What is the Substantia Nigra?

There is a large mass of gray matter between the soles of the brain and the midbrain, which is found in the full length of the midbrain. Nigra cells are rich in melanin and are the main nucleus for the synthesis of dopamine in the brain. The substantia nigra is mainly connected to the neostriatum of the telencephalon (caudate nucleus and putamen) with fibrous connections. Degeneration of substantia nigra cells and reduced dopamine synthesis are the main causes of tremor paralysis (Parkinson's disease) for some reasons. Under normal physiological conditions, substantia nigra is an important center for regulating movement.

There is a large mass of gray matter between the soles of the brain and the midbrain, which is found in the full length of the midbrain. Nigra cells are rich in melanin and are the main nucleus for the synthesis of dopamine in the brain. The substantia nigra is mainly connected to the neostriatum of the telencephalon (caudate nucleus and putamen) with fibrous connections. Degeneration of substantia nigra cells and reduced dopamine synthesis are the main causes of tremor paralysis (Parkinson's disease) for some reasons. Under normal physiological conditions, substantia nigra is an important center for regulating movement.

Chinese name

Substantia nigra

Foreign name

Substantia Nigra

Location

Between the soles of the brain and the midbrain cover

Features

Found in the full length of the midbrain

Substantia nigra

Substantia nigra

Neurons in the substantia nigra (SNpc) contain melanin. So in brain slices, these neurons appear black. This is the origin of the name "substantia". These neurons have long and thick dendrites, and many ventral dendrites project to the nigro reticulum. Many similar neurons are diffusely distributed in the midbrain outside the substantia nigra compact. All of these melanin-containing neurons project through the nigrostriatal pathway into the striatum and deliver a neurotransmitter called dopamine. In addition, neurons of the substantia nigra also project to the nucleus of other basal nuclei, including pale globules, substantia nigra and subthalamic nuclei.

Neurons in the dense substantia nigra receive collateral inputs from the axons of the reticulum. These inputs are inhibitory.

Substantia function

The function of the dopamine system is very complex. It is generally believed that the function of dopamine is to learn which behaviors can lead to rewards (such as food or sexual intercourse). There is experimental evidence that dopamine neurons in the substantia nigra dense area give out impulses when the reward received by the animal is greater than expected. These impulses can be used to update the animal's expectations for rewards.

Certain recreational drugs, such as cocaine, can mimic the reward response of the dopamine system. This can be used to explain why these drugs are addictive.

Another study has shown that dopamine function is also related to punishment.

Substantia nigra pathology

Apoptosis of dopamine neurons in the substantia nigra can cause Parkinson's disease. The disease may be hereditary or it may be caused by some unknown factor. Parkinson's disease can also be caused by some viral infections or by some toxins (such as MPTP).

The pathological changes of dopamine neurons may also be related to the symptoms of schizophrenia and some depression.

Substantia nigra reticulum

Substantia nigra

The distribution of neurons in the substantia nigra reticulum is much thinner than in the dense part. The neurons in the reticulum are similar in structure to those in the pale globule. Neurons in the reticulum mainly receive input from the striatum, subthalamic nucleus, and dense substantia nigra. The dendrites of these neurons are perpendicular to the axons of the striatum, just like the neurons of the pale bulb.

Neurons in the nigro reticulum synthesize an inhibitory neurotransmitter that becomes GABA. These neurons are projected through the nigrothalamic bundle onto the motor-related part of the thalamus, the ventral anterior nucleus (VA). The anterior nucleus of the thalamus is projected into the frontal lobe of the cerebral cortex, including the eye movement area.

Substantia function

Neurons in the substantia nigra reticulum spontaneously emit impulses without input. The spontaneous release rate can be as high as 68 impulses per second in some primates.

The substantia nigra reticulum is one of the two major channels from the basal nucleus to the thalamic motor. The other channel is the pale ball core. Since neurons in the reticular region are projected onto the thalamus and oculomotor-related functions, the function of the reticular region may involve control of saccades and fixation.