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MUSCULAR SYSTEM
DO NOT WRITE ON THIS PAPER!
The design and location of muscles allow efficient performance of complex motions in vertebrates.
Muscles are usually arranged on the skeleton in opposing pairs. Motion produced by muscular contraction also
depends on the design of the skeletal system. When muscles contract, they use bones for resistance and motion.
The end of the muscle attached to the bone that moves during a contraction of the muscle is called the muscle
insertion. The end attached to the bone that doesn’t move during the contraction is the muscle origin.
We will study nine superficial muscles of the rat. Read over the origin, insertion and action of them but
you will only need to know the location of the muscles. Your quiz will cover the first 7, and the last 2 muscles will
be extra credit.
1) Biceps – located on the anterior surface of the humerus (upper arm)
Origin: scapula (shoulder blade)
Insertion: radius (lower arm)
Action: to flex the lower arm
2) Triceps – located on the sides and back of upper arm
Origin: humerus and scapula
Action: extend lower arm
Insertion: elbow
3) Trapezius – located on the upper back
Origin: cervical vertebrae (backbone)
Insertion: scapula
Action: moves the scapula (shoulder blade) dorsally
4) External Oblique – covers the sides of the abdominal cavity from the hip to the rib cage
Origin: posterior ribs
Insertion: midline and pelvis
Action: retain the internal organs with the rectus abdominus, forming the body wall
5) Pectoralis major – located as a broad, fan-shaped muscle of anterior chest
Origin: sternum (breast bone)
Insertion: humerus
Action: draws forelimb (front legs/arms) toward the chest
6) Rectus abdominus – located as two parallel muscles in the mid-ventral area
Origin: pelvis
Insertion: ribs, clavicle, sternum
Action: compresses abdominal wall and supports viscera (internal organs)
7) Gastrocnemuis – the bulk of the calf muscle of the lower leg
Origin: end of femur (at the knee)
Insertion: heel by Achilles tendon
Action: extends the foot
8) Gluteus maximus (called Gluteus superficialis in rats) – large thin muscle forming the buttocks in humans
Origin: pelvis
Insertion: femur (upper leg bone)
Action: move thigh (upper leg)
9) Latissimus dorsi – located posterior to the trapezius group
Origin: thoracic & lumbar vertebrae (backbone)
Insertion: side of humerus
Action: moves humerus to the back and side
gluteus
superficialis