A&P Chapter 7

Primary functions of muscles

Primary functions of muscles

Move the skeleton, maintain posture and body position, support soft tissues, maintain body temperature, and guard entrances and exits

Move the skeleton

Muscles move bones and provide facial expressions

Maintain Posture

The ability to support the body against gravity

Maintain Body Position

Muscles, tendons, and ligaments help to stabilize poorly articulating joints

Maintain Body Temperature

Mitochondria makes ATP from glucose and oxygen; skeletal muscles use ATP for contractions and create heat as a by-product

How is the excess heat removed?

Blood vessels take heat away during circulation

Support soft tissues

Muscles support the weight of our visceral organs (in the abdominal wall and pelvic cavity floor) and shield our internal tissues from injury

Guard entrances and exits

Encircle openings of the digestive and urinary tracts. Gives us voluntary control over swallowing, defecating, and urinating

Epimysium

the connective tissue (collagen fibers) that covers the outside of the entire muscle. Separates muscles from surrounding tissues and organs

Perimysium

Divides the skeletal muscles into compartments. Wraps around a fascicle, contains fibers, nerves and blood vessels

Fascicle

Several muscle fibers bundled together

Endomysium

Repair damaged muscle tissue. Individual muscle cells (myofibril) in the fascicle are wrapped by this tissue. Contain capillaries that supply blood to the muscle fibers and neurons

Endomysium and Perimysium come together at the end of each muscle to form

Tendons (connect muscle to bone)

Sarcolemma

Flesh hulk, the plasma membrane of a muscle cell

Sacroplasm

Cytoplasm of the muscle cell

Transverse tubules/ t-tubules

Extensions of the sarcolemma that extend into the cell and carry nervous signals

Terminal Cisterna

Endoplasmic reticulum of the muscle that store calcium

Tubules extend into the cell and connect with portions of the sarcoplasmic reticulum. Nervous signals carried by t-tubules cause

Calcium to be released from the SR

Myofibril

Long organelles found inside the muscle cell. Contractile units that shorten the muscle during contraction. Banding pattern (striations)

Sarcomere

Unit of the myofibril that runs from one z line to the next z line

A band (Dark)

Part of the sarcomere that contains all of the thick filaments and only a portion of the thin filaments

I band (light)

Part of the sarcomere that contains the z line and only thin filaments

Sliding filament theory I band

It shortens due to thick filaments invading

Actin

Thin filaments. Troponin and tropomyosin anchored here

Myosin

Thick filaments. It’s heads attach to an active site on thin filaments during muscle contraction

H zone

Within the A band, only thick filaments

Sliding Filament Theory H zone

During muscle contraction it decreases (eventually disappears) due to the thin filaments invading

Z line (disc)

Zig-zag shaped line/ membrane where thick filaments are attached

Sliding Filament Theory Z line

Slides closer together (shortens) due to the myosin heads attaching to the thin filaments and pulling them in

Microfilaments

Long proteins made primarily of actin or myosin

Tropomyosin

These proteins coil over actin to prevent myosin heads from attaching to the active sites on actin

Troponin

Protein connected to tropomyosin. Calcium ions bind to it and allow tropomyosin to move and expose the active sites to allow myosin heads to attach to actin

Sarcoplasmic Reticulum

Wraps around the myofibril and releases calcium ions into the sarcoplasm to begin muscle contractions

This area causes both contraction and relaxation

Motor unit

The motor neuron and all the skeletal muscle cells it stimulates

Motor neuron (nerve cell)

Stimulates skeletal muscles

Neuromuscular junction

Where individual axon terminals stimulate one muscle cell. Nerve cells nearly contact the sarcolemma here

Synaptic cleft of the neuromuscular junction

The gap between the sarcolemma of the muscle cell and the axon terminals (synaptic knobs) of the nerve cell

Neurotransmitter released during contraction

Acetylcholine

After calcium ions diffuse into the sarcomere and muscle contraction occurs, the SR reabsorbs calcium causing:

Muscle relaxation

Sliding filament theory A band

Stays the same

Sliding filament theory sarcomere length

shortens or decreases