Summaries of All 14 Graphs

Graph 1 - Single Muscle Twitch

• The graph shows three phases: a short latent period before contraction begins, a contraction phase where the muscle shortens, and a relaxation phase where it returns to resting length.
• The muscle reaches a peak contraction height before fully relaxing back to baseline.

Graph 2 - Effect of Temperature on Muscle

• At higher temperatures, enzyme activity increases, speeding up contraction and producing a faster, sharper twitch.
• At lower temperatures, enzyme activity slows, reducing both the force and speed of contraction and prolonging the twitch duration.

Graph 3 - Graded Response / Recruitment

• A subthreshold stimulus produces no response.
• As stimulus intensity increases, more fibres are recruited and contraction force rises.
• At the maximal stimulus, all fibres are recruited and maximum contraction is achieved.
• A supramaximal stimulus produces no additional increase in contraction.

Graph 4 - Summation and Refractory Period

• A second stimulus delivered during the refractory period produces no response.
• A second stimulus delivered after the refractory period causes summation - the second contraction adds onto the first, producing a greater overall force.

Graph 5 - Tetanus (Fused Contraction)

• At moderate repetition rates, the muscle shows incomplete tetanus with partial relaxation between contractions.
• At high repetition rates, contractions fuse completely into complete tetanus - a sustained, smooth, maximal contraction with no relaxation intervals.

Graph 6 - Neuromuscular Fatigue

• With repeated stimulation, the force of contraction progressively decreases as the neuromuscular junction becomes fatigued.
• Direct muscle stimulation still produces contraction initially, showing the muscle itself is not the primary site of fatigue.
• After a rest period, contractile force is restored, confirming that fatigue is reversible.

Graph 7 - Effect of Load on Muscle Contraction

• A free (no) load allows the greatest degree of shortening.
• As load increases, the height of contraction decreases.
• With an after-load, the muscle must first lift the load before shortening begins, introducing a delay in the contraction curve.

Graph 8 - Nerve Conduction Velocity

• Stimulating at a farther point from the recording site increases the latency of the response.
• Velocity = Distance / Time, expressed in m/s.
• Myelinated nerves conduct much faster than unmyelinated nerves.

Graph 9 - Normal Cardiac Rhythm (Cardiogram)

• The cardiogram shows a series of regular, uniform beats at a consistent rate and amplitude.
• The graph is used to assess heart rate and rhythm and serves as a baseline for comparison with experimental interventions.

Graph 10 - Effect of Temperature on the Heart

• Warming the heart increases both the rate and force of contraction.
• Cooling the heart slows the pacemaker, decreasing heart rate, and may slow or arrest the heart entirely at very low temperatures.

Graph 11 - Stannius Ligatures

• The 1st ligature (placed between the sinus venosus and atria) blocks impulse conduction, stopping ventricular beats.
• The 2nd ligature (placed between the atria and ventricle) reveals the ventricle's own automaticity, restoring slow, independent ventricular beats.
• This confirms the SA node > AV node > ventricle pacemaker hierarchy.

Graph 12 - All-or-None Law, Extrasystole, and Staircase

• The graph demonstrates that each cardiac contraction is either full or absent (all-or-none).
• A premature stimulus during the relative refractory period produces an extrasystole (extra beat), followed by a compensatory pause.
• The staircase (Treppe) phenomenon shows that with repeated stimuli, successive contractions gradually increase in force.

Graph 13 - Vagal Stimulation

• Vagal stimulation slows or arrests the heart.
• With strong or prolonged vagal stimulation, the heart may escape inhibition (vagal escape) and resume beating spontaneously despite continued stimulation.

Graph 14 - Drug Effects on the Heart (Adrenaline and Acetylcholine)

• Adrenaline (acting on beta-adrenergic receptors) increases both the rate and force of contraction - a positive chronotropic and inotropic effect.
• Acetylcholine (acting on muscarinic receptors) decreases heart rate - a negative chronotropic effect.

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