Skeletal System
The bones of our skeleton function for support and protection, for muscle attachment and locomotion. Bones store calcium (Ca2+), a vital element which is in a constant exchange between the blood, bones and marrow, which form red and white blood cells. There are 206 bones in the body comprised of long bones, short bones, flat bones and irregular bones. Long bones are longer than they are wide (ex: humerus, femur), short bones have approximately equal dimensions, flat bones are thin, flattened and typically curved, and irregular bones are not even or balanced in shape and do not fit in any of the aforementioned categories. Osteology (study of bones) knowledge is vital due to the relative access sites. Specific landmarks of bone are often referenced during surgery (posterior fossa, lateral mass screws, pedicle screws, laminectomy, foraminotomy, etcetera.)
The Skull
The Skull has two major components: The calvarium (calvaria = skull) which is composed of 8 bones and 15 facial bones. The cranial bones surround the brain, housed in the cranial cavity, and provide a rigid protective covering for the brain. The cranial bones severely limit the expansion of the brain (even when expansion becomes necessary in response to disease). The cranial cavity is formed by the frontal, parietal, sphenoid, temporal and occipital bones. The floor of the human skull viewed from above is divided into three distinct compartments (fossae) on each side: anterior, middle and posterior. The cranial nerves emerge through symmetrically placed holes (foramina) in the base of the skull to innervate peripheral structures.
These are the major bones of the skull which can be seen clearly.
The floor of the skull is composed of bones that are deep
Sutures (a seam-like, immovable junction between two bones) join the calvarium bones
Facial Bones
These are the major bones of the skull which can be seen clearly.
- Frontal Bone - The frontal bone forms the forehead and inside (anterior fossa) of the base of the skull. (drilling to the interior is a sinus)
- Parietal Bones - There are two Parietal Bones which compose the roof and lateral portions of the posterior skull.
- Temporal Bone - The Temporal Bone, which compose the lateral portions of the skull around the ear is composed of 4 parts
- Squamous portion of the Temporal Bone; square-shaped, thin, flat
- Mastoid portion of the Temporal Bone; thin, flat
- Zygomatic Process; posterior portion of cheek
- Petrous portion of the temporal bone; houses the inner ear
- Occipital Bone - The Occipital Bone composes the posterior portion of the skull and includes the foramen magnum, the opening where the spinal cord attaches to the brain and articulates with the first cervical vertebrae (C1/Atlas) which holds up the skull
The floor of the skull is composed of bones that are deep
- Sphenoid Bone - The Sphenoid bone lies medio-laterally and is posterior to the frontal bone, it is the keystone of the floor of the skull. The sphenoid sinus forms the lateral wall of the orbit. It forms the sella turcica (Turkish saddle) which has four clinoid processes which surrounds the pituitary gland from anterior to posterior.
- Ethmoid Bone - The ethmoid bone is located in the anterior midline of the skull and houses the cribriform plate, which has many small openings, to allow smell impulses to reach small nerve fibers which transmit sensation to the olfactory nerve.
Sutures (a seam-like, immovable junction between two bones) join the calvarium bones
- The Coronal Suture - between the frontal and parietal bones
- The Lambdoidal Suture - (greek letter lambda) posterior aspect of the skull that joins the parietal lobe with the occipital lobe
- The Occipito-mastoid/Occipito-temporal Suture - joins the occipital lobe with the mastoid bone or temporal bone
- The Sagittal Suture - separates the left and right parietal bones
Facial Bones
- Nasal Bones - inferior medial orbit
- Zygomatic Bones - form the middle aspect of the cheek bone
- Zygomatic process of maxilla
- Zygomatic Bone
- Zygomatic process of the temporal bone
- Palatine Bones - 2 bones that form the posterior portion of the hard palate (roof of the mouth)
- Inferior conchae - lateral nasal cavity
- Vomer - medial nasal cavity; commonly referred to as the septum
- Hyoid bone - U-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. It lies at the level of the base of the mandible anterior to the third cervical vertebra (C3). It functions to support the tongue above it and larynx below it and also transmits force of muscles to help open the jaw.
The Bones of the Body
The skeleton is separated into two types:
The medial axis of the body is known as the Axial Skeleton;
The skull, vertebrae, ear ossicles, hyoid bone, sternum, ribs and vertebral column are part of the axial skeleton.
That which attaches to the Axial Skeleton is known as the Appendicular Skeleton;
The upper extremities (humerus, radius, ulna, bones of the wrist and hand, menubrium, sternum, xiphoid process, 12 ribs (7 true and 5 false (floating)) and the pectoral girdles (clavicles and scapulae), and the lower extremities (femur, tibia, fibula, bones of the talus and metatarsals) and the pelvic girdle (ilium, ischium and pubic bone).
The medial axis of the body is known as the Axial Skeleton;
The skull, vertebrae, ear ossicles, hyoid bone, sternum, ribs and vertebral column are part of the axial skeleton.
That which attaches to the Axial Skeleton is known as the Appendicular Skeleton;
The upper extremities (humerus, radius, ulna, bones of the wrist and hand, menubrium, sternum, xiphoid process, 12 ribs (7 true and 5 false (floating)) and the pectoral girdles (clavicles and scapulae), and the lower extremities (femur, tibia, fibula, bones of the talus and metatarsals) and the pelvic girdle (ilium, ischium and pubic bone).
The spine has 33 stacked vertebrae bones that structurally support the spinal cord and form the spinal canal. A typical vertebrae has a posterior and medial spinous process, lamina positioned laterally on either side of the spinous process which is adjacent to the vertebral canal which houses the spinal cord, a body which is a large portion positioned anteriorly, an articular process to articulate with vertebrae positioned superiorly and inferiorly and a process on the thoracic vertebrae specifically for articulation with the ribs/a costal facet.
- 7 Cervical (Neck) (Moveable/Flexible Vertebrae)
- 12 Thoracic (Moveable/Flexible Vertebrae)
- 5 Lumbar (Moveable/Flexible Vertebrae)
- 5 Sacral (Fused/Immoveable)
- 4 Coccyx (Fused/Immoveable)
Cervical, thoracic, lumbar, sacral and coccygeal vertebrae all have characteristics that are both similar and individual characteristics that make them unique. It is imperative to understand the fundamental anatomy of the vertebral bodies and how they relate to the functional surgery of the patient.
- C1/Atlas - articulates with the occipital bone at the foramen magnum and with C2. It's characteristic is that it is just a ring, it has no body
- C2/Axis - differs because the body of C1 fuses to the body of C2 at a projetion called the odontoid process
- Cervical - Smaller processes
- Thoracic - have facets for ribs, also have very large and longer spines than the adjacent vertebrae
- Lumbar - Weight bearing, largest bodies of the vertebrae
- Sacrum - Fused
- Coccyx - Fused
Each pair of vertebrae (except C1/C2) is attached by joints, intervertebral discs and a pair of gliding facet joints. Intervertebral disc material lies between and allows for movement of the bodies of the vertebrae and absorb shock. It is composed of rings of fibrocartilage (very strong); the annulus fibrosis ring, whose core is composed of a soft gelatinous center called a nucleus pulposus, attaches above and below each body. A herniated or "slipped" disc is the nucleus pulposus which comes out of the annulus fibrosis and presses on the nerve roots typically eliciting extreme pain. The discs are also subject to degenerative changes.
From the posterior view, the vertebrae in conjunction appear as a column (vertebral column) which gives form to the back and torso, dexterity and mobility function and flexibility, and spinal cord protection. From the lateral view, it has slight curves at each level. Abnormal curves have specific names;
From the posterior view, the vertebrae in conjunction appear as a column (vertebral column) which gives form to the back and torso, dexterity and mobility function and flexibility, and spinal cord protection. From the lateral view, it has slight curves at each level. Abnormal curves have specific names;
- An accentuated thoracic curve is called kyphosis
- An accentuated lumbar curve is called lordosis
- A deviated lateral curve, usually in the thoracic area is called scoliosis
The vertebral bodies have distinct landmarks and can be characterized
- body; anterior, thick and disc (rounded) shape, the weight bearing part of vertebrae
- lamina; posterior vertebral arch
- pedicle; extend from the body and unite with the lamina
There are a number of processes (appendage or outgrowth) arising from vertebral arch
- transverse processes; point where lamina and pedicle join
- spinous process; projects posteriorly
- superior articular processes; articulates with inferior processes
- inferior articular processes; articulates with superior processes of the vertebra above
- facets; articulating surfaces of articular processes
- intervertebral joints; articulations formed between bodies and articular facets of successive vertebrae
- mammilary process
- Intervertebral Foramen; opening on both sides of column that permits passage of spinal nerves and vessels