Anatomy - Skeletal System

• The skeletal system consists of bones, cartilages, and joints.

Human Anatomy

• Anatomy in Greek means "to cut".
• Anatomy in Latin means "to dissect".
• The levels of studying anatomy include Macroscopic/Gross Anatomy, Microscopic Anatomy/Histology, and Radiological Anatomy.

Anatomical Planes

• Sagittal (Longitudinal) Plane divides the body into right and left halves, with the median plane dividing the body equally.
• Coronal (Frontal) Plane divides the body into anterior and posterior parts.
• Transverse (Axial) Plane divides the body into upper and lower parts.

Anatomical Terms of Position

• "Superior" means towards the head while "Inferior" means away from it.
• "Anterior" means towards the front, while "Posterior" means towards the back.
• "Medial" means towards the midline, while "Lateral" means away from the midline.
• "Proximal" means closer to the point of attachment, while "Distal" means farther from the point of attachment.
• "External" (outer) means superficial, and "Internal" (inner) means deep.
• Other body positions include; Supine, Prone, Right Lateral, and Left Lateral.

The Skeleton

• The skeleton represents 20% of the body weight.
• It has two subdivisions consisting of the axial skeleton (80 bones) and the appendicular skeleton (126 bones).

Skeletal System Divisions

• The axial skeleton lies along the central axis.
• The axial skeleton is formed of the skull, vertebral column, and bones of the thoracic cage.
• The appendicular skeleton consists of the bones of the upper and lower limbs.
• The appendicular skeleton also includes the shoulder and pelvic girdles.

The Skull

• The skull is formed of two portions:
• The cranial portion consists of 8 bones.
• The facial portion consists of 14 bones.

Cranial Portion of the Skull

• The cranial portion consists of 8 flat bones.
• These flat bones are articulated via non-mobile strong fibrous joints called sutures.
• The cranial bones include one frontal bone, one occipital bone, one sphenoid bone, one ethmoid bone, two parietal bones, and two temporal bones.

Facial Portion of the Skull

• The facial portion is formed of 14 flat irregular bones joined by sutures.
• The facial bones include two nasal bones, two zygomatic bones, two maxillary bones, two lacrimal bones, two palatine bones, two inferior nasal conchae, one vomer, and one mandible.

Skull Openings

• The base of the skull contains the foramen magnum, a large opening that allows passage of the spinal cord.
• The skull contains multiple small foramina for the passage of nerves and blood vessels.
• The anterior view of the skull contains openings/cavities for the orbits, nose, and mouth.

Unique Skull Features

• The fetal skull bones are not completely united in newborns; areas that are covered by membranes are called fontanels that allow for growth with age.
• The skull contains paranasal air sinuses.
• The structure of the paranasal air sinuses is that bone contains air cavity.
• Functions include decreasing the weight of the skull.
• Sinusitis is a clinical anatomy related to the paranasal air sinuses.

The Vertebral Column

• The vertebral column forms the central part of the skeleton.
• The vertebral column supports the head and encloses the spinal cord.
• It transmits the body's weight and is formed of separate bones called vertebrae, with some being fused.

Vertebrae Groups

• The vertebral column consists of 33 vertebrae divided into five groups.
• There are 7 cervical vertebrae.
• There are 12 thoracic vertebrae.
• There are 5 lumbar vertebrae.
• 5 sacral vertebrae are fused into a single bone called the sacrum.
• 4 coccygeal vertebrae are fused in single bone called coccyx.

General Features of Vertebrae

• Each vertebra is formed of the body (anterior) and the vertebral (neural) arch (posterior).
• The vertebral arch is formed of two pedicles, two laminae, one spine, two transverse processes, two superior articular processes, and two inferior articular processes.
• Each vertebra has a vertebral foramen that allows for the passage of the spinal cord.
• The vertebrae are articulated with each other by the inter-vertebral discs.

Characteristics of Vertebrae Types

• Cervical vertebrae have bifid spinous processes, C1 is called atlas, and C2 is called axis.
• Thoracic vertebrae are characterized by articular surfaces on their body and transverse processes for the articulation with ribs.
• Lumbar vertebrae are the largest and have a kidney-shaped body.

Thoracic Cage

• The thoracic cage is formed of the sternum (anterior), 12 thoracic vertebrae (posterior), and 12 pairs of ribs.

Sternum

• The sternum is a flat bone that has three parts: manubrium, body, and xiphoid process.

Ribs

• There are three classifications.
• True ribs (1st-7th) are articulated to the sternum anteriorly and thoracic vertebrae posteriorly.
• False ribs (8th, 9th, and 10th) are attached to each other anteriorly and articulated posteriorly to the thoracic vertebrae.
• Floating ribs (11th, 12th) are articulated posteriorly to the thoracic vertebrae and are free anteriorly

Appendicular Skeleton: Shoulder Girdle

• The shoulder girdle consists of 2 bones.
• They are the clavicle (anteriorly) and scapula (posteriorly).

Appendicular Skeleton: Pelvic Girdle

• The pelvic girdle comprises the right and left hip bones.
• Each hip bone is formed of three fused bones named the ilium, pubis, and ischium.

Bones of the Free Upper Limb

• Humerus: located in the arm
• Radius and ulna: located in the forearm
• Carpal bones: 8 small irregular bones in the wrist
• Metacarpal bones: located in the hand
• Phalanges: 14 short irregular bones in the finger

Bones of the Free Lower Limb

• Femur: is located in the thigh
• Tibia and fibula: are located in the leg.
• Tarsal bones: which are 7 irregular bones are located in the heel and ankle
• Metatarsal bones: there are 5 bones
• Phalanges: there are 14 bones in the toes (digits)

Bone Classification by Shape

• Long bones include the humerus, femur, tibia, fibula, radius, and ulna.
• Short bones include the carpals and tarsals of the hands and feet.
• Irregular bones include the vertebrae.
• Flat bones include the scapula, sternum, hip, and bones of the skull.
• Sesamoid bones include the patella.

Functions of Bones

• They support the body and protect soft organs.
• Bones provide movement due to attached skeletal muscles.
• They store minerals and fats and facilitate blood cell formation.

Test your knowledge of the human skeletal system. Questions cover anatomical planes, the axial and appendicular skeletons, bone composition, and bone locations in the body. Ideal for anatomy and physiology students.