Skeletal System: Axial and Appendicular

Divisions of the Skeleton

• Axial skeleton includes the skull, vertebral column, sternum, and ribs
  • It protects internal organs
  • It provides a stable base for limb attachment
• Appendicular skeleton includes the upper and lower limbs and connecting girdles
  • It enables movement

Axial vs. Appendicular Skeleton: Bone Count

• The axial skeleton consists of 80 bones
• The appendicular skeleton consists of 126 bones

Bone Features / Surface Markings

• Structural features adapted for specific functions are called surface markings
• The two major types of surface markings are depressions/openings and processes
  • Depressions and openings allow passage for blood vessels and nerves, or formation of joints
  • Processes are projections or outgrowths that form joints or serve as attachment points for ligaments and tendons

Skull

• The skull has 22 bones
• The 8 cranial bones form the cranial cavity
  • These bones include the frontal bone, two parietal bones, two temporal bones, occipital bone, sphenoid bone, and ethmoid bone
• The 14 facial bones form the face:
  • These bones include two nasal bones, two maxillae, two zygomatic bones, mandible, two lacrimal bones, two palatine bones, two inferior nasal conchae and vomer
• The cranial and facial bones support special sense organs and the brain and protect from trauma
• Large cranial cavity and smaller cavities consist of the nasal cavity, orbits (eye sockets), paranasal sinuses, small cavities relating to hearing and/or maintaining equilibrium

Skull Features

• Sutures are immovable joints between skull bones
• The skull and facial bones serve as attachment points for muscles that move the head and create facial expressions
• Facial bones create the face's framework, and support digestive and respiratory entrances

Cranial Bones

• The frontal bone forms the forehead
• The parietal bones form the sides and roof of the cranial cavity
• The temporal bones form the cranium's lateral aspects and floor
• The occipital bone creates the posterior part and most of the base of the cranium
• The sphenoid bone is the middle part of the skull base
• The ethmoid bone is on the midline, in the anterior cranial floor, medial to the orbits
  • The ethmoid bone acts as the major superior support for the Nasal Cavity
  • Has thin conchae projections, lined by mucous membranes to increase surface area
  • The increased surface area is to humidify & trap particles from inhaled air

Facial Bones

• Nasal bones creates the bridge of the nose
• Maxillae creates the upper jawbone and most of the hard palate, separating the nasal cavity from the oral cavity
• Zygomatic bones (cheekbones) creates cheek prominences
• Lacrimal bones are part of the medial orbit wall
• Palatine bones makes up a posterior section of the hard palate
• Inferior nasal conchae are part of the Nasal Cavity's inferior lateral wall
• Vomer makes-up an inferior section of the Nasal Septum
• Mandible creates the lower jawbone, and is the only movable skull bone, as well as the largest and strongest facial bone
• The nasal septum which is made-up of the ethmoid's perpendicular plate combined with the vomer, divides the Nasal Cavity into left and right sections
• The eye socket (orbits) consists of the frontal, ethmoid, sphenoid, and maxillae bones
• Foramina are holes that allow the passage of blood vessels and nerves

Skull Features

• Sutures are immovable joins that fuse together skull bones
  • Coronal, lambdoid, sagittal, and squamous suture types
• Paranasal Sinuses are cavities in cranial and facial bones, close to the Nasal Cavity
  • Mucous membranes line it and drain into the nasal cavity
  • Acts as resonating chambers, so intensifying and prolonging sounds, warming combined with humidifying of air, and reduces bone mass
• Fontanelles consist of unossified tissue sections that connect cranial bones during birth
  • Also known as "soft spots" that will eventually be replaced by bony sutures
  • Provides some flexibility to the fetal skull, so allowing skull shape change as it passes through the birth canal

Associated Skull Bones

• Auditory ossicles are located in the inner ear, and consists of the malleus, incus, and stapes
• Hyoid bone is the only bone not articulating with another bone
  • Acts as a moveable base for tongue and attachment site for swallowing and/or vocalizing muscles

Vertebral Column

• It protects the spinal cord from trauma
• It supports the head
• Serves an attachment point combining the ribs, pelvic girdle, and muscles
• Curved to varying degrees
  • Increases column strength
  • Balances the upright position
  • Absorbs shock combined with protecting the fracture vertebrae

Spinal Curvatures

• A primary curve being the thoracic and sacral
  • Present from birth, creates a "C" shape
• A secondary curve being the cervical and lumbar
  • Develops over the first year of life and assists to balances trunk weight over the legs, combined with supporting the head

Vertebral Column

• Vertebrae consist typically of a body (weight bearing), which protects the Vertebral Arch, that surrounds the spinal cord and processes
  • Processes act act as points for muscle attachment
• There are 7 cervical vertebra located in the neck region
• 12 thoracic vertebra sit behind the Thoracic Cavity, and are joined at the ribs
• 5 Lumbar support the lower back
• The Sacrum consists single/five fused Sacral Vertebra
• The Coccyx consists single/four fused Coccygeal Vertebra
• Intervertebral discs consist of fibrocartilage between the adjacent Vertebrae, forming strong joints that absorb vertical shock, and allows spine movement

Vertebrae Regions

• Cervical (C1-C7) Region
  • The 1st Cervical is known as the Atlas (for head nod for "yes")
  • The 2nd Cervical is the Axis (for head shake for "no")
• In the Thoracic (T1-T-12) Region, it's the section that Articulates With The Ribs
• In the Lumbar (L1-L5) Region, it is the place for attachment to the Large Back Muscles
• Sacrum (S1-S5)
  • A Triangular bone created through five Sacral Vertebrae combined
  • Functions as the foundation for a Pelvic Girdle, known as Sacroiliac Joint
• Соссух
  • Just like the Structure of Sacrum, as the Coccyx is triangular
  • Created from merging four Coccygeal Vertebrae

Characteristics of regions:

• The Cervical region which has an elephant shaped structure, is thin and more slender with extra foramina
  • It often consists of a bifurcated (forked) spinous process
• The Thoracic region which has a giraffe shaped structure, has extra facets (for rib attachment)
  • It has a downward angled spinous process
• The Lumbar region which has a moose shaped structure, consist of a big and solid body

Atlas and Axis

• Atlas (C1) is the first cervical vertebra, and it holds up the head and articulates with occipital condyles
  • Condyle rockers allow the head to nod, doing a "yes" motion
• Axis (C2) has a dens/odontoid process through atlas
  • Acts as a rotation point, doing a "no" motion

Sacrum and Coccyx

• Sacrum is a triangular bone formed by the union of vertebrae
• Соссух is triangular like the sacrum, and formed by fusing coccygeal vertebrae

The Thoracic cage contains:

• Sternum, ribs, costal cartilage, and thoracic vertebrae that Encloses and protects Thoracic Cavity organs
  • Supports Pectoral Girdle and Upper Limb bones and sites for muscles of the shoulder, chest, neck and back, which also has a role in being able breathe freely
• The Sternum consisting of the Manubrium, Xyphoid Process and Body, is on the center's Thoracic Wall
• Ribs (12 pairs) that support its sides
  • Of those twelve
    • Ribs 1-7 consisting of True Ribs
    • Ribs 8-12 consisting of False Ribs- the vertebrae is without direct connection
    • Ribs 11-12 consisting of floating/false ribs- the sternum is without direct connection
• Costal Cartilages helps with Elasticity

Appendicular section

• Consisting of the Pectoral Girdle and the Clavicle

Upper Limbs

• The pectoral girdle consists of two Clavicle and Scapula bones
• The free portion consisting of thirty bones, includes the Humerus bones (arm), the Ulna bones (forearm-pinky side), and the Radius bones (forearm-thumb side)
  • In addition there is The Carpus bones (wrist), Metacarpus bones (palm), and Phalanges bones (fingers and/or digits)

Pectoral Girdle Clavicle

• Shaped S wise combined with articulating alongside a sternum with a sternal end
  • Smooth and compressed with scapula Articulations via Acromial End

Pectoral Girdle

• Scapula- Triangle shaped Humorous bone
• Freed from any Axial Skeleton bond, this means extra freedom for movement

Humerus

• (arm) bone is longest located at upper limbs
• This area is in union with Scapula as the Glenoid Cavity is here
• Has connection to The Radius and the Ulna sections around where the Elbow is -This area commonly called "Funny Bone" (medial epicondyle and ulnar nerve)

Radius and Ulna

• The Radius- is on same outside (thumb- area) , and in liaison with elbow
• The Ulna- is in the inside (little finger- area), and in liaison with Humorous
  • Large Upper End called Olecranon is its largest element, as its area is the bone's " Elbow Tip"
• Connected- These 2 by Intraosseous Membrane

Radius and Ulna Functions

• The Radius bears a rounded area connecting the capitulum of humerus
  • This structure helps rotating the forearm
• The Ulna or " distal" helps the coronoid act as a key structure to both Olecranon processes and the elbow combined area

Hand

• The portion is made-up of eight lesser Carpus bones.
  • Five Metacarpus bones exist for its Sole Section and area
  • There is fourteen fingers in the " Sole Area"
    • Of these their is only two fingers, which are referred to as the " Sole Section"
    • Of these there are 3 fingers and it referred to as this " Sole Section"

Lower Limbs

• An area which is in union and with Ossa Coxae bone
• Three bones here equal thirty bones, consisting of all of the Tibia (shinbone), the Kneecap, the Legs, and the Femur.