Systole heart beats—is cued by messages from the brain, reflecting the brain's responses to conditions of the body, such as pain, emotional stress, level of activity, and to ambient conditions including external temperature, time of day, etc. Electrical systole opens voltage-gated sodium, potassium and calcium channels in cells of myocardium tissue. Subsequently, a rise in intracellular calcium triggers the interaction of actin and myosin in the presence of ATP which generates mechanical force in the cells in the form of muscular contraction, or mechanical systole. The contractions generate intra-ventricular pressure, which is increased until it exceeds the external, residual pressures in
Muscular system of the horse Muscular system of the horse There are 3 types of muscle, all found within the equine: Skeletal muscle is made up of several muscle bundles, which in turn are made up of muscle fibers. Muscle fibers have bundles of myofibrils, which are all parallel to one another, and are able to contract due to actin and myosin. Muscle is covered by a fibrous tissue called fascia, to which other muscles can attach, and muscles attach to bone via tendons. Tendons attach muscles and bone, and are classified as flexors (flex a joint) or extensors (extend a joint). However, some tendons