Basal ganglia audio/ interactive audios

 

The Basal ganglia should actually be called the basal nucleus since it is a collection of nuclear groups which developed at the floor of the lateral ventricle close tot the 3rd ventricle and around the diencephalon and the lateral wall of lateral ventricle. They are actually telencephalic structures, having developed from the telencephalic brain vesicle which in turn comes from the prosencephalon. They have important function in the human body. The basal ganglia is said to be the head ganglion of proprioception in the body. When damaged or diseased, coordination of movement is impaired because again it is a strong center for the control of extrapyramidal system, together with the cerebellum. When clincians refer to the extrapyramidal system, most tend to assume it is the basal ganglia. This is because of the common condition known as parkinsonism or Parkinson's disease which is caused by impairment of a part of the basal ganglia.

The basal ganglia reaches its highest level of development in birds where it controls the motor function of this group of animals. When a bird (like the hen) has its cortex removed, it is able to function is if nothing has happened to it. But once the basal ganglia is damaged the bird is unable to perform all its intrinsic or instinctual mechanism such as laying egg, sitting or incubating the laid eggs, courtship, which is a complex repetitive process in birds etc. Hence, it is recognised as a center for instinctual mechanisms, whether motor or other wise. It is therefore not too bad to suggest that the basal ganglia in man may also be responsible for any instinctual mechanism in man, if present at all. The only type of instinct which may be recognized in man are probably the rudiments of temperaments. This shows the difference between temperaments as inheritable traits on one hand, character as modifiable behavior due to environmental  influences and personality which are conscious behavioral attitudes which usually do not have anything to do with temperament or indeed character.

The mesolimbic system described by Papez which seems to be related to human behaviour and emotion has a generous components from the basal ganglia

The basal ganglia consist of two parts

  • Corpus striatum

  • Amygdaloid nuclear complex

 

Another division of the basal ganglia recognizes the following parts

  • Archistratium, which is the amygdala

  • Paleostriatum, which is the globus pallidus

  • Neostriatum, which is the putamen and caudate nucleus

Another name for neostriatum is the striatum.

Another name for paleostriatum is pallidum for short.

Pallidum is mainly motor part of the basal ganglia while striatum is mainly sensory part. Hence striatum receive many afferent projections but gives out only a few efferent ones. On the other hand pallidum has mainly efferent projections but receives only a few afferent fibers.

 

Corpus striatum is therefore made up of the pallidum and the striatum as follows

1.                      Caudate nucleus

2.                      Lentiform nucleus

Lentiform nucleus is further divided into

1.                      Globus pallidus

2.                      Putamen

 
Basal ganglia: 1 putamen 2 globus pallidus 3 insular cortex 4 internal capsule 5 extreme capsule 6 claustrum 7 external capsule 8 lateral ventricle

Striatum

This is the sensory part of the the basal ganglia. It receives fibers from the following

  • Nigro striatal tract. This tract interconnects the midbrain with the basal ganglia and it manufactures dopamine which is extensively used in the basal ganglia. The deficiency of this amine will precipitate parkinsonism

  • Thalamostriatal tract. This tract begins from the thalamus and ends in the striatum

  • Pallidostriatal tract. This tracts begins from the pallidum and interconnects with the striatum

A few efferent projections are recognized

1.                      Strionigral tract (between the striatum and the substantia nigra)

2.                      Striopallidal tract. This important tract helps to keep information from the sensory part of the basal ganglia to the motor part (pallidum). It forms pencil like striations on the pallidum and is therefore called Wilsonís pencil.

 

Pallidum

The afferent projections are

  • Striopallidal tract (Wilson's pencil)

  • Subthalamopallidal tract

The pallidum is the motor part of the basal ganglia. It has numerous efferent projections of which the most important are as follows

  • Ansa lenticularis. This project from the pallidum to the Forelís field from where they enter Forelís field H2.

  • Lenticular fasciculus. This project into Forel's field H1.

  • Subthalamic fasciculus. This interconnects with the subthalamus

  • Thalamic fasciculus projects to the thalamus

  • Pallidotegmental fasciculus. This connects with the pontine reticular formation called nucleus tegmenti pedunculopontinus.

Amygdaloid nuclear complex

This complex is divided into the following parts

  • Dorsal part

  • Ventral part

  • Others

It is also divided into two main nuclear groups

  • Corticomedial nuclear group

  • Basolateral nuclear group

It is also related to associated nuclei called the periamgydaloid body. The periamygdaloid body is more related to the paleocortex than the basal ganglia. It is part of the smell brain. But its association with the amygdala suggest that at least in animals where the sense of smell is important, the basal ganglia functions effectively.

  Clinical applications

Destruction of the basal ganglia can lead to the following clinical conditions, which are all essentially dyskinesias (abnormal movements).

Tremor at rest

Athetosis: This is a slow worm like movement affecting mainly the extremities and also the muscles of the neck and face

Chorea: This is a graceful movement which appear to be purposeful but are involuntary and they involve facial muscles and distal extremities.

Ballism: This is violent involuntary movement especially involving the pelvic and pectoral girdles.

Hemiballism refer to ballism in only one side of the body

Parkinson's disease occurs as a result of depletion of dopamine at the nigrostriatal tract. It causes extrapyramidal symptoms which include cogwheel rigidity and early tremors.

 

 

 

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