Functions and Types of the Muscular System

Main functions of the muscular system

Motion, posture, heat production, and joint stabilization

Role of muscles in motion

Muscles contract to create movement

Muscles and posture

They stabilize the body's position

Muscles and temperature regulation

Muscle contractions generate heat

Muscles and joint stabilization

Muscles provide support and alignment to joints

Skeletal muscle

Attached to bones, striated, and voluntary

Cardiac muscle

Found only in the heart and is involuntary

Smooth muscle

Found in walls of hollow organs and is non-striated

Epimysium

Connective tissue that covers the whole muscle organ

Perimysium

Connective tissue that surrounds a fascicle

Endomysium

Connective tissue that surrounds an individual muscle fiber

Tendon

Connects muscle to bone

Sarcolemma

Plasma membrane of a muscle cell

Sarcoplasm

Cytoplasm of a muscle cell

Glycosomes

Stores glycogen in muscle cells

Myoglobin

Stores oxygen in muscle cells

Myofibrils

Rod-like structures that make up 80% of a muscle cell's volume and exhibit striations

Sarcomere

Functional unit of a myofibril

Dark A bands and light I bands

Bands that form the striations on myofibrils

Myofilaments

Filaments that make up myofibrils (thick and thin)

Myosin

Thick filaments that span the A band

Actin

Thin filaments that span the I band and part of A band

Z disc

Anchors thin filaments and defines sarcomere limits

H zone

Region where thick and thin filaments do not overlap

Myomesin protein

Holds adjacent thick filaments together at the M line

Cross-bridges

Myosin heads attaching to actin during contraction

Direct phosphorylation by creatine phosphate

Method 1 of ATP regeneration

Aerobic respiration

Method 2 of ATP regeneration

Anaerobic fermentation

Method 3 of ATP regeneration

Slow (Red) - Postural muscles

Skeletal muscle fiber that is slow-twitch and red

Fast (White) - Fingers and eyes

Skeletal muscle fiber that is fast-twitch and white

Intermediate - Soleus

Skeletal muscle fiber that is intermediate in function and color

Prime mover

Performs main movement

Antagonist

Opposes the prime mover

Synergist

Assists the prime mover

Treppe

Increasing contractions with repeated stimulation

Muscle twitch

Single, brief contraction response to stimulus

Incomplete tetanus

Unfused contractions; tension builds with brief relaxation

Complete tetanus

Sustained contraction with no relaxation

Isotonic contraction

Muscle shortens and moves a load

Isometric contraction

Muscle generates tension but does not change length

Features of smooth muscle

Spindle-shaped, no striations, slow contractions, involuntary, uses calmodulin

Smooth muscle contraction

Calcium → calmodulin → kinase activation → phosphorylates myosin → contraction

Calcium removal in smooth muscle

Calcium reabsorbed or pumped out of the cell

Multi-unit smooth muscle

Located in large airways, arteries, iris; precise movements; few gap junctions

Single-unit smooth muscle

Sheets that contract as a unit; may contract spontaneously

Characteristics of cardiac muscle

Self-exciting, intercalated discs, t-tubules in diads, uses mostly extracellular calcium