The Musculoskeletal System

Question 1

Identify the major bones of the body

Answer 1

Skeletal system:
1. Axial: we only have one of: skull, spine, rib cage and sternum
2. Appendicular: we have two of: pelvic girdles, shoulder girdles, arms, legs, feet and hands

Five basic tissues compromising the MSK system:
1. bones
2. ligaments (attaching bone to bone)
3. cartilage (protective gel like substance lining joins and intervertebral discs)
4. skeletal muscles
5. tendons (attaching muscles to bone)

Question 2

Describe the structure and functions of bone

Answer 2

Functions of the bones:
• providing the body framework
• giving attachment to muscles and tendons
• allowing movement of the body as a whole and of parts of the body, by forming joins that are moved by muscles
• forming the boundaries of the cranium, thorax and pelvis, and protecting the organs they contain
• haemopoiesis-> the production of blood cells in red marrow
• mineral storage, especially calcium phosphate - the mineral reservoir within bone is essential for maintenance of blood calcium levels, which must be tightly controlled

Type of bones:
1) flat bones: sternum, frontal bone
2) irregular bones: vertebrae, mandible
3) short: carpels, tarsals
4) long: femur, tibia, fibula
5) sesamoid: patella

Types of bone tissue:
1. Spongy bone tissue:
• Porous
• Highly vascularised
• Functions: ‘honeycomb’, reduces bone density, allows end of long bones to compress as a result repeated stress

2. Compact bone tissue:
   • Makes up the hard outer layer, compact due to its minimal gaps and spaces
   • Tissue gives bones their smooth, white and solid appearance, accounts for 80% of total bone mass
   • Contains nerves, and blood vessels

Long bone tissue:
• Shaft (diaphysis) – compact bone
• 2 extremities (epiphysis) – spongy bone
• Vascular membrane (periosteum)
• Outer layer is tough/fibrous to protect bone underneath
• Inner layer contains bone cells for bone production and breakdown, repair and remodelling
• Main arterial nutrient supply to diaphysis
• Epiphysis has own blood supply
• Bone is full of nerves – breaks painful!

Question 3

Discuss the development and growth of bone

Answer 3

Three types of bone cells:
1. Osteoblasts: bone-building cells - they deposit new bone tissue around themselves, they eventually become trapped in tiny pockets in the growing bone, and differentiate into osteocytes.
2. Osteocytes: mature bone cells – they do not divide and are responsible for bone formation and calcium homeostasis
3. Osteoclasts: bone-reabsorbing cells – breakdown bone releasing calcium and phosphate. As new bone calls are made, old ones are destroyed by osteoclasts

Skeletal system - osteogenesis aka ossification occurs pre-birth until 21 years
Stage 1: osteoblasts secrete osteoid (protein) - replaces cartilage in foetus
Stage 2: calcium and phosphate laid down - progressively calcifying it, converting it to hard rigid mature bone
Stage 3: osteoblasts form a matrix - cells become trapped and become osteocytes

Question 4

Describe the structure and functions of the vertebral column

Answer 4

Functions:
• Protect the spinal cord, nerve roots and several of the body’s internal organs.
• Provide structural support and balance to maintain an upright posture.
• Enable flexible motion

Question 5

Discuss the structure and function of the various joints

Answer 5

Joints are the site at which two or more bones articulate or come together, so the end or edges of the bones are held together by the connective tissues.

1. Fibrous joints:
   • Bones forming these joints are linked with tough, fibrous material
   • This arrangement Dosent really permit movement
   • E.g: skull bones, the sutures
2. Cartilaginous joints:
   • Formed by pad of tough fibrocartilage between bones that act as a shock absorber
   • Some of these allow movement like the symphysis pubis which is softened by hormones during pregnancy to allow expansion during childbirth but some do not allow movement
3. Synovial joints:
   • Most common type of joint in the body
   • Freely mobile
   • Ends of bone held close together by a sleeve of fibrous tissue and lubricated with a small amount of fluid
   • Contains synovial fluid

Question 6

Describe the relationship between bone and muscle

Answer 6

There are 3 main types of muscle tissues:
1. Smooth
2. Cardiac
3. Skeletal

Antagonistic pairs:

• one muscle of the pair contracts to move the body part, the other muscle in the pair then contracts to return the body part back to the original position. Muscles that work like this are called antagonistic pairs.
• In an antagonistic muscle pair as one muscle contracts the other muscle relaxes or lengthens. The muscle that is contracting is called the agonist and the muscle that is relaxing or lengthening is called the antagonists.

Question 7

Identify the common sites for intra-muscular injection

Question 8

Identify the hormones responsible for the changes in the musculoskeletal system