Chemistry Reference
In-Depth Information
Chapter 20
Metals in Brain
Introduction
379
The Brain and the Blood
e
Brain Barrier (BBB)
379
Sodium, Potassium, and Calcium Channels
384
Zinc, Copper, and Iron
388
Concluding Remarks
394
INTRODUCTION
Metal ions are absolutely essential to fulfil a series of important biological functions in the brain, including the
transmission of nerve impulses and the synthesis of neurotransmitters. They include spectroscopically silent metal
ions like potassium, sodium, calcium, magnesium, and zinc, together with the more spectroscopically accessible
iron, copper, manganese, and a few others. The role of some of these metal ions in brain function is particularly
important. As we saw in Chapter 9, the alkali metal ions Na
þ
and K
þ
are involved in the opening and closing of ion
channels which generate electrochemical gradients across the plasma membranes of neurons. This plays a crucial
role in the transmission of nervous impulses not only within the brain but also in the transmission of signals from
the brain to other parts of the body. Calcium and zinc fluxes are also important in regulating neuronal cell function.
We will also see that copper and iron play a major role in the brain, particularly in metalloenzymes.
THE BRAIN AND THE BLOOD
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BRAIN BARRIER (BBB)
The human brain is complex enough to coordinate the fingers of a concert pianist, and even the fingers, hands, and
feet of an organist, all playing on different keyboards; it can create three-dimensional images from light falling on
a two-dimensional retina. It constitutes just 2% of the human body mass, yet it consumes 20% of our resting O
2
consumption, varying little between sleep and intense concentration (eg., when we are involved in intensely
reading a book on biological inorganic chemistry).
The complexity of the nervous system is staggering, as it regulates all aspects of the functions of our bodies,
yet even today, in our post-genomic era, we are still a long way from understanding it. The human brain contains
about 10
12
specialised nerve cells, called neurons, each of which forms as many as 10
3
connections with other
neurons. Millions of neurons collect information about our environment (both external and internal), which they
transmit to other neurons, where the data is either processed or stored. Millions more respond to this information
to regulate the control of muscle contraction, hormone synthesis, etc. In spite of the overwhelming complexity of
what we call the central nervous system, we understand the structure and function of neurons quite well. Most
neurons contain four distinct regions
the cell body, the axon, the dendrites, and the axon terminals (
Figure 20.1
)
.
The cell body, which contains the nucleus, is the site of synthesis of all neuronal proteins and membranes. Most
neurons have one single axon which conducts the electrical impulses, called action potentials, and which
terminate in many axon terminals. The extensively branched dendrites receive signals at their interface with
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