muscle tissues

Muscle Tissue Types

Skeletal, Cardiac, and Smooth muscle

Skeletal Muscle

Voluntary, striated, long cylindrical cells, multinucleated, attached to bones

Cardiac Muscle

Involuntary, striated, short branched cells, single nucleus, connected by intercalated discs

Smooth Muscle

Involuntary, nonstriated, spindle-shaped, single nucleus, found in walls of hollow organs

Voluntary Muscle

Muscle that is consciously controlled (skeletal muscle)

Involuntary Muscle

Muscle that contracts without conscious control (cardiac and smooth muscle)

Excitability

Ability to respond to electrical stimulation

Contractility

Ability of cells to shorten with force

Extensibility

Ability to be stretched beyond resting length

Elasticity

Ability to return to resting length after contraction or stretch

Functions of Skeletal Muscle

Movement, posture, support soft tissues, guard body openings, maintain temperature, store nutrients

Prefix 'myo-' or 'sarco-'

Means 'muscle'

Epimysium

Connective tissue surrounding entire muscle

Perimysium

Connective tissue surrounding fascicles (bundles of fibers)

Endomysium

Connective tissue surrounding each muscle fiber

Tendon

Bundle of collagen fibers attaching muscle to bone

Aponeurosis

Sheet of collagen fibers attaching muscle to bone

Myosatellite Cells

Stem cells that repair muscle damage

Skeletal Muscle Fiber

Long, cylindrical, multinucleated cell; also called a muscle fiber

Myofibril

Long protein cords inside muscle fibers that contract

Myofilaments

Actin and myosin proteins that make up myofibrils

Sarcolemma

Cell membrane of a muscle fiber

Sarcoplasm

Cytoplasm of a muscle fiber

T-tubule

Tube extending from sarcolemma into the muscle fiber; carries electrical impulses

Sarcoplasmic Reticulum (SR)

Stores and releases calcium ions (Ca²⁺)

Terminal Cisternae

Enlarged areas of SR next to T-tubules

Triad

One T-tubule + two terminal cisternae

Thick Filament

Made mostly of myosin

Myosin

Thick filament protein with heads that bind actin to produce contraction

Thin Filament

Made mostly of actin, plus tropomyosin and troponin

Actin

Protein in thin filament with active sites for myosin binding

Tropomyosin

Protein that covers actin’s active sites to prevent binding

Troponin

Protein that controls position of tropomyosin; binds to calcium

Sarcomere

Smallest functional (contractile) unit of muscle fiber

Z-Line (Z-disc)

Boundary between sarcomeres

A Band

Dark band; thick filaments (and overlapping thin filaments)

I Band

Light band; thin filaments only

M Line

Center of A band; holds thick filaments together

H Zone

Lighter area around M line; thick filaments only, no overlap

Zone of Overlap

Area where thick and thin filaments overlap

Striations

Alternating light (I) and dark (A) bands in skeletal and cardiac muscle

Muscle Hierarchy

Myofilaments → Sarcomere → Myofibril → Muscle Fiber → Fascicle → Muscle

Myoblasts

Embryonic cells that fuse to form muscle fibers

Voluntary Control

Muscle movement initiated by the nervous system (skeletal muscle)

Intercalated Discs

Specialized junctions in cardiac muscle that allow electrical connection between cells

Autorhythmic

Cardiac muscle’s ability to contract on its own without neural stimulation