��General Anatomy� The Skeletal System 2� ��

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The Axial Skeletal System

Skeletal Organization

Axial Skeleton

• head
• neck
• trunk

Appendicular Skeleton

• upper limbs
• lower limbs
• pectoral girdle
• pelvic girdle

The Skull

• Cranial bones form the rounded cranium, which completely surrounds and encloses the brain.
• Facial bones form the bones of the face. They also
• protect the entrances to the digestive and respiratory systems as well as
• provide attachment sites for facial muscles

Cranium

Frontal (1)

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Cranium

Parietal (2)

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Cranium

Occipital (1)

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Cranium

Temporal (2)

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Cranium

Sphenoid (1)

Shaped like a butterfly or a bat, it has a central body and two lateral wings on either side.

Cranium

Ethmoid (1)

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The ethmoid bone is an unpaired cranial bone that is a significant component of the upper nasal cavity and the nasal septum. The ethmoid bone also constitutes the medial orbit wall. 

Cavities of The Skull

• The largest cavity is the cranial cavity, which encloses, cushions, and supports the brain.
• The skull also has several smaller cavities, including the orbits (eye sockets), the oral cavity (mouth), the nasal cavity, and the paranasal sinuses.

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Facial Skeleton

Maxillary (2)

Facial Skeleton

Palatine (2)

Facial Skeleton

Zygomatic (2)

Facial Skeleton

Lacrimal (2)

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Nasal (2)

Facial Skeleton

Vomer (1)

Facial Skeleton

Inferior Nasal Conchae (2)

Facial Skeleton

Mandible (1)

Sinuses

• Have a mucous lining that helps to humidify and warm inhaled air.
• Cause these skull bones to be lighter.
• Provide resonance to the voice.

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Hyoid Bone

Fontanels

• The regions between the cranial bones are thickened, fibrous membrane remnants that are not yet ossified.
• Sometimes referred to as the “soft spots” on a baby’s head.
• They close by 15 months of age.
• When a baby travels through the birth canal, the cranial bones overlap at these fontanels, in order to ease the baby’s passage.
• Newborns frequently have a “cone-shaped” head due to this temporary deformation.

Fontanels = fibrous membranes

Sutures of the Skull

• Sutures are immovable fibrous joints that form the boundaries between the cranial bones.
• Dense regular connective tissue seals cranial bones firmly together at a suture.
• Allow the cranium to grow and expand during childhood.
• In adulthood, when cranial growth has stopped, the sutures fuse and are obliterated.

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Functions Of Vertebral Column

1) Support weight

• Transmits weight to pelvis and lower limbs

2) Houses and protects spinal cord

• spinal nerves leave cord between vertebrae

3) Permits movements

4) Provides for muscle attachments

• muscles of back
• muscles of head
• Neck
• upper extremity
• thorax

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Regions and Normal Curvatures

• Formed from 33 bones in the adult
• Divided into five major regions
• Cervical vertebrae
• 7 vertebrae of the neck region
• Thoracic vertebrae
• 12 vertebrae of the thoracic region
• Lumbar vertebrae
• 5 vertebrae of the lower back
• Sacrum (5 fused)
• Inferior to lumbar vertebrae
• Articulates with coxal bones
• Coccyx (4 fused)
• Most inferior region of the vertebral column

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Regions and Normal Curvatures

• Four distinct curvatures give vertebral column an S-shape.
• Cervical and lumbar curvatures
• concave posteriorly
• Thoracic and sacral curvatures
• convex posteriorly
• Curvatures increase the resilience of the spine.

General Structure of Vertebrae

Cervical Vertebrae

• Atlas: the 1^st vertebra; carries the head; does not have a body.
• Axis: 2^nd vertebra; has a body and the odontoid process (dens) which forms the pivot upon which the Atlas rotates.
• Have transverse foramina.
• Bifid spinous processes.
• Vertebral prominens (C7) is a useful landmark.

Thoracic Vertebrae

• Heart-shaped body
• Rounded vertebral foramen
• Long spinous processes
• Rib facets

Lumbar Vertebrae

• Large kidney-shaped bodies
• Thick, short spinous processes.

Sacrum

• Five fused vertebrae
• Median sacral crest
• Anterior & posterior sacral foramina
• Forms the posterior wall of the pelvic cavity
• Sacral promontory

Coccyx

• Tailbone
• Four fused vertebrae

The Axial Skeleton Throughout Life

Curvatures of the vertebral column:

• Primary curvatures
• thoracic and sacral curvatures
• An infant's spine is C-shaped at birth
• Secondary curvatures
• cervical and lumbar curvatures
• Develop when a baby begins to walk
• Redistributes weight of the upper body over the lower limbs

Three Main Spinal Curvature �Deformities

• Kyphosis is an exaggerated thoracic curvature that is directed posteriorly, producing a “hunchback” look.
• Lordosis is an exaggerated lumbar curvature, often called “swayback,” that is observed as a protrusion of the abdomen and buttocks.
• Scoliosis is an abnormal lateral curvature that sometimes results during development when both the vertebral arch and body fail to form, or form incompletely, on one side of a vertebra.
• Scoliosis is the most common spinal curvature deformity.

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Thoracic Cage

• Consists of the thoracic vertebrae posteriorly, the ribs laterally, and the sternum anteriorly.
• Acts as a protective cage around vital organs, such as the heart, lungs, trachea, and esophagus.
• Provides attachment points for many muscles supporting the pectoral girdles, the chest, the neck, the shoulders, the back, and the muscles involved in respiration.

Ribs

• Both males and females have 12 pairs.
• Ribs 1–7 are called true ribs. At the anterior body wall, the true ribs connect individually to the sternum by separate cartilaginous extensions called costal cartilages.
• Ribs 8–12 are called false ribs because their costal cartilages do not attach directly to the sternum. The costal cartilages of ribs 8–10 fuse to the costal cartilage of rib 7 and thus indirectly articulate with the sternum.
• The last two pairs of false ribs (ribs 11 and 12) are called floating ribs because they have no connection with the sternum.

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