Muscular System

Striated (skeletal)

Composed of fascicles of several muscle fibers. Cells have multiple nuclei

What are muscle fibers made of?

bundles of myofibrils of actin and myosin myofilaments.

Sarcomeres

Actin and myosin of the myofilaments are arranged into contractile units; gives the muscle a striated appearance

Cardiac

Striated with branched cells, adjacent cells are connected with intercalated discs that contain gap junctions which enable the heart to function as a unit. Cells have one nuclei

Where are cardiac muscles found?

Only in the hearts of vertebrates.

Do cardiac muscles fatigue?

No

Neuromuscular Junction

Where somatic nerves synapses with muscle fibres

Motor Unit

A group of fibres controlled by one nerve. More precise movements requires more motor units, less precise movements requires more fibres per neuron.

Muscles are

antagonistic

Origin

attachement to bone that is stationary

Insertion

attachement to bone that moves

Isotonic

muscle tension doesn’t change, size does, ex. lifting weights

Isometric

Muscle tension changes, muscle size does not, ex. holding an object at your side

Arthropods only have \______ muscles

striated

Twitch

A quick contraction and then relaxes

Summation

Created when a second impulse is delivered immediately after the first

Increasing frequency of impulses \________ the relaxion period between twitches and \_______ the strength of a contraction

decreases, increases

Tetanus

A smooth sustained contraction which is achieved after a particular frequency of stimuli

Slow-twitch

Lots of capillaries, many mitochondria, numerous respiratory enzymes, lots of myoglobin

Red fibers

More myoglobin, operates aerobically and can sustain activity for a long time without fatigue

Fast-twitch

Fewer capillaries and mitochondria, less myoglobin

White fibres

Less myoglobin, can operate anaerobically and are adapted for rapid generation of power, lack endurance

A band (dark)

is overlapping thick (myosin) and thin (actin) filaments.

H band

shortens as myosin and actin move along one another also the thick filaments only.

Z line

is the end of each sarcomere.

I band (light)

is thin (actin) filaments only

________ leaves nerves and binds to receptors in muscles. This opens _________ ion channels which spread into the cell. T-tubules release _________ion which binds to troponin exposing____________binding sites on actin and allows muscles to contract

Acetylcholline, sodium, calcium, myosin