The Muscular System The Muscular System Myology The

The Muscular System

The Muscular System · Myology = The study of muscles · Functions of muscle tissue: · Move the body by pulling bones · Maintain body positions by continuous muscle contraction (ex. Neck holding up the head) · Move substances within the body such as blood, reproductive cells and food. · Produce heat- muscle contraction generates thermal energy · Regulate organ volume (controls opening from the bladder, stomach, and rectum)

There are 3 types of muscle tissue · Skeletal · Smooth · Cardiac

Skeletal Muscle Characteristics · Most are attached by tendons to bones · Cells- called muscle fibersare multinucleate · Striated – have visible banding · Voluntary – subject to conscious control · Cells are surrounded and bundled by connective tissue = great force, but tires easily

Smooth Muscle Characteristics · Has no striations · Spindle-shaped cells · Muscle fibers have a single nucleus · Involuntary – no conscious control · Found mainly in the walls of hollow organs and structures · Slow, sustained and tireless

Cardiac Muscle Characteristics · Has striations · Muscle fibers branch and contain a single nucleus · Joined to another muscle cell at an intercalated disc · Involuntary · Found only in the heart · Steady pace!

Naming of Skeletal Muscles · Location of the muscles origin and insertion · Example: sterno (on the sternum) · Shape of the muscle · Example: deltoid (triangular) · Action of the muscle · Example: flexor and extensor (flexes or extends a bone)

Naming of Skeletal Muscles · Direction of muscle fibers · Example: rectus (straight) · Relative size of the muscle · Example: maximus (largest)

Naming of Skeletal Muscles · Location of the muscle · Example: many muscles are named for bones (e. g. , temporalis) · Number of origins · Example: triceps (three heads)

Connective Tissue Wrappings of Skeletal Muscle · Epimysium – covers the entire skeletal muscle · Fascia – on the outside of the epimysium

Connective Tissue Wrappings of Skeletal Muscle · Perimysium – around a fascicle (bundle of fibers) · Endomysium – around single muscle fiber (cell)

Microscopic Anatomy of Skeletal Muscle · Sarcolemma – specialized plasma membrane of a muscle fiber · Sarcoplasm- cytoplasm of the muscle fiber · Sarcoplasmic reticulum – network of tubules in the muscle fiber that store calcium ions for muscle contraction · Myoglobin- pigment in the sarcoplasm that stores oxygen

Microscopic Anatomy of Skeletal Muscle · Myofibril- Cylindrical structure within a muscle fiber · Bundles of thick and thin filament (makes muscle striated) · I band = light band (thin) · A band = dark band (thick)

Microscopic Anatomy of Skeletal Muscle · Sarcomere · Contractile units of a muscle fiber which are separated by Z discs

Microscopic Anatomy of Skeletal Muscle · Organization of the sarcomere · Thick myofilaments = myosin filaments= have extensions called “heads” · Thin myofilaments = actin filaments · Myosin and actin somewhat overlap · Actin are anchored at the z-disc

Quick Review 1. For cardiac, smooth and skeletal muscle, indicate if they are: striated or not; voluntary or not; multinucleated or not 2. What are the differences in shape between the different muscle cells? 3. What is the outermost connective tissue layer of skeletal muscle? 4. What are bundles of muscle fibers called? 5. What tissue layer surrounds each muscle fiber?

Quick Review cont…. . 6. What is the plasma membrane of a muscle fiber called? 7. What is the cylindrical unit inside a muscle cell? 8. What are the 2 myofilaments in a muscle fiber? 9. What is another term for the thick band? 9. What is another term for the thin band? 10. What is the region between z-discs called? 11. What is the region where the actin filaments are anchored? 12. Where are calcium ions stored in a muscle fiber?

The Sliding Filament Theory of Muscle Contraction 1. Activation by a nerve causes myosin heads to attach to binding sites on the adjacent thin filament. 2. Myosin heads flex inward then reach ahead to attach to the next site of the thin filament. 3. This continued forward grabbing causes a sliding of the myosin along the actin. 4. The result is that the sarcomere shortens, thus shortening the entire muscle. 5. Myosin heads attach and detach to actin due to ATP (energy stored in mitochondria) and Ca+ (stored in sarcoplasmic reticulum).

Nerve Stimulus to Muscles · Neuromuscular junctions – Where motor neurons (nerve cells) and muscle fibers associate

Nerve Stimulus to Muscles · Synaptic cleft – gap between nerve and muscle · Nerve and muscle do not make contact · Area between nerve and muscle is filled with fluid

Transmission of Nerve Impulse to Muscle · Neurotransmitter – chemical released by a nerve to communicate with another nerve or muscle · The neurotransmitter for skeletal muscle is acetylcholine (ACh) · ACh attaches to receptors on the sarcolemma · Sarcolemma allows sodium (Na+) to enter the muscle fiber · Sodium rushing into the cell initiates muscle contraction by causing the release of Ca+ from the sarcoplasmic reticulum.

Contraction of a Skeletal Muscle • What happens if NMJs are blocked? – No muscle contraction!! • Why would someone want to purposely block NMJs? – No muscle contraction= No wrinkles!! • What is a drug that does that? – BOTOX!!

Botox “before” and “after”

What causes a muscle to relax after contraction? • The enzyme acetylcholinesterase rapidly breaks down acetylcholine in the synaptic cleft, preventing it from continuing to signal to the muscle fiber. • Ca 2+ ions are transported from the sarcoplasm back into the sarcoplasmic reticulum for storage. • The actin filaments slide back to their relaxed positions

Muscle Fatigue and Oxygen Debt · Muscle fatigue is the inability to contract after prolonged activity. · What are some possible reasons for why this happens? · The common reason for muscle fatigue is oxygen debt · Oxygen debt is the amount of oxygen taken into the body after exercise to “repay” what was taken from the myoglobin.

Muscle Fatigue and Oxygen Debt · Under anaerobic (low oxygen) conditions (during exercise when not taking in enough oxygen), muscle cells go through fermentation to produce energy. This results in a build up of lactic acid in the muscles. This is a very inefficient energy producing process. · Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less. · The body uses oxygen debt to remove lactic acid and produce more ATP.

Muscles and Body Movements · Movement is attained due to a muscle moving an attached bone Figure 6. 12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide

Muscles and Body Movements · Muscles are attached to at least two points · Point of Origin – attachment to an immovable bone · Point of Insertion – attachment to a moveable bone · Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6. 12 Slide

Types of Muscles · Prime mover – muscle with the major responsibility for a certain movement · Antagonist – muscle that opposes or reverses a prime mover · Synergist – muscle that aids a prime mover in a movement and helps prevent rotation · Flexor- bends a joint · Extensor- straightens a joint

Example: · Biceps curl· Prime mover- Biceps brachii · Antagonistic muscle- Triceps brachii · Synergist muscle- Pectoralis major · Flexor- Biceps brachii · Extensor- Triceps brachii

Disorders relating to the Muscular System • Muscular Dystrophy: inherited, muscle enlarge due to increased fat and connective tissue, but fibers degenerate and atrophy • Duchenne MD: lacking a protein to maintain the sarcolemma • Myasthemia Gravis: progressive weakness due to a shortage of acetylcholine receptors