Skeletal System Overview

Skeletal System

• The skeletal system is made of bones, cartilages, joints and ligaments
• The average adult skeleton has 206 bones
• Bones can be paired (e.g. ribs, hip bone) or unpaired (e.g. sternum)
• The axial skeleton includes the skull, vertebral column, ribs, and sternum
• The appendicular skeleton includes bones of the upper and lower limbs and their girdles

The Skull

• The skull contains the cranium and the mandible (facial bones)
• The cranium contains the brain

The Vertebral Column

• The vertebral column consists of 33 vertebrae and intervertebral discs
• There are 5 regions of vertebrae:
  • Cervical (7)
  • Thoracic (12)
  • Lumbar (5)
  • Sacral (5 fused…Sacrum)
  • Coccygeal (3-5 fused… coccyx)

The Ribs

• There are 12 pairs of ribs connected to the sternum via costal cartilages
• The last 2 ribs are called floating ribs

The Sternum

• The sternum, thoracic vertebrae, ribs and costal cartilages form the thoracic cage, which protects the heart and lungs

The Upper Limbs

• The upper limb bones include:
  • Clavicle
  • Scapula
  • Humerus
  • Ulna
  • Radius
• Bones of the hand include the phalanges (bones of the fingers), metacarpals and carpals (bones of the wrist)
• The thumb has proximal and distal phalanges
• The shoulder girdle is made of the clavicle and scapula

The Lower Limbs

• The lower limb bones include:
  • Hip bone
  • Femur
  • Patella
  • Tibia
  • Fibula
• The bones of the foot include phalanges (bones of the toes), metatarsals, and tarsals
• The big toe (medial) has proximal and distal phalanges
• The pelvic girdle is formed of the hip bones

Bone Types

• Long bones are hard and dense, providing strength and mobility, they feature a shaft (diaphysis) and two ends (epiphysis)
  • Examples include: Femur, Humerus, Radius & Ulna
• Short bones are wide and short, providing support and stability
  • Examples include: carpal and tarsal bones
• Flat bones provide protection (e.g. skull bones, sternum) and muscular attachment (e.g.scapula & ribs)
• Irregular bones have unique shapes
  • Examples include: facial bones, vertebrae, and hip bone
• Pneumatic bones contain air-filled spaces, making the skull lighter
  • Examples include: some skull bones
• Sesamoid bones are found in tendons, protecting them from excessive wear and tear
  • Example: patella

Functions of the Skeleton:

• Supports and allows body movement
• Protects vital organs
• Contains bone marrow
• Stores calcium, magnesium and other salts

Muscles

• Skeletal muscles are striated, voluntary and form the main bulk of the body (about 50% of body weight)
• Smooth muscles are non-striated, involuntary, and found in the walls of viscera (e.g. GIT)
• Cardiac muscles are striated, involuntary and found in the heart
• Skeletal muscles attach to bone (or sometimes to non-skeletal structures like skin, fascia, or other muscles)
• Skeletal muscle fibers are arranged in bundles
• Muscle attachments can be classified as origin (more proximal, less movable bone) and insertion (distal, more movable bone)
• Muscle action describes the movement that occurs when the more mobile bone moves toward the more stable bone during contraction

Muscle Groups

• Muscles of the head and neck
• Muscles of the trunk
• Muscles of the upper limbs
• Muscles of the lower limbs

Muscle Actions

• Prime mover (agonist) is the muscle that produces the desired action of the movement
• Synergist assists the agonist
• Antagonist opposes the agonist, restoring the original position
• Stabilizers keep bones immobile

Muscle Names

• Naming of muscles is descriptive and can be based on:
  • Size: magnus, major, minor, longus, brevis
  • Shape: deltoid (triangular), teres (cylindrical)
  • Orientation of fibers: rectus, oblique, transverse
  • Action: adductor, flexor, extensor, supinator
  • Number of heads: bi (two), tri (three), quad (four)
  • Attachments: sternocmastoid
  • Specific features: serratus (toothed)
  • Location: abdominis, femoris, pectoralis

Functions of Skeletal Muscles:

• Enable movement of the body
• Maintain body posture
• Support and stabilize bones
• Generate heat