Introduction: Structure and Function Muscular System Introduction: Structure and Function

Muscle Functions Producing movement Maintaining posture Muscle performs four important functions in the body: Producing movement Maintaining posture Stabilizing joints Generating heat Heat is generated from the mass of muscle. = cubic body area. Loss of heat is based on surface area. Elephant : 28 beats/minute. Human: 70 beats/minute, hummingbird: >200beats/minute. - mass compared to surface area is small so it needs to beat a lot more to maintain body heat. Shivering – body response to generate heat Fever: below 93 heart stops, 108 proteins denature.

Producing Movement Movement results from skeletal muscle contraction Skeletal muscle are responsible for all locomotion and manipulation Allows you to interact or react with your external environment

Producing Movement - eye movement - facial expression (skeletal) Skeletal Muscle controls (besides the obvious locomotion.) - eye movement - facial expression (skeletal) - circulation (cardiac) - moves gas, liquids, and solids through organs (smooth)

Maintaining Posture Skeletal muscles are utilized constantly to maintain sitting, standing, and moving postures Postural muscle develop to compensate for the never ending pull of gravity Our developmental milestones as an infant are our initial victories over gravity Curves of the spinal column are shaped by the interplay of skeletal muscle and gravity Most voluntary – concious control. Posture-holding head up, nod off -? In pairs because they can only contract Huge blood supply – high energy demand. Bleed a lot when cut through. Easily torn. Strong in ability to lift but not really against tearing.

Stabilizing Joints Skeletal muscle provide the dynamic stability of joints Many joints are poorly reinforced by ligaments and connective tissue Many joints have noncomplementary surface which do not contribute to stability

Generating Heat Muscles generate heat as they contract The heat generated is vitally important to maintain normal body temperature Skeletal muscle generates most of the heat because it represents 40% of body mass Excess heat must released to maintain body temperature Heat is generated from the mass of muscle = cubic body area. Loss of heat is based on surface area. Elephant: 28 beats/minute, human: 70 beats/minute, hummingbird: >200 beats/minute – mass compared to surface area is small so it needs to beat a lot more to maintain body heat. Shivering: body response to generate heat. Fever: below 93 heart stops, 108, proteins denature

Overview of Muscle Tissue There are three types of muscle tissue Skeletal muscle Cardiac muscle Smooth muscle

Overview of Muscle Tissue These muscle tissues differ in the structure of their cells, their body location, their function, and the means by which they are activated to contract

Overview of Muscle Tissue All skeletal and smooth muscle cells are elongated and are referred to as muscle fibers

Skeletal Muscle Tissue Skeletal muscle tissue appears as distinct skeletal muscle that attach to the skeletal system Skeletal muscle has obvious striations It is a voluntary muscle under conscious control

Cardiac Muscle Tissue Cardiac muscle occur only in the heart The muscle is striated but involuntary Cardiac fibers are short, fat, branched and interconnected Cardiac muscle cells are interlocked by intercalated discs and function as a single unit Not branching.

Smooth Muscle Tissue It is found in the walls of hollow organs such as the stomach, urinary bladder, and intestines (visceral organs) It has no striations It is not subject to voluntary control

Differences in Contractions Skeletal muscle can contract rapidly but tire easily and must be rested Skeletal muscle contractions vary in force depending on use Cardiac muscle contracts at a steady rate but can accelerate to cope with demand Smooth muscle contracts in steady, sustained contractions and continues on tirelessly

Skeletal Muscle

Anatomy of a Skeletal Muscle Each skeletal muscle is a discrete organ with thousands of fibers Muscle fibers predominate the tissue but it also contains, blood vessels, nerve fibers, and connective tissue

Connective Tissue of Muscle Fascia: broad band of dense connective tissue that may occupy the space between skin and muscle or may surround muscle and other organs 2. Deep Fascia: associated with muscles. Surrounds muscle and serves to support and hold it together. 3. Epimysium  perimosium  endomysium (Superficial to deep)  4. Tendon: thick band of connective tissue that attach muscle to bone.

Connective Tissue Wrappings Each muscle fiber is wrapped by a fine sheath of connective tissue called endomysium Several fibers are gathered side by side into bundles called fascicles Each fascicle is bound by collagen fiber layer

Connective Tissue Wrappings Fascicles are bound by a dense fibrous connective tissue layer called the epimysium The epimysium surrounds the entire muscle External to the epimysium is the deep fascia that binds muscles into functional groups

Connective Tissue Wrappings All the connective tissue layers are connected to each other as well as to the tendons that join muscles to bone When muscle fibers contract they pull these connective tissue sheaths which in turn transmit the force to the bone to be moved Connective tissues supports each cell EPImysium Perimysium endomysium superficial to deep

Naming Skeletal muscles Location of the muscle Shape of the muscle Relative Size of the muscle Direction/Orientation of the muscle fibers/cells Number of Origins Location of the Attachments Action of the muscle

By location Epicranius (around cranium) Tibialis anterior (front of tibia)

Shape Shape: deltoid (triangle) trapezius (trapezoid) serratus (saw-toothed) rhomboideus (rhomboid) orbicularis and sphincters (circular) Rhomboideus major

Size maximus (largest) minimis (smallest) longus (longest) brevis (short) major (large) minor (small)

Direction of fibers Rectus (straight)-parallel to long axis Transverse Oblique

Number of origins biceps (2) biceps brachii triceps (3) quadriceps (4)

For origin and insertion Sternocleidomastoid originates from sternum and clavicle and inserts on mastoid process of temporal bone

For action Flexor carpi radialis (extensor carpi radialis) –flexes wrist Abductor pollicis brevis (adductor pollicis) –flexes thumb Abductor magnus – abducts thigh Extensor digitorum – extends fingers