Muscular System

Types of Muscle Skeletal – striated & voluntary Smooth – involuntary Cardiac - heart The word “striated” means striped. Skeletal muscle appears striped under a microscope.

Pathology Connection: Strains and Tears Strains caused by overstretching tendons or muscles Severity of injury can range from mild to severe Mild: pulled muscle (slight overstretch of muscle) Severe: complete muscle tear or complete tendon rupture

Pathology Connection: Strains and Tears (cont’d) Injuries can be acute or chronic Acute: usually resulting from trauma Chronic: usually resulting from overuse or disease Signs and symptoms: vary depending on severity of injury Mild strain (no tear of muscle or tendon fibers): mild pain and possibly stiffness Moderate strain (some tearing of muscle or tendon fibers): more intense pain, bruising, obvious weakness Severe strain (complete tear of muscle or tendon): severe pain, swelling, extensive bruising, and often complete loss of movement

Pathology Connection: Strains and Tears (cont’d) Treatment: varies with severity of injury Strains In first 72 hours, PRICE therapy: Protection, Rest, Ice, Compression, Elevation After first 72 hours: gradual increase in activity and/or physical therapy, application of heat Pain relievers (like acetaminophen or ibuprofen)

Muscles and Muscle Fiber Structure Muscles are composed of many FIBERS that are arranged in bundles called FASCICLES

Individual muscles are separated by FASCIA, which also forms tendons

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 Muscle Fiber Endomysium Perimysium Epimysium

Epimysium Perimysium Endomysium

Muscles / Cells Sarcolemma = muscle fiber membrane Sarcoplasm = inner material surrounding fibers  (like cytoplasm) Sarcoplasmic Reticulum – transport, store, and release calcium ions in the muscle cell. Myofibrils  = individual muscle fibers,  made of myofilaments

Functional unit of the Muscle Each muscle cell is elongated fiber known as muscle fiber, can be up to 12 inches in length Several muscle fibers can be bundled together to form specific muscle segment Each muscle fiber composed of several myofibrils

Nucleus Sarcolemma Mitochondrion Sarcoplasm Myofibril

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

Functional Unit of the Muscle Sarcomeres: functional contractile units of each fiber Each has two types of threadlike structures called thick and thin myofilaments Thick myofilaments made up of protein myosin Thin myofilaments made up of protein actin 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)

Sarcomeres: functional contractile units of each fiber Sarcomere has actin and myosin filaments arranged in repeating units separated from each other by dark bands called Z lines which give striated appearance to skeletal muscle Z lines are borders of each sarcomere

It is important to remember the hierarchy fasicles myofibrils myofilaments actin myosin

How Muscles Work with the Nervous System

The neurotransmitter that cross the gap is ACETYLCHOLINE ACH is broken down by CHOLINESTERASE

The neurotransmitter that crosses the gap is ACETYLCHOLINE. This is what activates the muscle. Acetylcholine is stored in vesicles

SLIDING FILAMENT THEORY (MODEL) The theory of how muscle contracts is the sliding filament theory. The contraction of a muscle occurs as the thin filament slide past the thick filaments. What is needed: ATP Calcium Myosin & Actin Acetylcholine Cholinesterase

Contraction of muscle causes two types of myofilaments to slide toward each other and shorten each sarcomere, and therefore entire muscle Muscle contraction requires temporary connections of cross-bridges formed between myosin head and actin; these pull sarcomere together

ATP and Calcium Energy needed for contraction and relaxation; comes from adenosine triphosphate (ATP), which help myosin heads form and break cross-bridges with actin Calcium stored away from actin and myosin in sarcoplasmic reticulum (SR) during relaxation of muscle During contraction, calcium released from SR and causes actin, myosin, and ATP to interact, which causes contraction; when calcium leaves muscle and returns to SR, cross-bridge attachments are broken and muscle relaxes

When nervous system tells muscle to contract, signal causes muscle fiber to open sodium ion channels Sodium ions flow into muscle fiber, exciting it When muscle becomes excited, calcium released from SR It is calcium that causes muscles to contract Calcium is then pumped back into SR

Sliding Filament Handout (additional)

Energy Source -ATP is produced by CELLULAR RESPIRATION which 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. Threshold Stimulus 2. All-or-None Response 3. Motor Unit 5. Recruitment 6. Muscle Tone 7. Muscular Hypertrophy 8. Muscular Atrophy 9. Muscle Fatigue 10. Muscle Cramp 11.  Oxygen Debt

Threshold Stimulus All-or-None Response Minimal strength required to cause a contraction  Motor neuron releases enough acetylcholine to reach threshold All-or-None Response Fibers do not contract partially, they either do or don't

Motor Unit Recruitment Muscle Tone The muscle fiber + the motor neuron   The muscle fiber  +   the motor neuron  Recruitment more and more fibers contract as the intensity of the stimulus increases Muscle Tone Sustained contraction of individual fibers, even when muscle is at rest

Hypertrophy - muscles enlarge (working out or certain disorders)   Atrophy - muscles become small and weak due to disuse

Muscle Cramp - a sustained involuntary contraction Muscle Fatigue -  muscle loses ability to contract after prolonged exercise or strain Muscle Cramp  -  a sustained involuntary contraction Oxygen Debt  -  oxygen is used to create ATP, -- not have enough oxygen  causes Lactic Acid to accumulate in the muscles → Soreness                                            *See Magic School Bus 

11. Origin and Insertion Origin = the immovable end of the muscle Insertion = the movable end of the muscle The biceps brachii has two origins (or two heads).

What is rigor mortis? A few hours after a person or animal dies, the joints of the body stiffen and become locked in place. This stiffening is called rigor mortis. Depending on temperature and other conditions, rigor mortis lasts approximately 72 hours. The phenomenon is caused by the skeletal muscles partially contracting. The muscles are unable to relax, so the joints become fixed in place.

What is tetanus? Tetanus causes cholinosterase to not break down the acetylcholine in the synapse.  This results in a person's muscles contracting and not relaxing. A tetanus shot must be administered shortly after exposure to the  bacteria. Once you develop tetanus, there is no cure.