Muscle Types, Anatomy, Contraction, and Motor Units

Flashcards covering muscle types (skeletal, cardiac, smooth), skeletal muscle anatomy, sliding filament theory of muscle contraction, motor units, and degrees of muscle contraction.

Skeletal muscle

Moves the body, maintains body posture and body temperature

Cardiac muscle

Contracts the heart to pump blood throughout the body

Smooth muscle

Aids organ systems like the gastrointestinal, digestive, and circulatory system

Epimysium

Protective sheath around the skeletal muscle

Perimysium

Protective sheath around the muscle fascicles

Endomysium

Protective sheath around the muscle fibers

Sarcolemma

Cellular membrane of the muscle fiber

Sarcoplasm

Cytoplasm that holds the myofibrils

Sarcomere

Functional unit of skeletal muscle cells (muscle fibers) located in the myofibrils

Neuromuscular Junction (NMJ)

Connection between a motor neuron and a muscle cell

Troponin

Regulatory protein that calcium binds to when initiating cross-bridge cycling

Z lines

End of sarcomeres; thin actin filaments

M line

Middle of sarcomere; thick myosin filaments

I band

Only actin present

H zone

Only myosin present

A band

Spans the length of myosin; actin and myosin overlap

Motor unit

All the muscle fibers innervated by one neuron

Small motor units

Only a few muscle fibers innervated by a motor neuron; used for precise movements

Large motor units

Many muscle fibers innervated by a motor neuron; used for powerful movements

Wave summation (temporal summation)

Motor unit is depolarized during relaxation

Motor unit summation

Different motor units are stimulated at different times to create the intended amount of muscle contraction

Size principle of motor unit recruitment

Motor units are recruited from smallest to largest

Tetanus

Muscle fibers reach their maximum tension and there is a lack of relaxation

Muscle tone

A muscle’s default state of tension; tension is upheld by weak and involuntary twitches in small motor unit groups