Muscular System

Skeletal Muscle

Attached to bones across the skeleton, elongated, cylindrical, multinucleate fibers with prominent transverse striations. Voluntary. Primary function is body movement, posture, facial expression and heat production as a byproduct of cellular metabolism and muscle contraction.

Cardiac Muscle

Walls of the heart (myocardium). Short branching, striated cells connected by intercalated discs ( containing desmosomes and gap junctions); usually uninucleated. Involuntary because of the automatic nervous system and pacemaker cells. Its primary function is to pump blood through the cardiovascular system.

Smooth Muscle

Walls of hollow internal organs ( stomach, intestines, blood vessels, uterus). Short, spindle-shaped, non-striated cells, each with a single central nucleus.Involuntary (regulated by the autonomic nervous system, hormones, and local stretching). Moving substances through internal passageways (peristalsis, vasoconstriction, digestion).

Excitability of Skeletal Muscle

Ability to respond to chemical or electrical stimuli by producing action potentials.

Contractility of Skeletal Muscle

Ability to shorten actively and generate tension when stimulated.

Extensibility of Skeletal Muscle

Ability to stretch without being damaged.

elasticity of Skeletal Muscle

Ability of muscle fibers to return to their original resting length after stretching or contracting.

Epimysium of Skeletal Muscle

Dense irregular connective tissue sheath surrounding the entire skeletal muscle.

Perimysium of Skeletal Muscle

Connective tissue layer dividing the muscle into internal compartments called fascicles, housing blood vessels and nerves.

Endomysium of the Skeletal Muscle

Fine, delicate areolar connective tissue surrounding individual muscle fibers(cells), providing electrical insulation and capillary support.

Myofilaments of the Skeletal Muscle

Contractive protein filaments inside myofibrils. The two primary proteins are Actin (thin filaments) and Myosin (thick filaments)

Orgin

The fixed, stationary attachment point of a muscle(usually more proximal or medial)

Insertion

the movable attachment point attached to the bone that pulls closer to the organ during contraction (usually more distal or lateral )

Body(belly)

the thick, central, contractile portion of the muscle between the organ and insertion.

Neuromuscular Junction (NMJ)

Specialized intercellular synapse where a motor neurons axon terminal meets the sarcolemma( plasma membrane) of a skeletal muscle fiber.t is the critical site where electrical nerve signals are converted into chemical signals (acetylcholine, ACh), triggering an action potential across the muscle fiber membrane to initiate contraction.

Motor Unit

A single motor neuron and all the skeletal muscle fibers it innervates.

Small Motor Unit

provide fine control( eye muscles )

Large Motor Units

Provide powerful, gross movements (thigh muscles)

Sliding Filament Mechanism/ Contraction Process

1. A nerve impulse reaches the Neuromuscular junction, releasing Acetylcholine, ACh, into the synaptic cleft.

2. ACh binds to receptors on the sarcolemma( plasma membrane) , generating a muscle action potential that travels down T-tubules.

3. Calcium ion Ca2+ are released from the sarcoplasmic reticulum into the sarcoplasm(cytoplasm of a muscle cell or muscle fiber )

4. Calcium finds to troponin, shifting tropomyosin and exposing binding sites on actin

5. Myosin heads attach to actin, forming cross bridges and pulling the thin filaments toward the center of the sarcomere(shorten the muscle)

Isotonic skeletal contraction

Tension remains constant while muscle length changes, resulting in body movement(lifting weights)

Concentric Skeletal Muscle contraction

Muscle shortens as it contracts

Eccentric Skeletal muscle contraction

Muscle lengthens while maintains tension

Isometric Skeletal Muscle Contraction

The muscle generates tension, but its length remains unchanged because the load is too heavy to move. (pushing leg against wall)

ATP Storage

Muscle cells store only a small amount of ATP, meaning ATP must be continuously regenerated

Creatine Phosphate System

Provides immediate, rapid energy (about 15 seconds) by transferring a high-energy phosphate to ADP.

Anaerobic Cellular respiration (Glycolysis)

Breaks down glucose without oxygen to produce ATP quickly, generating lactic acid as a byproduct( supports short burst of high intensity activity)

Aerobic Cellular Respiration

Requires oxygen and occurs in the mitochondria; breaks down glucose, fatty acid , or amino acids to produce high yields of ATP for long term endurance activities.

Muscle Hypertrophy

Muscle fibers increase in diameter and size (rather than multiplying in number). This occurs because muscle cells synthesize more intracellular structural proteins (myofibrils, particularly actin and myosin), leading to larger muscle bellies.

Increased Strength and Power

The recruitment of motor units becomes more efficient, and the muscle develops a greater capacity to generate high-tension forces.

Agonist(Prime Mover)

The muscle primarily responsible for producing a specific movement .

Antagonist

A muscle that opposes or reverses the movement of the the prime mover

Synergist

Helps the prime mover by adding extra force or stabilizing nearby joints

Fixator

A synergistic that holds a bone firmly in place so another muscle can act efficiently

Flexion

Extension

Abduction

adduction

Dorsiflexion

Plantar Flexion

Masseter

Rotator Cuff

Respiration Muscles

Nervous System

Initiates, coordinates, and regulates all muscle contractions.

Skeletal System:

Provides the rigid levers and structural framework for muscles to pull against.

Cardiovascular and Respiratory Systems

Supply working muscles with a continuous flow of oxygen and nutrients while removing carbon dioxide and metabolic waste.

Myasthenia Gravis

An autoimmune disease where the immune system produces antibodies that bind to and block ACh receptors at the neuromuscular junction. Receptors are destroyed via endocytosis, resulting in insufficient muscle stimulation, severe muscle weakness, and rapid fatigue (often starting in facial and eye muscles).

Intramuscular Injections

Delivered directly into large, well-vascularized skeletal muscle bellies (such as the deltoid, vastus lateralis, or gluteus medius) for rapid systemic absorption into the bloodstream.

Orgin

A muscle’s attachment to a stationary bone

is called its

Actin, myosin

Which two proteins compose myofilaments

Heat production

The primary functions of muscles are movement, posture (muscle tone), and

Neuromuscular Junction

The point of contact between a nerve ending and the muscle fiber is called the

Isometric

When the muscle contracts and no movement results, it is called a(n) _____ contraction.

Masseter

Which of these muscles function in closing

the jaw?

Abduction

_____ means moving a part away from the midline of the body, such as moving your arm out to the side

Myasthenia gravis

Identify the muscular disease characterized by the immune system attacking muscle cells at the neuromuscular junction.

Strain

An Injury to a muscle or a tendon (the fibrous tissue that attaches muscle to bone) happens due to overstretching or tearing muscle fibers, often from heavy lifting or sudden movements.

Sprain

An injury to a ligament (the tough band of fibrous tissue that connects bone to bone at a joint). It usually happens when a joint is forced past its normal range of motion, such as rolling an ankle.

Angiogenesis

The formation of a denser network of microscopic blood vessels (capillaries) around muscle fibers, significantly improving the delivery of oxygen and nutrients and the removal of metabolic wastes.

Increase in Mitochondria

Muscle fibers increase the number and size of their mitochondria, boosting the muscle's capacity for aerobic cellular respiration and ATP production.

muscle atrophy

a lack of exercise or prolonged immobilization

Explain why muscle cells have only a little ATP in storage.

storing just a little ATP keeps cells light and stable, relying on rapid production systems to match energy demand on the fly.