Properties of skeletal muscle:
- Excitability and irritability: It’s the property of a muscle to respond to a stimulus. If the response occurs in the front of a contraction. It’s called as contractility.
- Tonicity: Muscles of a living organism are in the partially contracted state, even at rest. They are never fully relaxed and they will resist being stretched the resistance to stretch is called as tonicity.
- All or none response: When a stimulus is given to a muscle, the muscle either contracts to the maximum or it doesn’t contract at all. When a weak stimulus is applied to a muscle, it doesn’t produce any response. But when the stimulus is gradually increased, the muscle contracts at a point to the maximum level. Later even a greater degree of stimulus does not increase the degree of contraction.
- Summation: When a second stimulus is given to a muscle even while it’s contracting due to the first stimulus, the degree of contraction is more. This phenomenon is called as a summation. The increased response is due to stimulation of more and more motor units by repetitive stimuli.
- Treppe or staircase phenomenon: Stimulation of a muscle at regular short intervals increases the amplitudes of contraction *which goes on increasing like the steps of a staircase*. This occurs due to increased irritability of the muscle produced by chemical products of the earlier contractions.
- Tetanus: When a muscle is stimulated repeatedly at a very faster rate, the muscle contracts maximally. The muscle remains at this maximal state of contraction till 1- the stimulus continues or 2- it gets fatigued. This sustained maximal contraction is called tetanus.
- Refractory period: Muscle, like other excitable tissues, has a period following its action potential during which the membrane will not respond to stimulation regardless of the strength.
- Isotonic contraction: It’s the contraction in which the muscle shortens under constant load. It occurs in muscles during walking, running or lifting.
- Isometric contraction: In this type of contraction, the muscle develops tension but it does not shorten in length e.g. maintaining the posture against gravity.
- Fatigue: It’s a state of reduced excitability and contractility of a muscle. It’s produced by rapid and repeated stimulation of the muscle. Fatigue may occur due to depletion of energy and accumulation of metabolites like lactic acid.