专业词汇|口腔生理学术语(M)

Macrophages - cells derived^{1 from monocytes which have the ability to phagocytose foreign particles and dead tissue and to move through tissue, or to remain fixed2 in one place. There are many macrophages in the spleen where they remove dead red blood cells from the circulation.}

Major salivary^{3 glands4 - are three large glands on each side of the face; the parotid, submandibular and submaxillary.}

Malleus - one of the three bones of the inner ear. The others are the stapes and the incus.

Mastication^{5 - the process of preparing food for swallowing and digestion6 by chewing it.}

Matrix - comes from the Latin word matermeaning mother. It is a structure which encloses or holds something within it. Cells are held or enclosed in a matrix of fibres, water and large molecules^{8 called the ground substance.}

Matrix vesicles. - small bubble-like structures containing calcium-binding phospholipids and alkaline phosphatase. Crystals of hydroxyapatite from inside the vesicle which ruptures^{9 and releasing crystals into the surrounding osteoid or predentine so as to start mineralising it.}

Mechano-receptors- sensory^{10 receptors which respond when mechanically deformed11 by pressure, tension, vibration12 or touch.}

Mesenchyme - dental mesenchyme is tissue derived from the mesoderm of the embryo^{13 and which has been infiltrated14 and highly influenced by migrating cells from theneural crest15.}

Mesial drift - a gradual movement of all the posterior teeth in a mesial direction. It occurs only if there has been interproximal wear between the teeth. The drift is not a passive one however, as it has been shown that during chewing, the bite force has a a mesial component^16.

Mesial - towards the midline.

Mesoderm - the middle of the three cell layers which form, as the clump^{17 of early embryonic18 cells begins to differentiate19. The mesoderm will form the muscles, blood system, connective tissue, including bone and dentine, the kidneys and the dermis20 of the skin. The other two layers are the ectoderm and theendoderm.}

Messenger RNA - a ribose nucleic acid acid which caries the DNA^{21 code in matching nucleotides, from the nucleus22 to the ribosome of the cell.}

metabolise - to obtain energy by breaking down a molecule^{7 into smaller components23, as in respiration24 or to store energy by building a more complex molecule out of smaller components. It always takes place in a number of stages, controlled by enzymes25. Each step in the process follows a predictable metabolic26 pathway for that reaction.}

Microbiology - the study of the microscopic^{27 forms of life.}

Microfilaments - are the smallest filaments^{28 of the cytoskeleton. The filaments are made of hundreds of actin molecules, stacked in a line. They can be quickly broken down or extended. Actin filamanents give the cell its shape and help to change it. When cells move, in embryology and repair, or just during the continual patrol of lymphocytes, they must hold on to something in order to crawl. The filaments serve to anchor one part of the cell, via fibronectin to the cell matrix, so the rest of the cell can pull itself towards the anchor. Lymphocytes move and scavenge by sticking out arms and feet to help them crawl and engulf30 foreign particles. Muscle cells change their shape by using stacks of actin filaments as a ladder on which myosin climbs.}

Micron - 1000th part of a millimetre.

Microorganisms - single celled animals which may range from the very small viruses, through bacteria and fungi^{31 to almost visible protozoa.}

Microtubules - are the largest filament^{29 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 synapses32, inside microtubules.}

Minor^{33 salivary glands - are microscopic glands under the surface of the oral mucosplaya. They are found throughout the lining34 mucosplaya 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^{35 odontoblasts, have large numbers of mitochondria. Mitochondria are self replicating36 and contain their own DNA for this purpose.}

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

Mitotic activity - the rate of mitosis, and hence cell pision. 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^38.

Motoneurone - nerve cells with their cell bodies in the brain stem or spinal^{39 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 junction40. The group of muscle cells innervated by one motoneurone is called a motor unit.}

Mucoperiosteum - a type of oral mucosplaya which has a fibrous lamina propria, no submucosplaya, and is attached to the underlying^{41 periosteum of bone. The attached gingiva is a mucoperiosteum.}

Mucous^{42 - a secretion43 which is viscous44 and slimy due to the presence ofglycoproteins.}

Mutation^{45 - a change in the order of nucleotide bases on a gene37, which alters the configuration46 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 evade47 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 mediate^{48 adhesion between adjacent Schwann cells. These cell membrane49 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.