Ans as per frog physiology mbbs 1 yr

Reading File

Finding Sources

Reading File

Finding Sources

The textbook library doesn't have specific frog physiology practical content. I'll answer from core physiology knowledge, which is well-established for MBBS 1st year.

Graph 3 — Effect of Temperature on Frog Muscle Twitch (Frog Gastrocnemius-Sciatic Nerve Preparation)

Identifying the Graph

The graph shows single muscle twitches recorded at three temperatures — 18°C, 28°C, and 38°C — with PS (point of stimulation) marked on the x-axis. This is the classic frog muscle experiment demonstrating the effect of temperature on the components of a muscle twitch.

Key observations from the graph:

As temperature increases (18°C → 28°C → 38°C), the twitch curve becomes taller and the initial flat segment (latent period) becomes shorter
The oscillations on the right represent tetanic stimulation; at higher temperature, the fused tetanus appears smoother/higher

Question 1: What is Heart Rigor?

Your answer is correct. To expand with proper physiology:

Heat rigor (also called heat contracture) is a state of sustained, irreversible contraction of cardiac (and skeletal) muscle occurring when the muscle is heated to high temperatures (above ~40–45°C).

Mechanism:

Extreme heat causes protein denaturation of the sarcoplasmic reticulum (SR) membrane
This leads to uncontrolled, massive release of Ca²⁺ from the SR into the sarcoplasm
High cytosolic Ca²⁺ → permanent cross-bridge formation between actin and myosin
ATP becomes depleted and cannot dissociate the actin-myosin bond → irreversible rigidity

This is distinct from rigor mortis (death → ATP depletion) but both result in permanent cross-bridge locking.

Question 2: Reasons for the Decrease in Latent Period (LP) when the Muscle is Warmed

Your answer is partially correct. Here is the complete, exam-ready answer:

What is the Latent Period?

The latent period is the interval between the application of stimulus and the beginning of visible contraction. It includes:

Time for the action potential to travel along the nerve
Time for the action potential to travel along the muscle membrane
Time for excitation-contraction (E-C) coupling (T-tubule → SR → Ca²⁺ release → troponin binding)

Why does warming decrease the Latent Period?

Mechanism	Explanation
↑ Nerve conduction velocity	Warming increases axonal membrane fluidity and ion channel kinetics → faster AP propagation along the sciatic nerve
↑ Muscle membrane conduction velocity	Action potential travels faster along sarcolemma at higher temperatures
↑ Rate of E-C coupling	Sarcoplasmic reticulum releases Ca²⁺ more rapidly (chemical reaction rates ↑ with temperature — Q₁₀ effect)
↑ Metabolic enzyme activity	ATPase activity of myosin increases; cross-bridge cycling accelerates
↓ Viscosity of sarcoplasm	Lower viscosity at higher temperature → cross-bridges form faster

The Q₁₀ Principle (important for 1st year):

For every 10°C rise in temperature, the rate of biochemical reactions approximately doubles (Q₁₀ ≈ 2). This accelerates all the steps in the latent period.

Summary for Exam

Temperature	Latent Period	Contraction Height	Velocity
18°C	Longest	Lowest	Slowest
28°C	Intermediate	Intermediate	Moderate
38°C	Shortest	Highest	Fastest

Important note: Beyond ~40–45°C, muscle performance deteriorates due to protein denaturation → heat rigor. So the beneficial effect of temperature has an upper limit.

Your answers were on the right track — the key additions are the Q₁₀ effect, the role of T-tubule/SR kinetics in shortening the latent period, and distinguishing heat rigor from rigor mortis.

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