Inferior frontal gyrus

Gyrus frontalis inferior

Definition

The inferior frontal gyrus is a part of the frontal lobe situated in its lower portion. It extends forward from the lower part of the precentral sulcus and lies beneath the inferior frontal sulcus. On the inferior surface, it extends from the lateral side and connects with the orbital gyri.

The inferior frontal gyrus is divided into different sub-parts by the branches of the lateral sulcus. As the stem of the lateral sulcus reaches the lateral surface of the cerebral hemisphere, it splits into three branches or rami: the anterior horizontal ramus, the anterior ascending ramus, and the posterior ramus. The first branch, called the anterior horizontal ramus, stretches approximately 2.5 cm forward into the inferior frontal gyrus. The region of the inferior frontal gyrus below the anterior ramus is known as the orbital part of the inferior frontal gyrus, also referred to as pars orbitalis or the orbital operculum of the insula.

The second branch is called the anterior ascending ramus. The triangular cortical region of the inferior frontal gyrus, which lies between the anterior horizontal and ascending rami, is called the pars triangularis or the frontal operculum of the insula.

In the region where the pars orbitalis and pars triangularis are located, there is an important functional motor region known as Broca's motor speech area.

Finally, there is the posterior ramus. This branch is the longest and acts as the main continuation of the lateral sulcus towards the back. The cortical region behind the anterior ascending ramus and above the posterior ramus is called the fronto-parietal operculum of the insula. It is made up of two sub-parts: the frontal opercular sub-part and the parietal opercular sub-part. The frontal part originates from the inferior frontal gyrus and corresponds to the lower section of the pre-central gyrus. It also includes some extensions of the posterior region of Broca's motor speech area. The parietal part is contributed by the parietal lobe and encompasses the lower portion of the post-central gyrus.

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Text written by Muhammad A. Javaid, MD, PhD © 2023 IMAIOS.

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