2016.03.15 Chicken Muscle Dissection

Today we dissected a chicken carcass to help us understand how muscles work and where the major muscles were located. We skinned the carcass to reveal the muscles underneath and practiced identifying each muscle and their function.

yes, it really is a foster farms chicken; also note that it is missing the distal section of its left wing

the same chicken, with half of its skin removed

The bones, muscles, and tendons of an animal all work together to create movement. When a muscle contracts, since it is attached to bones with tendons, it pulls one bone closer to the other. For example, during the dissection, we pulled on the biceps brachii to mimic muscle contraction, which swung the radius and ulna closer to the humerus. Letting go of the biceps brachii to simulate muscle relaxation allowed the forearm (or forewing, on a chicken) to return to its original position.

We also observed the difference between the origin and the insertion, the two places a muscle is attached to the bone by tendons. The origin is immoveable, and when a muscle contracts, it pulls its insertion closer to its origin. In the case of the biceps brachii, the origin would be on the proximal end of the humerus, while the insertion would be on the distal end closer to the elbow joint. As the biceps brachii contracts, the insertion moves closer to the origin, bringing the forearm closer to the upper arm.

Compared to human muscles, a chicken's muscles are very similar. A chicken has the same muscles as a human, which are located in roughly the same area and work the same way. However, the proportions of these muscles are very different. For example, a bird's chest muscles (pectoralis major and pectoralis minor) are much larger than a human's due to the great strength that is needed for a bird to flap its wings (which are controlled by these chest muscles) to achieve flight. On this particular kind of chicken, the chest muscles and leg muscles are especially large because they have been bred for meat, and the breast, thighs, and drumsticks are the most valuable parts of a chicken. In contrast, the back muscles are extremely small and thin and so weak that the bird cannot even support its own weight upright.

As we studied the chicken's muscles, we labeled some major muscles and took pictures of them:

the pectoralis major pulls the wing down into the flap

the pectoralis minor pulls the wing up after the flap

the latissimus dorsi (1) extends the wing; the trapezius (2) moves the shoulder

the deltoid (1) raises the upper wing; the triceps humeralis (2) extends the wing; the biceps brachii (3) flexes the wing

the brachioradialis (1) pulls the distal section of the wing back; the flexor carpi ulnaris (2) flexes the distal section of the wing

the gastrocnemius (1) extends the foot and flexes the lower leg; the peroneus longus (2) extends the foot; the tibialis anterior (3) flexes the foot

the sartorius (1) flexes the thigh; the iliotibialis (2) extends the thigh and flexes the leg

the semimembranosus (1) extends the thigh; the semitendinosus (2) extends the thigh

the biceps femoris (1) flexes the leg;
the quadriceps femoris (2) flexes the thigh and extends the lower leg