14.3 - Movement and Locomotion

Mechanism of Human Forearm Movement

• Forearm movement involves the antagonistic action of the biceps and triceps.

Bending of the Forearm

1. The biceps contracts; the triceps relaxes.
2. Pulling force is transmitted to the radius through the tendon.
3. The radius is pulled upwards, bending the forearm.

Straightening of the Forearm

1. The triceps contracts; the biceps relaxes.
2. Pulling force is transmitted to the ulna through the tendon.
3. The ulna is pulled downwards, straightening the forearm.

Mechanism of Walking

• The biceps femoris is the flexor; the quadriceps femoris is the extensor.

1. The right calf muscle contracts and lifts the heel; the ball of the foot pushes against the ground.
2. The biceps femoris contracts at the same time, bending the leg at the knee joint and lifting the right leg.
3. As the right leg leaves the ground, the left leg supports the body weight; the quadriceps femoris contracts to straighten the leg.
4. The tibialis contracts to lower the heel; when the right heel touches the ground, body weight shifts to the right leg.
5. The sequence repeats with the left leg.

Mechanism of Locomotion in Animals

Fish

• The flexible vertebral column moves from side to side through the contraction and relaxation of myotomes, which are W-shaped muscle segments.
• Myotomes on opposite sides act antagonistically: contraction on one side and relaxation on the other whip the tail towards the contracting side.
• Alternating waves of contraction and relaxation along the myotomes move the body from side to side.
• The body pushes water backwards and sideways, moving the fish forwards.
• Fins control movement and direction.

Bird (Flight)

• Large, strong antagonistic chest muscles flap the wings.
• Downstroke: pectoralis major contracts; pectoralis minor relaxes; the wings are pulled down.
• Upstroke: pectoralis minor contracts; pectoralis major relaxes; the wings are pulled up.
• Air pressure provides upthrust.

Earthworm

• Alternate contractions and relaxations of the circular muscles and longitudinal muscles produce a wave of peristalsis along the body.

1. Posterior longitudinal muscles contract and circular muscles relax; the earthworm becomes shorter and thicker.
2. Posterior chaetae anchor to the ground; anterior chaetae release their hold.
3. Anterior circular muscles contract and longitudinal muscles relax; the earthworm becomes longer and thinner, extending the anterior segment forwards.
4. Anterior chaetae anchor to the ground; posterior chaetae release their hold.
5. The shortened posterior segment is pulled forwards.

Grasshopper (Jump or Leap)

• The flexor and extensor are antagonistic muscles attached to the inner surface of the exoskeleton.
• The flexor bends a joint; the extensor straightens it.
• The muscular, long hind legs are adapted for jumping.

1. At rest, the flexor contracts and pulls the hind leg towards the body; the hind leg folds into a Z shape.
2. The extensor contracts and straightens the hind leg backwards.
3. Catapult-like ejection of the hind legs projects the grasshopper forwards and upwards.