14.2 - Musculoskeletal System of Humans

Skeletal System

The human skeleton has 2 main parts.

• Axial skeleton , which consists of the skull, vertebral column, ribs and sternum (breastbone).
• Appendicular skeleton , which consists of the pectoral girdle, upper limbs, pelvic girdle and the lower limbs.

Figure 1 - The human skeletal system.

Human Vertebral Column

The vertebral column is also called the spine or backbone. It is composed of a series of bones called vertebrae (singular, vertebra). The vertebral column has 33 vertebrae of different size and shape.

1. Thoracic vertebrae

• Long spinous process
• Muscles and ligaments attach to spinous and transverse processes
• Transverse processes have facets that articulate with the ribs (except 11th and 12th thoracic vertebrae)

2. Lumbar vertebrae

• Largest and strongest vertebrae
• Short spinous process
• Large centrum to support weight of the lower back

3. Sacral vertebrae

• Triangular bone formed from fusion of 5 vertebrae

4. Caudal vertebrae

• Triangular bone which is pointed at the end
• Formed from fusion of 4 bones.

5. Atlas vertebrae

• First cervical vertebra
• Large neural canal
• Small spinous process
• A pair of transverse foramina
• No centrum
• Articulates with the skull

6. Axial vertebrae

• Second cervical vertebra
• Large spinous process
• Small transverse process
• A pair of transverse foramina
• Odontoid process articulates with facet of the atlas vertebra's neural canal

7. Cervical vertebrae

• Short spinous process
• Small centrum
• Wide and short transverse process
• A pair of transverse foramina

Cervical vertebrae, Thoracic vertebrae and Lumbar vertebrae

• Similarities

  • All have spinous and transverse processes, centrum and neural canal.

• Differences

  • Cervical vertebrae

    • Spinous process: Short
    • Transverse process: Wide and short
    • Centrum: Small
    • Transverse foramina: 2

  • Thoracic vertebrae

    • Spinous process: Long
    • Transverse process: Long
    • Centrum: Medium
    • Transverse foramina: Absent

  • Lumbar vertebrae

    • Spinous process: Short
    • Transverse process: Short
    • Centrum: Large
    • Transverse foramina: Absent

Joints

Bones are too rigid and cannot bend without being damaged. Flexible connective tissues form joints holding the bones together to allow movements. A joint is the place where two or more bones meet. Different kinds of joints allow different movements. The 3 types of joints are:

• Immovable joints , for example, suture at the cranium.

• Slightly moveable joints , for instance, cartilage discs between the vertebrae and cartilage between the first rib and sternum.

• Freely moveable joints , such as hinge joint and ball-and-socket joint.

Figure 2 - Capsule covers and protects the joint. Cartilage acts as cushion which absorbs shock and reduces friction between bone ends. The synovial membrane produces synovial fluid into the cavity as lubricant between the bones.

• Ball-and-socket joint
  • Allows rotational movement of bones in all directions
  • Allows swinging of arms and legs in circular motion
  • Examples include shoulder joints and hip joint

Figure 3 - Ball-and-socket joint at the hip

• Hinge joint
  • Allows movement of bones in one plane
  • Examples are elbows, phalanges and knees.

Figure 4 - Hinge joint at the elbow.

Other than bones and joints, support and movement also require the help of the skeletal muscle, tendon and ligament.