Axial muscles and appendicular muscles are responsible for all movements of skeletal structures. Axial muscles act on the head, vertebral column, and trunk. Appendicular muscles direct movement and control of the upper and lower limbs and the pelvic and pectoral girdles. Muscle actions vary widely in scale and function, ranging from breathing, chewing, blinking, or smiling to pointing, standing on toes, dancing, or running. Apparently simple actions are often instead complex events that rely on a host of connected, innervated muscles. Throughout the body, muscles of various sizes, shapes, strengths, and origins direct these diverse actions.
At A Glance
Axial muscles are a part of the central body, the head, neck, and trunk. Appendicular muscles are those attached to the upper and lower limbs, hands, and feet.
Head and neck muscles control facial expression, chewing and swallowing, and movements of these body parts.
- The intrinsic and extrinsic muscles of the tongue, along with the mandibular muscles and pharyngeal constrictors, work together to allow for chewing and swallowing of food.
- The contraction of the sternocleidomastoid flexes the neck forward whereas the trapezius extends the neck, pulling the head back.
- The trunk muscles consist of the diaphragm and external and intercostal muscles, which together make respiration possible; groups of abdominal muscles including the obliques, rectus abdominis, and transversus abdominis permit flexibility, stabilization, and rotation of the vertebral column.
- The muscles of the back, classified as deep, intermediate, and superficial, are not only involved in rotation and movement of the vertebral column but also extend and rotate the arm, elevate the scapulae, and aid in respiration.
- The pelvic floor muscles provide support to the bladder and bowel of men, and the bowel, bladder, and uterus of women; they allow for conscious control of bladder and bowel function and aid in the sexual function of both men and women.
- Muscles acting on the shoulder and arm, such as the pectoralis major and latissimus dorsi, make movements like throwing, pushing, and rowing possible.
- Palm-up rotation of the forearm is accomplished by the biceps brachii and the supinator; the pronator teres and pronator quadratus are responsible for palm-down rotation of the forearm.
Precise finger movements, such as those involved in playing a piano or plucking a guitar string, are made possible by the hypothenar, thenar, and midpalmar groups of intrinsic hand muscles.
- Muscle acting on the hip and femur, also called the thigh bone, enable a wide variety of motions: flexion, extension, abduction, adduction, and both medial and lateral rotation.
- The knee joint is controlled by a powerful tensor muscle, the quadriceps femoris; actions such as standing, running, jumping, and kicking would not be possible were it not for this muscle.
- Extrinsic to the foot, the lower leg crural muscles allow for dorsiflexion and eversion of the foot.