Thoracic Cage: Sternum and Ribs

• Axial Skeleton comprises the Thorax and Vertebrae
• The thoracic cage is made up of 37 bones

Components of the Thoracic Cage

• Sternum = 1
• Ribs = 12 pairs (24 total)
• Thoracic vertebrae = 12

Functions of the Thoracic Cage

• Protects organs of the thorax (heart and lungs)
• Provides attachment points for muscles involved in breathing

Sternum

• The sternum is a flat bone forming the anterior part of the thoracic cage.
• It is also called the Breast Bone

Parts of the Sternum

• The manubrium is the upper broad part
• The manubrium has a clavicular notch which gives attachment to the clavicle
• The manubrium has a 1st costal notch which gives attachment to the 1st rib and also a suprasternal notch.
• The body is the middle part
• The upper end of the body articulates with the manubrium and the lower end with the xiphisternum
• The body gives attachment to the 2nd to 7th costal cartilage
• The xiphisternum, also called the Xiphoid process, is the lower part

Ribs

• There are 24 ribs, or 12 pairs
• Ribs are flat, ribbon-like bony arches arranged one below the other
• The gaps between two ribs are called intercostal spaces

Classification of Ribs Based on Attachment

• True Ribs: Also called vertebrosternal ribs
• True ribs are attached to the sternum in front and vertebra behind
• Ribs 1-7 are true ribs
• False Ribs: They are attached to vertebra posteriorly and to the sternum indirectly through cartilage
• Ribs 8-12 are false ribs
• Floating Ribs: The costal cartilages of ribs 11-12 have no articulation with the sternum or vertebra

Classification of Ribs based on Shapes and Sizes

• Typical Ribs: Same shape and size
• Typical ribs are Ribs 3-9
• Atypical Ribs: They are of different shapes and sizes
• Atypical ribs are Ribs 1, 2, 10, 11, 12

Typical Rib Parts

• Has an anterior end, shaft, and posterior end
• Anterior end articulates with costal cartilage
• Posterior end has a head, neck, and tubercle
• The head has 2 facets that articulate with vertebra
• The neck lies between the head and tubercle
• The tubercle lies between the neck and the shaft
• The shaft is a flat part with inner and outer surfaces, and upper and lower borders
• The shaft changes its direction at the angle of the rib

Vertebral Column

• The vertebral column, also called the spine, spinal column, or backbone, is the main part of the axial skeleton
• It forms a strong and flexible support for the trunk and extends from the base of the skull
• It consists of 33 irregular bones called vertebrae
• The length of the vertebral column is 72 cm

Functions of the Vertebral Column

• Helps with posture
• Supports the body weight
• Assists with locomotion (movement)
• Protects the spinal cord and nerve roots
• Helps transmit body weight to the ground through the legs
• Absorbs shocks and keeps the body steady

Names of Vertebrae

• Cervical Vertebrae: 7 (C1= Atlas, C2= Axis)
• Thoracic Vertebrae: 12
• Lumbar Vertebrae: 5
• Sacral Vertebrae: 5, but are fused to form 1 bone
• Coccyx Vertebrae: 4, but unite to form 1 bone
• There are a total of 33 bones in the vertebral column

Curvatures of the Vertebral Column

• There are 4 curves in the spine: Cervical, Thoracic, Lumbar, and Sacral curves
• Primary Curvatures develop during fetal life
• Thoracic and Sacral curves are concave anteriorly
• Secondary Curvatures develop after birth
• Cervical and Lumbar curves are convex anteriorly, as seen in behaviors like lifting the head and walking

Parts of Vertebra

• Vertebral Body
• Vertebral Arch

Vertebral Body

• Flat, broad part separated from other vertebra through fibrocartilaginous intervertebral discs
• It is the weight-bearing structure of the spine

Vertebral Foramen

• An opening in a vertebra that allows the spinal cord to pass through

Intervertebral Foramen

• Spinal nerves from the spinal cord pass through it

Vertebral Arch (Neural Arch)

• Encloses the vertebral foramen
• Is attached on each side of the body
• Protects the spinal cord and spinal nerve roots from injury

Pedicle

• Short stout processes attached to the superior body on each side

Laminae

• Thin plates of bone forming the roof of the vertebral foramen
• Two laminae unite to form the spinous process

Transverse Process

• Projects postero-laterally from the junction of laminae and pedicles

Sacrum

• Triangular wedge-shaped bone formed by the fusion of 5 sacral vertebrae
• It has a base and apex
• The broad base articulates with L5, and the apex articulates with the coccyx
• The sacral promontory is an anterior projection from the base.

Coccyx

• Small triangular bone made of 4 coccygeal vertebrae
• It is also called the Tail Bone
• It has a base, apex, dorsal, and lateral surface
• The coccyx articulates with the sacrum at the sacrococcygeal joint