Muscle structure

Muscle

Little mouse

Makes up nearly haft of the body mass

contractibility

Myofilaments are responsible for shortening of

muscles cells

actin, and myosin

what are the two more common myofilaments

Excitability

Nerve signals excite muscle cells, causing electrical impulses to travel along the sarcolemma

Extensibility

Contraction of a skeletal muscle stretches the opposing muscle, Smooth muscle is stretched by substances within that hollow organ.

Food in stomach; urine in urinary bladder

Elasticity

recoils after being stretched

Myo, Sarco

Muscle, flesh

Sarcolemma

muscle membrane of a muscle cell

Sarcoplasm

Cytoplasm of a muscle cell

Function of muscle

Skeletal muscle: Moves body by moving the bones

Smooth muscle—squeezes fluids and other substances through hollow organs

Open and close body passageways Sphincters function as valves, Open to allow passage of a substance, Contract to close the passageway

Maintain posture and stabilize joints

Heat generation

Skeletal muscle tissue

Packaged into skeletal muscles

Makes up 40% of body weight

Cells are striated

Skeletal muscle is innervated by voluntary

division of the nervous system

Cardiac muscle tissue

Occurs only in the walls of the heart

• Cells are striated

• Contraction is involuntary

Smooth muscle tissue

Occupies the walls of hollow organs

• Cells lack striations

• Innervated by involuntary division of the

nervous system

An organ

Each Muscle is

Epimysium

dense regular connective tissue surrounding entire muscle

Perimysium

surrounds each fascicle group of muscle fibers

Endomysium

A fine sheath of connective tissue wrapping each muscle cell

Is connective tissue connected with tendons?

Connective tissue sheaths are continuous with

tendons

Muscle attachment

Most skeletal muscles run from one bone to another

Origin = less movable

insertion = more movable attachment,

Fleshy attachments

Connective tissue (CT) fibers are short

Indirect attachments

Connective tissue (CT) forms a tendon or aponeurosis

The skeletal muscle fiber (muscle cells)

• Fibers are long and cylindrical

• Are huge cells—diameter is 10–100 µm

• Length—several centimeters to dozens of centimeters

cell are multinucleate

Myofibrils

• Are long rods within cytoplasm

• Make up 80% of the cytoplasm

• Are a specialized contractile organelle found in muscle tissue

sarcomeres

Are a long row of repeating segments (functional unit of skeletal muscle tissue)

Z discs

boundaries of each sarcomere

Thin (actin)

filaments—extend from Z disc toward the center of the sarcomere

Thick (myosin)

filaments—located in the center of the sarcomere

A bands

full length of the thick filament, Includes inner end of thin filaments

H zone

center part of A band where no thin filaments occur

M line in center of H zone

Contains tiny rods that hold thick filaments together

I band

region with only thin filaments, Lies within two adjacent sarcomeres

Sarcoplasmic reticulum

A specialized smooth ER

Interconnecting tubules surround each myofibril

Contains calcium ions—released when muscle is stimulated to contract

terminal cisterns

Some tubules form cross-channels

Cisterns occur in pairs on either side of a

t tubule

T tubules

deep invaginations of sarcolemma

Triad

T tubule flanked by two terminal cisterns