Muscles

Four unique properties of muscle tissue

Excitability, contractility, elasticity, extensibility

Excitability

Muscle cells are responsive to input from stimuli.

Contractility

Stimulation of muscle fibre can lead to contraction and shortening of the muscle fibre.

Elasticity

A contracted muscle cell can return to resting length when applied tension is removed.

Extensibility

The ability of a muscle fibre to be stretched beyond its resting length.

Roles of skeletal muscle

Body movement, maintenance of posture, temperature regulation, storage and movement of materials, and support.

Organisation of skeletal muscles

Muscle, fascicles, muscle fibres, myofibrils, myofilaments

Where is connective tissue found in muscles?

Each muscle has three layers of concentric connective tissue composed of collagen and elastic fibres. Three layers: Endomysium, perimysium, epimysium.

What does the connective tissue do?

Protection, sites for blood vessel and nerve distribution, a means of attaching muscle to skeleton.

Endomysium

Innermost layer of CT that surrounds and electrically insulates muscle fibres (areolar CT)

Perimysium

Surrounds the fascicles (dense irregular CT)

Epimysium

Surrounds the entire muscle, dense irregular CT. Deep fascia surrounds each muscle and separates muscles from each other. Superficial fascia separates muscle from skin.

Explain how and where muscles attach to other body structures

At the ends of each muscle all of the CT merges to form a tendon. Tendons attach muscle to bone, skin, or another muscle. Most muscles extend over a joint and have attachments to both articulating bones of that joint.

How to muscles move?

Upon contraction of the muscle, one of the articulating bones moves and the other does not. The less moveable point of attachment is called the origin. The more moveable point of attachment is called the insertion.

Muscle tone

Refers to the constant tension in a resting muscles. Motor units are stimulated randomly to avoid fatigue. Two types of muscle contractions: Isometric and Isotonic.

Isometric muscle contractions

Length is constant, tension is changing

Isotonic muscle contractions

Tension is constant, length is changing. Concentric contraction: Muscle is shortening. Eccentric contraction: Muscle is lengthening.

Components of skeletal muscle cells

Many of the same components of a typical cells. Plasma membrane: sarcolemma. Cytoplasm: sarcoplasm. Smooth ER: sarcoplasmic reticulum.

Skeletal muscle sliding filament theory

Muscle fibres shorten by the interaction between thick and thin filaments within each sacromere (functional contractile unit in skeletal muscle fibres). The mechanism for contraction is explained by the sliding filament theory.

Features of cardiac muscle

Found almost exclusively within the heart wall. One or two nuclei, form y-shaped branches. Join other adjacent cells to form junctions named intercalated discs comprised of gap junctions. Autorhythmic (able to generate a muscle impulse without nervous stimulation). Under involuntary control.

Features of smooth muscle

Found in the walls of visceral and blood vessels. Short fuse form cells (widest in the middle and tapered at each end). On centrally located nucleus, no striations. Thin filaments attach to dense bodies, under involuntary control.

Four organisational patterns in fascicles

Circular, parallel, convergent, pennate (unipennate, bipennate, multipennate)

Actions of skeletal muscles

Agonist, Antagonist, Synergistic

Agonist

Produces a specific movement when it contracts. Also called a prime mover. E.g. the triceps brachii is an antagonist that causes forearm extension.

Antagonist

A muscle whose action opposes that of an agonist. E.g. the biceps brachii is an antagonist to the triceps brachii.

Synergist

A muscle that assists the agonist in performing its action.