Substantia nigra


1. Cerebral aqueduct (aqueduct of Sylvius)

Shown very clearly in cross-section in Image 10, the cerebral aqueduct can also be seen immediately anterior to the superior colliculus in Image 2. The cerebral aqueduct is a single midline channel allowing cerebrospinal fluid to flow between the third and fourth ventricles.

  • 1.
    Cerebral aqueduct (aqueduct of Sylvius)
  • 2.
    Periaqueductal grey
  • 3.
    Substantia nigra
  • 4.
    Cerebral peduncle
  • 5.
    Interpeduncular fossa
  • 6.
    Superior colliculi
  • 7.

In this view we see:

  • A hugely magnified cross-sectional view of the upper brainstem, showing the dark lines of the substantia nigra on each side of the midbrain. The human midbrain is about 2.5 centimetres from anterior to posterior at this level.
  • We are looking down from above, with posterior at the top and anterior at the bottom (remember that this is the opposite of CT and MRI images where the view is as though we are standing at the foot of a patient's bed with the patient lying on their back, therefore anterior is at the top and posterior at the bottom in CT and MRI images).
  • Some features of the midbrain mentioned in Image 8 are only visible in Image 10, including the cerebral aqueduct, periaqueductal grey and interior of the cerebral peduncles.


The substantia nigra is a major component of the basal ganglia, and in Image 10 it is shown on each side of the midbrain posterior to the cerebral peduncle.

The substantia nigra is located in the midbrain at the top of the brainstem, between the tegmentum posteriorly and each cerebral peduncle anteriorly. It is in close proximity to other basal ganglia components such as the subthalamus in the diencephalon, and is interconnected with other components of the basal ganglia (see caudate nucleus, putamen and globus pallidus text under Image 5). The proximity of the substantia nigra and subthalamic nucleus can be seen in Image 6.


Each substantia nigra has two parts: substantia nigra pars compacta (compact part) and substantia nigra pars reticulata (reticular part).

The compact part of substantia nigra contains densely packed dopaminergic neurons whose axons terminate in the caudate nucleus and putamen (striatum).

The reticular part of the substantia nigra contains GABAergic neurons that are less densely packed, and receives fibres from the striatum and sends axons to the thalamus, superior colliculus and reticular formation. Therefore, the pars reticulata is a basal ganglia output nucleus.


Pars compacta – sends input to all the basal ganglia nuclei, especially the striatum (caudate and putamen). The ultimate effect of this input is to modify the output of the internal part of the globus pallidus and the pars reticulata of the substantia nigra. As the source of most output from the basal ganglia, these two nuclei are centrally involved in modulating cortical output. Where the axons from the internal globus pallidus and pars reticulata substantia nigra terminate determines their effect: output from these nuclei affects movement, learning and memory, sensory processing and many aspects of behaviour.

Pars reticulata – there is a significant resemblance between this part of the substantia nigra and the internal part of globus pallidus, with both receiving inputs from the striatum, external globus pallidus and subthalamic nucleus. While both project to the thalamus, it is only the pars reticulata that projects to the reticular formation and superior colliculus. By sending axons to the superior colliculus, the pars reticulata assists with the control of eye movement.

Parkinson's disease – it is degeneration of dopaminergic neurons in the substantia nigra, and the subsequent effect on inputs to the striatum, that causes the signs and symptoms of Parkinson's disease. These include: slow movement (bradykinesia), difficulty initiating movements (akinesia), increased muscle tone (rigidity), and tremors of the hands and jaw, more pronounced when the patient is resting and not attempting to move.

Schizophrenia – despite research attributing a role for dopamine and the substantia nigra in schizophrenia, there is limited evidence that there is disruption of domaminergic neurons in the cortex in this condition.