move. They determine the axis of motion of a joint by limiting the directions in which it
may move. Ligaments have a blood supply and a nerve supply. They have no
regenerative powers so if they are damaged they heal by repair, forming a scar. The scar
is unlikely to result in healing at the correct length, and scar tissue is liable to stretch
under tension. Therefore the healing of ligaments quite often leaves a less efficient
structure than the original one. If the sensory receptors and nerves in a ligament are
damaged this can cause the loss of the ability to provide the central nervous system with
accurate sensory information. The loss of sensory information is particularly serious as
this prevents the reflex contractions of antagonist muscles to protect a joint from
abnormal loads or from being placed in unsatisfactory positions.
3.6 Menisci
Some joints, the knee, the wrist and the jaw for example, have small fibrocartilage
structures within them which separate the cartilaginous articular surfaces. These are
properly called the menisci or articular discs. Their function is incompletely
understood, but primarily it is almost certainly load distribution, particularly where a
joint is subject to a lot of rotation. This is classically seen in the knee. It is perhaps
significant that the only mammal that cannot rotate its knees, the fruit bat, has no
menisci. The menisci also help in distributing synovial fluid over a larger surface area
but this is probably not a major function.
MENISCI
ARTICULAR DISCS
SAQ 9
(a) Name two functions of ligaments.
(b) Name two joints which have menisci.
SAQ Answers
3.7 Joints
Joints, also called articulations, are the regions of contact between bones. They hold
the bones together and some allow movement to take place. They are classified into
three types according to their structure and degree of mobility.
 Immobile joints. The bones are held firmly together by short collagen fibres. These
joints are known as fibrous joints and allow no movement. Examples are found in
the skull and at the distal ends of the tibia and fibula (the distal tibio-fibular joint).
 Slightly mobile joints. The bones are held together by fibrocartilage. These joints
are known as cartilaginous joints. Examples are found between the vertebrae and
between the innominate bones of the pelvis. The latter joint is called the symphysis
pubis and it allows a little “give” which is desirable, particularly when giving birth!
 Very mobile joints. The bones are held together by ligaments and muscles. The
bones may also be shaped to fit well together at the joint thus helping to hold the
bones in place but also allowing certain types of movement. These joints are called
synovial joints (see Figure 8) and allow a wide range of movements.
JOINTS
IMMOBILE JOINTS
SLIGHTLY MOBILE
JOINTS
VERY MOBILE JOINTS
SYNOVIAL JOINTS
Examples of this type are the hip and knee joints. The ends of the bones in a
synovial joint are covered with articular cartilage. A sleeve of tough fibrous material
called the capsule is attached to the bones and encloses the joint. The inner layer of
the capsule is lined with a synovial membrane which produces synovial fluid. The
synovial fluid fills the synovial cavity, lubricating the joint and providing nutrients
to the articular cartilage. These joints in particular allow us the movement that is not
only a major factor in our survival but also a prime source of our enjoyment of life.
3.7.1 Synovial Joints - general structure
The synovial joint derives its name from the presence of synovial fluid. This is
produced by the synovial membrane which is a thin layer of cells lining the joint
capsule (see Figure 8).
Unit 1 – Basic Anatomy
10
SYNOVIAL FLUID
SYNOVIAL MEMBRANE