EXCITABLE TISSUE
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Transcript of EXCITABLE TISSUE
EXCITABLE TISSUE
• The contractile property of the muscle is studied by using the frog‘s gastrocnemious –sciatic nerve preparation. This is also called muscle –nerve preparation.
• When the stimulus with a threshold strength is applied, the muscle contracts and then relaxes.
• These activities can be recorded graphically by using suitable instruments.
• The contraction is recorded as upward deflection from base line. And the relaxation is recorded as downward deflection back to the base line.
• This simple contraction & relaxation is called a “simple muscle twitch” (SMT).
Simple muscle twitch
• PS- Point of stimulation.• PC- Point of contraction.• PMC- Point of maximum contraction (height of
contraction)• PMR- Point of maximum relaxation.• LP- latent period. 10 ms• CP- Contraction period. 40 ms• RP- Relaxation period. 50 ms
Effect of Temperature on SMT
When warm ringer solution is applied to the muscle nerve preparation and a simple muscle twitch is recorded then we notice that
• All the durations are shortened (latent period,contraction period,& relaxation period)..
• The height of contraction has increased.
When cold ringer solution is applied to the muscle nerve preparation and a simple muscle twitch is recorded then we notice that
• All the durations are prolonged (latent period,contraction period,& relaxation period).
• The height of contraction has decreased.
• A fatigue curve is obtained when the nerve muscle preparation is stimulated repeatedly till a fatigue curve is obtained.
• A fatigue curve has a prolonged refractory period, low height of contraction no point of
• complete relaxation (contracture remainder).
• Fatigue is a reversible phenomenon.
• Following fatigue if the nerve muscle preparation is rested for a while and then stimulated by a threshold stimulus then a normal simple muscle twitch is obtained.
• The site of fatigue in an nerve muscle preparation is the neuromuscular junction.
• The site of fatigue in an intact animal is the CNS.
Effect of multiple successive stimuli
Genesis of Tetanus
• Beneficial effect is obtained when the second stimulus falls after the complete relaxation of the first response.
• Super position or super imposition occurs when the second stimulus falls during the relaxation period of the 1st curve.
• Summation occurs when the second stimulus falls during the contraction period of the previous curve.
• When multiple stimuli at the rate of 5 stimuli per minute are applied to the nerve muscle preparation then the staircase phenomenon is recorded.
• Here each successive contraction is recorded separately (there is complete relaxation).
• Here each successive contraction is higher than the previous one due to beneficial effect.
When multiple stimuli at the rate of 10-15 stimuli per minute are applied to the nerve muscle preparation then the recorded phenomenon is called clonus, incomplete tetanus.
• Here each successive contraction occurs during the relaxation of the previous one.
• There is incomplete relaxation.
• When multiple stimuli at the rate of 30 stimuli per minute are applied to the nerve muscle preparation then the recorded phenomenon is called Tetanus.
• Tetanus is a state of sustained contraction.
• This happens when successive stimuli falls during the contraction of the previous one.
• Cardiac muscle cannot be tetanized due to prolonged absolute refractory period.