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What are the internal and external medullary laminae of the thalamus?

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Diagram of a human brain showing a median sagittal section, highlighting the fourth ventricle and cerebellum in the hindbrain, with labeled anatomical structures including the pons, medulla oblongata, and central canal of the spinal cord. — thalamus Sagittal section of the human brain, showing structures of the cerebellum, brainstem, and cerebral ventricles.

The internal and external medullary laminae are distinct structures composed of myelinated neural fibers that serve to organize the anatomy of the thalamus.

Internal Medullary Lamina

The internal medullary lamina consists of sheets of myelinated fibers that divide the major thalamic nuclear groups—specifically the anterior, medial, and lateral regions—from one another.1

External Medullary Lamina

The external medullary lamina serves as a boundary that separates the reticular nucleus from the remainder of the thalamic nuclei. Unlike the other nuclear groups, the reticular nucleus forms a shell around the lateral aspect of the thalamus and is distinguished by its unique connectivity and inhibitory neurochemistry.12