Muscular System

Intro to Muscles 1.Nearly half our weight comes from muscle tissue 2.There are 650 different muscles in the human body

Three Main Functions 1.Responsible for body movement 2.Responsible for body form and shape (posture) 3.Responsible for body heat and maintaining body temperature

4 Characteristics of a Muscle 1.CONTRACTILITY – the capability or quality of shrinking or contracting 2.EXCITEABILITY– the ability to respond to certain stimuli by producing impulses 3.EXTENSIBILITY – the ability to be stretched. 4.ELASTICITY – ability of muscle to return to its original length when relaxing.

Types of Muscle ● Skeletal – striated, voluntary, multinucleated, long and run parallel to eachother, found on bones ● Smooth – non-striated, involuntary, single nucleus, tapered, found in many organs, contract using peristalsis ● Cardiac – striated, involuntary, 1-2 nuclei, long and branched, found in heart, contain intercalated discs, rhythmic contractions The word “striated” means striped. Skeletal muscle appears striped under a microscope.

Muscles and Muscle Fiber Structure Individual muscles are separated by FASCIA, which also forms tendons **Tendonitis – inflammation of the tendons Muscle fibers (cells) are arranged in bundles called FASCICLES

EPIMYSIUM = outermost layer, surrounds entire muscle. PERIMYSIUM = separates and surrounds fascicles (bundles of muscle fibers) ENDOMYSIUM = surrounds each individual muscle fiber This model of the muscles uses straws to represent fibers. Green = endomysium Yellow = perimysium Blue = epimysium

Muscle Layers

Epimysium Perimysium Endomysium

It is important to remember the hierarchy ACTIN (light) FASCICLES MUSCLE FIBERS MYOFIBRILS FILAMENTS MUSCLE MYOSIN (dark) Wrapped in EPIMYSIUM Wrapped in PERIMYSIUM Wrapped in ENDOMYSIUM

Sarcolemma = muscle fiber membrane Sarcoplasm = inner material surrounding fibrils (like cytoplasm) Myofibrils = individual threads within muscle fiber made of myofilaments Muscles / Cells

Sarcolemma Mitochondrion Sarcoplasm Myofibril Nucleus

Myofibrils are made of ACTIN = thin filaments MYOSIN = thick filaments

Myofilaments ACTIN (thin) and MYOSIN (thick) -- form dark and light bands  A band = dArk thick (myosin)  I band = lIght thIn (actin)

SLIDING FILAMENT THEORY (MODEL) - theory of how muscle contracts This occurs as the thin filament (actin) slides past the thick filaments (myosin)

Explanation of Skeletal Muscle and Sliding Filament Theory Start at 1:40

How Muscles Work with the Nervous System NEUROMUSCULAR JUNCTION - where a nerve and muscle fiber come together

Neuromuscular Junction

Motor neurons stimulate muscle fibers to contract Motor neuron secretes neurotransmitter known as ACETYLCHOLINASE One motor neuron connected to muscle fibers make up a motor unit

Energy Source -ATP is produced by CELLULAR RESPIRATION; occurs in the mitochondria -Creatine phosphate increases regeneration of ATP * Only 25% of energy produced during cellular respiration is used in metabolic processes - the rest is in the form of HEAT. -maintains body temperature.

Other Terms 1. All-or-None Response 2. Motor Unit 3. Recruitment 4. Muscular Hypertrophy 5. Muscular Atrophy 6. Muscle Cramp 7. Origin & Insertion 8. Strain 9. Sprain 10. Hernia

1. All-or-None Response Fibers do not contract partially, they either do or don't 2. Motor Unit The muscle fiber + the motor neuron

3. Recruitment More fibers contract as the intensity of stimulus increases 4. Hypertrophy - muscles enlarge (working out or certain disorders) 5. Atrophy - muscles become small and weak due to disuse Cardiomyopathy

6. Muscle Cramp - a sustained involuntary contraction 7. Origin and Insertion Origin = the immovable end of the muscle Insertion = the movable end of the muscle

8. Strain – tear in muscles/tendons from excessive use 9. Sprain – tear in ligaments

10. Hernia – protrusion of an organ or tissue through a weak muscle or opening 11. Ligaments vs. Tendons Ligaments – bone to bone Tendons – muscle to bone

Treatments (R.I.C.E.) 1.Rest 2.Ice 3.Compression 4.Elevation