Skeletal System

Source ¹  licensed under Creative Commons Attribution 4.0 International License.

Function

• Supports the body
• Facilitates movement
• Protects internal organs
• Produces blood cells
• Stores and releases minerals and fat

Anatomy

• Includes all of the bones, cartilage, and ligaments of the body
• The skeleton consists of the bones of the body.
  • Provides a rigid, internal structure that can support the weight of the body against the force of gravity, and to provide a structure upon which muscles can act to produce movements of the body.
  • Protects the internal organs, including the brain, spinal cord, heart, lungs, and pelvic organs.
  • Bones of the skeleton serve as the primary storage site for important minerals such as calcium and phosphate.
  • The bone marrow found within bones stores fat and houses the blood-cell-producing tissue of the body.
  • 206 bones for adults.

Axial Skeleton

• Forms the vertical, central axis of the body and includes all bones of the head, neck, chest, and back.
• Protects the brain, spinal cord, heart, and lungs.
• The attachment site for muscles that move the head, neck, and back, and for muscles that act across the shoulder and hip joints to move their corresponding limbs.
• Consists of 80 bones including the skull, the vertebral column, and the thoracic cage.
• The vertebral column consists of 24 bones, each called a vertebra, plus the sacrum and coccyx.
• Thoracic cage includes the 12 pairs of ribs, and the sternum.
• Cranium or skull supports the face and protects the brain. It is subdivided into the bones of the skull and the bones of the face.

Bones of the Skull

• Frontal – forms the forehead
• Parietal – the upper lateral sides of the cranium
• Occipital – the posterior skull and base of the cranial cavity
• Temporal – the lower lateral sides of the cranium
• Sphenoid -the ‘keystone’ bone that forms part of the base of skull and eye sockets
• Ethmoid – forms part of the nose and orbit and base of cranium
• Auditory ossicles – the small bones of the middle ear
• External auditory meatus – the external opening of ear and temporal bone

Bones of the Face

• Zygomatic – the cheekbone
• Maxillary – the upper jaw and hard palate
• Palatine – the lateral walls of the nose
• Lacrimal – the walls of the orbit
• Inferior conchae – the lower lateral wall of the nasal cavity
• Vomer – the separates the left and right nasal cavity
• Mandible – the lower jaw bone (The only movable bone of the skull)
• Hyoid – the bone located between the mandible and larynx, not connected to other bones

Vertebrae

• Cervical – C1 to C7 – the first 7 vertebrae in the neck region
• Thoracic – T1 to T12 – the next 12 vertebrae that form the outward curvature of the spine
• Lumbar – L1 to L5 – the next 5 vertebrae that form the inner curvature of the spine
• Sacrum – the triangular-shaped bone at the base of the spine
• Coccyx – the tailbone

Ribs

• There are 12 sets of ribs and can be divided as:
  • 7 true ribs as they are attached to the front of the sternum
  • 3 false ribs as they are attached to the cartilage that joins the sternum
  • 2 floating ribs as they are not attached to the front of the sternum

Sternum

Also known as the breast bone, is divided into 3 parts:

• Manubrium – the upper portion of the breast bone
• Body – the middle portion of the breast bone
• Xiphoid process – the lower portion of the breast bone and is made up of cartilage

Appendicular Skeleton

• Includes all bones of the upper and lower limbs, plus the bones that attach each limb to the axial skeleton.
• 126 bones in the appendicular skeleton of an adult.

Bones of the Pectoral Girdle

• Scapula – the shoulder blades
• Clavicle – the collar bones. It connects the sternum to the scapula
• Acromion – the extension that forms the bony point of the shoulder

Bones of the Upper Limbs

The bones of the upper limbs include the bones of the arms, wrists, and hands.

Bones of the Arm

• Humerus – the bone in upper arm
• Radius – the bone that runs thumb-side of the forearm
• Ulna – the bone that runs on the side of the little finger of the forearm

Bones of the Wrist and Hand

• Carpals – the wrist bones
• Metacarpals – the bones in the palm of hand
• Phalanges – the finger and toe bones

Bones of the Pelvic Region

Protect the reproductive, urinary, and excretory organs.

• Pelvic girdle – the hip or coxal bone.
• Illium – the largest part of the hip bone
• Ischium – the lower portion of pelvic girdle
• Pubis – the anterior portion of pelvic girdle
• Pelvis – consists of four bones: the left and right hip bones as well as the sacrum and coccyx
• Acetabulum – the large socket in the pelvic bones that holds the head of the femur

Bones of the Lower Limbs

The bones of the lower limb include bones of the leg and the feet.

Bones of the Leg

• Femur – the thigh bone and is also referred to the upper leg bone. It is the longest and strongest bone in the human body
• Patella – the kneecap
• Tibia – the shin bone. It is a medial bone and the main weight-bearing bone of the lower leg
• Fibula – the smaller of the lower leg bone

Bones of the Ankles and Feet

• Tarsals – the ankle bones (7 total)
• Malleous – the bony protrusions of the ankle bones
• Talus – the superior ankle bones
• Calcaneous – the heel bones
• Metatarsals – the foot bones
• Phalanges – the bones of the toes

Joints

Most bones connect to at least one other bone in the body. The area where bones meet bones or where bones meet cartilage are called articulations.

Joints can be classified based on their ability to move:

• At movable joints, the articulating surfaces of the adjacent bones can move smoothly against each other.
• However, other joints may be connected to each other by connective tissue or cartilage.
• These joints are designed for stability and provide for little or no movement.
• Importantly, joint stability and movement are related to each other.
• This means that stable joints allow for little or no mobility between the adjacent bones.
• Conversely, joints that provide the most movement between bones are the least stable.

3 Types of Joints

• Synarthrosis joints allow no movement, e.g., joints of the skull
• Amphiarthrosis joints allow some movement, e.g., joints of the pubic symphysis
• Diarthrosis joints allow for free movement, e.g., joints of the knee

Structures associated with Joints

• Cartilage – the elastic connective tissue that is found at the ends of bones, nose tip, etc.
• Synovial membrane – the lining or covering of synovial joints
• Synovial fluid – the lubricating fluid found between synovial joints
• Ligaments – the tough, elastic connective tissue that connects bone to
  bone
• Tendons – the fibrous connective tissue that attaches muscle to bone
• Bursa – the closed, fluid-filled sacs that work as a cushion
• Meniscus – C-shaped cartilage that acts as shock absorbers between bones

Body Movements

Can you think of an example in the body for each of these movements?

• Flexion and extension
• Abduction and adduction
• Circumduction
• Rotation
• Supination and pronation
• Dorsiflexion and plantar flexion
• Inversion and eversion
• Protraction and retraction
• Elevation and depression

Bookmark

1. Betts, J.G., Young, K.A., Wise, J.A., Johson, E., Poe, B., Kruse, D. H., Korol, O., Johnson, J.E., Womble, M. & DeSaix, P. (2013). Anatomy and Physiology. OpenStax. http://cnx.org/content/col11496/latest/[↩]