Arm & Hand Muscles. One of the features that distinguishes humans from other animals is our ability to use our arms and hands for a whole range of different tasks.Lifting a heavy weight, writing a letter, hitting a tennis ball, painting a picture, or hammering in a nail : all of these, and the many other tasks we perform, require the muscles of the hand and arm to work together. The hand is capable of a wide range of movement, from delicate manipulation to strong grasping. The flexibility and precision of the hand are due to the intricate framework provided by the 27 hand bones and to the many muscles of the hand and forearm.
The muscles of the hand are small and serve to flex or extend the fingers, or to move them sideways. The forearm muscles taper into long tendons that extend into the hand. If the forearm muscles themselves extended into the hand, your finger would be very thick and unable to perform their normal activities. The long tendons pass through slippery sheaths that enable them to move smoothly when you move your fingers.
Hand Movements
The muscles of the lower arm and hand enable you to perform a wide range of movements. For example, you can hold a pen or chopsticks and use both with precision, you can point at an object; and you can use the hand as a hook or pincers for a firm grip.
Finger movers
Here you can see the muscle of the upper part of the left forearm and hand. Most of the muscles in this part of the arm straighten the wrist or the finger. The long fore arm muscles taper into narrow tendons that are attached to the finger bones. The extensor retinaculum is a "wrist band" that keep the long tendons in place.
Arms outstretched
The children here move their arms and hands during a gymnastic display. They have learned these movements in advance. The brain recalls them from its memory and then sends instructions to the muscles of the arms, shoulders, chest, and back to enable each child to perform the dance.
Traffic duty
A women police officer moves her right arm and hand in order to direct the traffic. She has learned to make certain movements that drivers will understand and respond to. As she surveys the traffic, her brain sends instructions to produce the movement shown here.
Shoulder and upper arm
This is back view of the left upper arm and shoulder. The deltoids, trapezius and other muscles move the shoulders and pull the arm forward and backward, out to the side, and back toward the body. The shoulder join is very flexible and enables the arm to be moved in nearly all directions. The muscles of the upper arm bend and straighten the arm at the elbow.