Bma Illustrated Medical Dictionary

blood flow and metabolic activity in the

brain to be measured.

Ultrasound scanningis used only in

premature or very young babies since

ultrasound waves cannot penetrate the

bones of a mature skull.

brainstemA stalk of nerve tissue that

forms the lowest part of the brain and

links with the spinal cord. The brainstem

acts partly as a highway for messages

travelling between other parts of the

brain and spinal cord. It also connects

with 10 of the 12 pairs of cranial nerves

(which emerge directly from the under-

side of the brain) and controls basic

functions such as breathing, vomiting,

and eye reflexes. Brainstem activities

are below the level of consciousness,

and they operate mainly on an auto-

matic basis.

The brainstem is composed of 3 main

parts: the midbrain, pons, and medulla.

The midbrain contains the nuclei (nerve-

cell centres) of the 3rd and 4th cranial

nerves. It also contains cell groups invol-

ved in smooth coordination of limb

movements. The pons contains nerve

fibres that connect with the cerebellum.

It also houses the nuclei for the 5th–8th

cranial nerves. The medulla contains the

nuclei of the 9th–12th cranial nerves. It

also contains the “vital centres”(groups

of nerve cells that regulate the heart-

beat, breathing, blood pressure, and

digestion (information on which is relay-

ed via the 10th cranial nerve (see vagus

disease is a rare, fatal brain disease

associated with an infective agent called

a prion which, in some cases, has been

linked with BSE (bovine spongiform

encephalopathy), a disease in cattle.

Multiple sclerosis is a progressive

disease of the brain and spinal cord.

Degenerative brain diseases include Alz-

heimer’s diseaseand Parkinson’s disease.

Emotional or behavioural disorders are

generally described as psychiatric ill-

nesses; but the distinction between

neurological and psychiatric disorders

is now much less clear.

brain failureSee brain syndrome,

organic.

brain haemorrhageBleeding within

or around the brain that is caused

either by injury or by spontaneous rup-

ture of a blood vessel. There are 4

possible types of brain haemorrhage:

subdural, extradural, subarachnoid, and

intracerebral. Extradural and subdural

haemorrhages are usually the result of

a blow to the head (see head injury).

Subarachnoid and intracerebral haem-

orrhages usually occur spontaneously

due to rupture of aneurysmsor small

blood vessels in the brain.

brain imagingTechniques that provide

pictures of the brain; they are used to

detect injury or disease and include

X-rays, angiography, CT scanning, MRI,

PET (positron emission tomography)

scanning, and SPECT (single photon

emission CT). X-ray films can show

changes in the skull caused by a fracture

or, rarely, by a brain tumouror aneur-

ysm. Angiography shows up the blood

vessels in the brain, and is used to

investigate subarachnoid haemorrhage,

aneurysms, abnormalities of the blood

vessels, and other circulatory disorders.

CT scanning gives images of the brain

substance; it gives clear pictures of the

ventricles (fluid-filled cavities) and can

reveal tumours, blood clots, strokes,

aneurysms, and abscesses. MRI is espe-

cially helpful in showing tumours of the

posterior fossa (back of the skull). PET

and SPECT scanning are specialized

forms of radionuclide scanningthat use

small amounts of radioactive material

to give information about brain func-

tion as well as structure. They enable

BRAIN FAILURE BRAINSTEM

B

Medulla

Spinal

cord

Brainstem

Midbrain

Pons

Thalamus

BRAINSTEM

LOCATION