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Basal Ganglia, Thalamus, Limbic System

Notes

Basal Ganglia, Thalamus, Limbic System

Sections


Summary

Basal ganglia (basal nuclei)

Structures

  • Caudate (head) is anterior-most portion of the basal ganglia.
  • Lentiform nucleus: lens-shaped, posterolateral
  • Internal capsule
    • Space between the lentiform nucleus, caudate head, and thalamus
    • Comprises tightly packed fiber bundles that originate from widespread brain regions

Thalamic Structures

See: Thalamic structures

  • Hypothalamus
    • Cerebral center for the autonomic nervous system
    • Clinical Correlation - Hypothalamic injury causes widespread autonomic dysfunction, sometimes called "autonomic storm."

Limbic System

The cornerstone of memory consolidation

  • The hippocampus projects via the fornix across the thalamus and down to the mammillary nuclei and basal frontal lobe.
  • The mammillary nuclei project to the anterior thalamic nuclei.
  • The anterior thalamic nuclei project to the cingulate gyrus, which projects back to the hippocampus via the cingulum, closing the circuit.

Additional Clinical Correlations

Full Text

Overview

  • Here, we'll draw the basal ganglia, thalamic, and limbic systems.
  • First, let's learn why we'll pay special attention to these specific brain regions.
  • As an oversimplification, denote that the basal ganglia is the key relay center for motor output.
  • The thalamus is the key sensory integration center.
  • And the limbic system is key to emotion and memory.
    • Here we specifically learn about the Papez circuit because it integrates with the thalamus and hypothalamus and is fundamental to memory consolidation.

brain: inferior view

Cerebral Lobes

  • Begin with an inferior view of the brain. Draw only one half now.
  • In this view, we can see, most notably, the frontal (orbital) surface and the temporal lobe.
  • Shade the lobes of the brain as follows:
    • Anterior is the frontal lobe.
    • Lateral middle is the temporal lobe.
    • Medial middle is the limbic lobe.
    • Posterior is the occipital lobe.

Basal Ganglia

Now, on the other half of the brain, let's focus on the basal ganglia.

  • First, as a reference point, draw a cerebral ventricle: the frontal horn of the lateral ventricle.
  • Denote that the basal ganglia (aka basal nuclei) are most notably involved in motor function but have numerous other functions, as well.
  • Along the lateral wall of the frontal horn of the lateral ventricle, draw the head of the caudate, which is the anterior-most portion of the basal ganglia.
    • Denote that it is a major relay center, which is essential to motor output in a similar way, as we'll see, that the thalamus is a major relay center, essential to sensory integration.
  • Posterolateral to it, draw the lens-shaped lentiform nucleus.
  • Subdivide it into the putamen, laterally, and the globus pallidus, medially. Imagine a putaminal shell around a globus pallidus core.
  • Next, medial to the lentiform nucleus, draw the thalamus (of the diencephalon), which is the primary sensory relay center.
  • Next, label the space between the lentiform nucleus, caudate head, and thalamus as the internal capsule, which comprises tightly packed fiber bundles that originate from widespread brain regions.
    • Denote that the motor function of the internal capsule is the most clinically-relevant: a stroke within the internal capsule causes a "pure motor stroke."
    • As an oversimplification, think of the thalamus for sensory input and the internal capsule for motor output.

Brain: Center

Next, let's draw the center of the brain in mid-sagittal view, so we can explore key aspects of the thalamic and limbic systems specifically where they interrelate in the Papez circuit.

  • First, draw the hypothalamus (of the diencephalon) in the center of the cerebrum.
    • Denote that it is the cerebral center for the autonomic nervous system, thus hypothalamic injury causes widespread autonomic dysfunction, sometimes called "autonomic storm".
  • Indicate the pituitary gland, which produces and secretes hormones (its posterior division is part of the hypothalamus).
  • Indicate one of the mammillary bodies, which are involved in memory consolidation.
  • Then, draw the pineal gland, which, notably, creates and secretes melatonin.
  • Next, include the thalamus, which is the primary sensory relay center.
    • Denote that it is the major relay center – most notably, it's essential to sensory integration, however, it relays motor, cognitive another functions, as well; we'll see that it's anterior nucleus plays an important role in the Papez circuit, which we draw next.

Limbic Lobe

To do so, let's draw key components of the limbic lobe, which is central to memory and emotional processing.

  • Draw the corpus callosum, which, again, is a major white matter pathway.
  • Then, the basal frontal lobe, a key frontal connection within the limb system.
  • Superiorly, draw the cingulate gyrus, which functions in motivation, attention, anteriorly and learning and memory, posteriorly.
  • Inferiorly, draw the parahippocampal gyrus, which shuttles information into and out of the hippocampus.
  • Draw the hippocampus along the superior length of the parahippocampal gyrus; it is the major memory-processing center.
  • Anterior to it, draw the amygdala, which is the seat of emotional and behavioral processing.
  • Next, draw the anterior thalamic nucleus.
  • Show that the hippocampus projects via the fornix across the thalamus and down to the mammillary nuclei and basal frontal lobe.
  • Show that the mammillary nuclei project to the anterior thalamic nuclei.
  • Finally, show that the anterior thalamic nuclei project to the cingulate gyrus, which projects back to the hippocampus via the cingulum to close the Papez circuit, which, again is the cornerstone for memory consolidation.