Human Physiology - William F. Ganong 2002

Physiology of Nerve and Muscle Cells
Excitable Tissue: Muscle
Introduction

Muscle Cells, much like Neurons, can be excited by chemical, electrical, and mechanical stimuli. This excitation generates an Action Potential that propagates along The Cell membrane. A key distinction between muscle cells and neurons is that muscle cells possess a contractile mechanism activated by the action potential. The contractile Proteins Actin and Myosin are abundant in Muscle tissue and drive contraction. They are also present in many other cell types. As noted in Chapter 1, the actin-binding protein myosin acts as a molecular motor, converting The energy released from ATP Hydrolysis into the movement of cellular components past one another.

Muscles are generally classified into three main types: skeletal, cardiac, and smooth, although smooth muscle does not represent a uniform, single category. Skeletal muscles make up the bulk of the somatic musculature. They exhibit distinct cross-striations and do not contract under normal conditions in the absence of neural stimulation. These muscles show no anatomical or functional connections between individual muscle fibers. Their contraction is under voluntary control. Cardiac muscle is also striated; however, it Functions as a functional syncytium and contracts rhythmically even without visible external innervation, owing to pacemaker¹ cells in the myocardium that generate spontaneous impulses. Smooth muscles lack cross-striations. This type of musculature is found in the walls of most hollow Organs; yet, it likewise functions as a syncytium and contains pacemaker cells that produce irregular impulses. The Eyeball and certain other organs contain a specialized type of muscle tissue devoid of spontaneous activity, which structurally somewhat resembles Skeletal Muscle.