Bma Illustrated Medical Dictionary

procedure is performed under general
anaesthesiaand involves removing the
protruding tissue via a small incision in
the outer coat of the disc.
microorganismA tiny, single-celled liv-
ing organism. Most microorganisms are
too small to be seen by the naked eye.
microphthalmosA rare congenital dis-
order of the eye. Affected children are
born with an abnormally small eye on
one or both sides.
microscopeAn instrument for produc-
ing a magnified image of a small object.
Microscopes are used to examine the
structure and chemical composition of
cells and tissues, and to investigate
microorganisms and diseased tissues.
In the operating theatre, microscopes
are used in microsurgery.
Compound microscopes are the most
widely used type. They have 2 lens sys-
tems (the objective and the eyepiece),
mounted at opposite ends of a tube
called the body tube. There is a stage to
hold the specimen, a light source, and
an optical condenser which concentrates
the light. The maximum magnification is
about 1,500 times.
Phase-contrast and interference micro-
scopes are modified light microscopes
that allow unstained transparent speci-
mens to be seen. They are used for
examining living cells and tissues.
Fluorescence microscopes use ultra-
violet light to study specimens stained
with fluorescent dyes.
Electron microscopes give much higher
magnifications than light microscopes
by using a beam of electrons instead of

M

light. There are 2 types: transmission

electron microscopes (TEMs) and scan-

ning electron microscopes (SEMs). TEMs

can magnify up to about 5,000,000

times, enabling tiny viruses and molec-

ules to be seen. SEMs have a lower

maximum magnification (100,000 times),

but produce 3-dimensional images.

This makes them useful for studying

surface structures of cells and tissues.

microsurgerySurgery in which the

surgeon views the operation site via a

special binocular microscope with

pedal-operated magnification, focusing,

and movement. The technique of micro-

surgery is used for surgery involving

minute, delicate, or not easily accessi-

ble tissues. Examples include surgery

on the eye or the inside of the ear.

micturitionA term for passing urine.

midazolamA benzodiazepine drugused

as premedication. Adverse effects include

confusion, drowsiness, and dizziness. If

benzodiazepines are taken for a long

period, dependencemay result.

midbrainThe top part of the brainstem,

situated above the pons. The midbrain

is also called the mesencephalon.

middle earSee ear.

middle-ear effusion, persistentSee

glue ear.

middle-ear infectionSee otitis media.

mid-life crisisA popular phrase to

describe the feelings of distress that

affect some people in early middle age

after they realize that they are no longer

young. Counselling and support are

usually effective in helping people to

come to terms with the changes of age.

MICROORGANISM MID-LIFE CRISIS

MICRODISCECTOMY

Spinal

nerves

Compressed

nerve root

BEFORE THE OPERATION

SITE OF

INCISION

Fibrous outer

coat of disc

Protruding core

Normal

nerve root

Repaired

fibrous coat

Gelatinous core

AFTER THE OPERATION