What Is the Pars Compacta?

The basal nucleus (Basal ganglia, or basal ganglia) is a functional whole composed of a series of neural nucleuses deep in the brain. It is a collective term for a group of motor nucleus located under the cerebral cortex, connected to the cerebral cortex, thalamus and brain stem. The basal nucleus of human brain includes: striatum, globus pallidus, substantia nigra, and subthalamic nucleus. Its main functions are the control of autonomous movements, the integration and regulation of meticulous conscious activities and motor responses. It also participates in advanced cognitive functions such as memory, emotion, and reward learning. Basal nucleus lesions can cause a variety of motor and cognitive disorders, including Parkinson's and Huntington's.

The basal ganglia is called the basal ganglia, also known as the basal nucleus. It is a gray matter nucleus in the white matter of the cerebral hemisphere. Because it is located near the base of the brain, it is called the basal ganglia. Includes striatum (including caudate and bean-shaped nuclei), amygdaloid clusters and screen-shaped nuclei. The bean-shaped nucleus is divided into two parts, the shell and the pale ball. In phylogeny, the caudate nucleus and the shell appeared later and originated from the telencephalon, which is called neostriatal; the pale globus appeared earlier and originated from the mesencephalon, called old striatal. The striatum is one of the centers of the extrapyramidal system and is related to the motor function of the body. The amygdaloid nucleus is the oldest part of the basal nucleus, also known as the striatum, and is an important structure of the limbic system [1]
The English name of the basal nucleus is "Basal ganglia". The "Basal" means that the anatomical location is deep and bottom of the brain. "Ganglia" is a misnamed name. The term Ganglia originally refers to the aggregation of neuronal cell bodies in the peripheral nervous system, but in fact the basal nucleus is located in the central nervous system. The accumulation of neuronal cell bodies in the central nervous system should be called "nucleus" (eg, Red nucleus). This wrong name in English has been used ever since and has become a habit. But the Chinese term "basal nucleus" corrects this error. However, there are now many English literature called "basal nuclei", which can be regarded as correcting this misnamed.
The structure of the basal nucleus was first documented by British anatomist Thomas Willis in 1664. For many years afterwards, the term "corpus striatum" was used to refer to a series of nuclei in the cortex. However, it was later discovered that many of them were not directly linked. For example, there is no direct connection between the putamen and the caudate nucleus. The term "striatum" refers to the whole of the caudate nucleus, putamen and nucleus accumbens, which is the main input channel of the basal nucleus system. The nomenclature was proposed by Cécile and Oskar Vogt (1941). The striatum is named for its striated image in the brain section. The shape comes from a large number of dense striatum-
as the picture shows,
The striatum (including caudate nucleus and shell) is the main input channel of the basal nucleus system. Many movements of the cerebral cortex, the prefrontal lobe and sensory zones project into the striatum. As shown in Table 2, neurons in different nucleus groups in the basal nucleus synthesize different neurotransmitters. Glutamate is an excitatory neurotransmitter, and GABA is an inhibitory neurotransmitter. As shown in the table below, dopamine excitation or inhibition depends on the type of receptor. Dopamine input from the dense substantia nigra can stimulate all dopamine receptors in the striatum, but the effect of dopamine input is different because of the different types of receptors in the indirect and direct pathways. As can be seen from the table below, since the effect of dopamine input on the direct pathway is excitation and the effect on the indirect pathway is inhibition, the overall function of the neurotransmitter is to activate the thalamus.
The basal nucleus contains two major circuits, namely the direct pathway and the indirect pathway. They are two major parts of the Cortico-basal-thalamic loop.
Table 1.Direct and indirect pathways of the basal nucleus
Path name
The composition of the pathway (+ table excitatory output,
-Table inhibitive output
Number of inhibitory connections
Function description
There are about 100 million neurons in the human striatum. More than 70% are output neurons. These output neurons have very dense spines on their dendrites, so they are called spiny neurons. These spines are the sites where spinous neurons and axons of the afferent striatum form synapses. The axons entering the striatum are mainly from the cerebral cortex, thalamus and amygdala. After these axons entered the striatum, they exhibited a wide range of side branches, forming synapses with a large number of striatum neurons. Each striatum neuron, in turn, forms synapses with a large number of input axons. It is estimated that each spiny neuron receives input from 7500-15000 different axons. This connection mode is similar to
The remaining neurons in the striatum are Interneurons. These neurons are all inhibitory, including cholinergic neurons, GABA / Parvalbumin neurons, and Somatostasin / NOS neurons. These inhibitory midline neurons also receive
As mentioned above, Parkinson's disease manifests as symptoms of bradykinesia, loss of movement, and resting tremor, mainly due to the degradation of the dense substantia nigra and subsequent reduction in dopaminergic output. The reduction of dopamine caused the inhibition of the direct pathway of the striatum and the de-inhibition of the indirect pathway, which led to the loss of thalamic excitement in the basal nucleus. A disease that is almost the opposite of Parkinson's disease is Huntington's disease, which is manifested as abnormal excess movements (dance tremor) and lack of coordination, caused by the degradation of the striatum and the pale globules. Hemispheric throwing, manifested as repetitive upper limb movements (such as throwing a baseball), is due to degeneration or damage to the subthalamic nucleus. The subthalamic nucleus acts as the last stage of the indirect pathway and its role in exciting the pale globules. This excitement did lead to a weakened inhibition of the thalamus by the inner pale globules, which in turn led to redundant movements (hyperactivity disorder) seen in hemithrowing. Tourette's syndrome, manifested by symptoms such as motor cramps, attention problems, and bad language, is also thought to be related to the loss of balance between the excitatory and inhibitory effects of the basal nucleus. Diseases thought to be related to basal nucleus function also include dystonia, spastic aphasia, and stuttering [1] .

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