1. 19.2.13 Types of Muscle Contractions

3. Total Tension of a Muscle Each of these forces will be the sum of active forces (developed by contractile machinery) and passive forces (due to stretching of elastic elements) Forcibly stretching a muscle well beyond its resting length will generate a force higher than that produced by active contraction

4. Types of Skeletal Muscle Contraction Isometric contraction Isotonic contraction Concentric contraction Eccentric contraction

5. Isometric Skeletal Muscle Contraction When a muscle is stimulated such that it develops tension but does not shorten or lengthen. This is called an isometric contraction (iso = same, metric = measurement or length). This is a contraction in which no movement takes place

6. Careful observation reveals that in the isometric contraction, the sarcomeres shorten and stretch the series elastic component even though the muscle as a whole does not shorten. Even though the muscle develops tension, but because it does not shorten, it does no external work (work = force x distance moved) but there is internal work being done The total tension is the sum of active and passive tension (the curve of total tension is the curve of isometric contraction)

7. Isotonic Skeletal Muscle Contraction When a muscle is stimulated such that the muscle shortens or lengthens with a constant load but its tension remains the same, the contraction is isotonic (iso = same, tonic = tension) This is a contraction in which movement does take place, because the tension generated by the contracting muscle exceeds the load on the muscle.

8. Types of isotonic skeletal muscle contraction 1. Conentric contraction A concentric contraction is a type of isotonic contraction in which the muscles shorten while generating force such as lifting a weight up (a bicep curl) 2. Eccentric contraction During an eccentric contraction, the muscle elongates while under tension against an opposing force (load). For example, lowering a load to ground

9. Force (tension)-velocity relationship of a muscle The force a muscle can generate depends upon both the length and shortening velocity of the muscle Force declines in a hyperbolic fashion relative to the isometric force as the shortening velocity increases, eventually reaching zero at some maximum velocity.

10. The force generated by a muscle depends on the total number of cross-bridges attached. Because it takes a finite amount of time for cross-bridges to attach, as filaments slide past one another faster and faster (i.e., as the muscle shortens with increasing velocity), force decreases due to the lower number of cross-bridges attached. Conversely, as the relative filament velocity decreases (i.e., as muscle velocity decreases), more cross-bridges have time to attach and to generate force, and thus force increases. Force (tension)-velocity relationship of a muscle

12. Types of skeletal muscle contractions at a glance

13. Cardiac Cells The heart consists of three special types of cardiac cells Pacemaking cells: Have the properties of automaticity and are capable of generating electrical impulses. These cells are present in the sinoatrial node and entire His-Purkinje system Conducting cells: Specialized for rapid conduction of electrical impulses and are present within the entire His-Purkinje system Muscle cells: Specialized for contraction and are present in the atria and ventricles

14. Cardiac Action Potentials

15. In cardiac autorythmic cells, membrane does not have a resting potential Pacemaker potential - membrane slowly depolarizes “drifts” to threshold, initiates action potential, membrane repolarizes to -60 mV.