Microorganisms - single celled animals which may range from the very small viruses, through bacteria and fungi6 to almost visible protozoa.

Microtubules - are the largest filament in the cytoskeleton. They are the hollow tubes along which cell products are conducted long distances. The system is not unlike a railway network around the cell, sometimes involving long distances. For example, neurones transport out neurotransmitter substances along the axons to distant synapses, inside microtubules.

Minor salivary glands - are microscopic glands under the surface of the oral mucosa. They are found throughout the lining mucosa of the mouth including the tongue.

Mitochondria - a cell organelle found in eucaryotic cells which produces ATP as a product of the kreb cycle and the electron transport system Cells requiring large amounts of energy, such as secreting odontoblasts, have large numbers of mitochondria. Mitochondria are self replicating and contain their own DNA for this purpose.

Mitosis- the division of a cell into two daughter cells, each of which is identical.

Mitotic activity - the rate of mitosis, and hence cell division. The mitotic activity of basal cells in an epithelium must match the rate of desquamation.

Molecules - a combination of atoms joined together in fixed proportions.

Monocytes - remain in the blood only a short time before they migrate into the tissues particularly where dead tissue must be removed, where they are calledmacrophages.

Morphogenesis - the process in which tissue shapes and organ structures are developed during embryology.

Morphogenic fieled - an environment in which the shape or pattern of a developing organ is determined.

Motoneurone - nerve cells with their cell bodies in the brain stem or spinal cord, which transmit impulses along their axons to effector organs, including endocrine, exocrine glands and muscles fibres. The axons of most motoneurones have many branches, each of which ends at a neuromuscular junction. The group of muscle cells innervated by one motoneurone is called a motor unit.

Mucoperiosteum - a type of oral mucosa which has a fibrous lamina propria, no submucosa, and is attached to the underlying6 periosteum of bone. The attached gingiva is a mucoperiosteum.

Mucous - a secretion8 which is viscous and slimy due to the presence ofglycoproteins.

Mutation - a change in the order of nucleotide bases on a gene, which alters the configuration of the protein produced, and thus may alter the behaviour of the cell. A mutation may cause a cell to die, or become cancerous. Mutations in bacteria and viruses help them to evade detection by their hosts.

Myelin - the fatty covering of myelinated nerves which appears white to the naked eye. The parts of the brain and spinal cord, in which myelinated nerves run, has therefore been called the "white" matter as distinct from the "grey" matter composed of nerve cells. Myelin also contains about 20% of proteins whose prime role is to mediate13 adhesion between adjacent Schwann cells. These cell membrane glycoproteins are also members of the immunoglobulin family of cell surface proteins. Defects in the these surface proteins may cause them to act as antigens to the immune system. The disease multiple sclerosis is caused by antibodies to the myelin proteins, which results in inflammation and loss of myelin.

Myelinated - nerves axons which are completely wrapped in a sheath of myelin by schwann cells. One cell wraps about a millimetre of nerve axon. Myelinated nerve axons carry impulses faster then unmeyelinated nerves as the impulse jumps across the myelin sheath of each adjacent Schwann cell to that of the next.