3.4 Joints Flashcards
What is the definition of a joint and what is a joint also known as?
A joint is also known as an articulation. A joint is a point of connection between 2 or more bones
Give the purposes of joints
To hold bones together, to allow for flexibility in the skeleton and to make bone growth possible.
Describe the 2 different ways that joints can be categorised by
Categorised by structure - the material of the joints and whether or not there is a joint cavity
Categorised by function - the amount of movement allowed at the joint
Describe the 3 functional categories of joints
synarthroses joints - fixed
amphiarthroses joints - limited range of motion
diarthroses joints - free range of motion, e.g shoulder or knee joints
Describe the 3 structural categories of joints
Fibrous joints are held together by fibrous connective tissue, they have no synovial cavities and are generally fixed. e.g joints in the cranium, pelvis and vertebrae
Cartilaginous joints are held together by cartilage which allows for slightly moveable joints. e.g intervertebral discs
Synovial joints are freely moveable and have 6 different types
What are the 3 types of movement a synovial joint can have
Uniaxial - rotation about only one axis
Biaxial - movement about two perpendicular axes
Multiaxial - movement about several axes
Describe the 6 types of synovial joint
Ball and socket joint - a multiaxial joint where one of the bones ends in a ball shape and fits into a cup shaped bone end. e.g in the shoulder and hip
Hinge joint - A uniaxial joint operating like a hinge, one bone surface is convex and one is concave which allows for smooth movement. e.g in the elbow and knee
Pivot joint - A uniaxial joint with a pivoting action. e.g the radius and ulna joint
Gliding/Plane joint - A multiaxial joint where the bones meet at flat surfaces and glide over each other. e.g the carpals in the hand
Saddle joint - A biaxial joint where the bone surfaces are shaped like a saddle. e.g in the thumb
A condyloid joint - A biaxial oval shaped joint with a convex and a concave bone surface. e.g the metacarpalphalyngeal joint
Briefly explain the layout of a synovial joint
The ends of each bone are surrounded by articular cartilage. The bones and the cartilage are then surrounded by the synovial cavity which contains synovial fluid. The synovial cavity is enclosed by the articular capsule. The synovial cavity is made up of the synovial membrane (inside) and the fibrous membrane (outside).
Describe synovial fluid
Synovial fluid in the synovial cavity has important roles in lubrication of the joint, preventing joint friction, allowing flow of movement and acting to cushion force on the joint. The fluid is made of the ultrafiltrate of blood plasma, it has similar levels of glucose and uric acid to the plasma but less protein. More fluid causes less stress on the joint. If the joint is immobilised, the fluid becomes more viscous. The production of synovial fluid involves the synovial membrane.
What is arthrocentesis
The removing and testing of synovial fluid in order to diagnose joint diseases
Describe the articular cartilage in synovial joints
The articular cartilage is a hyaline cartilage which prevents friction between the two bones by absorbing shock. The cartilage is avascular and anervous (so no pain is felt). The cartilage does not regenerate easily.
Describe the fibrous membrane of the articular capsule
It is made of lots of densely packed irregular fibres. It is attached the the periosteum of the bones.
Describe the synovial membrane of the articular capsule
The synovial membrane is involved in the production of synovial fluid. It is comprised of areolar connective tissue which is loose and contains elastic fibres and collagen. Synoviocytes are meshed in the collagen matrix along with the elastic fibres. The synovial membrane has a rich capillary network and regenerative abilities. The synovial membrane has no epithelial lining.
Describe the 2 types of synoviocytes in the synovial membrane
Type A synoviocytes are macrophage cells derived from bone marrow. They act to remove debris, play an immune role and contribute to the synovial fluid.
Type B synoviocytes are fibroblast cells with lots of RER and dendritic processes. They are the main replenishers of synovial fluid
Describe 2 structures that can strengthen and stabilise joints
Both tendons and ligaments help to hold joints together. They are connective tissue made of compact linear collagenous fibres, the collagen intermingles with the collagen in the periosteum of the bone.
Describe tendons
Tendons are made of dense connective tissue which attaches muscle to bone. This allows the muscle to move the bone at the joint. The tendons have parallel bundles of fibres to pull the bone in certain directions
Describe ligaments
Ligaments are formed of bands of fibrous connective tissue that anchor bones together. They strengthen and support the joint by preventing over movement. Ligaments can be found inside and outside the articular capsule
Describe 3 additional joint structures that can be found on some joints e.g knee
Cartilage - extra bits of cartilage known as menisci are made up of fibrocartilage and attached to the fibrous capsule. This allows the bones to fit together tightly
Bursae - fluid filled sacs similar to joint capsules that reduce friction
Fat pads - accumulations of adipose tissue that add extra cushioning
How does articular cartilage receive nutrients.
Articular cartilage is avascular, however it can receive nutrients through the synovial fluid, blood vessels at t the edges of the cartilage and from the underlying spongey bone
Describe how joint position is determined and controlled
Via proprioception - the knowledge of body position, both static and dynamic. It is dependent on the degrees of angulation of all the joints and their rates of change. This is detected via the degree of stretch of the muscles as the joints are moved and stabilised by the muscles around them
What are the 2 types of receptors that determine joint angulation
Muscle associated and non muscle associated
Describe the muscle associated joint receptors
Muscle spindle receptors - located in the intrafusal muscle fibres, adapted to detecting rapid rates of change in the stretch of muscles
Golgi tendon receptors - measure tension in the tendons to gauge the force generated by a muscle. They are made of bare nerve endings surrounded by collagen and are located at the junction between the skeletal muscle fibres and tendons
Describe the non muscle associated joint receptors
-receptors in the skin the measure the stretch in the skin around the joint
-pacinian corpuscles in joint capsules that respond to joint pressure (depending on the different angles)
- ruffinis endings in the joint capsule that detect joint position and the velocitiy of joint movement
Where is information from the proprioceptors processed
In the thalamus
Why is joint mobility important and what contributes to this joint mobility
Joint flexibility is important or efficiency of movement, reduction in muscle strain, posture and sports skills. Joint structure, soft tissue around the joint and the length of muscles and ligaments all contribute to the degree of mobility.
Describe double jointedness
Hypermobility due to high amounts of flexibility in articular capsules and ligaments. It can increase the incidence of injury and lower isometric muscle strength.
Describe 3 joint pathologies other than arthiritis
Torn Cartilage- common in the menisci of knee, can lead to arthritis, can to be surgically removed
Bursitis - inflammation of the bursa, can be treated with anti-inflammatories
Tumours- e.g a synovial cyst, tesosynovial giant cell tumours and synovial sarcomas (often found in hands and feet)
Describe the different types of arthritis
Infectious arthritis - caused by lyme disease
Gout/pseudogout - where crystals are found in the joint, caused by elevated levels of uric acid in the joints
Osteoarthritis (degenerative) - breakdown of joint cartilage underlying the bone (most common arthritis), common in old age in the knee and hip. It is caused by mechanical stress on the joint and low grade inflammatory processes
Rheumatoid arthritis - An autoimmune disorder caused by genetic and environmental factors that primarily affects joints. It causes inflammation of the synovial membrane and a typical symptom is synovial hyperplasia where there is an increase in synoviocytes (which are heavily implicated in rheumatoid arthritis).
Give 2 areas that have been helped by research on joints
robotics and prosthetics
