Substantia nigra in the context of "Oculomotor nucleus"

Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor and non-motor systems. The motor symptoms are collectively called parkinsonism and include tremors, bradykinesia (slowness in initiating movement), rigidity, and postural instability (difficulty maintaining balance). Non-motor symptoms such as dysautonomia (autonomic nervous system failures), sleep abnormalities, anosmia (decreased ability to smell), and behavioral changes or neuropsychiatric problems, such as cognitive impairment, psychosis, and anxiety, may appear at any stage of the disease. Symptoms typically develop gradually and non-motor issues become more prevalent as the disease progresses.

Most Parkinson's disease cases are idiopathic, though contributing factors have been identified. Pathophysiology involves progressive degeneration of nerve cells in the substantia nigra, a midbrain region that provides dopamine to the basal ganglia, a system involved in voluntary motor control. The cause of this cell death is poorly understood, but involves the aggregation of alpha-synuclein into Lewy bodies within neurons. Other potential factors involve genetic and environmental influences, medications, lifestyle, and prior health conditions.

The basal ganglia (BG) or basal nuclei are a group of subcortical nuclei found in the brains of vertebrates. Positioned at the base of the forebrain and the top of the midbrain, they have strong connections with the cerebral cortex, thalamus, brainstem and other brain areas. The basal ganglia are associated with a variety of functions, including regulating voluntary motor movements, procedural learning, habit formation, conditional learning, eye movements, cognition, and emotion.

The main functional components of the basal ganglia include the striatum, consisting of both the dorsal striatum (caudate nucleus and putamen) and the ventral striatum (nucleus accumbens and olfactory tubercle), the globus pallidus, the ventral pallidum, the substantia nigra, and the subthalamic nucleus. Each of these components has complex internal anatomical and neurochemical structures. The largest component, the striatum (dorsal and ventral), receives input from various brain areas but only sends output to other components of the basal ganglia. The globus pallidus receives input from the striatum and sends inhibitory output to a number of motor-related areas. The substantia nigra is the source of the striatal input of the neurotransmitter dopamine, which plays an important role in basal ganglia function. The subthalamic nucleus mainly receives input from the striatum and cerebral cortex and projects to the globus pallidus.

Lewy bodies are inclusion bodies – abnormal aggregations of protein – that develop inside neurons affected by Parkinson's disease, the Lewy body dementias (Parkinson's disease dementia and dementia with Lewy bodies (DLB)), and in several other disorders such as multiple system atrophy. The defining proteinaceous component of Lewy bodies is alpha-synuclein (α-synuclein), which aggregates to form Lewy bodies within neuronal cell bodies, and Lewy neurites in neuronal processes (axons or dendrites). In some disorders, alpha-synuclein also forms aggregates in glial cells that are referred to as 'glial cytoplasmic inclusions'; together, diseases involving Lewy bodies, Lewy neurites and glial cytoplasmic inclusions are called 'synucleinopathies'.

Lewy bodies appear as spherical masses in the neuronal cytoplasm that can displace other cellular components such as the nucleus and neuromelanin. A given neuron may contain one or more Lewy bodies. There are two main kinds of Lewy bodies – classical (brainstem-type) and cortical-type. Classical Lewy bodies occur most commonly in pigmented neurons of the brainstem, such as the substantia nigra and locus coeruleus, although they are not restricted to pigmented neurons. They are strongly eosinophilic structures ranging from 8-30 microns in diameter, and when viewed with a light microscope they are seen to consist of a dense core that is often surrounded by a pale shell. Electron microscopic analyses found that the core consists of a compact mass of haphazard filaments and various particles surrounded by a diffuse corona of radiating filaments. In contrast, cortical-type Lewy bodies are smaller, only faintly eosinophilic, and devoid of a surrounding halo with radial filaments. Cortical-type Lewy bodies occur in multiple regions of the cortex and in the amygdala. Cortical Lewy bodies are a distinguishing feature of dementia with Lewy bodies, but they may occasionally be seen in ballooned neurons characteristic of behavioural variant frontotemporal dementia and corticobasal degeneration, as well as in patients with other tauopathies.

The subthalamic nucleus (STN) is a small lens-shaped nucleus in the brain where it is, from a functional point of view, part of the basal ganglia system. In terms of anatomy, it is the major part of the subthalamus. As suggested by its name, the subthalamic nucleus is located ventral to the thalamus. It is also dorsal to the substantia nigra and medial to the internal capsule.

The tegmentum (from Latin for "covering") is a general area within the brainstem. The tegmentum is the ventral part of the midbrain and the tectum is the dorsal part of the midbrain. It is located between the ventricular system and distinctive basal or ventral structures at each level. It forms the floor of the midbrain (mesencephalon) whereas the tectum forms the ceiling. It is a multisynaptic network of neurons that is involved in many subconscious homeostatic and reflexive pathways. It is a motor center that relays inhibitory signals to the thalamus and basal nuclei preventing unwanted body movement.

The tegmentum area includes various different structures, such as the rostral end of the reticular formation, several nuclei controlling eye movements, the periaqueductal gray matter, the red nucleus, the substantia nigra, and the ventral tegmental area.

The putamen (/pjuˈteɪmən/; from Latin, meaning "nutshell") is a subcortical nucleus with a rounded structure, in the basal ganglia nuclear group. It is located at the base of the forebrain and above the midbrain.

The putamen and caudate nucleus together form the dorsal striatum. Through various pathways, the putamen is connected to the substantia nigra, the globus pallidus, the claustrum, and the thalamus, in addition to many regions of the cerebral cortex. A primary function of the putamen is to regulate movements at various stages such as in preparation and execution; and to influence various types of learning. It employs GABA, acetylcholine, and enkephalin to perform its functions. The putamen also plays a role in neurodegenerative diseases, such as Parkinson's disease.

The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a major component of the subcortical basal ganglia in the brain. It consists of two adjacent segments, one external (or lateral), known in rodents simply as the globus pallidus, and one internal (or medial). It is part of the telencephalon, but retains close functional ties with the subthalamus in the diencephalon – both of which are part of the extrapyramidal motor system.

The globus pallidus receives principal inputs from the striatum, and principal direct outputs to the thalamus and the substantia nigra. The latter is made up of similar neuronal elements, has similar afferents from the striatum, similar projections to the thalamus, and has a similar synaptology. Neither receives direct cortical afferents, and both receive substantial additional inputs from the intralaminar thalamic nuclei.