Brain stem

The brain stem is similarly structured as the spinal cord: it consists of grey matter sur-
rounded by white matter fibre tracts. Its major regions are the midbrain, pons and medulla
oblongata. The midbrain, which surrounds the cerebral aqueduct, provides fibre pathways
between higher and lower brain centres, contains visual and auditory reflex and subcortical
motor centres. The pons is mainly a conduction region, but its nuclei also contribute to the
regulation of respiration and cranial nerves. The medulla oblongata takes an important role
as an autonomic reflex centre involved in maintaining body homeostasis. In particular,
nuclei in the medulla regulate respiratory rhythm, heart rate, blood pressure and several
cranial nerves. Moreover, it provides conduction pathways between the inferior spinal cord
and higher brain centres.

Cerebellum

The cerebellum, which is located dorsal to the pons and medulla, accounts for about 11% of
total brain mass. Like the cerebrum, it has a thin outer cortex of grey matter, internal white
matter, and small, deeply situated, paired masses (nuclei) of grey matter. The cerebellum
processes impulses received from the cerebral motor cortex, various brain stem nuclei and
sensory receptors in order to appropriately control skeletal muscle contraction, thus giving
smooth, coordinated movements.

The cerebral circulatory system

Blood is transported through the body via a continuous system of blood vessels. Arteries
carry oxygenated blood away from the heart into capillaries supplying tissue cells. Veins
collect the blood from the capillary bed and carry it back to the heart. The main purpose of
blood flow through body tissues is to deliver oxygen and nutrients to and waste from the
cells, exchange gas in the lungs, absorb nutrients from the digestive tract, and help forming
urine in the kidneys. All the circulation besides the heart and the pulmonary circulation is
called the systemic circulation.
Since it is the ultimate aim of this research project to image cerebral oxygenation and
haemodynamics some aspects of the cerebral circulatory system are described below.

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