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Anatomic Divisions and Terms

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Anatomic Divisions and Terms

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Anatomic Divisions and Terms with Skeletal Overview

Introduction

The 206 bones of the body divide into two major groups

Axial bones - comprise the vertical axis of the skeleton; 80 bones.
Appendicular bones - bones that append (aka attach) to the axial skeleton; 126 bones.

Anatomical position

The vertebral column is vertical, the arms are extended with palms facing anteriorly, and the legs are extended with toes pointing anteriorly (towards the front of the body).

Axial skeleton

Skull

Encloses and protects brain

Hyoid bone

U-shaped bone; muscles of speech and swallowing attach to the hyoid bone

Vertebral column

Bones of the spine, terminates in the sacrum

Thoracic cage

Sternum – breast bone
Ribs – form the lateral walls of the thoracic cage

Appendicular skeleton

Pectoral girdle

Comprises the scapula (aka shoulder blade), which articulates with the humerus; and, the clavicle, which articulates with the sternum and scapula

Arm

The humerus articulates with the scapula

Forearm

The radius (laterally)
The ulna (medially)

Hand

Carpals (wrist)
Metacarpals (palm)
Phalanges (fingers)

Pelvic girdle

Bilateral os coxa bones (aka hip bone), articulate with the sacrum posteriorly

Thigh

Femur (aka thigh bone) articulates with the lateral side of the coxal bone; it is the longest and strongest bone in the body

Leg

Fibula, laterally; very slim, attachment site for muscles
Tibia, medially ("shin" bone); thick, weight-bearing bone of the leg

Kneecap

Patella; encased within tendons that pass over the knee, so is a sesamoid bone

Foot

Tarsals (ankle)
Metatarsals (foot base)
Phalanges (toes)

Directional nomenclature

Proximal

Closer to the center of the body or limb attachment

Distal

Further from the center of the body or limb attachment

Contralateral

On opposite sides of the body

Ipsilateral

On same side of the body

Intermediate

A structure between two others

Superior

Towards the top of the head

Inferior

Towards the feet

Medial

Towards the midline of the body

Lateral

Away from the midline of the body

Sagittal plane

Divides body into right and left sides

Transverse plane

Divides body into superior and inferior divisions

Superficial

Structure that is close to the surface of the body

Deep

A structure that is near the center of the body

Full-Length Text

Here we will learn the general organization of the skeleton and its directional nomenclature.

First, start a table.

Indicate that the bones of the body divide into two major groups: axial bones, which comprise the vertical axis of the skeleton, and appendicular bones, which are the bones that append (aka attach) to the axial skeleton.

Denote that there are 206 bones in the adult body.

Then, denote that the axial skeleton contains 80 bones whereas the appendicular skeleton contains 126.

Here we will address only the major bones of the skeleton.

To begin, let's draw the axial skeleton.

First, draw the skull.

Inferior to the skull, draw the hyoid, which is a small, u-shaped bone.
- Several muscles necessary for speech and swallowing attach to the hyoid bone.

Next, draw a consolidated vertebral column, with an inverted triangle at the bottom to represent the terminal end: the sacrum.

Now, draw the rectangular-shaped sternum (aka breast bone), and indicate that ribs project anteriorly from the vertebral column.

Show that the ribs and sternum comprise the anterior thoracic cage.

Next, draw the appendicular skeleton.

Begin with the pectoral girdle.

Draw the wing-shaped scapula (aka shoulder blade).
- This bone primarily sits posterior to the thoracic cage and projects laterally to articulate with the upper arm.

Next, draw the curved clavicle (aka collarbone), which extends from the sternum to the scapula.
- This is a point of articulation between the axial and appendicular skeletons; palpate each of your clavicles at the base of your anterior neck.

Before we draw the upper extremity, pay attention that our drawing is in anatomical position.

Denote in our table that in anatomical position: the vertebral column is vertical, the arms are extended with palms facing anteriorly, and the legs are extended with toes pointing anteriorly (towards the front of the body).

Now, draw the humerus, which articulates with the scapula superiorly.

Then, laterally, draw the radius and medially, draw the ulna; they are the two bones of the forearm.

Indicate that the carpals, which comprise the bones of the wrist, articulate with the bones of the forearm.

Attached to these carpals, draw 5 metacarpals, which are the bones of the palm.

Lastly, show that phalanges, which are the small bones of the fingers, articulate with the metacarpals.
- Your thumb has two phalanges whereas the other digits (fingers) have three.

Next, let's address the pelvic girdle, which are the bilateral coxal bones (aka hip bone), which articulate with the sacrum posteriorly.

Now, show that the femur (aka thigh bone) articulates with the lateral side of the coxal bone.
- The femur is the longest and strongest bone in the body.

Next, draw the two bones of the lower leg: laterally, draw the fibula and medially, draw the tibia.
- Palpate your "shin bone," which is the tibia: the primary weight-bearing bone of the lower leg.
- The fibula is much slimmer and functions as an attachment site for various lower limb muscles.

Now, draw the patella (aka knee cap) where the femur meets with the lower leg bones.
- The patella is encased within tendons that pass over the knee, which makes it the largest sesamoid bone in the body.

Then, draw the tarsals, which are the bones of the ankle that lie inferior to the tibia and fibula.

Show that 5 metatarsals, or bones of the base of the foot, extend from the tarsals.

Lastly, indicate that phalanges articulate with the metatarsals; as discussed in the hand, the first digit, the "big toe," has only two phalanges, but the other digits have three phalanges, each.

Now, let's address anatomical directional nomenclature.

Draw the opposite upper extremity and within it, draw a double-sided arrow.

Label the arrow closest to the thoracic cage as proximal and the arrow furthest away, where the fingers would be, as distal.

These terms describe distance from the point of attachment of the limb; for instance, we say "the phalanges are distal to the humerus" or "the carpals are proximal to the metacarpals."

Now, let's address the terms used to describe whether two structures are on the same or opposite sides of the body:

Indicate that the right coxal bone is contralateral to the left coxal bone, meaning they are on opposite sides of the body.

Conversely, denote that the left arm and left coxal bone are ipsilateral, or on the same side of the body.

Next, show that an intermediate structure, such as the patella, is one that lies between two structures; the patella lies between the thigh and lower leg.

Now, an anterior view of the skull.

Underneath, draw a vertical double-sided arrow.

Label the top arrow "superior" and the bottom arrow "inferior".

We use these terms to describe vertical anatomical relationships; for instance, to say "the skull is superior to the pelvic girdle" and "the foot is inferior to the thoracic cage."

Next, draw a horizontal double-sided arrow.

Label the arrow directed towards (closest to) midline of the skull as "medial" and the arrow directed away (furthest) from midline as "lateral."

These terms describe whether a structure is closer to the midline or the side of the body; for instance, "in anatomical position, the ulna is medial to the radius."

Now, let's address the planes of the body.

Draw another a vertical line for the sagittal plane; show that it divides the body into right and left sides (remember: in anatomical position, the arms are extended with palms facing anteriorly).

Next, draw a horizontal line for the transverse (aka horizontal) plane; show that it divides the body into superior and inferior divisions.

Now, draw a side-view (aka sagittal view) through the skull.

Indicate that the frontal (aka coronal) plane divides the body into anterior and posterior divisions.

Then, show that superficial refers to a structure that is close to the surface of the body (such as the scalp); whereas, deep refers to a structure near the center of the body, such as the basal ganglia, which lie deep within the brain.