The Skeletal System- The Axial Skeleton PDF

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The Skeletal System- The Axial Skeleton...

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The Skeletal System: The Axial Skeleton 10th October 2017 INTRODUCTION  

Bones protect the soft body parts and make movement possible; they also serve as landmarks for locating parts of other bod1y systems. The musculoskeletal system is composed of the bones, joints, and muscles working together.

DIVISIONS OF THE SKELETAL SYSTEM    

The skeleton consists of 206 named bones. Skeletons of infants have more than 206 bones because their bones fuse later in life. The axial skeleton consists of bones arranges along the longitudinal axis. The parts of the axial skeleton are the skull, auditory ossicles, hyoid bone, vertebral column, sternum and ribs. The parts of the appendicular skeleton are pectoral girdles, bones of the upper limbs, pelvic girdles, and bones of the lower limbs. Axial skeleton: 80 bones Skull -Cranium -Face Hyoid bone Auditory ossicles Vertebral column Thorax -Sternum -Ribs

8 14 1 6 26 1 24

Appendicular skeleton: 126 bones Pectoral Girdles -Clavicle -Scapula Upper limbs -Humerus -Ulna -Radius -Carpals -Metacarpals -Phalanges Pelvic girdle -Hip, pelvic or coxal bone Lower limbs -Femur -Paella -Fibula -Tibia -Tarsals -Metatarsals -Phalanges

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2 2 2 2 2 16 10 28 2 2 2 2 2 14 10 28

TYPES OF BONES Type Long bones

Short bones

Flat bones

Irregular bones

Sesamoid bones

Sutural bones

Feature -Greater length than width. -Consists of a shaft. -Variable number of epiphyses. -Slightly curved for strength to absorb stress of body weight at different points thus it is evenly distributed. -Bones would fracture easily if they were straight. -Consists mostly of compact bone tissue in diaphyses. -Considerable amounts of spongy bone tissue in epiphyses. -Cube shaped. -Consists of spongy bone tissue with a thin layer of compact bone tissue on the surface.

Examples Femur Tibia Fibula Humerus Ulna Radius Phalanges

-Generally thin. -Composed of two nearly parallel plates of bone tissue enclosing a layer of soft bone tissue. -Afford considerable protection. -Provide extensive areas for muscle attachment. -Complex shapes. -Vary in amount of spongy and compact bone tissue.

Cranial bones Sternum Scapula Ribs

-Shaped like a sesame seed. -Develop in certain tendons or ligaments where there is considerable friction, tension, and physical stress. -Number varies from person to person. -Not always completely ossified. -Protect tendons from excessive wear and tear. -Improve the mechanical advantage at a joint by changing the direction of pull of a tendon. -Classified by location. - Small bones located in sutures between certain cranial bones.

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Carpals Tarsals

Vertebrae Hip bones Certain facial bones Calcaneus Patella

BONE SURFACE MARKINGS 

Depressions and openings: Allow the passage of soft tissues (i.e. blood vessels, nerves, ligaments, and tendons) or form joints. Type Fissure Forame n Fossa Sulcus Meatus

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Description Narrow slit between adjacent parts of bones through which blood vessels or nerves pass. Opening through which blood vessels, nerves, or ligaments pass. Shallow depression. Groove along bone surface that accommodates blood vessel, nerve, or tendon. Tube like opening.

Processes: Projections or outgrowths that help form joints or serve as attachment points for connective tissue (i.e. ligaments and tendons). Type Processes that form Condyle joints Facet Head Processes that form attachment points for connective tissue

Crest Epicondyle Spinous process Trochanter Tubercle Tuberosity

Description Large, round protuberance with a smooth articular surface at the end of bone. Smooth, flat, slightly concave or convex articular surface. Usually rounded articular projection supported on neck (constricted portion) of bone. Prominent ridge or elongated projection. Roughened projection above condyle. Long, narrow ridge or border (less prominent than crest). Very large projection. Variably sized round projection. Variably sized projection that has a rough, bumpy surface.

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THE AXIAL SKELETON AND HOMEOSTASIS  

The bones of the axial skeleton protect many of the body’s organs such as the brain, spinal cord, heart, and lungs. They are also important in support and calcium storage and release.

SKULL - CRANIAL BONES  

The skull contains 22 bones, not counting the bones of the middle ear. The 8 cranial bones for the cranial cavity, which encloses and protects the brain. They include: o The frontal bone o Two parietal bones o Two temporal bones o The occipital bone o The sphenoid bone o The ethmoid bone Cranial Bones Frontal Bone Parietal Bones Temporal Bones Occipital Bone Sphenoid Bone

Ethmoid Bone

-Forms the forehead, the roofs of the orbits and most of the anterior part of the cranial floor. -Forms the greater portion of the sides and roof of the cranial cavity. -Forms the inferior lateral aspects of the cranium and part of the cranial floor. -Forms the posterior part and most of the base of the cranium. -The sphenoid bone lies at the middle part of the base of the skull. -It is the keystone of the cranial floor as it articulates with all the other cranial bones, holding them together. -The greater wings form part of the lateral wall of the skull. -The lesser wings form part of the floor of the cranium and the posterior part of the orbit of the eyes. -Forms: (1) part of the anterior portion of the cranial floor. (2) the medial wall of the orbits. (3) the superior portion of the nasal septum. (4) most of the superior sidewalls of the nasal cavity.

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SKULL - FACIAL BONES 

The 14 facial bones form the face. They include: o Two nasal bones o Two lacrimal bones o Two palatine bones o Two inferior nasal conchae o The vomer o Two maxillae o Two zygomatic bones o The mandible Facial Bones Nasal Bones Lacrimal Bones Palatine Bones Inferior Nasal Conchae Vomer Maxillae

Zygomatic Bones Mandible

-Forms the bridge of the nose. -Forms a part of the medial wall of each orbit. -The smallest bones of the face. -Form the posterior portion of the hard plate, part of the floor and lateral wall of the nasal cavity, and a small portion of the floors of the orbits. -Forms part of the inferior lateral wall of the nasal cavity. -Forms the inferior portion of the bony nasal septum, the partition that divides the nasal cavity into right and left sides. -Forms part of the floors of the orbits, part of the lateral walls and floors of the nasal cavity, and most of the hard plate. -The paired maxillae unite to form the upper jawbone. -They articulate with every bone of the face except the mandible. -Forms the prominences of the cheeks and part of the lateral wall and floor of each orbit. -The only movable skull bone. -The largest, strongest facial bone.

SKULL – UNIQUE FEATURES  

Seven skull bones form each of the orbits. Sutures are immovable joints in adults that connect most bones of the skull. Examples are the coronal, sagittal, lambdoid, and squamous sutures.

HYOID BONE  

The hyoid bone is a U-shaped bone that does not articulate with any other bone. It supports the tongue and provides attachment for some tongue muscles and for some muscles of the pharynx and neck.

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VERTEBRAL COLUMN 

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Functions of the vertebral column include: o Act as a strong flexible rod that can move forward, backward, sideways, and rotate. o Encloses and protects the spinal cord. o Supports the head. o Serves as a point of attachment for the ribs, pelvic girdle, and muscles of the back and upper limbs. The total number of vertebrae during early development is 33. Several vertebrae in the sacral and coccygeal region will then fuse. The adult vertebral column typically contains 26 vertebrae. They are distributed as follows: Cervical vertebrae Thoracic vertebrae Lumbar vertebrae Sacrum (Consisting of 5 fused sacral vertebrae) Coccyx (Consisting of 4 fused coccygeal vertebrae)

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7 12 5 1 1

The adult vertebral column contains four normal curves (cervical, thoracic, lumbar and sacral) that provide strength, support, and balance. Each vertebra usually consists of a vertebral body, vertebral arch, and seven processes. Intervertebral discs are avascular.

THORACIC BONES - STERNUM   

The sternum is a flat, narrow bone located in the center of the anterior thoracic wall. The superior part is the manubrium; the middle part is the body; the smallest part is the xiphoid process. The segments of the sternum typically fuse by age 25.

THORACIC BONES - RIBS     

Twelve pairs of ribs, numbered 1-12 from superior to inferior give structural support to the sides of the thoracic cavity. Length increase from rib 1-7 then decrease in length to rib 12. The first 7 pairs of ribs attach to sternum by a strip of costal cartilage, which contribute to the elasticity of the thoracic cage. The ribs that have costal cartilage and attach directly to the sternum are called true ribs. The remaining five pairs of ribs are termed false ribs as their costal cartilages either attach indirectly to the sternum or do not attach to the sternum at all.

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DIAGRAMS

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SUMMARY Skull – Cranial bones Frontal bone Parietal bones Temporal bones Occipital bone Sphenoid bone Ethmoid bone

(8) 1 2 2 1 1 1

Skull- Facial bones Nasal bones Lacrimal bones Palatine bones Inferior nasal conchae Vomer Maxillae Zygomatic bones Mandible

(14) 2 2 2 2 1 2 2 1

Hyoid bone

(1)

Auditory ossicles Malleus (hammer) Incus (anvil) Stapes (stirrup)

(6) 2 2 2

Vertebral column Cervical vertebrae Thoracic vertebrae Lumbar vertebrae Sacrum Coccyx

(26) 7 12 5 1 1

Sternum

(1)

Ribs

(24) Total

END OF NOTES

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