Physiological Aspects of Muscle
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Physiological Aspects of Muscle
Movement and Locomotion of Class 11
Action involves alternate phenomena: contraction and relaxation:
To elicite contraction, it requires stimulus of a particular minimum strength known as threshold stimulus, below which there is no contraction threshold varies for different muscle types.
It contracts fully if given a threshold stimulus or more, but below this level it does not contract at all, hence, this is called as all or none type phenomenon.
Contraction is the result of interaction of actin and myosin proteins forming actomyosin complex, with hydrolysis of ATP.
On the basis of number and frequency of impulse, there are two types of contraction:
Twitch contraction:
Single contraction followed by relaxation if single impulse is applied.
Force generated is too less, hence performs no body function.
Tetanic contraction:
Many twitches fused together (continued contraction) without relaxation, if multiple impulses are given continuously.
Force generated is higher due to addition of forces (summation) of each twitches.
All body functions are performed only by this contraction.
The manner of summation is called as staircase phenomenon.
Isotonic and Isometric Contraction:
The term ‘contraction’ means shortening of length but in muscle this term is used for general action. The fact is that muscle may or may not shorten in length when it contracts and this depends upon load.
On this basis there are two types of contraction:
| Isotonic contraction | Isometric contraction |
| When load is lower than the force generated by the muscle | When load is higher than the force generated by the muscle |
| Muscle shortens in length. | No shortening (length remains same). |
| Contraction velocity decreases with increasing load. | When velocity of contraction is zero. |
| Work done due to displacement of load | No work done as no displacement of load |
| EEnergy consumption is lower at lower load and increases with increasing load | Energy consumption is higher and is wasted asheat since no work is done. |
Muscle tone (Tonus) : Even at complete rest of the body some muscles keep contracting continuously to ‘maintain the body posture, this is called tonus.
Tetanus : A disease caused by bacteria, Clostridium tetranii, which produces a toxin that gives continued impulse to the muscles of the body causing its continued contraction. In this case death is caused due to respiratory and cardiac failure. This is also called as locked jaw phenomenon.
Rigor : Due to absence of ATP in muscle it doesn’t relax and remains in contracted state. This occurs most commonly in jaw muscle, finger and limb muscles.
Rigor mortis : After death, muscles of the body go in permanently contracted state.
Fatigue : Due to accumulation of lactic acid, muscle refuses to contract as at low pH the activity of myosin (ATPase enzyme) stops.
