The brain is like a computer or any smart device with a CPU, a motherboard, and other smaller components controlling specific functions. Each has a vital role that keeps the brain and body functioning. One of these components is the substantia nigra.
The substantia nigra function is to produce dopamine and assist in controlling movement as part of structures and circuits in the brain. Other functions of this midbrain nucleus are controlling body movements and regulating muscle tone through dopamine levels.
Dopamine is an essential hormone and neurotransmitter in the body. It is responsible for motivation and making you anticipate a reward after a task. A well-functioning substantia nigra is vital for your mental health and well-being. Let’s investigate this critical nucleus.
What Is The Function Of The Substantia Nigra?
The primary function of the substantia nigra is to produce and regulate dopamine. The other role of the substantia nigra is to control movement. The substantia nigra is a critical relay hub in the brain’s motor system.
When projections leave the substantia nigra from the forebrain, they form synapses on neuronal populations in the entire basal ganglia and also in the following areas –
- Putamen
- Caudate nucleus
- Precentral cortex
- Anterior cerebral cortex
The substantia nigra is a critical function element for the basal ganglia and its primary input for the circuits managing functions such as –
- Reward center
- Cognition
- Learning
- Cognitive planning
- Voluntary movement
- Emotions
The substantia nigra is situated in the midbrain. It is posterior to the cerebral peduncle’s crus cerebri fibers and is divided into two segments, namely –
The substantia nigra pars compacta - The majority of the brain’s dopamine neurons are located in the ventral tegmental and substantia nigra. The substantia nigra pars compacta express high levels of neuromelanin, a dark-colored substance giving them a black appearance.
The substantia nigra pars reticulata – The majority of the brain’s GABA neurons are located in the substantia nigra pars reticulata region.
What Does The Substantia Nigra Do?
The substantia nigra forms connections with the brain as part of the basal ganglia producing dopamine that, in turn, controls muscle tone and movement.
The production of dopamine is critical for the body. Dopamine is the neurotransmitter and hormone responsible for mental health stability and is linked to the pleasure and reward center of the brain.
Dopamine is essential in many developmental stages of the body, and it's important to have a positive association with dopamine release. If the dopamine levels are too high or too low, it will affect a person's mental health and can indicate a neurological disease.
The two different segments of the substantia nigra have defined roles remarkably different from one another; for example –
The substantia nigra pars compacta neurons are full of dopamine and are connected to things such as –
- Learning ability
- Emotional wellness
- Risk analysis and management
- Motivation
The substantia nigra reticulata is full of GABA receptors or chemicals. GABA means gamma-aminobutyric acid, and this chemical is responsible for inhibiting certain brain activities. It controls aspects such as –
- Eye movements
- Thinking ability
- Learning ability
- Redirection of signals that should not go to the muscle
- Stopping signals that should not go to the muscle
The Anatomy Of The Substantia Nigra
The substantia nigra is situated in the midbrain or center of the brain, just above the brain stem. From there, it leads down to where the skull and neck meet. There it connects to the spinal cord.
The substantia nigra is on either side of the mid-brain. Even though it is a singular term, the plural would be substantiae nigrae. The entire substantia nigra comprises the substantia nigra pars compacta and the substantia nigra reticulata.
What Does The Substantia Nigra Look Like?
The substantia nigra forms part of the basal ganglia, but it is not classified as a ganglion but instead as a nucleus. A nucleus is a collection of cells that make up a structure with the same function or connections in the brain.
The substantia nigra is a small band of cells streaking across the midbrain area on both sides, almost like two thin paint brush strokes.
What Color Is The Substantia Nigra?
The substantia nigra is black in appearance and looks like a band, and the dark color is due to the melanin in the cells. The name substantia nigra means “black substance” in Latin. The rest of the brain matter is a grey-pink color making it stand out more.
How Big Is The Substantia Nigra?
The substantia nigra is small and not very noticeable except for its color. The average substantia nigra is so tiny that you can fit almost 30 into a space the size of a golf ball.
What Cells Are The Substantia Nigra Made Of?
The substantia nigra shares several similar cells to the basal ganglia. The following cells make up the substantia nigra and basal ganglia –
Glial Cells – The glial cells support other cells in the body’s nervous system. They do not relay or transmit messages or signals but enhance what the neurons do.
Neurons – Neurons are cells that collectively make up the nerves and brain. They are responsible for relaying and transmitting signals. In addition, neurons can convert signals into electrical or chemical forms.
What Are Neurons?
Neurons are special cells that relay and send signals through the nervous system. They use chemical and electrical signals to forward these messages. Neurons are made of the following structures -
The Cell Body – The cell body is the central part.
The axon is an elongated arm-like extension that protrudes out of the cell body and ends in finger-like extremities called synapses. At the end of the fingers, the neuron’s electrical signal becomes chemical. Here is where the electrical signal in the neuron becomes a chemical signal. The synapses extend to the nearby nerve cells.
The Dendrites – Dendrite in Latin means “tree-like.” These small tree-like extensions are on the cell body and receive chemical signals from nearby neurons through their synapses. Dendrites on one neuron can be connected to thousands of synapses due to the complexity of neurons. They are not all the same shape or size either. Some neurons are short, and some are long, depending on their function and position.
The Myelin layer – The myelin sheath or layer is a thin fatty coating around the axon of neurons. It is vital for the protection of the nerves.
The Glial Cells – Glial cells are multi-purpose and develop during childhood. The glial cells function throughout the life of a human being. Glial cells protect the nervous system from severe infections and control the nervous system's chemical balance.
Glial cells are up to ten times more abundant than neurons and are responsible for creating the protective myelin sheath that coats the neurons' axons.
Disorders And Conditions Of The Substantia Nigra
Several disorders and conditions can affect the substantia nigra but are not specific to these conditions. The following diseases have been identified –
- Lupus and other inflammatory autoimmune diseases
- Traumatic brain injuries
- Concussion
- Stroke
- Multiple system atrophy
- Wilson’s disease
- Progressive supranuclear palsy
- Alzheimer’s disease
- Encephalitis and other bacterial or viral infections
- Brain tumors
- Lewy body dementia
- Parkinson’s disease
- Huntington’s disease and other hereditary conditions
- Toxins and poisons such as TCE - trichloroethylene
- Multiple system atrophy.
Conditions That Affect The Substantia Nigra – Common Signs And Symptoms
Because many conditions present similarly clinically, they must be investigated thoroughly to identify if it affects the substantia nigra.
Some signs and symptoms you can expect would be among the following –
- Tremors and shaking of the hands and head
- Loss of balance
- Difficulty in coordination
- Spasms in the muscles
- Muscle weakness
- Difficulty in controlling eye movement
- Vision problems
- Difficulty in focussing on tasks and problem solving
Diagnostic Tests To Diagnose Conditions Affecting The Substantia Nigra
In modern medicine, several tests can successfully diagnose conditions affecting the brain, specifically the substantia nigra. They are as follows –
- CT scans of the brain – computerized tomography
- Complete blood tests that can detect specific markers like immune system disorders, heavy metal counts such as lead and mercury, copper, as well as poison and toxins
- SPECT scan – Single-photon Emission Computed Tomography
- Genetic testing, such as DNA markers
- PET Scan or Positron Emission Tomography
- Sensory tests like evoked potentials test.
- MRI scans – Magnetic Resonance Imaging
What Treatments Are Available For Conditions Of The Substantia Nigra?
With so many conditions that can adversely affect the substantia nigra, there are many treatment options available. But, of course, the treatments will significantly depend on the situation and other clinical issues.
As with any serious or debilitating medical condition, there are always two types of treatments available, non-invasive with medication and therapy and invasive such as surgery. The treatment will depend on the situation, the stage of advancement, and the patient's health.
While some patients may respond positively to a specific treatment, some may not, and it is up to the medical team to develop the best plan to assist their patient. Sometimes the treatment is symptomatic over a prolonged period.
The following clinical aspects are essential when considering treatment of the substantia nigra -
Lymphatic System And Blood Supply
The branches of the posterior and basilar arteries have split irrigation of the substantia nigra. As a result, the corticospinal tracts of the crus cerebri and the medial portion of the substantia nigra receive blood supply from the basilar artery’s paramedian branches.
The basilar artery also gives vascular supply to the accessory oculomotor nucleus and the oculomotor nucleus. The lateral portions of the crus cerebri and substantia nigra are supplied by the shorter circumferential branches of the posterior choroidal artery.
Stroke-induced or triggered Parkinsonism is the least common form of acute onset Parkinsonism. It is referred to as vascular Parkinsonism. It usually presents about 12 months after the stroke.
Physiological Variants
A condition such as Parkinson’s disease is usually attributed to the degeneration of the substantia nigra. Typically this will happen over time, and the onset is generally in older patients. Currently, it is still not known what causes the onset of Parkinson’s, and it is an idiopathic disease.
There are a number of tested theories as to the cause or underlying trigger of Parkinson's. Still, the reasons linked to the condition that affects the substantia nigra are environmental toxins, poisons, peripheral inflammation, and metabolic deficiencies.
The dopamine-producing neurons of the substantia nigra can be affected by other conditions, such as drug-induced Parkinsonism from pharmaceuticals. This will mimic Parkinson’s disease symptoms, especially if compounds like antipsychotics are involved.
A condition such as Progressive Supranuclear Palsy can create issues such as –
- Vertigo
- Vertical gaze paresis
- Slurred speech
- Balance problems
- Difficulty of movement
- Problems with gait
- Rapid onset dementia
Lewy bodies dementia is a progressive form of Parkinsonism and presents a rapid decline in cognition, attention span, alertness, and concentration. Certain degenerative conditions may show as Parkinson's, but it is mainly due to multi-system atrophy. Some of these failures are-
- Striatonigral degeneration or dementia
- Ataxia
- Incoordination
- Shy-Drager Syndrome
- Olivopntocerebellar atrophy – Incontinence
- Corticobasal degeneration
It should be noted that corticobasal degeneration can manifest as severe coordination impairing form of Parkinsonism.
Surgical Options And Considerations
Surgery or surgical intervention is a good option in palliative care treatment options for diseases like Parkinson’s and conditions that affect the substantia nigra. A procedure called DBS or deep brain stimulation is recommended.
The DBS procedure is done by implanting an electrode intracranially. For example, when a patient has Parkinson's disease, the electrode is placed in the targeted area of the brain and basal ganglia. These areas, such as the globus pallidus internus and the subthalamic nucleus, will be affected by the electrode to bridge and alter the communication and activity between the areas' direct and indirect basal ganglia pathways.
The electrode or catheter implantation disinhibits motor movement when there is an absence of dopamine released in the striatum. This catheter in the striatum targets the putamen with apomorphine.
The Clinical Significance Of Substantia Nigra Conditions
Dopamine is a neurochemical and affects several central nervous system areas. This substance is produced by the substantia nigra in a critical brain area and is responsible for executive cognitive functions, emotional limbic functions, and movement control.
When the dopaminergic neurons are significantly reduced, it leads to the onset of Parkinson’s disease. These symptoms can be effectively treated by supplementing dopamine.
L-DOPA is an effective oral dopamine supplementation. This treatment is one of few that can cross the blood-brain barrier, a typically tricky obstacle in treating cerebral conditions. L-DOPA synthesizes dopamine throughout the central nervous system.
By using monoamine oxidase inhibitors, the metabolic breakdown of dopamine can be inhibited.
How Can You Prevent Problems With Your Substantia Nigra?
You can delay and possibly prevent several conditions that affect the substantia nigra in the brain. Unfortunately, it is impossible to determine or prevent sudden onset conditions or diseases like Parkinson's, but you can do whatever possible to minimize the risk.
Things you can so that is within your power are –
- Suppose you are working in dangerous environments or at height. In that case, it is recommended that you wear the mandatory PPE, such as hard hats or helmets, to prevent a traumatic head injury or severe concussion in the event of a fall or getting struck by falling debris.
- Eat a healthy and balanced diet, so your body remains strong and healthy. In addition, keep regular doctor appointments to check up on your heart and overall health.
- If you have a chronic condition, ensure it is managed well, so it doesn't worsen over time.
- Exercise regularly or swim to stay as active as possible. Being fit can delay certain conditions that may affect your brain health.
Conclusion
As part of the crucial neurological network of the body, the small dopamine-creating substantia nigra is one of the most critical and life-sustaining areas of your brain.
Keeping a finger on the pulse of your brain health is vitally important to delay or eliminate potentially debilitating conditions. So the next time you feel that surge of feel-good hormones while enjoying something you love, take a minute and thank your substantia nigra!
