Chapter 40: Human Musculoskeletal System

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Structure and function of the human skeleton

  • Shape and support
  • Protection: of internal organs
  • Movement: muscles use skeleton as levers
  • Production of red and white blood cells
  • Hearing: ossicles vibrate and amplify vibrations
  • Ingestion and digestion: physical digestion in the mouth
  • Storage: of minerals (calcium and phosphorus) that can be taken by the body when needed
Axial Skeleton:

There are 80 bones in the axial skeleton, including:

  • Skull
  • Ossicles
  • Spine
  • Ribs
  • Sternum

Skull:
Also known as the cranium, consisting of 8 fused bones and facial bones

Vertebral column:
Consists of 33 small bones which appears as only 26 due to fusion of the vertebrae of the sacrum (5 fused vertebrae) and coccyx (4 fused vertebrae)

Vertebrae:

  • Protect spinal cord
  • Give support to thoracic cavity and abdomen

Invertebral discs:

  • Located between each vertebra – held in place by ligaments
  • Elastic and compressible
  • Provide flexibility and act as shock absorbers
  • Can “slip” – where soft centre of disc bulges out. It is called prolapsed invertebral disc. Can push against nerve often causing severe pain.

Ossicles:
Consist of three small bones – the smallest in the human body

  • Hammer (malleus)
  • Anvil (incus)
  • Stirrup (stapes)

Ribs:

  • 12 pairs originate from the vertebral column
  • 7 pairs are “true ribs” (attached directly to sternum)
  • 3 pairs are “false ribs” (attached indirectly to the sternum by only cartilage)
  • 2 pairs are “floating ribs” (attached to spine only)
Appendicular Skeleton:

Consists of 126 bones involving:

  • Pelvic girdle (hips)
  • Pectoral girdle (shoulders):
  • Scapula
  • Clavicle (collar bone)
  • Limbs:

– Arms: humerus, radius, ulna, carpals, metacarpals, and phalanges
– Legs: femur, tibia, fibula, tarsals, metatarsals, and phalanges

Macroscopic Anatomy of a Long Bone

Bone is mixture of organic (35%) and inorganic (65%) material

Periosteum:

Thin layer of connective tissue that covers the outer surface of bone in all places except at joints (which are protected by articular cartilage)

Compact bone:

Dense and hard and forms the outer parts of a bone (80% of the weight of human skeleton).
Function: support and protection

Medullary cavity:

Central cavity of the bone where red and yellow marrow are stored.

Located mainly in the shaft of the bone (diaphysis).

Function: storage of fat and formation of red blood cells.

Spongy bone:

Found at the expanded heads of long bones and is found throughout the inner cavity of long bones. It is where arteries and veins are found within bones.

Low density (has lots of ‘spaces’) but still strong due to the ‘lattice’ structure. Prevents the bone being too heavy.

In some bones the spaces are filled with red bone marrow where the production of blood cells occurs

Functions: production of RBCs and delivery of oxygen and nutrients

Cartilage:

Type of dense, gel-like connective tissue made of collagen.
Cartilage is found at the ends of long bones at joints, between the ribs and sternum, the ear, the nose, the trachea and bronchi (rings of cartilage) and between intervertebral discs.
Functions: shock absorption and provides for friction-free movement.

Joints:

  • Immovable – fused joints of the skull
  • Slightly movable – vertebral joints
  • Free-moving/Synovial:

– ball-and-socket joints of the shoulder and hip
– hinge joints such as the elbow and knee

Ligaments and Tendons:

  • Ligaments are strong, slightly elastic bands of fibrous tissue (collagen) – they control the range of movement of a joint
  • Tendons are extremely strong, inelastic bands/cords of collagen – they attach muscles to bone

Skeletal Muscle:

  • Contractile tissue – has ability to shorten and generate a pulling force
  • Voluntary muscles – we can consciously control contractions of skeletal muscle
  • Function: movement and temperature regulation in the body as they generate a lot of heat during movement

Antagonistic Muscle Pairs:

  • Antagonistic muscle are pairs of muscles where when one contracts the other relaxes and in doing so they have opposite effects.
  • e.g. biceps and triceps of the upper arm
  • e.g. hamstrings and quadriceps of the upper leg

Musculoskeletal Disorder – osteoporosis:

  • Brittle-bone disease – bones are porous/less dense
  • Often results in compression fractures in the vertebrae and in the neck of the femur (broken hip)
  • Possible cause: Bone replacement has slowed down
  • Prevention: Physical exercise during puberty reduces – risk of developing the disease in old age
  • Calcium-rich diet and drinking fluoridated water maintains bone density
  • Treatment: Females use HRT (but bone material – already lost is not replaced!
  • Physical exercise, dietary calcium, and – vitamin D are recommended

Musculoskeletal Disorder – Rheumatoid Arthritis:

  • Joint (fingers, wrists, ankle most common) become stiff and sore (inflammation occurs)
  • Articular cartilage has been destroyed and bones fuse
  • Possible cause: Immune reaction against the body’s own cartilage
  • Prevention: No known preventative measure yet
  • Treatment: Pain-killers and anti-inflammatory drugs are administered
  • Badly affected areas, such as hip or knee can be replaced with artificial joints

Growth and Development in Bones:

  • Skeleton of early embryo is mostly cartilage
  • Bone formation begins just before week 8
  • Specialised cells called osteoblasts secrete a thick layer of bone around the cartilage of the diaphysis – a tube of bone now encircles the diaphysis
  • Cartilage continues to grow at ends – epiphyses – bone elongates
  • After birth the epiphyses start to calcify
  • Cartilage remains at the junctions between the diaphyses and epiphyses – this area is called the growth plate
  • The growth plates enable the bones to elongate during childhood and puberty and eventually calcify and are replaced by bone at the end of puberty then fully grown – 18 in females and 21 in males

Bone Renewal:

  • Bone is a living organ and is capable of self-renewal.
  • Bone is constantly broken down (by osteoclasts) and replaced (by osteoblasts).
  • Skeleton is completely replaced every 7 years and complete replacement slows down with age.
  • Osteoclasts remove calcium and osteoblasts lay calcium down.
  • Renewal of bones is affected by the hormone parathormone, which causes an increase in the breakdown of bone. Parathormone is secreted by the parathyroids (see chapter 38). Bone renewal is also affected by exercise levels and dietary calcium.