Anatomical Directional Terms and Body Planes

Anatomical Directional Terms and Body Planes Anatomical directional terms are like the directions on a compass rose of a map. Like the directions, North, South, East and West, they can be used to describe the locations of structures in relation to other structures or locations in the body. This is particularly useful when studying anatomy as it provides a common method of communication that helps to avoid confusion when identifying structures. Also as with a compass rose, each directional term often has a counterpart with converse or opposite meaning. These terms are very useful when describing the locations of structures to be studied in dissections. Anatomical directional terms can also be applied to the planes of the body. Body planes are used to describe specific sections or regions of the body. Below are examples of some commonly used anatomical directional terms and planes of the body. Anatomical Directional Terms Anterior: In front of, frontPosterior: After, behind, following, toward the rearDistal: Away from, farther from the originProximal: Near, closer to the originDorsal: Near the upper surface, toward the backVentral: Toward the bottom, toward the bellySuperior: Above, overInferior: Below, underLateral: Toward the side, away from the mid-lineMedial: Toward the mid-line, middle, away from the sideRostral: Toward the frontCaudal: Toward the back, toward the tailBilateral: Involving both sides of the bodyUnilateral: Involving one side of the bodyIpsilateral: On the same side of the bodyContralateral: On opposite sides of the bodyParietal: Relating to a body cavity wallVisceral: Relating to organs within body cavitiesAxial: Around a central axisIntermediate: Between two structures Anatomical Body Planes Imagine a person standing in an upright position. Now imagine dissecting this person with imaginary vertical and horizontal planes. This is the best way to describe anatomical planes. Anatomical planes can be used to describe any body part or an entire body. (View a detailed body plane image.) Lateral Plane or Sagittal Plane: Imagine a vertical plane that runs through your body from front to back or back to front. This plane divides the body into right and left regions. Median or Midsagittal Plane: Sagittal plane that divides the body into equal right and left regions.Parasagittal Plane: Sagittal plane that divides the body into unequal right and left regions. Frontal Plane or Coronal Plane: Imagine a vertical plane that runs through the center of your body from side to side. This plane divides the body into front (anterior) and back (posterior) regions. Transverse Plane: Imagine a horizontal plane that runs through the midsection of your body. This plane divides the body into upper (superior) and lower (inferior) regions. Anatomical Terms: Examples Some anatomical structures contain anatomical terms in their names that help identify their position in relation to other body structures or divisions within the same structure. Some examples include the anterior and posterior pituitary, superior and inferior venae cavae, the median cerebral artery, and the axial skeleton. Affixes (word parts that are attached to base words) are also useful in describing the position of anatomical structures. These prefixes and suffixes give us hints about the locations of body structures. For example, the prefix (para-) means near or within. The parathyroid glands are located on the posterior side of the thyroid. The prefix epi- means upper or outermost. The epidermis is the outermost skin layer. The prefix (ad-) means near, next to, or toward. The adrenal glands are located atop the kidneys. Anatomical Terms: Resources Understanding anatomical directional terms and body planes will make it easier to study anatomy. It will help you to be able to visualize positional and spatial locations of structures and navigate directionally from one area to another. Another strategy that can be employed to help you visualize anatomical structures and their positions is to use study aids such as anatomy coloring books and flashcards. It may seem a bit juvenile, but coloring books and review cards actually help you to visually comprehend the information.

Introduction to Bipedal Locomotion

Introduction to Bipedal Locomotion Bipedal locomotion refers to walking on two legs in an upright position, and the only animal to do that all the time is the modern human. Our ancestor primates lived in trees and rarely set foot on the ground; our ancestor hominins moved out of those trees and lived primarily in the savannas. Walking upright all the time is thought to have been an evolutionary step forward if you will, and one of the hallmarks of being human. Scholars have often argued that walking erect is an enormous advantage. Walking erect improves communication, allows visual access to farther distances, and changes throwing behaviors. By walking upright, a hominins hands are freed to do all sorts of things, from holding babies to making stone tools to throwing weapons. American neuroscientist Robert Provine has argued that sustained voiced laughter, a trait which greatly facilitates social interactions, is only possible in bipeds because the respiration system is freed to do that in an upright position. Evidence for Bipedal Locomotion There are four main ways scholars have used to figure out whether a particular ancient hominin is primarily living in the trees or walking upright: ancient skeletal foot construction, other bone configurations above the foot, footprints of those hominins, and dietary evidence from stable isotopes. The best of these, of course, is foot construction: unfortunately, ancient ancestral bones are difficult to find under any circumstances, and foot bones are very rare indeed. Foot structures associated with bipedal locomotion include a plantar rigidity- flat foot- which means the sole stays flat from step to step. Secondly, hominins that walk on the earth generally have shorter toes than hominins who live in trees. Much of this was learned from the discovery of a nearly complete Ardipithecus ramidus, an ancestor of ours who apparently walked upright sometimes, some 4.4 million years ago. Skeletal constructions above the feet are slightly more common, and scholars have looked at the configurations of the spine, the tilt, and structure of the pelvis, and the way the femur fits into the pelvis to make assumptions about a hominins ability to walk upright. Footprints and Diet Footprints are also rare, but when they are found in a sequence, they hold evidence that reflects the gait, length of stride, and weight transfer during walking. Footprint sites include Laetoli in Tanzania (3.5-3.8 million years ago, probably Australopithecus afarensis; Ileret (1.5 million years ago) and GaJi10 in Kenya, both likely Homo erectus; the Devils Footprints in Italy, H. heidelbergensis about 345,000 years ago; and Langebaan Lagoon in South Africa, early modern humans, 117,000 years ago. Finally, a case has been made that diet infers environment: if a particular hominin ate a lot of grasses rather than fruit from trees, it is likely the hominin lived primarily in grassed savannas. That can be determined through stable isotope analysis. Earliest Bipedalism So far, the earliest known bipedal locomotor was Ardipithecus ramidus, who sometimes- but not always- walked on two legs 4.4 million years ago. Fulltime bipedalism is currently thought to have been achieved by Australopithecus, the type fossil of which is the famous Lucy, approximately 3.5 million years ago. Biologists have argued that foot and ankle bones changed when our primate ancestors came down from the trees, and that after that evolutionary step, we lost the facility to regularly climb trees without the aid of tools or support systems. However, a 2012 study by human evolutionary biologist Vivek Venkataraman and colleagues points out that there are some modern humans who do regularly and quite successfully climb tall trees, in pursuit of honey, fruit, and game. Climbing Trees and Bipedal Locomotion Venkataraman and his colleagues investigated behaviors and anatomical leg structures of two modern-day groups in Uganda: the Twa hunter-gatherers and Bakiga agriculturalists, who have coexisted in Uganda for several centuries. The scholars filmed the Twa climbing trees and used movie stills to capture and measure how much their feet flexed while tree-climbing. They found that although the bony structure of the feet is identical in both groups, there is a difference in the flexibility and length of soft tissue fibers in the feet of people who could climb trees with ease compared with those who cannot. The flexibility that allows people to climb trees only involves soft tissue, not the bones themselves. Venkataraman and colleagues caution that the foot and ankle construction of Australopithecus, for example, does not rule out tree-climbing, even though it does allow upright bipedal locomotion.   Sources Been, Ella, et al. Morphology and Function of the Lumbar Spine of the Kebara 2 Neandertal. American Journal of Physical Anthropology 142.4 (2010): 549-57. Print. Crompton, Robin H., et al. Human-Like External Function of the Foot, and Fully Upright Gait, Confirmed in the 3.66 Million Year Old Laetoli Hominin Footprints by Topographic Statistics, Experimental Footprint-Formation and Computer Simulation. Journal of The Royal Society Interface 9.69 (2012): 707-19. Print. DeSilva, Jeremy M., and Zachary J. Throckmorton. Lucys Flat Feet: The Relationship between the Ankle and Rearfoot Arching in Early Hominins. PLoS ONE 5.12 (2011): e14432. Print. Haeusler, Martin, Regula Schiess, and Thomas Boeni. New Vertebral and Rib Material Point to Modern Bauplan of the Nariokotome Homo Erectus Skeleton. Journal of Human Evolution 61.5 (2011): 575-82. Print. Harcourt-Smith, William E. H. Origin of Bipedal Locomotion. Handbook of Paleoanthropology. Eds. Henke, Winfried, and Ian Tattersall. Berlin, Heidelberg: Springer Berlin Heidelberg, 2015. 1919-59. Print. Huseynov, Alik, et al. Developmental Evidence for Obstetric Adaptation of the Human Female Pelvis. Proceedings of the National Academy of Sciences 113.19 (2016): 5227-32. Print. Lipfert, Susanne W., et al. A Model-Experiment Comparison of System Dynamics for Human Walking and Running. Journal of Theoretical Biology 292.Supplement C (2012): 11-17. Print. Mitteroecker, Philipp, and Barbara Fischer. Adult Pelvic Shape Change Is an Evolutionary Side Effect. Proceedings of the National Academy of Sciences 113.26 (2016): E3596-E96. Print. Provine, Robert R. Laughter as an Approach to Vocal Evolution: The Bipedal Theory. Psychonomic Bulletin Review 24.1 (2017): 238-44. Print. Raichlen, David A., et al. Laetoli Footprints Preserve Earliest Direct Evidence of Human-Like Bipedal Biomechanics. PLoS ONE 5.3 (2010): e9769. Print. Venkataraman, Vivek V., Thomas S. Kraft, and Nathaniel J. Dominy. Tree Climbing and Human Evolution. Proceedings of the National Academy of Sciences (2012). Print. Ward, Carol V., William H. Kimbel, and Donald C. Johanson. Complete Fourth Metatarsal Andarches in the Foot of Australopithecus Afarensis. Science 331 (2011): 750-53. Print. Winder, Isabelle C., et al. Complex Topography and Human Evolution: The Missing Link. Antiquity 87 (2013): 333-49. Print.