Extra information

Supraspinatus

rotator-cuff muscle above the spine of the scapula; helps with abduction of the arm

Infraspinatus

rotator-cuff muscle below the spine of the scapula; helps with external rotation

Teres minor

small rotator-cuff muscle below the infraspinatus

Subscapularis

rotator-cuff muscle on the anterior surface of the scapula; helps with internal rotation

Pronator teres

forearm muscle involved in pronation

Teres major

muscle near the lower scapula and upper arm

Coracobrachialis

upper-arm muscle connecting the coracoid region to the humerus

Rectus abdominis

straight abdominal muscle; vertical muscle on the front of the abdomen

Extrafusal muscle fibers

regular skeletal muscle fibers that contract to produce muscle force

Intrafusal muscle fibers

specialized muscle fibers inside the muscle spindle

Alpha motor neuron

motor neuron that stimulates extrafusal muscle fibers to contract

Type I muscle fibers (slow)

lots of mitochondria, high capillary density, much myoglobin, smaller fibers, slow contractions, fatigue-resistant

Type II muscle fibers (fast)

fewer mitochondria, lower capillary density, less myoglobin, larger fibers, fast and powerful contractions, fatigue more quickly