Myology – study of the structure, arrangement and action of muscles Muscle Tissue

I. Introduction There are 650 skeletal muscles in the body that comprise about 40% of body weight

II. Basic Characteristics 1. Excitability – capacity to generate electrical impulses (Action Potential) 2. Contractility – capacity to shorten in length

Functions of the Muscular System 1. Voluntary Movement – includes speech and breathing (diaphragm; intercostal muscles) 2. Maintenance of Body Posture 3. Heat Protection

Microanatomy (Histology) of skeletal muscles - striations (lines) - multinucleated

A. General Characteristics of the skeletal muscle fibers 1. multinucleated 2. striations 3. numerous mitochondria 4. transverse tubules (T-tubules) 5. sarcoplasmic reticulum – acts like the circulatory system in the cell 6. myofibrils within the cytoplasm - bundles of protein filaments

Endoplasmic reticulum or sarcoplasmic reticulum – acts like the circulatory system of the cell It is named sarcoplasmic reticulum because of the lateral sacs or terminal cisterns attached on it and it is found only on muscle cells

B. Protein Arrangement within the Myofibrils 1. Sarcomere Units (a) the region between the two Z-lines (b) types of protein filaments (1) actin (thin) myofilaments (2) myosin (thick) myofilaments

A.

B.

B.

C. Myofibril – bundle of muscle proteins

D. Sarcomere – distance between two z lines

Sarcomere – muscle unit

D. Myofilament – muscle proteins filament = proteins

Light areas for one protein and dark areas whenever they converge

- in the 1940’s they could only see light and dark bands

The invention of the electron microscope allowed them to see the arrangement of actin and myosin myofilaments

E. Myosin – thicker proteins and have little projections on them

Actin – attached to the z lines and extend inwards and no attachments at the middle

Andrew F. Huxley’s Theory = 1950s – 1960s

Chemical bond in muscle is “actinomyosin bond” ATP – high-powered molecule

A rough analogy to the sliding filament theory is to imagine men, bent double with a pole (thick filament) along their backs, running along a thinner pole (the thin filament). If the thick pole is fixed then the thin pole will move below them. As the polarity of the cross-bridges at each end of the thick filaments are in opposite direction the filaments are pulled inwards (Huxley).

Muscle cell membrane – sarcolemma – forms a deep vertical tube that extends inward deep into the muscle - you call this T-tubule (sarcolemmal invagination)

There is always fluid surrounding a cell and 80% inside a cell is fluid The fluid outside of muscle cells is surrounded with sodium ions as well as into T-tubules Muscle and Nerve Cells – these are the only cells where sodium ions can into

(1) Na+ flow into the muscle cell Action Potential (AP) = electrical current (Excitation) (2) AP causes the release of Ca+ from the lateral sacs (coupling) (3) the Ca+2 causes the myosin cross-bridges to start pushing the actin myofilaments inward (“Contraction”) or shortening “calcium is the coupling ion

1. once sodium gets into the cell, it will start an electric current 2. calcium ions will start to flow out of the muscle sac 3. calcium activates the myosin bridges or the feet of the men

Action Potential – excitation

The effect of physical training on muscle fibers 1. Brief Maximal-Type Training – power – hypertrophy growth a. (1) weight lifting (2) sprinting (3) jumping b. muscle fiber characteristics: (1) large diameter muscle fibers (2) fast rate of contraction (3) high power development

(2) low myoglobin content (a) minimal storage of oxygen within muscle fibers (b) “white” coloration of muscle fibers

2. sustained, sub-maximal type training – endurance (aerobics) – prolonged exercise a. examples (1) long-distance running (2) swimming (3) cycling

b. muscle fiber characteristics (1) small diameter muscle fibers (a) slow rate of contraction (b) high endurance (2) high myoglobin content (a) permits storage of oxygen

Hyper – increase; trophy – growth

Skeletal muscle

Smooth muscle – spindle-shaped and uninucleated

Skeletal Muscle

Skeletal Muscle

Cardiac Muscle