Anatomy and Structure of the Corpus Striatum
- Caudate nucleus (nucleus caudatus) and lentiform nucleus (including the putamen and globus pallidus) are the core components connected by numerous fine bridges of grey matter. On anatomical sections, these bridges resemble stripes, giving the structure its name.
- Internal capsule (capsula interna): During embryogenesis, its fibers grow through the initially homogenous basal ganglia, creating the characteristic striated appearance.
- Nucleus accumbens: Represents the ventral striatum.
- Cellular composition: The most abundant cell type in the striatum is the GABAergic medium spiny neuron (MSN).
Afferent Pathways (Inputs to the Striatum)
The striatum receives extensive inputs from multiple brain regions:
- Corticostriatal fibers: Receives massive input primarily from the motor areas of the frontal lobe. Fibers originate from pyramidal cells in layer V of the cerebral cortex, descend ipsilaterally, and exhibit strict somatotopic organization. These pathways are glutamatergic.
- Nigrostriatal fibers: Dopaminergic projections from the substantia nigra (pars compacta) exert a crucial modulatory influence.
- Thalamostriatal fibers: Excitatory inputs originate from the centromedian nucleus of the thalamus, conveying signals from the cerebellum and midbrain reticular formation.
- Raphe-striatal fibers: Serotonergic projections arrive from the raphe nuclei (nuclei raphes).
Efferent Pathways (Outputs from the Striatum)
The primary sources of output are GABAergic medium spiny neurons, which constitute the vast majority of striatal neurons.
- Striatopallidal fibers: Project to both the external and internal segments of the globus pallidus. The globus pallidus receives its primary major input from the striatum.
- Striatonigral fibers: Project to both the pars compacta and pars reticulata of the substantia nigra.
Note: Direct feedback projections from the striatum back to the cerebral cortex do not exist.
Blood Supply
The vascular supply of deep brain structures follows a strict territorial distribution:
- Middle cerebral artery (a. cerebri media) gives off deep striate branches (rami striati, or lenticulostrirate arteries). These vessels ascend vertically to supply the basal ganglia, including the putamen, globus pallidus, and caudate nucleus.
- Anterior cerebral artery supplies the anterior regions of the basal ganglia via medial striate branches (e.g., recurrent artery of Heubner).
Functions and Clinical Significance
As a core component of the basal ganglia, the striatum is involved in motor planning, emotional expression, and the integration of sensory and motor signals into cognitive processes.
- Parkinson disease: The pathogenesis involves the degeneration of dopaminergic neurons in the substantia nigra, which normally project to the striatum. The loss of this dopaminergic input alters the direct and indirect pathways, leading to increased inhibitory output from the striatum to the external globus pallidus (GPe). This triggers downstream hyperactivity of the subthalamic nucleus and internal globus pallidus, excessive thalamic inhibition, and reduced excitatory drive to the motor cortex, manifesting as hypokinesia.
- Psychiatry: Disruption of neural circuits linking the striatum, thalamus, limbic system, and prefrontal cortex is implicated in emotional and behavioral disorders, including anxiety, depression, apathy, and psychosis.
- Infectious pathology: In epidemic typhus, typhus granulomas (Popov–Frankel–Davydovsky nodules) form in the striatum, medulla oblongata, and cerebral cortex. CNS involvement presents with serous meningoencephalitis, tissue edema, swelling, and petechial hemorrhages.