Exercise 1: Body Symmetry, Body Planes, and Body Regions PDF

Exercise No. 1 SPA Body Symmetry, Body Planes, and Body Regions A. Body Symmetry...

Exercise No. 1 SPA Body Symmetry, Body Planes, and Body Regions A. Body Symmetry The arrangement of body parts in animals differs, and these differences can be described best in relation to certain reference planes, or axes. The three major categories of body symmetry in animals are: asymmetry, radial symmetry, and bilateral symmetry (Fig. 1.1).  Asymmetry—lack of symmetry; irregular arrangement of body parts with no plane of symmetry to divide them into similar halves  Radial symmetry—arrangement of body parts around a central axis; any plane passing through the central axis divides the body into two similar halves  Bilateral symmetry—division of body parts into similar halves (mirror images) by a single plane of symmetry Figure 1.1 Patterns of body symmetry in animals: (A) asymmetry; (B) radial symmetry; and (C) bilateral symmetry. B. Body Planes, Axes, and Regions All body movements occur in different planes and around different axes (Fig 1.2). A plane is an imaginary flat surface running through the body. An axis is an imaginary line at right angles to the plane, about which the body rotates or spins. Anatomical Axes: APA - DVA - LRA  Anterior-posterior axis – it is a line in the median APA - LA - ZA - SA sagittal plane extending from head to tail; also known as longitudinal axis, z axis, or sagittal axis. (at right angle)  Dorso-ventral axis – a line that runs orthogonal to DVA - VA - YA both the anterior/posterior and left/right axes. Also known as vertical axis or y- axis.  Left-Right axis – any line in the transverse plane running from side to side. It is also known as frontal axis, transverse axis, mediolateral axis or x-axis. LRA - FA - TA - MLA - XA Planes of the Body: CP - SP - AP - MP  Coronal Plane (Frontal Plane) - A vertical plane running from side to side; divides the body or any of its parts into anterior and Figure 1.2 Plans and Axes.  posterior portions.  Sagittal Plane (Lateral Plane) - A vertical plane running from front to back; divides the body or any of its parts into right and left sides.  Axial Plane (Transverse Plane) - A horizontal plane; divides the body or any of its parts into upper and lower parts.  Median plane - Sagittal plane through the midline of the body; divides the body or any of its parts into right and left halves. Anatomical references to body planes, axis, and regions often differ between radially symmetrical and bilaterally symmetrical animals, ventral surf. - dog anterior surf. - human as well as between quadrupedal oral surf. - jellyfish animals and bipedal animals (such as humans) (Fig. 1.3). For example, the ventral surface of a dog is equivalent to the anterior surface of a human and the oral surface of a jellyfish. Many of the animals you will encounter in this manual are bilaterally symmetrical and some are quadrupedal; therefore, the following terms will be used to refer to the regions of the body and the orientation of the organs and structures you will Figure 1.3 Axes between bipedal and quadrupedal animal. identify. A section perpendicular to the long axis of the body separating the animal into anterior and posterior portions is called a transverse plane (Fig. 1.4). The terms anterior and posterior refer to the head and tail regions, respectively. When referring to quadrupedal animals, the terms cranial and caudal may be appropriately substituted for anterior and Bipedal: anterior & posterior Quadrupedal: cranial & caudal Transverse - anterior / posterior Sagittal - - right / left Medial - midline Figure 1.4 Body planes and body regions in an animal. posterior. A longitudinal section separating the animal into right and left sides is called a sagittal plane. The sagittal plane running down the midline of the animal has a special name, the median plane. Structures that are closer to the median plane are referred to as medial. Structures farther from the median plane are referred to as lateral. Dorsal refers to the back or upper surface of the body, and ventral refers to the front or lower side of the body. A longitudinal section dividing the animal into dorsal and ventral parts is called a frontal plane or coronal plane. Proximal refers to a point of reference nearer the median plane or point of attachment on the body than another structure (for example, when your arm is extended, your elbow is proximal to your hand). Distal refers to a point of reference farther from the body’s median plane or point of attachment than another structure (for example, when your arm is extended, your elbow is distal to your shoulder). Rostral refers to a point closer to the tip of the nose. C. Additional Descriptive Terms  Dorsal - the back or upper side (posterior in human body).  Ventral - the underside or pertaining to the belly (anterior in human body).  Lateral - the sides. DV - AP - PD - SD - SI - PRPO  right (dextral)  left (sinistral)  Anterior or cranial - the head end of the animal (superior in human anatomy).  Posterior or caudal - the tail end of the animal (inferior in human anatomy).  Median - the middle; in or near the longitudinal plane in the middle of the body.  Medial - pertaining to the sagittal plane.  Central - the part of a system nearest the middle of the animal.  Proximal - near the main mass of the body (e.g., thigh).  Distal - away from the main mass of the body (e.g., toes).  Superficial or ectal - on or near the surface.  Deep or ental - some distance below the surface.  Superior - above.  Inferior - below.  Preaxial - toward the inner or near the axis or median plane.  Postaxial - away or far from the axis or median plane of the body. Figure 1.5 Four (4) anatomical planes of references. Table 1.1 Directional terms and virtual planes of the animal body. Questions: 1. Which type of symmetry do you think is most prevalent among animals? 2. How does an asymmetrical body plan differ from radial or bilateral body plans? 3. List the three types of body symmetry, and for each type list an animal (that isn’t used in the manual) that has that kind of symmetry. Symmetry Type Animal