Muscle Structure and Function

Types of Muscle Skeletal muscle Smooth muscle Cardiac muscle The human body is comprised of over 600 muscles Muscle makes up 30-35% (in women) and 42-47% (in men) of body mass. Three types of muscle: Skeletal muscle Smooth muscle Cardiac muscle

Key Terms Tendons - tough bands of connective tissue that join muscle to bone Aponeurosis – a sheet-like membrane that serves as a fascia to bind muscles together or to connect muscle to bone ex. Palmar aponeurosis Fascia – connective tissue that covers, supports, and separates muscles ex. Fascia lata (thigh), brachial fascia (upper arm) Tissue - masses of cells that have similar function and form Muscle tissue - collection of cells that shorten during contraction, therefore creating tension that results in movement

A. Skeletal (Striated) Muscle Muscles that are attached to the bones via connective tissue tendons During muscle contraction, skeletal muscle shortens and moves various parts of the skeleton We have voluntary control of our muscles, meaning they are activated through signals carried to the them via nerves Referred to as striated, because their appearance is a series of alternating light and dark stripes (myofilaments) Repetitive contraction leads to fatigue

B. Smooth Muscle Muscles surrounding your body’s internal organs, as well as your blood vessels, respiratory tract, iris (eye) & gastro-intestinal tract The contractions are slow and uniform and can remain for long periods of time Activation is involuntary Fatigue resistant Fibres are arranged in dense sheets, therefore appearing smooth

C. Cardiac Muscle Muscles found only in the heart. Functions to provide the contractile activity of the heart (pumping blood to the rest of the body) Is very fatigue resistant Activation of cardiac muscle is involuntary Striated

Components of skeletal muscle a) Muscle b) Fascicle c) Muscle fiber d) Myofibril

Muscle Structure Beginning at the muscle (superficial to deep): Epimysium: connective tissue surrounding the whole muscle (many fascicles) Perimysium: connective tissue surrounding each fascicle Fascicle: perimysium wrapped muscle fibres Endomysium: connective tissue surrounding each muscle fibre Muscle fiber: muscle cell Sarcolemma: a plasma membrane beneath the endomysium that contains the cells sarcoplasm Sarcoplasm: similar to cytoplasm of other cells, containing large amounts of glucose & myoglobin (protein that stores oxygen)

Muscle Structure Cont’d Myofibrils: rodlike contractile elements, that occupy most of the muscle cell and are composed of sarcomeres arranged end to end Sarcomeres: a contractile unit composed of myofilaments (actin & myosin) Myofilaments: Myosin (thick): made up of a “head” (attachment site for actin) & “tail” Actin (thin): tropomyosin: arranged along the actin filament, and when relaxed prevent myosin head from binding to actin troponin: binding site for calcium

Properties of a Muscle Fibre Irritability - ability of muscle to respond to stimulus Conductivity - ability to transmit nerve impulses Contractibility - ability to shorten in length Extensibility - ability to extend in length Elasticity - ability to stretch and return to normal position

Muscle Teamwork Agonist (prime mover): Antagonist: the muscle or group of muscles producing a desired effect Antagonist: the muscle or group of muscles opposing the action lengthens when the agonist muscle contracts

Contractile Machinery: Origin & Insertion In order for muscles to contract, they must be attached to the bones to create movement. Origin: the end of the muscle attached to the bone that does not move (proximal attachment) Insertion: the point of attachment of the muscle on the bone that moves (distal attachment)