science

Nigrostriatal pathway

Nigrostriatal pathway is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Nigrostriatal pathway rather than just read about it. In short: The nigrostriatal pathway is a bilateral dopaminergic pathway in the brain that connects the substantia nigra pars compacta (SNc) in the midbrain with the dorsal striatum (i.e., the caudate nucleus and putamen) in the forebrain. It is one of the four major dopamine pathways in the brain, and is critical in the production of movement as part of a system called the basal ganglia motor loop.

Key takeaways

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Reference excerpt

The nigrostriatal pathway is a bilateral dopaminergic pathway in the brain that connects the substantia nigra pars compacta (SNc) in the midbrain with the dorsal striatum (i.e., the caudate nucleus and putamen) in the forebrain. It is one of the four major dopamine pathways in the brain, and is critical in the production of movement as part of a system called the basal ganglia motor loop. Dopaminergic neurons of this pathway release dopamine from axon terminals that synapse onto GABAergic medium spiny neurons (MSNs), also known as spiny projection neurons (SPNs), located in the striatum. Degeneration of dopaminergic neurons in the SNc is one of the main pathological features of Parkinson's disease, leading to a marked reduction in dopamine function and the symptomatic motor deficits of Parkinson's disease including hypokinesia, tremors, rigidity, and postural imbalance.

Anatomy The connection between the substantia nigra pars compacta and the dorsal striatum is mediated via dopaminergic axons.

Substantia nigra pars compacta (SNc) The substantia nigra is located in the ventral midbrain of each hemisphere. It has two distinct parts, the pars compacta (SNc) and the pars reticulata (SNr). The pars compacta contains dopaminergic neurons from the A9 cell group that forms the nigrostriatal pathway that, by supplying dopamine to the striatum, relays information to the basal ganglia. In contrast, the pars reticulata contains mostly GABAergic neurons. The SNc is composed of a thin band of cells that overlies the SNr and is situated laterally to the A10 group of dopaminergic neurons in the ventral tegmental area (VTA) that forms the mesolimbic dopamine pathway. The SNc is easily visualized in human brain sections because the dopamine neurons contain a black pigment called neuromelanin which is known to accumulate with age. The dopaminergic cell bodies in the SNc are densely packed with approximately 200,000 to 420,000 dopamine cells in human SNc and 8,000 to 12,000 dopamine cells in mouse SNc. These dopamine cell bodies are localized to one of two chemically defined layers. Those in the upper layer (or dorsal tier) contain a binding protein called calbindin-D28K which can buffer calcium levels inside the cell when it becomes too high or toxic. Dopamine cells in the lower layer (or ventral tier) lack this protein and are more vulnerable to the effects of neurotoxins (e.g. MPTP) that can cause Parkinson disease-like symptoms. The dorsal tier dopamine cells have dendrites that radiate horizontally across the pars compacta, whereas ventral tier dopamine cells have dendrites that extend ventrally into the pars reticulata.

Dopaminergic axons The axons from dopamine neurons emanate from a primary dendrite and project ipsilaterally (on the same side) via the medial forebrain bundle to the dorsal striatum. There is a rough topographical correlation between the anatomical localization of the dopamine cell body within the SNc and the area of termination in the dorsal striatum. Dopaminergic cells in the lateral parts of the SNc project mainly to the lateral and caudal (posterior) parts of the striatum, whereas dopamine cells in the medial SNc project to the medial striatum. In addition, dopamine cells in the dorsal tier project to the ventromedial striatum, whereas the ventral tier neurons project to the dorsal caudate nucleus and putamen. In general, there is a greater density of dopaminergic input to the dorsolateral striatum. Each dopamine neuron has an extremely large unmyelinated axonal arborization which can innervate up to 6% of the striatal volume in a rat. Although all SNc dopamine cells project to both the striosome (or patch) and matrix neurochemical compartments of the striatum, most of the axonal territory of a dorsal tier neuron is in the matrix compartment while the majority of the axonal field of ventral tier neurons is in the striosomes. Nigrostriatal dopamine axons can also give rise to axon collaterals that project to other brain regions. For example, some SNc nigrostriatal dopamine axons send axon collaterals to the pedunculopontine nucleus, ventral pallidum, subthalamic nucleus, globus pallidus, amygdala, and thalamus. A small number of SNc dorsal tier dopamine neurons also project directly to the cortex, although most of the dopaminergic innervation of the cortex comes from the adjacent VTA dopamine neurons.

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Illustrations

Worked examples

Example 1 — a first encounter with Nigrostriatal pathway

Start with the simplest possible case. Write down what Nigrostriatal pathway claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nigrostriatal pathway before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nigrostriatal pathway ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nigrostriatal pathway

In research: Nigrostriatal pathway appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Nigrostriatal pathway in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Nigrostriatal pathway is common in secondary-school and first-year university syllabi. It links to neighbouring topics Basal ganglia connections, Dopamine, so understanding it makes those chapters shorter.
In everyday life: Look for Nigrostriatal pathway outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Nigrostriatal pathway in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Nigrostriatal pathway means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Nigrostriatal pathway out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nigrostriatal pathway in simple terms?

Why does Nigrostriatal pathway matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nigrostriatal pathway?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nigrostriatal pathway.