Materials for auditory self-work. 4.1. List of study practical tasks necessary to perform at the practical class.
4.1. List of study practical tasks necessary to perform at the practical class.
Materials and methods: vertical myograph, stimulator, irritating electrods,
kymograph, universal stand, preparating instruments
set, pipette, gauze napkin, Ringer’s solution.
Investigation object: frog.
Task 1. Acquaintance with devices for the work performing.
Electrofeeding source - has the function of voltage creating (till 0 to 40 V).
Kimograph – has the aim of graphic registration of mechanical transitions through the paper tape.
Universal stand – is for fixing the investigation object and registrating devices on it. It allows to rotate the subjects vertically and horizontally.
Myograph – is situated on universal stand. The aim of its usage is the registration of muscular contraction on kimograph drum. The main part of it are:
– Engelman’s lever with the writing device at the long arm end.
– Hook for muscle fixating on the short arm.
One should fix another muscular end in a squeeze.
Myogram – the record of muscular contractions the altitude of which are increased.
Task 2. To prepare nervous-muscular preparation.
Frog is taken in a left hand. Her abdomen must be orientated to the investigator’s palm. He must incline frog’s head forward with his thumb. One should find small deepening behind occipital bone and take in the preparation needle in suboccipital opening on depth of 1-2 mm. Having performed several transverse movements with the needle end it’s necessary to separate brain from spinal cord. After that one must turn the needle toward the trunk. They take the needle in spinal canal while destroying spinal cord.
After that taking the animal by his posterior legs one cut spine (vertebral column) by the distance of 2 cm in front of spine articulation with pelvis bones. One should remove all anterior body surface cutting the skin and visceral organs. Legs posterior with pelvis and spine residue are raised up and urostyle is cutted. Urostyle is the bone formed by tail vertebras articulation. The investigator tightens the skin from posterior legs.
Then one seperates legs one from another cutting carefully in the middle line the vertebral column residue and the pelvis in mons articulation. One of the legs is preparated, the another one is put in Ringer’s solution.
One should bring the glass stick to lumbo-sacral plexus and separate pelvis bone from spinal with scissors. The plexus should be connected with spine. One should preparate lumbo-sacral plexus to the hip joint.
One should move apart biceps brachii and musculus semimembranosus at femur dorsal surface. Then the investigator must find sciatic nerve and preparate it through all the distance carefully cutting its branches. The investigator must remove all the tissues above the hip joint. They receive the preparation “ sciatic nerve-legs muscles”.
For the muscular contraction registration by means of kymograph one should use the preparation “sciatic nerve-gastrocnemius muscle”. For its receiving on the preparation “ sciatic nerve-legs muscles” one should separate gastrocnemius muscle together with the tendon from bones and other tibia muscles alongside with the preservation of femur bone residue (1 cm). Then they remove tibia below hip joint. Gastrocnemius muscle with hip joint and sciatic nerve remain as a result. The hip joint is used for the preparation fixating in myograph.
The preparation must be often damped (moisted) with Ringer’s solution for drying prevention.
Task 3. Nerve and muscle excitability measurement.
The investigation is performed on the preparation “ sciatic nerve-legs muscles”. The investigator put the preparation on the plate. The scientist puts sciatic nerve to the electrods. Then he slowly increases the voltage till the level at which the muscle will have minimal answer. The founded minimal irritation force is called the irritation threshold.
Then one should determine the muscle irritation threshold at its direct irritation by electrical current. For this gaim the investigator brings up the electrods to one of tibia muscles. Then he finds minimal irritation force causing muscular contraction.
Compare irritation and excitability threshold at direct muscular irritation and nerve irritation (indirect irritation). Make the final conclusion.
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