**3. Understanding the origins of human tremor**

The study of tremor is not new and it can be found in the biblical texts and documents of antiquity coming from India and Egypt [3]. The interest in the study of tremor increased over the past decades and, lately, many researches can be found in this area, especially related to the quantification of human tremor signals. Quantification of tremor allows studying it in an objective way, making it possible to establish relationships between the tremor activity and variables, such as age or the presence of neurological dysfunctions.

Regarding to the study of tremor's origins only relatively recently such ideas have received great interest [8].

6 Practical Applications in Biomedical Engineering

physical limitations of these individuals [1].

component.

personal care [7].

resources.

stereotactic surgery on the ventral medial nucleus of thalamus can control the postural

Thousands of people each year begin to present some type of motor dysfunction, which interferes in their daily activities and reduces significantly the quality of life of these individuals. A number of studies and governmental statistics have shown that the elderly population is the most affected by tremor and its consequences, which are responsible for

The manifestation of the tremor can cause considerable functional incapacity leading to social isolation by interference in the activities of daily living (ADLs) and instrumental activities of daily living (IADL) such as eating, writing, dressing and maintaining some

Moreover, recent researches from the Brazilian Ministry of Health (available on www.saude.gov.br) suggest that signs like tremor and loss of balance do not always mean the presence of neurological diseases such as Parkinson's disease, which affects mainly the population with age over 50 years old. According to this Ministry about 25% of patients who exhibit signs of Parkinson do not have the disease. The imprecise diagnosis of these diseases and the consequent use of unnecessary or inappropriate drugs also results in waste of public

Generally, current therapies are limited because they relieve symptoms more than cure. The most commonly used drugs are: propranolol, primidone, gabapentin, topiramate and others to be considered comprise in the second row like alprazolam, atenolol, sotalol and clonazepam and, in the third line: clozapine, nadolol, nimodipine, being the botulinum toxin

Some studies have suggested that moderate tremor, which accompanies the natural aging process can be diagnosed as pathological tremor. It is also possible that the pathological

The human tremor is a public health problem faced all over the world. Costs related to medical and social aspects, necessary for diagnosis and treatment of tremor, have grown constantly in past decades and currently reach billions of dollars in many countries. A treatment that seeks to mitigate the symptoms and create the possibility of a person with tremor accomplish everyday tasks constitute an important intervention. In this context,

The study of tremor is not new and it can be found in the biblical texts and documents of antiquity coming from India and Egypt [3]. The interest in the study of tremor increased over the past decades and, lately, many researches can be found in this area, especially related to the quantification of human tremor signals. Quantification of tremor allows studying it in an objective way, making it possible to establish relationships between the tremor activity and variables, such as age or the presence of neurological dysfunctions.

studies that contribute to the understanding of tremor are of paramount importance.

the first line for hands, head and voice tremors, in cases of essential tremor.

tremor is wrongly diagnosed as physiological tremor [5].

**3. Understanding the origins of human tremor** 

The movement caused by tremor can be associated to factors such as neurological disorders and natural processes. [2; 11; 12] The former is called pathological tremor whereas the latter is often referred to as physiological tremor.

There are several hypotheses to explain the appearance of physiological tremor (PT). One explanation for the existence of physiological tremor is the effect of ballistocardiogram, i.e., the passive vibration of the body tissues produced by the mechanical activity of the heart [13], i.e., a result of mechanical reflexes of the heartbeat and also of neural reflexes [14]. Another hypothesis is that physiological tremor is induced by mechanical properties of limbs and motor neurons firings.

It is also believed that the physiological tremor is a peripheral manifestation of neural oscillatory activity in the central nervous system (CNS) and that some types of pathological tremors are resultant of distortions and amplifications of these central oscillations [8].

According to Hallett (1998), the sources of tremor can be summarized into three groups: mechanical, reflex and central oscillations [9].

The first source is the mechanical oscillations, in which joints and muscle movements satisfy the laws of physics and the complex joint-muscle-tendon system can be compared to masses and springs. Therefore, the oscillations can be interpreted as the movements of masses and springs [10].

The second source of tremor is the reflex oscillations that are reported in the central and peripheral circuits. On the peripheral circuit the path occurs from muscles to the spinal cord and from the spinal cord to the muscles. On the central circuit the path occurs from peripheral to the spinal cord and supraspinal segments including the brain, cerebellum, basal ganglia and cerebral cortex [10].

The third and last source of tremor is central oscillations that can be observed since the first recordings of the electroencephalography (EEG). The neural activity follows rhythmic behavior. Therefore, the cerebral cortex, the basal ganglia, the cerebellum and the brainstem nucleus are all involved in the genesis of tremor [10].

Detailed analysis of oscillations in the CNS are imprecise due to the difficulty in performing measurements directly in the human brain [8]. As these neural oscillations can directly influence motor control and indicate the status of the CNS, the interest in the study of various types of tremor, as peripheral manifestations of central oscillations, has grown in recent years.

We still do not have a precise definition of the origin of tremor in humans. It is believed that it is a product of several factors. Thus, the tremor is considered a peripheral oscillation that may also have, in addition to contributions of neural activities, activities originating from the motor units and from the resonances of reflex arcs [8].

Moreover, the pathological tremor can be associated with several factors, such as neurological disorders [2].
