Boning Up on the Skeletal System
Chapter 12: Boning Up on the Skeletal System Facial bones
All the facial bones except one are joined together. Only the mandible, or lower jaw bone, is capable of moving, which is necessary for chewing and speaking. Other facial bones include the nasal bones, and the maxillary bones. Two large bones compose the upper jaw. Both the mandible and maxilla contain sockets called alveoli, in which the teeth are embedded. The mandible joins the skull at the temporal bone, forming the lengthily named temporomandibular joint. The zygoma or zygomatic bones form the cheek.
Vertebral column
The vertebral column, or spinal column, is composed of 26 bone segments called vertebrae (singular vertebra), which are arranged in five divisions:
cervical, thoracic, lumbar, sacrum, and coccyx (tailbone).
The first seven vertebrae are called the cervical vertebrae (C1-C7). These ver- tebrae do not join with the ribs. The first cervical vertebra, C1 (also known as the atlas), articulates with the occipital bone of the skull at the back of neck.
It supports the head and allows it to move forward and back. The second cervical vertebra, C2 (the axis), acts as a pivot, about which the atlas rotates, allowing head to turn from side to side, extend, and flex.
The second division consists of 12 thoracic vertebrae (T1-T12). These verte- brae join with the 12 pairs of ribs. The third division consists of five lumbar vertebrae (L1-L5). They are the strongest and largest of the back bones. The sacrum is a slightly curved triangular bone, composed of five separate seg- ments, or sacral bones, that gradually become fused. The coccyx is the tail- bone. It is also a fused bone, formed from four small coccygeal bones.
The Greek diskos means “flat plate.” An example is the lumbar disk. And coccyx comes from the Greek word for cuckoo; it resembles a cuckoo’s beak.
A vertebra is composed of a disk-shaped portion called the vertebral body, which is the solid anterior portion (closest to body front, farthest from the body back). A lamina is a part of the posterior (back) portion of a vertebra.
Spinous processes, thoracic processes, and transverse processes are little wing- like projections that project or extend from each vertebra. The foramen is the opening in the middle of each vertebra that the spinal cord passes through.
Between the body of one vertebra and the bodies of vertebrae lying beneath, are vertebral disks which help to provide flexibility and cushion shock to the vertebral column.
The thorax (not to be confused with something invented by Dr. Seuss) starts with the clavicle, or the collarbone, connecting the sternum (breastbone) to each shoulder. The scapula is the shoulder blade, consisting of two flat trian- gular bones, one on each back side of the thorax. The scapulae extend to join with the clavicle at the acromion.
The sternum is the breastbone, the flat bone extending down the midline of the chest. The uppermost part of the sternum joins to the sides of the clavicle and ribs, whereas the other, narrowed portion is attached to the dia- phragm. The lower portion of the sternum is the xiphoid process, the small, mobile bone tag on the very end of the sternum. This is the thing you would feel for when placing your hands on a chest to perform CPR. The 12 pairs of ribs are close neighbors with the sternum. The first seven pair join the ster- num anteriorly (at the chest) by attachments of costal cartilage. Ribs 1–7 are called true ribs. Ribs 8–12 are called false ribs. The false ribs join with the vertebral column in the back, but join the 7th rib anteriorly and do not attach to the sternum. Ribs 11 and 12 are called floating ribs because they are com- pletely free at their anterior end.
Pelvis
The pelvic girdle or hip bone is a large bone that supports the trunk of the body and joins with the femur (thigh bone) and sacrum. The adult pelvic bone is composed of three pairs of fused bone: the ilium, the ischium, and the pubis.
The ilium is the uppermost and largest portion. The connection between the iliac bones and the sacrum is so firm that they are often referred to as one bone, the sacroiliac. The iliac crests are found on both the anterior and poste- rior portions of the pelvis. They are filled with red bone marrow and serve as an attachment for abdominal wall muscles.
The ischium is the posterior portion of the pelvis. The ischium and the muscles attached to it are what we sit on.
The pubis is the anterior portion containing two parts that are joined by way of a disk. This area of fusion is called the pubic symphysis. The region within the bone formed by the pelvic girdle is called the pelvic cavity. The rectum, sigmoid colon, bladder and female reproductive organs are contained in this cavity.
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Chapter 12: Boning Up on the Skeletal System
Appendicular skeleton
Think of the word appendage when your thoughts turn to the appendicular skeleton. Your reachers, grabbers, and hoofers are all covered in this section.
Appendages fall into two major categories of bones.
Upper extremeties
Arms and hands are part of this category. The bones of the arm and hand include the humerus, the upper arm bone. The large head of the humerus is round and joins the scapula and clavicle. The ulna and radius are the bones of the lower arm or forearm. The bony prominence of the ulna at the elbow is called the olecranon. Carpals are wrist bones. Finally, there are two rows of four bones. The metacarpals are five bones radiating to the fingers. Phalanges (the singular is phalanx) are the finger bones.
Each finger has three phalanges: the proximal, middle, and distal. The proximal is the phalange closest to the point of origin, whereas the distal is farthest from the point of origin. So, the proximal would be the first after the knuckle, the middle would be in the middle, and the distal at the fingertip. The thumb has only two phalanges: medial and distal at tip of the thumb.
Diaphysis comes from Greek diaphusis, meaning “state of growing between.”
Diaphysis is the shaft of long bones that grows as children grow.
Leg and foot
The femur is the thigh bone. At the top end of it, a rounded head fits into a socket in the hip bone called the acetabulum. The patella, or kneecap, is a small flat bone that lies in front of the joint between the femur and one of the lower leg bones called the tibia. The tibia is the largest of the two lower bones of the leg, often referred to as the shin bone. The fibula is the smaller of the two bones.
The tarsals, or ankle bones, are short bones that are much like the carpal bones of the wrist, but larger. The calcaneus, the largest of these bones, is also called the heel bone. Metatarsals compose the forefoot or bones leading to the phalanges in the toes. There are two phalanges in the big or great toe and three in each of the other four toes. Just like the fingers, all the bones in the toes are phalanges, from proximal to distal. In the big or great toe they are called the proximal and distal, differing slightly from the thumb.
The femur is the longest bone in the body.
Joints
Now think about the “glue” that holds all these bones together. Okay, joints aren’t really made of glue, but they sure do a good job of keeping everything connected. Let us articulate that concept a bit better: Joints, also called artic- ulations, are the coming together of two or more bones. Some are not mov- able, such as the suture joints between the cranial bones. Some joints only partially move, such as joints between the vertebrae.
Most joints do allow movement. These freely movable joints are called synovial joints. An example is the ball and socket type — the hip joint, for example, in which the head of the femur fits into the acetabulum. Another synovial joint is the hinged type as seen at the elbow, knee, or ankle joints.
The bones of a synovial joint are separated by a capsule, composed of fibrous cartilage. Ligaments of connective tissue hold the bones together around the capsule to strengthen it. The bone surfaces at a joint are covered with a smooth surface called the articular cartilage. The synovial membrane is the inner layer of the capsule, the layer beneath the capsular surface.
The synovial cavity is filled with a lubricating fluid produced by synovial membranes. This fluid contains water and nutrients that help to lubricate the joints so that friction on the articular cartilage is minimal.
Bursae (singular bursa) are closed sacs of synovial fluid lined with synovial membrane. They lie in the spaces between tendons, ligaments, and bones and lubricate areas where friction would normally develop close to the joint capsule. The olecranon bursa at the elbow joint and the patellar bursa at the knee are examples of bursae.
Skeletal Root Words
Now that you’ve gotten to know the specific parts of the skeletal system a bit better, it’s time to put your expertise into practice by breaking down the root words into meanings and useful applications. The roots, as always, are essential medical terminology knowledge because once you master these roots (those good ol’ Greek and Latin ones, that is), you can break down any skeletal-related word and discover its meaning.
Table 12-1 lists important skeletal system root words and combining forms.