This document describes experiments performed on frog skeletal muscle to study muscle physiology. It involves dissecting the gastrocnemius muscle and sciatic nerve of a frog. Simple muscle twitches are recorded in response to nerve stimulation. The effects of various factors like temperature, stimulus strength and frequency on the muscle contraction are investigated. Muscle fatigue is also studied. Determination of conduction velocity of the sciatic nerve is described. The document provides details of the procedures, appliances used, and observations made in these amphibian experiments.

1. Amphibian
graph & charts
By Shama
Physiology Department

2. General
introduction
• Gastrocnemius- sciatic
preparation by dissecting Frog
• Why Frog? Easily available, cold
blooded animals, tissue can
survive in vitro without
oxygenationand temp0erature
control.
• Easy to handle

3. Appliances used
in amphibian
experiments
• Stimulating device
• Recording device
• Lucas chamber,
kymograph, galvanic
current

4. Procedure of preparation
• Stunning of Frog- blow on its head
against the edge of table.
• Pithing of frog – destroy brain and
spinal cord
• Dissection of sciatic nerve
• Dissection of gastrocnemius muscle.
• Ringer solution ( NaCl, CaCl2, KCl,
NaHCO3)

5. Simple muscle twitch- An adequate stimulus applied to the nerve of a
skeletal muscle gives rise to a brief contraction of the muscle followed by
relaxation.

6. Causes of
latent
period:-
• Conduction of impulse along
nerve
• Neuro muscular transmission
• Excitation- contraction
coupling
• Stretching of SEC
• Inertia of lever

7. Action potential & SMT

8. Effect of
Temperature
on SMT
• By changing temperature of
ringer solution
• First, record in warm ringer
solution (38°-40°) then cold
ringer solution (10 -12°) cos cold
ringer inactivates muscles & it is
defficult to revive it.
• Should not exceed 42° coz it
may denatured muscle proteins.
• What is heat rigor?

9. Effect of 2
successive
stimuli on
skeletal
muscle
contraction
• Summation means increase in the activity of a
tissue produced by multiple stimulation.
• 2 types of summation:- summation of stimuli
and summation of contraction.
• If second stimulus falls during latent period of
muscle, no additional response will be there
(completely refractory)
• If applied later, second response leading to
development of tension (summation of effects)
due to beneficial effects (release of Ca++,
increase in temp, decrease in viscosity,
decrease in inertia of recording)

10. Effect of 2 successive stimuli on skeletal muscle contraction

11. Effect of
increasing
strength of
stimulus on
skeletal
muscle
contraction
• Threshold of excitation of different
motor neurons which supply a
single skeletal muscle varies.
Therefore, with the increase in
strength of stimulus more and
more motor units get recruited
and the height of contraction
increases.
• Each motor neuron and all muscle
fibers it supplies constitute a
motor unit.

12. Dubois Raymond induction coil consist
of primary and secondary coil.
Induced current is stronger at break
than at make.
Tap key to start giving stimulus

13. Effect of increasing strength of stimulus on skeletal muscle contraction.
Height of muscle contraction at make and break shocks

14. Effect of load on skeletal
muscle contraction.
• Load applied to muscle n 2 ways: Afterload & pre-load
ways
• After-loaded is the condition in which the load starts to
act on muscle after contraction has begun.
• Example: lifting of a weight from ground under normal
condition.
• Pre-loaded is the condition in which the load acts on the
muscle before it begins to contract.
• Example: continuous contraction of antigravity muscle to
maintain body posture.

15. Muscle movements and contraction

16. Pre-load & After-load

17. Calculation of work done

18. Effect of increasing
frequency of stimuli
on skeletal muscle
(12.5mm/sec)
• Treppe & staircase phenomenon-
when a series of maximal stimuli are
applied to muscle at a frequency so
successive stimuli fall during relaxation
phase therefore, it occurs an increase
in tension developed.
• Clonus: successive stimuli falls during
mid relaxation period.
• Tetanus: repeated maximal stimuli
during contraction phase, activation of
contractile mechanism occurs
repeatedly before any relaxationand
fuse into a continuous contraction.

19. Effect of increasing frequency of stimuli on skeletal muscle
contraction

20. Genesis of Fatigue
in skeletal muscle
(640mm/sec)
• Fatigue is a temporary reduction of
working capacity of a cell, organ or
organism.
• Reversible phenomenon.
• No longer response because of
 Lack of of nutrition
 Accumulation of waste metabolites
 Depletion of Ach stores

21. Genesis of Fatigue
(contration remainder due to incomplete relaxation
following depletion of ATP)

22. Determination of conduction velocity of
sciatic nerve (640mm/sec)
• Stimulate the nerve at its muscle end (M-curve)
• Stimulate the nerve at its vertebral end (V-curve)

23. Conduction velocity of sciatic nerve

24. Factors affect conduction
velocity of nerve
• Diameter of nerve fiber
• Presence or absence of myelination.
• Temperature
• Conducting media in which nerve is
placed.
• RMP

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