14.3 - Movement and Locomotion

The movement of the human forearm involved the biceps and triceps.

Bending the forearm

• When the biceps contracts , the tendons transmit the pulling force produced by the contraction to the forearm.
• Meanwhile, the triceps relaxes.
• As a result, the elbow joint bends, and the forearm moves upwards.

Straightening the forearm

• When the triceps contracts andthe biceps relaxes, the forearm is straightened.

The action of walking also involves the cooperation between the antagonistic muscles. The biceps femoris acts as the flexor while the quadriceps femoris is the extensor.

1. The calf muscle contracts and raises the heel. This exerts a forward thrust by pushing the ball of the right foot against the ground.
2. Meanwhile, the biceps femoris contracts to bend the knee. The right leg is raised.
3. As the foot loses contact with the ground, the weight of the body is now supported by the left leg. The quadriceps femoris contracts to extend the right leg.
4. When the extension of the leg is completed, the tibialis contracts to lower the heel. As the heel regains contact with the ground, the body is now supported by the right leg. The whole sequence is repeated with the left leg.

Mechanism of Locomotion in Animals

Figure 5 - In fish, the myotome muscles contract and relax to help the fish in swimming. When the muscles on one side contract, those on the other side will relax. This allows the fish to whip its tail. When the left myotome muscles contract, the tail is whipped to the left. The same happens on the right side. Alternating waves of contraction and relaxation pass down the myotomes on either side of the body from the head to the tail. These cause the different parts of the body to bend from side to side, pushing the water backwards and sideways, and the fish forward. The fish uses its fins to control its movement and direction.

Figure 6 - In birds, the pair of antagonistic muscles that are involved during flight are pectoralis major and pectoralis minor. When the pectoralis minor muscles contract, the wings are pulled up (upstroke). When the pectoralis major muscles contract, the wings are pulled down (downstroke). The rhythmic movement of the wings up and down generate the forward thrust and provide the lift for the flying bird.

Figure 7 - The two layers of antagonistic muscles involved in the locomotion of an animal with hydrostatic skeleton such as earthworm are the circular muscle and longitudinal muscle. 1. The posterior longitudinal muscle contracts while the circular muscle relaxes. The earthworm becomes shorter and thicker. 2. The chaetae anchor the shortened segments in the posterior to the ground, while the anterior segment is released from the ground. 3. At the anterior segment, the circular muscles contract while the longitudinal muscles relax. The earthworm becomes thinner and longer. The anterior segments extend forward. 4. Now, the chaetae anchor the anterior segment to the ground, while the posterior segment is released from the ground. 5. The shortened posterior segment is pulled forward.

Figure 8 - The antagonistic muscles ( flexor and extensor muscles ) of a grasshopper are attached to the interior surface of the exoskeleton. Flexors are muscles that bend a joint while extensors straighten it. 1. While at rest, the flexor muscle contracts so the hind legs are folded in, forming a Z shape. The grasshopper is ready to jump. 2. When the extensor muscle contracts, the hind legs are straightened backwards. 3. The hind legs jerk to propel the grasshopper forward and upwards into the air.