Skeletal System Divisions

Divisions of the Skeletal System

• The skeletal system includes bones, cartilage, and ligaments.
• The adult skeleton has 206 bones - children have more
• The skeletal system provides support, aids in movement, assists in calcium homeostasis.
• The skeleton is divided into axial and appendicular divisions.

Axial Skeleton

• The axial skeleton forms the vertical, central axis of the body.
• It protects internal organs and allows movement of the head, neck, back, and respiratory muscles.
• The axial skeleton consists of 80 bones.
• These include the skull, vertebral column, ribs, and sternum.

Appendicular Skeleton

• The appendicular skeleton forms the upper and lower extremities.
• It includes bones that attach the extremities to the axial skeleton.
• There are 126 bones in the appendicular skeleton.
• The appendicular skeleton is discussed further in Chapter 9.

Organs Protected by the axial skeleton.

• Internal organs protected by the axial skeleton include the brain, heart, lungs, and spinal cord.
• The brain is particularly well-protected by bone.

Axial vs Appendicular Skeleton

• Axial bones are located along the central axis of the body.
• Appendicular bones attach to the axial skeleton.
• Appendicular bones are generally more moveable and have more varied shapes than axial bones.

Introduction to the Skull

• The skull is composed of 22 bones divided into two groups: cranial and facial.
• Cranial bones surround and protect the brain.
• Facial bones form the face, nasal cavity, mouth, and orbits.
• The skull contains openings called cavities to house soft organs and decrease skull weight.

Bones of the Skull

• The cranium includes the frontal (1), parietal (2), occipital (1), temporal (2), sphenoid (1), and ethmoid bones (1).
• The face includes the mandible (1), maxillae (2), lacrimal (2), nasal (2), palatine (2), zygomatic (2), inferior nasal conchae (2), and vomer (1).
• Paired skull bones are found on both the left and right sides, whereas some bones are unpaired.

Cavities of the Skull

• Skull cavities house softer structures.
• Cavities include the cranial cavity, orbits, nasal cavity, oral cavity, and paranasal sinuses.

Frontal Bone

• The frontal bone forms the forehead and part of the cranium.
• Key bony markings include the glabella, supraorbital margin, and supraorbital foramen.

Parietal Bones

• The parietal bones form the superior lateral sides of the skull.
• Parietal bones articulate with the frontal, temporal, and occipital bones.

Occipital Bone

• The occipital bone forms the posterior skull and posterior base of the cranial cavity.
• Bony markings include the external occipital protuberance, superior nuchal line, foramen magnum, and occipital condyles.

Temporal Bones

• The temporal bones form the lower lateral sides of the skull.
• Bony markings include the squamous portion, zygomatic process, mastoid process, external acoustic meatus, mandibular fossa, articular tubercle, and styloid process.

Sphenoid Bone

• The sphenoid bone forms a large part of the base of the central skull and part of the temples.
• Key bony markings are the greater and lesser wings, sella turcica, pituitary fossa, and medial and lateral pterygoid processes.

Ethmoid Bone

• The ethmoid bone forms part of the orbit and the nasal cavity.
• Bony markings include the perpendicular plate, superior and middle nasal conchae, crista galli, cribriform plate, and olfactory foramina.

Mandible

• The mandible forms the lower jaw.
• The mandible is the only moveable bone of the skull.
• Bony markings include the body, ramus, angle, coronoid and condylar processes, mandibular notch, mental foramina, and mental protuberance.

Maxillary Bone

• The maxillary bone, also called the hard palate or maxilla, forms the upper jaw.
• It accounts for most of the roof of the mouth and part of the orbit.
• It also accounts for the lateral base of the nose.
• The maxillary bone's bony markings: alveolar processes, and infraorbital foramen.

Lacrimal Bones

• The lacrimal bones form part of the orbit and contain lacrimal glands which secrete tears.

Palatine Bones

• The palatine bones form the posterior portion of the hard palate and contribute to the medial part of the orbit and the vertical section of the nasal cavity.

Zygomatic Bones

• The zygomatic bones, known as the cheekbones, form much of the lateral part of the orbit.
• A key feature is the temporal process, which unites with the zygomatic process of the temporal bone to form the zygomatic arch.

Vomer, Nasal, and Inferior Nasal Conchae Bones

• The vomer forms part of the nasal septum.
• The nasal bones form the bony base (bridge) and lateral walls of the nose.
• The inferior nasal conchae project into the nasal cavity.

Articulated Skull

• The articulated skull shows how many skull bones are visible from an anterior view.

Sutures

• Sutures are immobile joints filled with dense, fibrous connective tissue that attach cranial bones.
• Specific sutures include:
  • Sagittal suture connects the two parietal bones.
  • Coronal suture connects the frontal bone to the parietal bones.
  • Lambdoid suture connects the parietal bones to the occipital bone.
  • Squamous suture connects the parietal and temporal bones.

The Orbit

• The orbit protects the eyeball and the muscles that move it.
• The orbit is formed from the frontal, zygomatic, maxilla, ethmoid, lacrimal, palatine, and sphenoid bones.
• The optic canal allows entry of the optic nerve.
• The superior orbital fissure allows entry of blood supply.

Nasal Cavity

• The nasal cavity is bordered by the maxillae and nasal bones.
• The nasal septum, which divides the nasal cavity, is formed by the perpendicular plate of the ethmoid, vomer, and septal cartilage.
• Nasal conchae, covered with mucous membranes, warm, filter, and moisten inhaled air.

Paranasal Sinuses

• Paranasal sinuses are hollow, air-filled spaces in the frontal, maxillary, sphenoid, and ethmoid bones.
• They connect to the nasal cavity, adding volume to the skull without extra weight and allowing voice resonance.

Oral Cavity

• The oral cavity is formed by the maxillae, mandible, and palatine bones.
• Teeth are embedded in alveolar processes.
• The hard palate is formed by the palatine process of the maxillae and the horizontal plate of the palatine bones. Mandibular (mental) foramen allows entry of nerves and blood vessels to lower jaw.

Midsagittal Section of Skull

• The frontal and parietal bones are united by the coronal suture.
• The temporal bone contains the internal acoustic meatus.
• The sphenoid sinus and nasal septum are also visible.

Brain to Body Size Ratio

• Humans have a greater brain-to-body size ratio than other primates. -A human neonate head's size approaches that of the pelvic outlet thus increasing difficulty of vaginal delivery.

Skull development

• The skull is not fully fused at birth.
• Fontanelles ("soft spots") in the infant skull allow change during birth and aid in rapid brain growth during infancy.
• Bones are not fully fused until adulthood.

Fusion disorders

• Cleft lip results from a failure of the upper lip to fuse together completely, or only partially.
• Cleft palate is the result of the hard palate failing to fuse completely.
• Craniosynostosis is premature fusion of a suture line, causes abnormal growth of skull and cranial deformity.

Hyoid Bone

• The hyoid bone is U-shaped and located in the superior part of the neck.
• It does not articulate with other skull bones.
• It is used primarily for muscle attachment.
• It’s location in the neck makes it susceptible to be broken during strangulation.

Vertebral Column

• The vertebral column has 24 vertebrae, plus the sacrum and coccyx.
• The five regions of the vertebral column are cervical (7 vertebrae), thoracic (12), lumbar (5), sacral (5 fused), and coccygeal (4 fused).
• Four curves (cervical, thoracic, lumbar, and sacrococcygeal) provide strength, flexibility, and shock absorption.
  • Cervical curve is posteriorly oriented.
  • Thoracic curve is anteriorly oriented.
  • Lumbar curve is posteriorly oriented.
  • Sacrococcygeal curve is anteriorly oriented.

Abnormal curvature

• An excessive posterior curvature of thoracic region is Kyphosis.
• An excessive anterior curve of lumbar region is Lordosis.
• An abnormal lateral curvature is called Scoliosis.

General Vertebra Structure

• Vertebral structures include: -Vertebral body. -Vertebral arch with pedicles and lamina. -Vertebral foramen. -Transverse, spinous, and articular processes. -Intervertebral foramen.
• Intervertebral discs are fibrocartilage pads between the bodies of each vertebrae.
• Superior and inferior articular processes unite the vertebrae posteriorly.
• Intervertebral foramen allow spinal nerves to exit.

Cervical Vertebrae

• There are seven cervical vertebrae.
• They have small vertebral bodies.
• Transverse foramina are for vertebral arteries. There are also bifid spinous processes.
• C1 (atlas) and C2 (axis) allow rotation of the head.
• C1 allows head to move in a “yes” motion.
• C2 = axis, contains the dens and allows head to move in a “no” motion.

Thoracic Vertebrae

• There are 12 thoracic vertebrae.
• Vertebral bodies increase in size as you descend the spinal column.
• There are long and downward angled spinous processes, and these articulate with ribs.

Lumbar Vertebrae

• There are five lumbar vertebrae.
• These have Largest vertebral bodies and short, blunt spinous processes.

Sacrum and coccyx

• The sacrum is a thick triangular shaped bone formed by fusion of five vertebrae, and with a median sacral crest, a sacral promontory and sacral foramina..
• The coccyx is form by fusion of four vertebrae.

Intervertebral Discs

• These are fibrocartilage pads between vertebrae.
• Anulus fibrosus – a fibrous outer layer.
• There is a Nucleus pulposus - soft, gel-like area.
• They Anchor vertebrae to each other and cushion and allow movement.

Thoracic Cage

• The sternum:
• Manubrium
• Clavicular notch
• Suprasternal notch
• Body
• Joins to manubrium
• Xiphoid process Clavicles and some ribs attach to sternum.

Ribs

• There are 12 pairs of curved flat bones that have a costal cartilage and articulate with the sternum.
• Features of ribs: -Head, neck, body, tubercle, and angle of the rib -Costal groove Only some ribs have costal cartilage.

Types of Ribs

• True ribs (1–7)—costal cartilage directly attaches to sternum.
• False ribs (8–12)—costal cartilage does not attach to sternum.
• Floating ribs (11–12)—do not have costal cartilage.

Chest Compression

• Major consequence of improper chest compressions that may fractur the xiphoid process
• This Can further complications if the xiphoid process punctures the pericardium of the heart or the pleura of the lungs.