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To do this, distinct ends of an organism are chosen, and the axis is named according to those directions. An organism that is symmetrical on both sides has three main axes that intersect at right angles. [3] An organism that is round or not symmetrical may have different axes. [3] Example axes are: The anteroposterior axis [8] The cephalocaudal ...
The latter flexure mainly appears in mammals and sauropsids (reptiles and birds), whereas the other two, and principally the cephalic flexure, appear in all vertebrates (the sum of the cervical and cephalic ventral flexures is the cause of the 90-degree angle mentioned above in humans between body axis and brain axis).
Rotation. Rotation of body parts may be internal or external, that is, towards or away from the center of the body. [22] Internal rotation (medial rotation or intorsion) is rotation towards the axis of the body, [22] carried out by internal rotators.
For example, blood can be said to flow in a proximal or distal direction, and anteroposterior, mediolateral, and inferosuperior axes are lines along which the body extends, like the X, Y, and Z axes of a Cartesian coordinate system. An axis can be projected to a corresponding plane.
The standard anatomical position, or standard anatomical model, is the scientifically agreed upon reference position for anatomical location terms.Standard anatomical positions are used to standardise the position of appendages of animals with respect to the main body of the organism.
The Hox genes, which define features along the anterior-posterior axis of a developing organism, determine at which points along the axis that limb buds will form. [9] Though limbs emerge at different locations in different species, their positions always correlate with the level of Hox gene expression along the anterior-posterior axis. [ 9 ]
The cortical rotation is powered by microtubules motors moving along parallel arrays of cortical microtubules. This gray crescent marks the future dorsal side of the embryo. Blocking this rotation prevents formation of the dorsal/ventral axis. By the late blastula stage, the Xenopus embryos have a clear dorsal/ventral axis.
An example of this process is where the anteroposterior axis (the axis drawn between the head and tail end of an embryo) becomes longer as the lateral tissues (those that make up the left and right sides of the embryo) move in towards the dorsal midline (the middle of the back of the animal). [1]