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