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

Isotopes

  Isotopes The atoms of the same element may have different numbers of neutrons in the nucleus. Although this difference in number does not affect the property of the atom, the weight of the atoms may differ (Re-member, neutrons are of the same mass and size as protons.). Hydrogen, for example, may have a proton and no neutrons or one neutron or two neutrons in the nucleus. The atoms of an element that has a dif-ferent number of neutrons in the nucleus are known as  isotopes . Isotopes are referred to by the combined  number of protons and neutrons (i.e.,   mass num-ber ).  The mass number is the number of protons andneutrons in an atom. In the above example, hydrogen with one proton is hydrogen-1 ( 1 H); with one proton and one neutron, hydrogen-2 ( 2 H); and with one pro-ton and two neutrons, hydrogen-3 ( 3 H). Some of the isotopes of certain elements contain nuclei, which spontaneously emit subatomic parti-cles known as  radioisotopes. Radioisotopes are ...
Read more

Movement in the Colon and Defecation

Image
  Movement in the Colon and Defecation The movement in the colon is similar to the small in-testine in that peristalsis and a segmentation type of contraction are present. In addition, there is a third type of contraction,  mass action  contraction, in which there is simultaneous contraction of the smooth muscle over a large area. This movement pushes material from one portion of the colon to an-other and into the rectum. When the rectum is dis-tended, it initiates the  defecation reflex.  When the pressure increases a little, there is a desire to defe-cate. Beyond a pressure of 55 mm Hg, both the inter-nal and external sphincters relax and the contents of the rectum are expelled. This is the reason for the in-voluntary expulsion seen in infants and individuals with spinal cord injury. In humans, sympathetic stimulation causes contrac-tion of the internal anal sphincter and parasympathetic stimulation relaxation. The external anal sphincter, which is comprised o...
Read more

Human Skeleton

Image
  The Human Skeleton The human skeleton (see Figures 3.5 and 3.6) can be considered to have two main divisions—the  axial  and the  appendicular skeleton.  The axial portion is made of bones in the central or longitudinal axis; the  skull, vertebrae, ribs,  and  sternum.  Tiny bones ( os-sicles ) located in the middle ear and the  hyoid bone,  located in the neck, are also part of this division.   The appendicular skeleton is made up of bones that form the appendices—the limbs—and includes the bones that attach the limb to the axial skeleton: the  bonesof the shoulder  and  pelvic girdle  and the  bones of the upper  and  lower limb. The skeletal system consists of 206 bones, of which approximately 40% (80 bones) is part of the axial skeleton. The axial skeleton creates a framework that supports and protects delicate organs of the body and provides a large surface area for the attachment of mu...
Read more