The Brain and Mercury
This article examines the architecture of the brain, along with the particular effects of mercury on the central nervous system.
The nervous system consists of the central nervous system (CNS) which is made of the brain and the spinal cord, and the peripheral nervous system (PNS).
The peripheral nervous system is composed of all the sensory nerves which gather information from the internal environment of the body and transmit it to the brain for processing and the motor neurons which then pass instructions to the tissues to bring about some kind of response.
Within the central nervous system the nerve cell bodies are dark and are referred to as grey matter and the long nerves with their myelin sheath insulation appear light and are referred to as white matter. In the spinal cord the white matter is outermost, whereas in the brain the grey matter is outermost.
Both the spine and brain are suspended within tough meninges in cerebrospinal fluid which provides nourishment and cushioning and also receive protection from the bony vertebrae and skull respectively.
The peripheral nerves either originate from the base of the skull (cranial nerves) or are trunked together in the spinal cord to emerge between the vertebrae.
The central nervous system is further protected by the blood-brain barrier which is a system of tight junctions surrounding capillaries. This prevents the ingress of larger objects such as bacteria and large molecules whilst allowing the diffusion of small molecules. The cells involved in forming the barrier are also responsible for actively transporting substances such as glucose across the barrier.
Mercury in both its organic and elemental vaporous form can pass through the blood-brain barrier and the vapour has particular access through the perforated plate in the roof of the nose. Mercury is also absorbed into and tracks up the nerves to ultimately accumulate within the brain and spinal cord where it causes conditions such as Parkinson's disease, Alzheimer's disease, multiple sclerosis, dementia and amyotropic lateral sclerosis (ALS).
Mercury is, of course, highly neurotoxic and causes tremendous damage to brain and nerve cells. It generates massive free radical damage, depletes glutathione, kills or inhibits production of brain tubulin cells and inhibits production of neurotransmitters. Also, because mercury is able to cross the placenta, it is incorporated into the developing nervous system of the foetus to cause attention deficit disorders, hyperactivity and autism.
The main structures of the brain are detailed below.
The cerebrum or cerebral cortex is the largest part of the human brain, and is associated with higher brain function such as thought and action. It has a six-layered structure with the cell bodies outermost and is thought to be a recently evolved structure.
The cerebrum is effectively two brains - right and left brains or hemispheres - which are connected by a broad structure called the corpus callosum. This acts as an information superhighway between the two hemispheres which have different functions and is wider in women than men.
Broadly speaking the right hemisphere is associated with creativity and synthesis and the left hemisphere is associated with language and logic.
The cerebral cortex is highly wrinkled and this allows the brain to be more efficient, by increasing the surface area of the brain and the amount of neurons within it. The functions of the different lobes of the brain are:
Frontal Lobe: Reasoning, planning, speech, movement, emotions and problem solving
Parietal Lobe: Movement, orientation, recognition and perception of stimuli
Occipital Lobe: Sight. Mercury has been shown to accumulate here in direct proportion to the number of amalgam fillings.
Temporal Lobe (not shown - to the side): Perception and recognition of sound, memory and speech
The cerebellum literally means 'little brain' and has two hemispheres and is suspended beneath the base of the cerebrum. It is highly folded and is associated with regulation and coordination of movement, posture and balance.
The cerebellum is in evolutionary terms a more ancient structure than the cerebrum, although it is not found in reptiles.
It is very vulnerable to decreased oxygen supplies and also preferentially accumulates mercury. Both lack of oxygen and toxicity will results in a lack of coordination and poor balance.
The limbic system
This is a term which evolved before much was known about the brain and the term is derived from the Latin word limbus for border and many feel that it should now be abandoned as being meaningless.
The limbic system, often referred to as the 'emotional brain', is found buried within the cerebrum. Like the cerebellum, the limbic system is fairly old in evolutionarily terms and is shared by reptiles and mammals.
The limbic system is highly interconnected with the brain's pleasure centre (the nucleus accumbens), which plays a role in sexual arousal and the 'high' derived from some recreational drugs.
In fact, a lobotomy, used until relatively recently to treat severe emotional disorders, involved severing this connection. Patients who underwent this procedure often became passive and lacked all motivation.
The term limbic system encompasses the structures of the thalamus, hypothalamus, amygdala and hippocampus which support a variety of functions including emotion, behaviour, long term memory and smell.
Thalamus This is a large mass of gray matter deep within the forebrain that has both sensory and motor functions. Almost all sensory information (with the exception of smell) enters this structure before being redirected to the cerebrum for which reason it is sometimes referred to as a 'relay station'.
Hypothalamus This structure is involved in all functions involving homeostasis including maintaining blood pressure, heart rate, circadian rhythms and control of the autonomic nervous system along with other functions relating to hunger, emotion, thirst and sexual arousal.
In addition, this little cluster of sensors controls the endocrine system via the pituitary gland which lies beneath. Mercury is known to particularly accumulate within the hypothalamus and pituitary glands leading to depression and profound effects upon the mental, emotional and physical status of the individual and this is thought to be key to fatigue syndromes.
Amygdala This large structure lies beneath the surface of the temporal lobe and is involved in memory, emotion and fear. This structure can activate the hypothalamus.
Hippocampus This lies within the temporal lobe and is the part of the brain which is thought to be important in converting short term memory to long-term memory - and also in spatial navigation. It is one of the areas known to be affected by mercury toxicity and is particularly implicated in Alzheimer's disease. This may account for the deterioration in memory many consider to be a normal part of ageing.
The brain stem
Underneath the limbic system is the brain stem. This structure is responsible for maintaining basic vital life functions such as breathing, heartbeat and blood pressure. This is the simplest part of the brain, because reptilian brains resemble our brain stem.
Midbrain This is involved in functions such as vision, hearing, eye movement and body movement. The front part carries a huge bundle of nerves travelling from the cerebral cortex through the brain stem which control voluntary motor function.
Pons This is linked to the cerebellum and controls movement, posture and sensory analysis. For example, information from the ear enters the brain via the pons. It is also related to levels of consciousness and sleep.
Medulla Oblongata This is located between the pons and spinal cord and is responsible for maintaining vital body functions, such as breathing and heart rate.
Reticular activating system This structure contains the majority of the brain's nerve cells and acts as a filter between the vast amount of unconscious information that are constantly being processed and the relatively tiny amount which is drawn to conscious awareness. It is also involved in motivation, arousal, sleep/wake cycles, maintenance of muscle tone, heart rate, breathing and modulating perceptions of pain. Many think that dysfunction of this region may be largely responsible for many of the symptoms associated with fatigue syndromes.