Skeletal System

Published on 14th May 2018

COMMON ANATOMICAL TERMS

 

  • Planes run through the body – side to side and front to back e.g. median plane
  • Surfaces of the body are also named e.g. anterior surface

FUNCTION

1. Protection

2. Locomotion

3. Support and rigidity

4. Production of red blood cells

5. Attachment of muscles, tendons and ligaments

6. Storage (minerals)

 

ANATOMY

  • 206 skeletal bones
  • Bones are dense dry connective tissue
    • Mixture of organic and inorganic material
    • Inorganic material mainly magnesium and calcium salts
    • Living bone has plastic quality ie. its shape can change
    • Bone has good blood and nerve supply

OSSIFICATION

  • Fetal skeleton is a cartilage model becoming bone by process know as ossification
  • Ossification is carried out by cells called osteoblasts
  • Ossification completed by age 25 but osteoblasts continue to make new bone eg. repairing fractures

TYPICAL BONE

 2 main types of bone tissue: 

COMPACT: which is solid, smooth and forms the shafts and ends of bone

CANCELLOUS:  which has latticework structure and forms the insides of the ends of bones.  This is where red bone marrow is found

  • MEDULLARY CAVITY It is a narrow cavity in the shaft of bones containing yellow bone marrow
  • PERIOSTEUM  It is a strong covering over the whole bone.  It has a rich blood supply and osteoblasts here are stimulated to work by action of muscle attachments
  • CARTILAGE  It is found on joint surfaces and is a smooth connective tissue.  It has no blood supply

 

CLASSIFICATION OF BONES

  • Long Bones – greater dimension in one direction  
  • Short Bones – same dimension in all directions  
  • Flat Bones – sandwich of compact/cancellous/compact bone  
  • Irregular Bones – do not fit above definitions  
  • Sesamoid Bones – held inside tendons.  Protective function

BONE GROWTH AND DEVELOPMENT

  • Like skin, bone replaces itself throughout adult life.  When old bone tissue is replaced by new bones tissue this is called remodeling.  In long bones, new bone is formed externally and the diameter of the bone increases 

 

  • Bone growth and development depend on: 
    • Sufficient quantities of calcium and phosphorus (makes bones hard)
    • Vitamin D (for the absorption of calcium from the diet)
    • Vitamin C (to help maintain the matrix of bone)
    • Vitamin A (to help regulate the number of osteoblasts)
    • Perhaps Vitamin B12
    • The right hormones

 

JOINT MOVEMENTS               

  • Flexion / Extension
  • Abduction / Adduction
  • Medial rotation / Lateral rotation
  • Pronation / Supination
  • Elevation / Depression
  • Retraction / Protraction
  • Side flexion  
  • Rotation
  • Dorsiflexion / Plantarflexion
  • Eversion / Inversion
  • Accessory movements
  • Circumduction
  • Opposition
  • Hyperextension                                                   

Some specific joints also have special movements exclusive to them: 

  • Spine  - Lateral flexion 
  • Scapula and jaw  - Protraction / retraction elevation / depression 
  • Forearm / wrist - Pronation / supination - radial deviation / ulnar deviation 
  • Thumbs  - Opposition 

 

JOINTS

3 types: 
 

  • FIXED (Fibrous) – held together by fibrous ligament.  No movement
  • SLIGHTLY MOVEABLE (Cartilaginous) - cartilage pad between bone ends.  Some movement
  • FREELY MOVEABLE – wide range of movement. Also known as synovial joints

SYNOVIAL JOINTS

  • Freely moveable
  • Ends of bones covered with cartilage
  • Joint surrounded by synovial membrane
  • Joint space filled with synovial fluid.  This is secreted by synovial membrane and has the consistency of egg white.  It provides nutrients to the cartilage and lubrication for joint
  • Capsular ligament forms a sleeve of dense fibrous tissue around the joint
  • Bursae found between muscle tendons and ligaments are small pouches of synovial membrane.  Protective function.

 

TYPES OF SYNOVIAL JOINTS

BALL & SOCKET 
 
The ball-like head of one bone fits into the socket-like head of another, permitting all movements.  Eg. shoulder and hip joints 
 
 
SADDLE 
 
The concave surfaces of two bones articulate with one another.  Forward and back and side-to-side movements are possible. Eg. The trapezium and metacarpal bones of the thumb 
 
 
PIVOT 
 
A ring of bone rotates about a process of bone.  Movement is limited to rotation.  Eg. skull on its atlas (1st cervical vertebra) rotates about the odontoid process of the axis (2nd cervical vertebra) 
 
 
HINGE 
 
The C-shaped surface of one bone swings about the rounded surface of another.  Movement is limited to flexion/extension.  Eg. elbow, interphalangeal joints 
 
 
ELLIPSOID 
 
This is a reduced ball and socket configuration in which rotation is not permitted.  Found between radius and ulna of the forearm where they articulate with the scaphoid and lunate carpals of the wrist 
 
 
GLIDING 
 
Bones glide across one another.  Eg. intercarpal joints 

 

 

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