Chapter 5 : Cerebellum and Basal Ganglia

Brain: Contents Page

The Cerebellum and Basal Ganglia                         Topics :     

Abnormalities of Movement: Tremor and Ataxia

Normal tremor

Most people notice some tremor of the hands when they are held out, and this normal tremor can get worse when people feel stressed, angry or anxious.

Essential tremor is more severe than normal tremor and it gradually gets worse over time, and can become so severe that everyday activities can become difficult. It can be made worse by tiredness, lack of sleep, smoking, caffeine and certain medicines. Essential tremor can run in families and appears to be due to a faulty gene.

A number of medical conditions  may cause tremor, including hyperthyroidism, alcohol withdrawal in alcoholics, and a series of neurological conditions. Prominent amongst these are Parkinson's Disease, Multiple Sclerosis, Stroke and Peripheral Neuropathies.

Observation of patients with tremors results in a division of tremors caused by neurological disease into two categories- Intention Tremor and Non-Intention Tremor, depending on whether the tremor starts when the patient attempts a voluntary movement (Intention Tremor), or whether it occurs at rest.

Ataxia is a disorder in wihch the patient has difficulty in movement and balance and a failure to coordinate muscle movements.


Intention Tremors

Cerebellar Ataxia.

Cerebellar ataxia is a disorder in wihch the patient has difficulty in movement and balance and a failure to coordinate muscle movements.

Cerebellar lesions give rise to an intention tremor: the coarse tremor increases as the limb attempts to reach the object of the desired voluntary movement. The intention tremor is usually at right angles to the direction of movement, and the hand alternates between overshooting and undershooting their target.

Unilateral cerebellar lesions cause a loss of muscle tone on the same side as the lesion. Nystagmus and disturbances of the vestibulo-ocular reflexes may also be present.

Cerebellar Ataxia is sometimes a feature of Multiple Sclerosis.

Intention Tremor in the left arm of the patient, attempting to touch his right index finger

The French neurologist Jean-Martin Charcot identified the difference between intention an non-intention tremors.

He realised that patients with Parkinson's disease had a tremor at rest, and which disappeared during voluntary movements. In contrast there were a different group of patients with different signs and symptoms, including a tremor that only occurred during a voluntary movement and which prevented the limb reaching its desired destination, i.e. an intention tremor. These patients often had cerebellar disorders..

Charcot's triad is a group of symptoms and signs including an intention tremor, nystagmus and scanning speech. Many of these patients had Multiple Sclerosis, but others had other forms of cerebellar pathology.

The most common cause of intention tremors is damage to the cerebellum. These patients have difficulty in executing movements, such as a problem with attempting to touch their nose or another obejct with a finger (known as dysdiadokokinesis).

Common sites for cerebellar lesions that lead to intention tremors include:

  • lesions of the dentate nucleus and its output pathway, the superior cerebellar peduncle, by which the cerebellum reports back to the motor areas of the cerebral cortex.
  • damage to the vermis caused by alcohol.
  • multiple sclerosis, in which demyelination and plaques of abnormal glia disrupt neuronal activity in the brainstem or cerebellum.

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Non-Intention Tremors

The commonest non-intention tremor is found in patients with Parkinson's disease - a chronic and progressive movement disorder in which the symptoms continue and worsten over time. There are about one million sufferers in the US.

The specific symptoms of the disease vary from person to person.

Motor signs include:

  • tremor of the hands arms legs jaw and face
  • bradykinesia- slowness of movement
  • rigidity - stiffness of the limbs and trunk
  • postural instability or impaired balance and coordination
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Most people with Parkinson's disease develop a tremor that is most prominent in the hands and fingers at rest, and disappearing when performing tasks such as drinking or eating. About 30% of people with Parkinson's disease never develop a tremor.

Stiffness is a common early sign of Parkinson's disease and is most obvious in the arms, shoulder or neck, although it can occur in all muscle groups. People may have difficulty getting out of a chair, turning or rolling over in bed, or walking. Fine finger movements such as those involved in doing up a button or tying a shoelace may also be difficult. Pain or a deep aching sensation in the muscles may also be felt.

Bradykinesia means slowness of movement and is a disabling and frustrating symptom of Parkinson's disease. People have difficulty initiating movement and movement may be slow. There may also be a lack of coordination when moving and normal activities can prove difficult. Activities once performed quickly and comfortably, such as washing or dressing, may take several hours if not assisted. Bradykinesia can also make the face seem flat or expressionless.

Loss of balance tends to develop later in this disease. Because of impaired balance and co-ordination (postural instability) a Parkinson's patient can develop a forward or backward lean. They may start to walk with small steps as if hurrying forward to keep balance. Frequent falls are also common.

A range of other symptoms may be experienced including pain, depression, slow slurred speech, decreased blinking and difficulties in walking or writing.

Chorea

Chorea is an abnormal involuntary movement disorder, in which quick movements of the feet or hands occur that have been compared to dancing. If the movements are confined to one side of the body, the term hemichorea is sometimes used.

Chorea can occur in a variety of conditions and disorders, including Huntington's disease, an inherited progressive neurological disease, and Sydenham's Chorea, which is complication of rheumatic fever.

Athetosis

Athetosis is an involuntary movement characterized by slow, convoluted, writhing movements of the fingers, hands, toes, and feet and in some cases, arms, legs, neck and tongue.

Lesions to the striatum are the usual cause of the symptoms and are commonly associated with cerebral palsy.



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Ataxias

Spino-Cerebellar Ataxia

Spino-Cerebellar ataxia encompasses a large group of genetic disorders characterised by the presence of  a progressive, degenerative ataxia, for which there is often a family history. Possibly as many as 150,000 people in the United States have Spinocerebellar Ataxia. Spino-Cerebellar Tracts.

Several genes have been identified, and a protein, ataxin, which has several mutations, is found in many of these patients..

Peripheral Neuropathy

Peripheral neuropathy is a common, often distressing, and sometimes disabling or even fatal condition, in which demyelination of axonal degeneration give rise to sensory and motor disturbances.

Ataxia is common and occurs because of loss of proprioceptive and other sensory inputs to the spinal cord; diabetes and alcoholism are two of the most common causes of peripheral neuropathy.


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Chapter 5 : Cerebellum and Basal Ganglia

Brain: Contents Page

The Cerebellum and Basal Ganglia                         Topics :     

HumanPhysiology.Academy 2014-2015