Directional References - Human Anatomy and Physiology

 Directional References

In the anatomic position, a structure is described as superior/cranial or cephalic when it lies toward thehead, or top, and inferior orcaudal when it lies to-ward the bottom, or away from the head (Figure 1.6). For example, the tip of the nose is superior to the lips; the chin is inferior to both. A structure lying in front of another is anterior or ventral. A structure lying behind another is posterior ordorsal. For example, the ear is posterior to the cheek, and the cheek is an-terior to the ear.

Those structures lying closer to an imaginary line passing through the middle of the body in the sagit-tal plane are said to be medial,while those away from the middle are lateral. For example, my belly button will always be medial to my widening waist-line.

A structure lying away from the surface of the body is considered to be deep or internal, while a structure closer to the surface is considered superfi-cial or external. For example, the skin is superficialto the muscles; however, the bone is deep to the mus-cles.Proximal describes structures closer to the trunk (chest and abdomen) and distal describes structures away from the trunk. For example, the el-bow is proximal and the finger is distal to the wrist.

Comments

Post a Comment

Popular posts from this blog

Effect of Cold on Skin

  EFFECT OF COLD ON SKIN The rate of skin cooling is faster than the rate of re-warming, implying that a shorter period of cold appli-cation suffices to cool the skin. The depth of cold pen-etration depends on the duration and the area of application. Areas of the body containing more adi-pose tissue take a longer time to change temperature. If deeper structures are to be cooled, the duration of application is increased. When cold, in the form of wa-ter, is applied locally, it results in peripheral vasocon-striction and pallor. The vasoconstriction, in turn, re-sults in a decrease in skin temperature and reduction of edema, muscle spasm, and further hemorrhage. Analgesic effects begin when skin temperature is lowered to approximately 13.6°C (56.5°F). Analgesia is produced by the reduction in nerve conduction ve-locity by cold. Systemic reactions, such as increase in heart rate, respiratory rate, blood pressure, and shiv- ering, may be produced. Soon after cold application has ended...
Read more

Muscle Spindles

Image
  MUSCLE SPINDLES Muscle tone is maintained by stimulation of special-ized tissue ( muscle spindles ) scattered within the muscle. Muscle spindles are modified muscle fibers: 3–10 fibers that are surrounded by a capsule, giving it a spindle shape (see Figure 4.12). The ends of the muscle spindle capsule are attached to endomysium and perimysium. The muscle spindles are located parallel to other muscle fibers, and their length is al-tered as the whole muscle stretches or contracts. On average, the length of the muscle spindle varies be-tween 2–4 mm (0.08–0.16 in). The number of muscle spindles in each muscle is variable. Muscles of the arms and legs have the highest number, with the muscles of the hand and foot having an abundance. The specialized muscle fibers in the muscle spindle are known as  intrafusal fibers.  The actin and myosin in the intrafusal fibers are concentrated to-ward the ends of the capsule. The intrafusal fibers have their own sensory and motor nerve su...
Read more

The Spinal Cord, Spinal nerves, and Dermatomes

Image
  THE SPINAL CORD, SPINAL NERVES, AND DERMATOMES From the area of supply, the peripheral branch of the sensory neuron continues toward the CNS. As a result of the way the body is developed in the embryo, there is a specific pattern in the way nerves from different regions of the skin converge to the CNS. Thirty-one spinal nerves and certain cranial nerves are responsible for all body sensations. Figure 2.6, ,  shows the area of the skin and the spinal cord segment to which sensory nerves go from spe-cific areas of the body. The region of the body wall supplied by the cutaneous branches of a single pair of spinal nerves (right and left) is known as a  der-matome.  Although the dermatomes appear to havedistinct borders, there is some overlap between adjacent areas. The sensations from the face reach the brain via cranial nerve V (trigeminal nerve). It is of interest that the anal region lies in the dermatome of the sacral nerves; the most distal segment of the spinal c...
Read more