Substantia Nigra (SN)

What is the substantia nigra?

The substantia nigra (SN) is a part of your brain that helps control your movements. It’s part of the basal ganglia, a group of structures that form connections and circuits throughout your brain. The substantia nigra is important because of its role in your movements and how it influences your brain’s chemistry.

What does the substantia nigra do?

The substantia nigra (sub-stan-chee-uh ny-grah) is a part of your basal ganglia, forming connections with different parts of your brain. It produces dopamine, which controls movements and muscle tone.

The substantia nigra has two different sections, and they both have different roles and connections. The two sections are:

• SN pars reticulata: This section has connections relating to the movement of your eyes and your ability to learn and think. The cells in this area of your brain hold a chemical called gamma-aminobutyric acid (GABA). This chemical inhibits activity in your brain cells. Your brain uses it to redirect and stop signals that it decides shouldn’t go out to your muscles.
• SN pars compacta: The neurons here hold a chemical called dopamine. That’s why this section has connections that involve your emotions, ability to learn, how you judge risks and rewards, your motivations and more.

Where is the substantia nigra located?

The SN is in your midbrain. As the name suggests, this section of your brain is at the center of your brain. It’s just above your brainstem, leading down to where your skull meets your neck and connects to your spinal cord.

Though the term “substantia nigra” refers to just one of these structures, you actually have two. They're on either side of your midbrain, and each has a pars reticulata and a pars compacta. The plural name is “substantiae nigrae.”

What does it look like?

Though it's part of your basal ganglia, the SN is not a ganglion ("ganglia" refers to more than one ganglion). It's a nucleus, a type of nervous system structure made up of cells with the same job or connections.

What color is the substantia nigra?

The substantia nigra gets its name from Latin and means "black substance.” That’s because while most of your brain is a lighter shade of pinkish-gray, the substantia nigra is much darker, appearing as a band of black tissue surrounded by much lighter tissue. That’s because the brain cells here also contain melanin. That’s the chemical in your skin cells that makes them darken because of sun exposure, which causes your skin to tan.

How big is it?

The SN is very small. About 25 average-sized substantiae nigrae could fit into a golf ball.

What is the substantia nigra made of?

Making up your basal ganglia, including the substantiae nigrae, are the following (with more information below):

• Neurons: These cells make up your brain and nerves, transmitting and relaying signals. They can also convert signals into either chemical or electrical forms.
• Glial cells: These are support cells in your nervous system. While they don’t transmit or relay nervous system signals, they help the neurons that do.

Neurons

Neurons are the cells that send and relay signals through your nervous system, using both electrical and chemical signals. Each neuron consists of the following:

• Cell body: This is the main part of the cell.
• Axon: This is a long, arm-like part that extends outward from the cell body. At the end of the axon are several finger-like extensions where the electrical signal in the neuron becomes a chemical signal. These extensions, known as synapses, lead to nearby nerve cells.
• Dendrites: These are small branch-like extensions (their name comes from a Latin word that means “tree-like”) on the cell body. Dendrites are the receiving point for chemical signals from the synapses of other nearby neurons.
• Myelin: This thin, fatty layer surrounds the axon of many neurons and acts as a protective covering.

Neuron connections are incredibly complex, and the dendrites on a single neuron may connect to thousands of other synapses. Some neurons are longer or shorter, depending on their location in your body and what they do.

Glial cells

Glial (pronounced glee-uhl) cells have many different purposes, helping develop and maintain neurons when you’re young, and managing how the neurons work throughout your entire life. They also protect your nervous system from infections, control the chemical balance in your nervous system and create the myelin coating on the neurons’ axons. Your nervous system has 10 times more glial cells than neurons.

What are the common conditions and disorders that affect the substantia nigra?

Conditions that affect the substantia nigra include, but aren’t limited to:

• Alzheimer’s disease.
• Brain tumors.
• Concussions and other traumatic brain injuries.
• Poisons or toxins such as trichloroethylene (TCE).
• Infections (including those that cause encephalitis).
• Inflammatory or autoimmune conditions like lupus.
• Inherited conditions like Huntington's disease.
• Lewy body dementia.
• Multiple system atrophy.
• Parkinson’s disease.
• Progressive supranuclear palsy.
• Stroke.
• Wilson’s disease.

What are some common signs or symptoms of conditions affecting the substantia nigra?

The symptoms that can happen with conditions that affect the basal ganglia depend strongly on the type of condition.

• Balance and coordination problems.
• Muscle weakness and spasms.
• Shakiness and tremors.
• Trouble with focusing, thinking or problem-solving.
• Difficulty controlling eye movements, causing vision problems.

What tests can help diagnose conditions affecting the substantia nigra?

Several tests can help diagnose conditions that affect your brain, including the substantia nigra. The most common tests used for this include:

• Blood tests (these can detect many problems, ranging from immune system problems to toxins and poisons, especially metals like copper, mercury or lead).
• Computerized tomography (CT) scan.
• Evoked potentials (sensory tests).
• Genetic testing.
• Magnetic resonance imaging (MRI).
• Positron emission tomography (PET) scan.
• Single-photon emission computed tomography (SPECT scan).

What are some treatments for conditions affecting the substantia nigra?

A wide range of conditions can affect the substantia nigra, with an even wider variety of treatments for those conditions. The available treatments depend strongly on the condition. In some cases, these conditions are treatable with medication, while others may require surgery. Curing some of these conditions is also possible in some cases, but others may resist treatment. When curing a condition isn’t an option, treating the symptoms is usually the best option.

How can I prevent problems with my substantia nigra?

It’s possible to prevent — or at least delay — many conditions that affect your brain, including the substantia nigra. You can't prevent other conditions, such as Parkinson’s disease, because they happen unpredictably. Some of the most important things you can do include:

• Eat a balanced diet. Your diet affects your circulatory health and your weight, both of which affect your brain health.
• Stay physically active and maintain a weight that's healthy for you. Your weight and activity level can prevent or delay conditions that affect your brain, especially problems like high blood pressure or stroke.
• Wear safety equipment as needed. Head injuries, especially concussions and traumatic brain injuries, can cause brain damage. That damage is sometimes permanent. Wearing safety equipment to prevent brain injuries is essential while working or during your free time.
• Manage your chronic conditions. Many conditions that affect your brain and nervous system get worse over time. Treating those chronic conditions can sometimes delay how long it takes for them to worsen and reduce the impact of their symptoms.

A note from Cleveland Clinic

The substantia nigra is a tiny part of your brain, but it has an essential job. While experts still have much to learn about it, there’s much we already know. It’s a key part of your brain’s electrical and chemical signaling systems, and it helps coordinate your movements, vision and more. As technology and medical research advance, we'll continue to understand more about its inner workings and how to treat the conditions affecting it.