The main area of the brain involved in production of movement is the frontal lobe, most importantly the premotor cortex and the primary motor cortex. The premotor cortex is involved in preperation of movement and is used in complicated sequences of action such as playing the piano. It is divided into two parts the Lateral premotor cortex -external preperation of movement
Medial premotor cortex -preperation of internally generated movements
The primary motor cortex -involved in the movement of voluntary muscles
When looking at movement disorders it is important to understand that we have two subcortical loops with in our brain. The direct pathway and the indirect pathway.
The Direct pathway is excitatory and makes it more likely for a movement to happen
The Indirect pathway is inhibitory and makes it less likely that a movement will happen.
The subcortical structure most commonly involved in motor dysfunction is the Basal ganglia - a collection of nuclei that act as a cohesive unit. Disorders caused by the basal ganglia often result in excessive or restricted motor activity, an example of such a disease is Parkinsons Disease.
The main symptoms that are used to classify Parkinsons are;
Akinesia which means a general loss of movement, movement becomes slower and harder to coordinate
Rigidity which is a stiffness of muscles
Tremors particularly when the body is at rest.
The cause of this disorder is due to a depletion of dopamine-generating cells in the substantia nigra (a region of the midbrain). There are a number of modern treatments that are effective at managing the early motor symptoms, mainly thorugh the use of dopamine agonists such as LDopa, thease are compounds that activate dopamine receptors in the abscense of dopamine. The reason dopamine agonists are used is because we can not give dopamine directly, since it is unable to pass through the blood brian barrier, where as agonists can. Agonists helps to reduce the early symptoms but as the disease progresses, these drugs eventually become inaffective. Once this happens rehabillitation has been shown to help reduce the symptoms and there is also the option of surgery. Newer techniques such as stem cell transplants using fetal tissue and gene therapy are also being researched .
Another motor disorder is Huntingtons Disease, which is caused by a degeneration of the caudate nucleous and Putamen (both involved in voluntary movement) -A loss a GABA neurons in the striatum reduces cell activity in the indirect loop. The resulting symptoms are;
Behaviour changes - Moodiness, Paranoia, Psychosis
Abnormal and Unusual Movements- Jerky movements/ slow uncontrolled movements
Dementia- A loss of judgement/ memory/disorientation.
Currently there is no cure for Huntingtons disease, drugs can be given to reduce symtoms but they do not stop the progrssion of the illness, which eventually reuslts in death.
It is important to note that huntingtons disease is 100% genetic.
Another movement disorder is Tourettes Syndrome.
This disorder is classified by multiple motor tics and atleast one vocal tic. Symptoms include head jerking, grimacing, mouth twitching and rapid eye blinking aswell as limb tics. Vocal tics include uttering wrds out of context and vocalising socially unacceptble words. The severity of the disorder varies greatly, some people have tourettes very mildly where as others can be severely affected. Tourettes can be particularly limiting since vocal tics can include coprolalia - using obscene language and echolalia which involves repition of phrases that the sufferer hears others use. Sufferers of tourettes are often found to have other psychologicl disorders such as ADHD, COD and self harming.
As of yet there is no clear cause of the disorder but specialists believe that the drug dopamine is implicated, since at has been found that drugs that block dopaine D2 receptors are reduce the degree of coprolalia.
Early diagnosis and treatment of this disorder is essential. The diagnosis is confirmed by observing the pattern of symptoms and al though there is no set cure, most people are able to live a pretty normal life. For those patients whos symptoms get in the way of their daily routine they can be prescribed drugs to keep some of their symptoms under control. Psychotherapy or behavioural therapy can also be used, as can relaxation therapy.
Apraxia is another movement disorder but is different from the previous three because it is caused by brain damage. The most common causes are a tumour, dementia, stroke and traumatic brain injury. If you ask a patient with apraxia to do something they will be unable to perform the required task even though they understand exactly what they are needed to do. Depending on the type of apraxia they will either have trouble performing an action or speaking even though there muscles work fine and they understand what they are required to do. The problem is that the muscle movements are uncoordinated and therefore a completely different action or word is produced rather than the one that is required, it is important to note that the patient is often aware of there mistake.
There are several different types of Apraxia;
- Apraxia of speech: sounds and words may be distorted, repeated of left out, - difficulty putting words together i the correct order.
- Buccofacial or orofacial apraxia: Cannot carry out movements of the face, such as licking the lips, sticking out the tongue, or whistling.
- Ideational apraxia: Cannnot carry out learned complex tasks in the proper order, such as putting on socks before putting on shoes.
- Ideomotor apraxia: Cannot voluntarily perform a learned task when given the necessary objects. For instance, if given a screwdriver, the person may try to write with it as if it were a pen.
- Limb-kinetic apraxia: This condition involves difficulty making precise movements with an arm or leg.
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