Practical work.........83
31. Electrical stimulation on leg muscle of frog
Procedure
1.
Kill a frog with double pith method.
2.
Cut open the abdominal wall of the
frog.
3.
Nerve-muscle preparation:
•
Identify the sciatic nerve and tie
it with a cotton thread (Fig.1).
•
Trace along the sciatic nerve to
the leg muscle.
•
Tie Achilles tendon of leg
muscle with another cotton
Fig.1 Identifying the sciatic nerve
thread.
•
Separate the leg muscle from the
sciatic nerve
bones and neighbouring tissues
by cutting the connective tissue
and Achilles tendon.
4.
Place the nerve-muscle preparation
in Ringer’s solution completely until
in use (Fig.2).
5.
Use a pin to hold the muscle at knee
joint at one side.
6.
Fig.2 Nerve -muscle preparation
Apply an electric current with a low
voltage of about 2 V to stimulate the
electrodes
nerve to cause muscle twitch (Fig.3).
7.
Apply a higher voltage of about 6 V
to stimulate the nerve again.
Fig.3 Applying an electric current
84.........Practical work
Note
1.
The frog should not be killed by over anaesthesia
with chemicals, as this will damage the irritability
of nervous system of the frog.
2.
The frog can be killed by the following methods:
Method 1
•
use a needle pin to destroy the nervous tissues
of the brain;
•
insert the needle pin into the spinal cord to
damage its nervous tissues, until both legs
become straightened.
Method 2
•
cut the upper jaw of the frog with a bone cutter
to expose the spinal cord;
•
insert a needle pin in the spinal cord to damage
the nervous tissues until both legs become
straightened.
3.
A 2 V electrical stimulus is strong enough to cause
depolarisation of the nerve fibre and evoke an
action potential as well as a single twitch of
muscle contraction.