BMS175: Topic 5: The Skeletal System

Part 1 - Bone Tissue

Bone and Skeletal Tissues

• Most assume bones are lifeless however they are living organs

• Bone tissue is formed and remodelled through ones life

• Bones form the base structure of humans

Functions of bone

• There are six main functions of bone including:

  • Providing framework that supports the body and body’s main organs

  • The fused bones that make up the skull protect the brain. The vertebrae surrounds the spinal cord and the ribs protect the vital organs in the thoracic cavity

  • Skeletal muscles that attach to bones via tendons use bones as lever like structures to move the body

  • Bone is a reservoir for minerals

  • Cells that in the body are created in the red bone marrow of certain bones

  • Fat is stored as yellow bone marrow in the cavities of long bones

Why bone is classified as connective tissue?

• It is a type of connective tissue due to its cells and matrix

• Cells - four kinds of cells in bone including

  • Osteogenic cells

  • Osteoblasts

  • Osteocytes

  • Osteoclasts

• Matrix - cells are surrounded by Bone Matrix which is made of two parts including

  • The soft organic components

  • The hard inorganic components

Identify and list the cells present in bone tissue

• Osteogenic cell - the only cells that undergo cell division. The result of these cells develop into bone producing cells (osteoblasts)

  • Found mostly alongside membranes that surround the bones and blood vessels in bone canals

• Osteoblast - Bone producing cells that synthesise and secrete collagen fibres and other organic components that are used to make the extra cellular matix of bone tissue

• Osteocyte - They maintain the daily metabolism of bone tissue

  • Compose the main cell found in the mature bone

  • Come from Osteoblasts and are found in the matrix of the bone

• Osteoclast - Responsible for the local removal of bone

Define the two types of bone tissue

• Compact bone - made of hollow tubes (osteoblasts) of the bone matrix

  • Through the middle of each osteoblasts is a canal that has blood vessels and nerves

  • There are central canals connected by another set of canals

• Spongy bone - Structured like unorganised even haphazard tissue

  • Trabecular in spongy bone lines up perfectly along the lines of stress and help bone resist stress

Describe the structure of a flat bone

• Thin, flattened and usually slightly curved

• Consist of a layer of spongy bone in the middle of two small layers of compact bone

• In the spongy bone of flat bone is generally where red bone marrow is found

  • Example: the skull and rib bones

Describe the structure of a long bone

• Consist of a shaft, larger bone ends and inner and outer membranes

• The shaft which is called diaphysis forms the long axis of compact bone which surrounds a central hollow cavity

• Enlarged bone ends have a small outer shell of compact bone whilst the inside of contains spongy bone

• Joint surfaces are then covered by cartilage

Describe how bones grow in width

• Appositional growth - bones increase in diameter with the addition of bony tissue at the surface of bones

• Osteoblasts at the bone surface secrete bone matrix, and osteoclasts on the inner surface break down bone

• The osteoblasts differentiate into osteocytes

• A balance between these two processes allows the bone to thicken without becoming too heavy

Explain Wolff’s law of bone

• Wolffs law states that the build of a bone is decided by the mechanical stress placed on it further leading to the bone adapting to withstand the stresses

Describe the process of bone remodelling

• Mostly targets bones that are injured or areas where additional strength is required

• Bone → osteoclasts break down old bone →new bone is formed

Part 2 - The Skeletal System

The Skeleton

• The Skeleton/skeletal system is made up of bones, cartilages, joints, ligaments and about 20% of the human body is made up of this system

The Skull

• The cranial and facial bones form the skull (there are 22 all together)

• The cranial bones cover and protect the brain and create attachment areas for the head and neck muscles

• Facial bones are the framework of where the teeth, nose, and eyes sit

  • The openings in the facial structure allow for water and food to enter the body

The Thoracic Cavity

• The thoracic cage includes the thoracic vertebrae, ribs, sternum and costal cartilages

  • The costal cartilages secure the ribs to the sternum

The Vertebral Column (Spine)

• Consists of 26 irregular bones joined in a way that they are able to be flexible

• The spine starts at the skull and goes down to the pelvis

  • Surrounds and protects the spinal cord

  • Provides attachment points for the ribs and muscles of the back and neck

The Vertebrae

• As a fetus/infant the vertebrae consists of 33 bones

  • 9 of these bones eventually fuse together to form two bones: the Sacrum and the Coccyx

• The other 24 bones are individual vertebrae bones that are seperated by intervertebral discs

The pectoral girdle

• Made up of the clavicle and scapula

• The clavicle joins the sternum and scapulae by a joint

• Muscle joins the scapulae to the thorax and vertebral column

The upper limbs

• Each upper limb is made up of 30 separate bones

• The Humerus articulates:

  • with the scapula at the shoulder

  • with the radius and ulna at the elbow

• The Radius and the Ulna are the two long bones that form the skeleton of the forearm

• Upper limbs also include the skeleton of the hand which includes

  • The bones of the carpus - the wrist

  • The bones of the metacarpus - palm

  • The phalanges - bones of the fingers

The Pelvic Girdle (hip girdle)

• Formed by the sacrum and a pair of hip bones

  • Each hip bone joints with its partner anteriorly with sacrum

The lower limbs

• Includes the:

  • Femur

  • Patella

  • Tibia

  • Fibula

  • Tarsals

  • Metatarsals

  • Phalanges

Part 3 - Articulations (Joints)

Define Articulation

• A movement in the body that occurs due to muscle contractions

• They have two main functions

  • Give the skeleton mobility

  • Holding the skeleton together

    • Sometimes plays a part in protecting the body

Describe the different ways that joints can be classified

• There are two ways

  • On the basis of their structure

  • On the basis of their function

For each of the fibrous joints describe what is between the bones and how much that joint moves

• Bones are joined by collagen fibres of connective tissue

• There is no joint cavity present

• Amount of movement allowed depends on length of connective tissue fibres

• Three kinds of fibrous joints

  • Suture - immovable

  • Syndesmosis - slightly moveable

  • Gomphosis - immoveable

For each of the cartilaginous joints describe what is between the bones and how much that joint moves

• In these joints the articulating bones are joined by cartilage

• Cartilage is a supportive connective tissue

• There is no joint cavity present

• Two types of cartilaginous joints

  • Synchondroses - immoveable

  • Symphyses - slightly moveable

For each of the synovial joints describe what is between the bones and how much that joint moves

• The articulating bones that are separated by a fluid containing joint cavity

• Most joints of the body

• Six types of synovial joints

  • These are all freely moveable

Describe the general structure of a synovial joint

• Glassy smooth cartilage that covers the opposite bone surface to articular cartilage

• Thin sponge like cushions that absorb compression placed on joints and keep bones endings from being crushed

• Synovial joints have synovial cavities which contain a small amount of synovial fluid

• The synovial cavity is closed in by a doubled layered capsule

• The strong outer fibrous layer consists of connective tissue that is continuous with periosteum which strengthens the joint so the bones do not pull apart

• The inner layer is the synovial membrane made of connective tissue

• Synovial membrane makes synovial fluid

• Synovial joints are strengthened by a number of band like ligaments

Define the terms flexion, extension and rotation

• Flexion

  • A bending movement that decreases the angle between two body parts and brings bones closer

  • Example - bending the elbow so the hand is moving towards the shoulder

• Extension

  • The reverse of flexion

  • A movement where one increases the angle between two body parts

  • Example - straightening the arm so the hand is moving further away from the shoulder

  • Continuing this movement further that anatomical position is known as hyperextension

• Rotation

  • The movement in which a bone turns around its own long axis