MUSCLE

MUSCLE TYPES

• Smooth -- Involuntary Contraction
• Cardiac -- Involuntary Contraction
• Skeletal -- Voluntary Contraction

GENERAL CHARACTERISTICS OF MUSCLE

• Extensibility --» can be stretched
• Elasticity --» can return to normal resting shape
• Excitability --» can be stimulated by an electrical impulse
• Contractility --» can develop mechanical tension creating a pulling action.

SKELETAL MUSCLE SYSTEM & STRUCTURES

Central Nervous System

• Brain & spinal cord (conscious and nonconscious control of skeletal muscle)

Motor Unit

• Motor Neuron Cell Body, Axon, Motor End Plate, Innervated Muscle fibers.

• A given number of muscle fibers connected to a motor nerve -- there are small, medium, and large motor units.

• Different Motor Units have different performance characteristics -- see later table of motor unit characteristics.

Muscle Connective Tissue

• Used to protect the fibers, to connect multiple fibers, to hold together all the fibers, and to attach fibers to bones.

• Three distinct connective protective layers of tissue (Endomysium, Perimysium, Epimysium)

  • Endomysium -- most inner sheath, constitutes the skin of the individual muscle fibers.

  • Perimysium -- middle sheath that bundles groups of fibers together into Fasciculi (plural) or a Fasciculus (single)

  • Epimysium -- most outer sheath that bundles all the fasciculi together forming a complete muscle.

• Vertical (Depth) Structure: Three levels of structure (fibers, myofibrils, myofilaments)

• Muscle is composed of fibers which are composed of myofibrils which are composed of myofilaments  (Muscle Magnification & Fiber Magnification).

• Myofibrils are made of myofilaments that slide across each other. (Myofibril Magnification) 

  • Actin (small filaments, also known as thin) have the active sites for cross-bridging.

  • Myosin (large filaments, also know as thick) have the attaching heads

• Horizontal (Length) Structure: Sarcomere -- the smallest complete contraction unit of the muscle!!!

  • a muscle fiber (cell) is made of many sarcomeres connected end to end.

Major Components of muscle

• Sarcolemma final thin elastic sheath that contains the individual fibers' contents -- it is the mucle cell's membrane.

• Sarcoplasm -- the muscle cell's (fiber) cytoplasm

• Sarcoplasmic reticulum -- provides structural support and longitudinal stimulation of fibers

• t-tubules (transverse tubules) -- conducting pathways that carries stimulation through the fiber's cross section.

• terminal cisternae (lateral sacs) -- location of stored calcium (Ca++) that is actively pumped into and out of the sarcomeres.

• "triad" -- Junction where the t-tubules, sarcoplasimic reticulum, and terminal cisternae meet is known as the "triad".