Lesson 1 Chapter 6 – The Skeletal System

LESSON 1 Chapter 6 – The Skeletal System [Axial Division] Unit 3 Study Guide Skeleton Axial and Appendicular (covered in Unit 3.2) The adult human skeleton is made up of 206 bones, and is divided into two main divisions: the axial and appendicular. The axial skeleton consists of the bones along the axis of the body. The appendicular skeleton consists of the bones of the appendages (arms and legs) and the girdles (shoulder and pelvic) that connect them with the axial skeleton. (Axial: 80 bones, Appendicular: 126 bones) 1 LESSON 1 Chapter 6 – The Skeletal System [Axial Division] Axial Division: The axial skeleton includes the skull, the hyoid bone, the vertebral column (spine, sacrum, and coccyx), the sternum, and the ribs. Its components are aligned along the long axis of the body.              Skull: 22 bones. Rests on the superior end of the vertebral column. Two sets of bones: cranial (8 bones) and facial (14 bones) Cranial bones are flat, rounded, and fused to protect the brain 8 bones include: frontal (1), parietal (2), temporal (2), occipital (1), sphenoid (1), and ethmoid (1). Facial bones provide a framework for the facial muscles, form eye sockets, and form jaws for the teeth 14 bones include: nasal (2), maxillae (2), zygomatic (2), mandible (2), lacrimal (2), palatine (2), inferior nasal conchae (2), vomer (1) Sutures: "seam" unmovable joint found only between skull bones. Four prominent sutures: coronal, sagittal, lambdoidal, squamosal Fontanels: at birth, membrane filled spaces are found between the cranial bones. These "soft" spots are areas of dense connective tissue that will eventually be replaced by bone. They function to enable the fetal skull to compress during birth and permit the rapid growth of the brain. Nasal Bone (2) forms the bridge of the nose Zygomatic Bone (2) are cheekbones Vomer (1) forms the posterior and inferior border of the nasal septum (sharp edge) Maxilla (2) forms the upper jaw Mandible (1) forms the lower jaw Palatine Bone (2) back cavity of the nasal cavity between maxilla bone Lacrimal Bone (2) Minor contribution to the medial wall of each orbit. Part of the passage way that permits tears to drain from the eye surface into the nasal cavity. Inferior Nasal Concha Bone (2) extends horizontally along the lateral wall of each nasal cavity 2 LESSON 1 Chapter 6 – The Skeletal System [Axial Division] 3 Axial Division: Sutures (holding the Cranial bones) Sutures are immovable joints. The four major sutures are the:     Coronal suture (between the parietal and frontal bones) Lambdoidal suture (between the occipital and parietal bones) Sagittal suture (between the two parietal bones) Squamous suture (between the parietal and temporal bones). [anterior] [posterior] [top] [sides] Axial Division: Foramen Magnum The large opening in the base of the skull through which the spinal cord passes. Axial Division: Paranasal Sinuses The sinuses are air filled cavities located in the face and around the nose. The sinuses are named according to the bone in which they are located. Sinuses serve many functions. They first filter and humidify the air we breathe. In evolutionary terms, they lighten the weight of the head, and also act as a resonating chamber to give each person’s voice an individual character. Maxillary Sinus = cheekbone Ethmoid Sinus = between the eyes Frontal Sinus = forehead, above eyes Sphenoid Sinus = back of the head, behind the ethmoid LESSON 1 Chapter 6 – The Skeletal System [Axial Division] 4 Axial Division: Vertebral Column The vertebral column has three groups of vertebrae and two sets of fused bones. These vertebrae include 7 cervical (neck) vertebrae, 12 thoracic (upper back) vertebrae, and 5 lumbar (lower back) vertebrae. Five fused vertebrae form the sacrum and from three to five fused small vertebrae form the coccyx (tail bone). [Breakfast at 7, lunch at 12 and dinner at 5] Cervical Vertebrae: C1 - C7 Smallest and lightest First two are atypical. Features: Body is broader from side to side. Except C7 the spinous process is short and projects directly back and is split at its tip (bifid). Vertebral foramen are large and generally triangular. C7 spinous process is not bifid, and larger. Used as a landmark for counting vertebra. "Vertebra Prominens" Atlas: C1. Highly modified. Has no body or spinous process. Essentially a ring of bone consisting of anterior and posterior arches and a lateral mass on each side containing articular facets to receive the occipital condyles. Axis: C2. Projecting superiorly from the body is a tooth-like process called the dens. Acts as a pivot for the rotation of the atlas Thoracic Vertebrae: T1 - T12. Articulate with the ribs. Increase in size from the first to the last. Body is roughly heart-shaped. 2 demifacets on each side articulate with the head of the rib. Vertebral foremen is circular. Spinous process - long and hooks sharply downward. Transverse processes (1-10) have facets mat articulate win the tubercles of the ribs. Lumbar Vertebrae: L1 - L5. Largest and strongest. Enhanced weight bearing function. Bodies are massive and kidney shaped. Spinous processes are short, flat and hatchet shaped. Vertebral foremen is triangular. Articular processes lock the lumbar vertebrae together and provide stability by preventing rotation of the lumbar spine. Sacrum: Triangular bone formed by fission of 5 sacral vertebrae. Shapes posterior wall of the pelvis. Strengthens and stabilizes the pelvis. Articulates superiorly with Ls and inferiorly with the coccyx. Two wing-like alae articulate with the 2 hip bones to form the sacroiliac joints. Coccyx: 3-5 fused vertebrae. Forms a small triangular bone. Muscle attachment site. LESSON 1 Chapter 6 – The Skeletal System [Axial Division] 5 Axial Division: Thorax Chest area. Elements forming the bony thorax include: thoracic vertebrae dorsally, ribs laterally, sternum and costal cartilages anteriorly. Intercostal spaces occupied by intercostal muscles which elevate and depress the thorax during breathing. The twelve (12) pairs of ribs are long, flattened, and curved bones that form a protective cage for the heart, lungs, and other internal organs. The vertebrosternal (true) ribs are the first seven ribs; they are "true" because they attach directly to the sternum (breast bone). Ribs eight through twelve are the false ribs because they indirectly attach to the sternum or they lack a sternal attachment. Ribs eight through ten are the vertebrochondral ribs because they attach indirectly to the sternum by cartilage. Ribs eleven and twelve are called floating (vertebral) ribs because they do not attach to the sternum. Instead, their floating position allows them to bend sideways while providing protection for the kidneys. Sternum: Breastbone. Midline of thorax. Consists of three regions: manubrium, body, xiphoid process. Manubrium articulates with the clavicles. Body forms the bulk of the sternum. Xiphoid serves as the attachment point for the diaphragm and some abdominal muscles. Ribs: 12 pair. All attached posteriorly to the thoracic vertebrae, then curve down and forward toward the anterior. Upper 7 pair attach directly to the sternum (true ribs). Other 5 pair (false ribs) either attach indirectly to the sternum or lack a sternal attachment entirely. Ribs 11 and 12 are floating ribs. Ribs gradually increase in length from the first to 7th pair. Pairs 8-12 decrease in length. Typical rib is a bowed flat bone. Bulk of the rib is the shaft. Wedged shaped head has two facets. The neck of the rib is the constricted portion. Lateral to the head is the knoblike tubercle that articulates with the transverse process of the thoracic vertebrae. LESSON 1 Chapter 6 – The Skeletal System [Axial Division] 6 Axial Division: Rib Structure 12 pair. All attached posteriorly to the thoracic vertebrae, then curve down and forward toward the anterior. Upper 7 pair attach directly to the sternum (true ribs). Other 5 pair (false ribs) either attach indirectly to the sternum or lack a sternal attachment entirely. Ribs 11 and 12 are floating ribs. Ribs gradually increase in length from the first to 7th pair. Pairs 8-12 decrease in length. Typical rib is a bowed flat bone. Bulk of the rib is the shaft. Wedged shaped head has two facets. The neck of the rib is the constricted portion. Lateral to the head is the knoblike tubercle that articulates with the transverse process of the thoracic vertebrae. Chondral means pertaining to cartilage. Costal means pertaining to ribs. Parts of a typical rib: A typical rib consists of 5 parts: Head, Neck, Tubercle, Shaft and Angle.      Head: It has two facets, the inferior of which articulates with the body of the numerically corresponding vertebra and the superior articulates with the vertebra immediately above Neck: It is a constricted portion of the bone situated between the head and the tubercle Tubercle: It is a prominence on the outer surface of the rib at the junction of neck and shaft. It contains a facet for articulation with the transverse process of numerically corresponding vertebra. Thus we see that a typical rib forms a total of three joints with the vertebral column. Shaft (Body): It is thin, flattened and twisted on its long axis. The inferior border has a grove known as costal grove. Angle: Angle is formed where the shaft of the rib bends sharply forwards. The anterior end of each rib is attached to the corresponding costal cartilage thorough which it is jointed to the sternum. Costal angle: the abrupt change in curvature of the body of a rib posteriorly, such that the neck and head of the rib are directed upward. Costal groove: a groove along the inferior margin of the superior rib that accommodates the intercostal nerves and associated major arteries and veins. Intercostal space: the space between two adjacent ribs. (11 spaces – named superiorly) LESSON 1 Chapter 6 – The Skeletal System [Axial Division] Additional information for Sternum Sternum angle: the angle between the sternum body and the manubrium. Suprasternal notch: aka jugular notch; the depression in the top of the sternum between its articulations with the two clavicles. “u” Xiphoid process: the pointed process of cartilage, supported by a core of bone, connected with the lower end of the sternum. 7