November 12, 2008

What is Parkinson’s Disease ?

In our daily life we don’t even think how we move our bodies. It just happens whenever we want it to. But in order to understand what happens to the body during Parkinson’s disease , it is quite useful to have some knowledge about how brain controls our movements, or in other words our “motor functions ”.

Brain is a very complex structure. There are many different areas which control different functions in our body . So it is divided into different regions depending on their functions. For instance occipital lobe is concerned with many aspects of vision, temporal lobe concerned with perception and recognition of auditory stimuli (hearing) and memory (hippocampus).

In humans, motor system controls a complex neuro-muscular system . Commands have to be delivered to lots of muscles. Motor system consists of cortical and subcortical grey matter, efferent nerves, cerebellum and impulses that arise from basal ganglia . The basal ganglia are a collection of nuclei deep to the white matter of cerebral cortex . The name includes: caudate, putamen, nucleus accumbens, globus pallidus, substantia nigra, subthalamic nucleus. Parkinson’s disease is the slow and steady loss of dopaminergic neurons in substantia nigra .

What is a dopaminergic neuron?

Communication between neurons

The entire nervous system is made up individual units called neurons. They have to communicate each other in order to transmit messages. Two neurons do not attach to each other, instead of there is a gap between two neurons called “synapse”. In synapses there is a variety of chemical messengers called neurotransmitters. Neurotransmitters carries messages between two neurons by traversing the synapses between neurons. These chemical messengers also allow the nervous system to communicate with the muscles. “Dopamine” is one of these neurotransmitters which is produced by the substantia nigra. Dopamin is necessary for movement.

Synaptic cleft between two neurons and neurotransmitter

It helps transmit messages to the striatum. Striatum is responsible for balance, control of movements, and walking. When pigmented cells of substantia nigra deteriorate, as in the case of Parkinson’s disease, there is a parallel decrease in the amount of dopamine. If dopamine level decrease the neurons of the striatum uncontrollably fire, finally patients are not able to direct motor functions.

Another neurotransmitter “Acetylcholine” is also involved in the process of movement. Depending on what you want to do, some neurons in the brain can use either dopamine or acetylcholine to send different messages. For a smooth movement acetylcholine and dopamine work together in a balance. Because the motor function of the striatum depends on the equilibrium reached between dopamine and acetylcholine. The disruption of this balance is important for the progression of Parkinson’s disease.

Parkinson’s disease is the most common chronic, late onset, progressive, neurologically based movement disorder. It is named after English physician James Parkinson, who identified it in 1817. Parkinson’s disease is characterized clinically by bradykinesia, resting tremor, coghwell rigidity, and postural reflex impairment and affects over 1 million people in North America. Approximately 1% of the United States and Europian populations over the age of 60 have Parkinson’s disease. It is affecting about 1% of 65-year-old individuals and rising to 5% by 85 years of age.

Lewy body in pigmented neurons of substantia nigra in Parkinson

Pathologically, it is mainly manifested by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta, in other words loss of pigmented neurons, specially in substantia nigra, and presence of associated characteristic cytoplasmic Lewy bodies, which are named after Frederick H. Lewy first described them in 1912. He investigated Lewy bodies in the substantia innominata and the dorsal vagal nucleus in Parkinson’s disease. It is now known that Lewy bodies can be seen in pigmented neurons of the substantia nigra in almost every case of Parkinson’s disease.

In Parkinson’s disease, Lewy bodies are found in many regions, including the subtantia nigra, locus ceruleus, hypothalamus, nucleus basalis, cranial nerve motor nuclei, and the central and peripheral divisions of the autonomic nervous system.