Explain all amphibians physiology graph of mbbs 1 st year
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MBBS 1st year physiology frog amphibian experiments graphs practical
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amphibian frog physiology graphs MBBS experiments muscle nerve
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amphibian graphs MBBS physiology practical all experiments simple twitch summation tetanus fatigue conduction velocity frog heart
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frog gastrocnemius sciatic nerve experiment tetanus summation kymograph
Now I have a solid foundation. The textbook library doesn't have a dedicated "amphibian experiments" practical section, but I have all the content knowledge from physiology textbooks (Ganong, Guyton, Costanzo). Let me compile a comprehensive answer from my knowledge of this well-established MBBS 1st year practical physiology topic.
Amphibian Physiology Graphs — MBBS 1st Year Practical Physiology
Amphibian (frog) experiments are a cornerstone of MBBS 1st year practical physiology. The gastrocnemius–sciatic nerve preparation of a frog is used because frogs are cold-blooded, tissues survive in vitro without oxygenation, and responses are easy to record.
Apparatus Used
| Instrument | Purpose |
|---|---|
| Kymograph | Rotating drum that records muscle contractions on smoked paper |
| Lucas chamber | Holds the nerve–muscle preparation moist |
| Inductorium (stimulator) | Delivers controlled electrical stimuli to the nerve |
| Signal marker | Marks the exact moment of stimulus on the tracing |
| Writing lever | Attached to the muscle; transcribes movement onto drum |
| Ringer's solution | Keeps the tissue viable (NaCl + KCl + CaCl₂ + NaHCO₃) |
PART A — SKELETAL MUSCLE EXPERIMENTS
Graph 1: Simple Muscle Twitch (Simple Muscle Curve)
A single adequate (threshold) stimulus to the sciatic nerve produces one brief contraction.
│
│ ╭───╮
Ht │ / \
│ / \
│____/ \_______
│←LP→← CP →← RP →
Time →
Three phases on the myogram:
| Phase | Frog (seconds) | Events |
|---|---|---|
| Latent Period (LP) | ~0.01 s | Stimulus → AP → Ca²⁺ release → cross-bridge formation. No visible shortening yet |
| Contraction Period (CP) | ~0.04 s | Actin–myosin interaction → muscle shortens → lever rises |
| Relaxation Period (RP) | ~0.05 s | Ca²⁺ re-uptake by SR → cross-bridge detachment → muscle returns to rest |
Key point: LP is the shortest phase; RP is the longest phase in a simple twitch.
Graph 2: Effect of Increasing Stimulus Strength (Strength–Response Curve / Graded Response)
Increasing stimulus strength from sub-threshold to maximal:
Height of
contraction
│ ─────────── Maximal
│ /
│ /
│ ──────/
│ /
│───────/
│_________________________
Threshold Maximal
Stimulus Strength →
| Term | Meaning |
|---|---|
| Sub-threshold | Stimulus too weak; no contraction |
| Threshold (liminal) | Minimum stimulus producing a just-perceptible contraction |
| Sub-maximal | Increasing recruitment of motor units → graded increase in height |
| Maximal | All motor units recruited; maximum contraction height |
| Supra-maximal | No further increase; plateau maintained |
Principle: A single muscle fibre follows the all-or-none law, but the whole muscle shows a graded response because it consists of many motor units with different thresholds.
Graph 3: Effect of Temperature on Muscle Twitch
| Temperature | Effect on contraction |
|---|---|
| Cold (~10°C) | Low, broad, slow twitch; prolonged LP and RP |
| Normal (~25°C) | Standard twitch |
| Warm (~38°C) | Tall, faster twitch; shorter phases |
| Very hot (>45°C) | Contracture → heat rigor → no relaxation |
Height │ Hot → /\
│ Normal→ / \
│ Cold → / \___
│__________________
Time →
Warm temperature ↑ metabolic reactions and Ca²⁺ cycling speed; cold does the opposite.
Graph 4: Effect of Two Successive Stimuli — Summation
When two adequate stimuli are applied in rapid succession (S1 and S2), the second contraction adds on top of the first if S2 arrives before complete relaxation:
Height │ ╭─╮ ← Summated height
│ / | \
│ ╭───╯ | \
│ / S2 \
│_/S1____________\_______
Time →
| Condition | Result |
|---|---|
| S2 after full relaxation | Two separate equal twitches (no summation) |
| S2 during relaxation phase | Partial summation — second twitch taller |
| S2 during contraction phase | Complete summation — maximum height |
Mechanism: Residual Ca²⁺ in sarcoplasm from first contraction adds to Ca²⁺ from second, producing a stronger cross-bridge interaction.
Graph 5: Effect of Increasing Frequency of Stimuli — Tetanus
As stimulus frequency increases beyond the relaxation period:
Height │ ═══════ Complete Tetanus
│ /\/\/\/\/
│ /\/\/\ Incomplete Tetanus
│ /\/\/
│ Single twitches
│_________________________________
Stimulus frequency →
| Frequency | Response |
|---|---|
| Low | Separate muscle twitches |
| ~20–30/sec (frog) | Incomplete (partial) tetanus — no time for full relaxation; oscillating but sustained |
| ~50/sec (frog) | Complete (fused) tetanus — no oscillations; smooth, maximum sustained contraction |
Why tetanus is stronger than a single twitch: Summation of Ca²⁺ keeps intracellular [Ca²⁺] continuously high, maintaining maximum cross-bridge cycling.
Graph 6: Muscle Fatigue (Ergogram)
When repeated stimuli are applied at constant frequency, the height of successive contractions progressively decreases until the muscle cannot contract (fatigue):
Height │ ██
│ ████
│ ██████
│ █████████
│ █████████████░░░░░░░
│______________________________
Number of stimuli →
Causes of muscle fatigue:
- Depletion of ATP and glycogen
- Accumulation of lactate and Pi (inorganic phosphate)
- Failure of neuromuscular transmission
- Depletion of Ca²⁺ from SR
The site of fatigue in in vitro experiments is primarily the muscle itself (not the neuromuscular junction or nerve).
Graph 7: Effect of Pre-loading and After-loading
| Term | Definition |
|---|---|
| Pre-load | Load placed on muscle before stimulation (stretches muscle to optimal length; ↑ tension by Starling mechanism) |
| After-load | Load applied after stimulation; muscle must lift it during contraction |
- Increasing pre-load → ↑ height of contraction (up to optimal length)
- Too much pre-load → ↓ height (overstretched, poor overlap)
PART B — NERVE EXPERIMENTS
Graph 8: Determination of Conduction Velocity of Sciatic Nerve
Two pairs of electrodes placed at different distances on the nerve:
Kymograph
tracing │ ↑S₁ ↑S₂
│ _____|______ _____|______
│ | | |
│ Stim→R₁ Stim→R₂
│←t₁→ ←t₂→
Formula:
Conduction velocity = Distance between electrodes (d) ÷ Difference in latency (t₂ − t₁)
- Normal frog sciatic nerve: ~30 m/s (myelinated A-β/A-α fibres)
PART C — CARDIAC EXPERIMENTS (Frog Heart)
Graph 9: Normal Cardiogram of Frog
The frog heart has a sinus venosus, atria, and ventricle. The kymograph records:
Height │ ╭──╮ ╭──╮ ╭──╮
│ / \ / \ / \
│___/ \/ Diastole \___
│
│← Systole →← Diastole →
- Upstroke = ventricular systole
- Downstroke = ventricular diastole
- Regular rhythm reflects the sinus node as pacemaker
Graph 10: Effect of Vagal Stimulation on Frog Heart
Stimulating the vagus nerve (parasympathetic) causes:
Height │ ██ ██ ██ ██ ██ ░░░░░ Vagal escape → ██ ██
│ ↑
│ Vagal stimulation
│ (bradycardia → cardiac arrest → escape)
| Phase | Description |
|---|---|
| Initial normal beats | Before stimulation |
| Vagal inhibition | ↓ rate, ↓ force → diastolic standstill (heart stops in diastole) |
| Vagal escape | After prolonged stimulation, heart resumes beating independently |
Mechanism: Vagal ACh → M₂ receptors → ↑ K⁺ permeability → hyperpolarization → sinus slowing. Vagal escape is due to an ectopic pacemaker taking over.
Graph 11: Starling's Law — Ventricular Function Curve
In the frog heart experiment, increasing venous return (pre-load) → increasing stroke volume up to a point:
Stroke │ ╭──── optimum
Volume │ /
│ /
│ /
│______/___________________
End-diastolic volume (pre-load) →
Frank–Starling mechanism: Greater stretch of cardiac muscle → greater overlap of actin/myosin → stronger contraction.
Summary Table of All Amphibian Graphs
| # | Graph | Key Teaching Point |
|---|---|---|
| 1 | Simple muscle twitch | 3 phases: LP → CP → RP |
| 2 | Strength–response curve | All-or-none (fibre) vs. graded (muscle) |
| 3 | Effect of temperature | Heat ↑ speed & height; cold slows it |
| 4 | Summation | Residual Ca²⁺ adds to next twitch |
| 5 | Tetanus | Incomplete → complete at high frequency |
| 6 | Muscle fatigue | ↓ ATP + ↑ metabolites → failure |
| 7 | Pre-load/after-load | Starling mechanism in skeletal muscle |
| 8 | Conduction velocity | Velocity = distance ÷ latency difference |
| 9 | Normal frog cardiogram | Sinus venosus pacemaker, regular rhythm |
| 10 | Vagal stimulation | Inhibition → standstill → escape |
| 11 | Starling's law (heart) | ↑ preload → ↑ stroke volume (up to limit) |
Why the Frog is Used
- Cold-blooded — tissues survive at room temperature without special incubators
- Large sciatic nerve and gastrocnemius — easy to dissect
- Heart continues beating ex vivo — ideal for cardiac experiments
- Tissues remain viable in simple Ringer's solution — no oxygenation needed
- Ethical considerations — lower-order animal compared to mammals
These experiments form the foundation of understanding skeletal muscle mechanics, nerve conduction, cardiac physiology, and core principles like the all-or-none law, summation, tetanus, fatigue, and Starling's law — all key topics in MBBS 1st year physiology exams. For visual aids and recorded kymograph tracings, the Physiology Open YouTube playlist covers all these graphs in detail.
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