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This diagram illustrates the principle that brain circuits travel up and down the neuroaxis, from one side of the brain to the other, as well as back and forth between many different brain components at several levels within the forebrain, thalamus, hypothalamus, midbrain, medulla, cerebellum and spinal cord.

Why is it important to learn how brains are constructed?

For a brain to perform all the functions that it must do, it must: 1. Detect and locate the great variety of stimulus types, sources, and happenings in the environment; 2. Make sense of all these sensory events; 3. Respond to all these features by expressing an elaborate behavioral repertoire; and 4. Make judgments, learn, and think about all these things.

This diagram indicates that the circuits of the brain have evolved to extract (from the great complex flux of energies that course through space) a representation of the physical world that is realistic. Thus the brain creates a reasonable conception of reality to which the brain can behave in adaptive and creative ways.


Over the last 50 years, a great number of neuronal cell groups, circuits and connections have been identified and named in the several different regions of the brain. In addition, the functions of these different nuclei and circuits have been identified. Moreover, the neuroanatomical and neurochemical mechanisms by which these circuits operated to produce and enable them to function effectively have begun to be clarified. But much remains to be done, and in the next two decades, it is estimated that modern technology will provide ever greater insight as to how the circuits of the brain perform the functions that they do.

However, a major part of learning about the architecture of the brain and its parts involves becoming familiar with the names of the different structures.

External Structures visible by mere inspection of the brain include the cerebrum: brain lobes + hemispheres; cerebellum, gyri and sulci, Olfactory bulbs & tract, cranial nerves, peduncles, midbrain, medulla, and spinal cord)

Internal regions of the brain as viewed in cross section include the following structures or nuclei and fiber tracts:

NOMENCLATURE: abbreviations used for brain structures and nuclei

Telencephalon (Forebrain):

Cerebral cortex
Basal ganglia

Olfactory cortex
Anterior commissure
Subfornical organ
Corpus Callosum
Basal forebrain
Olfactory tubercle
Olfactory cortex

Caudate nucleus
Globus pallidus (internal & external)
Ventral striatum
Amygdalar complex


Pineal body
Red nucleus
Substantia nigra

Mesencephalon (Midbrain):

Superior colliculus
Inferior Colliculus
Periaquaductal nuclei
Posterior commissure
Superior olive
Inferior olive

Metencephalon (Hindbrain):

Cerebellum (basal cerebellar nuclei, cerebellar cortex; convoluted into lobes, lobules and folia)

Myelencephalon (Brainstem, medulla):

Basic Brain nuclei and fiber tracts
Neurons; their structure and connectivities. Major sensory, motor, and other functional connections.

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