Anatomy & Organs

Substantia nigra – structure, function & diseases

Substantia nigra

The substantia nigra represents a nucleus in the midbrain that is dark in color and belongs to the extrapyramidal motor system. It thus contributes to the control of movements. Atrophy of the substantia nigra occurs in Parkinson’s syndromes and leads to the development of the cardinal symptoms of rigidity , tremor , bradykinesia and postural instability.

What is the substantia nigra?

The substantia nigra is located symmetrically in both halves of the brain (hemispheres) and is part of the midbrain . There it borders on the crura ( crura cerebri ) and the midbrain cap (tegmentum mesencephali). The name of the substantia nigra goes back to its black color, which is based on the high amount of melanin and iron in this area.

Dopamine functions as the most important neurotransmitter in the substantia nigra , occurs exclusively in the central nervous system as a messenger substance and belongs to the group of biogenic amines . These are neurotransmitters that are made from the amino acid tyrosine and lose a carbon dioxide molecule through decarboxylation. In addition to dopamine, the biogenic amines also include serotonin , adrenaline and noradrenaline .

Anatomy & Structure

Anatomically, the substantia nigra can be divided into two areas: the pars compacta, also known as the zona compacta, and the pars reticulata. The pars compacta is made up of closely arranged nerve cells that contain a large amount of the pigment melanin. Nerve fibers connect the pars compacta to the striatum .

In addition, the pars compacta belongs to the black system (nigrostriatal loop). Also included are the red nucleus, which is also located in the midbrain, and nuclei of the striatum. The neurons of the pars reticulata are less densely packed than the nerve cells of the pars compacta and contain a lot of iron, which gives the tissue a reddish color. This area also includes the pars lateralis, which some experts consider to be a separate part. The pars reticulata of the substantia nigra has connections to the striatum and ventrolateral thalamus . Other nerve fibers lead from the substantia nigra to the cerebral cortex and the subthalamic nucleus, among others.

Function & Tasks

The substantia nigra belongs to the extrapyramidal motor system and is thus involved in the control of movements. In this context, it mainly has a starter function, since it is particularly involved in initiating movement and planning.

The extrapyramidal motor system also includes the basal ganglia , the motor cortex, and various nuclei in the brain , including the red nucleus in the midbrain and the reticular formation , which runs through the hindbrain, midbrain, and diencephalon . Like the substantia nigra, all of these structures depend on dopamine as a neurotransmitter: nerve cells form the messenger substance in their terminal nodules and store it in vesicles. If an electrical impulse – a so-called action potential – reaches the end of the nerve fiber and thus the end knobs, the cell releases the dopamine into the synaptic cleft.

The messenger substance crosses the gap between the presynaptic and postsynaptic nerve cell and attaches itself to receptors in the postsynaptic membrane, whereupon ion channels in it open. Charged sodium particles can flow into the cell through the channels and change the electrical charge of the neuron. If the change exceeds the threshold potential, a new action potential is created in the postsynaptic nerve cell. A lack of dopamine leads to a disruption in this process and thus impairs the human motor function. As a whole, the extrapyramidal motor system is primarily responsible for gross motor movements.

Diseases

Parkinson’s disease is accompanied by a loss of the substantia nigra, which leads to the development of the characteristic symptoms of the disease. Parkinson’s disease is a neurodegenerative disease also known as shaking palsy.

In 1917 James Parkinson was the first to describe the syndrome; Today, around 250,000 people in Germany suffer from the disease, three quarters of which are due to idiopathic Parkinson’s syndrome. The cardinal symptoms are rigidity, tremor, bradykinesia/akinesia and postural instability. Rigor is muscle rigidity or stiffness that occurs due to increased resting tone: the affected muscles are overly tense. On the other hand, the second key symptom, the tremor, manifests itself as muscle tremors and primarily affects fine motor movements.

Those affected also typically suffer from slowed movements; this phenomenon is known in medicine as bradykinesia. While patients with bradykinesia can basically perform movements – albeit at a slower pace – with akinesia they are only partially able to do so (lack of movement) or not at all (immobility). Postural instability leads to an unsteady posture and, as a result, often to a slightly stooped gait. Gait disturbances and other functional impairments are common due to the combination of bradykinesia with rigidity, tremor and/or postural instability.

In addition to idiopathic Parkinson’s syndrome, medicine distinguishes between three other forms. The familial Parkinson’s syndrome is due to errors in the genome – various genes can be considered as the cause. In contrast, symptomatic or secondary Parkinson’s disease arises as a result of another underlying condition, such as Binswanger ‘s disease or Wilson’s disease , or as a result of medication, drugs , intoxication, or injury. The fourth form of Parkinson’s syndrome is also a consequence of other diseases; however, these are specifically neurodegenerative diseases that manifest themselves in the loss of nerve cells.

These include Lewy body dementia , multiple system atrophy , progressive supranuclear palsy, and corticobasal degeneration. L-Dopa is often used to treat Parkinson’s disease. The precursor of dopamine can cross the blood-brain barrier and at least partially compensate for the lack of dopamine in the brain, which leads to alleviation of symptoms. A causal treatment is not possible.

Website | + posts

Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.