of cooling is the reverse .i.e. all periods are prolonged and the amplitude of contraction is decreased.

The minimum temperature below which there is no further decrease in the amplitude of contraction is 5°C

Effect of Fatigue

Definition: It is the inability of the muscle to contract after repetitive contractions.

Repeated stimulation of the nerve- muscle preparation produces progressive decline in the height of contraction of the recorded twitches with prolongation of their duration (latent period, contraction, relaxation)

Site of fatigue is: the neuromuscular junction. Causes of fatigue:

Depletion of the neurotransmitterDepletion of muscle ATP, glycogen.Accumulation of metabolites e.g. lactic acid.

Effect of Fatigue