Roger Soames

6 – The head, neck and trunk

Publisher Summary This chapter describes one of the major features that distinguishes human beings from other animals is their bipedal posture and gait. As the hindlimbs progressively take over the locomotor function, the vertebral column assumes a new role. No longer is it held horizontally, where it is under compression, but has become a vertical weight-bearing rod, held erect by ligaments and muscles. The change in function of the vertebral column has been accompanied by changes in its form, as well as by changes in its relationship to the skull and pelvic girdle. In human beings, the tail is reduced to between three and five fused coccygeal vertebrae, which curve ventrally and help form the pelvic cavity. Ligaments running from the coccyx to the ischium play an important role in maintaining this relationship, and in so doing contribute to the function of support of the abdominal and pelvic viscera. The abdominal viscera are carried in a sacklike cavity supported behind by the vertebral column, below by the pelvis and anterolateral by the abdominal muscles.

3 – Skin, its appendages and special senses

Publisher Summary The skin is a tough, pliable waterproof covering of the body, blending with the more delicate lining membranes of the body at the mouth, nose, eyelids, urogenital, and anal openings. It is the largest single organ in the body. Not only does it provide a surface covering, it is also a sensory organ endowed with a host of nerve endings that provide sensitivity to touch and pressure, changes in temperature and painful stimuli. The chapter explains that as far as general sensations are concerned, the skin is the principal source. The waterproofing function of the skin is essentially concerned with the prevention of fluid loss from the body. Reduction of body temperature is a special function of the skin because of the variability in its blood supply and the presence of sweat glands. Heat is lost through radiation, convection, and evaporation. The total thickness of the skin depends on the thickness of both the epidermis and the dermis. The colour of the skin also depends on the presence of pigment (melanin) and the vascularity of the dermis.

Components of the musculoskeletal system

This chapter discusses the components of musculoskeletal system. Skeletal tissues are modified connective tissues, whereby the cells and fibres have a particular organization that becomes condensed so that the tissue is rigid. Within the body there are three varieties of muscle: (1) smooth muscle also referred to as involuntary or non-striated muscle; (2) cardiac muscle, and (3) skeletal muscle, also known as voluntary or striated muscle. Smooth muscle forms the muscular layer of the walls of blood vessels and of hollow organs such as the stomach. The chapter also reviews that the bones of the body come together to form joints. It is through these articulations that movement occurs. However, the type and extent of the possible movement depend on the structure and function of the joint. Moreover, the variation that exists in the form and function of the various joints of the body allows the joints to be grouped into well-defined classes: fibrous, cartilaginous, and synovial with the degree of mobility gradually increasing from fibrous to synovial.

The upper limb

The human upper limb has almost no locomotor function. It is instead an organ for grasping and manipulating. With the evolutionary adaptation of bipedalism, the upper limb acquired a great degree of freedom of movement. During that adaptation, the upper limb retained its ability to act as a locomotor prop, as when grasping an immobile object and pulling the body toward the hand. The upper limb is used in conjunction with a walking aid to support the body during gait. The upper limb is attached to the trunk by the pectoral girdle, which consists of the scapula and the clavicle. The functional effectiveness of the hand is an important contribution made by the extensive vascular network in supporting its metabolic requirements. The upper limb is also used for carrying loads and supporting the body. During the development, the upper limb bud appears as a swelling from the body wall at about 4 weeks. It develops at the level of the lower cervical and first thoracic segments.