CEREBRO (TELENCÉFALO): Configuración Externa | Neuroanatomía

The Structure and Function of the Brain

Overview of the Encephalon

• The encephalon, or brain, is a major part of the central nervous system located in the cranial cavity. Its numerous folds are due to the development of gray matter in a confined space.

• As the brain develops from intrauterine life, it becomes increasingly wrinkled to accommodate more gray matter within the limited cranial cavity. This is likened to fitting a larger cloth onto a smaller board, which necessitates folding.

Hemispheres and Their Anatomy

• The brain is divided into two hemispheres by the interhemispheric fissure (longitudinal fissure), connected by large commissures like the corpus callosum and fornix. Each hemisphere has three faces, three edges, and two ends.

• The anterior end is termed the frontal pole while the posterior end is called the occipital pole, corresponding with their respective lobes. The superolateral face corresponds to the cranial cap while other faces relate to various cranial fossae and structures like cerebellum through dura mater folds.

Classification of Brain Folds

• Brain folds are classified into primary, secondary, and tertiary furrows:

• Primary Furrows: Constant and uninterrupted; separate lobes (interlobar fissures).

• Secondary Sulci: More variable than primary; separate gyri within each lobe (intergyral fissures).

• Tertiary Sulci: Inconstant and vary significantly; not emphasized in descriptions due to variability.

• Communication folds connect adjacent gyri while passage folds interrupt sulci between lobes.

Description of Lobes

• There are five essential lobes in the brain: frontal, parietal, occipital, temporal, and insula.

• Starting with dorsal face analysis:

• Lateral Sulcus (Sylvian Fissure): Begins at lower face level; separates frontal/parietal from temporal lobe as it extends laterally across surfaces. Provides important branches for understanding gyri structure later on.

• Central Sulcus (Rolandic Fissure): Starts behind mid-part of hemisphere; descends anteriorly with characteristic flexions known as knees before ending near lateral sulcus junction.

Neuroanatomy: Understanding the Sulci and Gyri

Overview of Incisures and Sulci

• The transcript begins with a discussion on three key incisures, specifically the sulcus-presental or pre-Rolandic, which is parallel to the central sulcus.

• It introduces the superior frontal and inferior frontal sulci, which are also parallel to each other but perpendicular to the central and precentral sulci, delineating four gyri.

Detailed Description of Frontal Gyri

• The precentral gyrus is located between the precentral and central sulcus; above it lies the superior frontal gyrus, while below is the inferior frontal gyrus.

• The inferior frontal gyrus can be segmented into three parts: orbital (head), triangular (cape), and opercular (foot), with connections to both frontal and parietal lobes.

Parietal Lobe Structure

• The interparietal sulcus runs parallel to the central sulcus, originating near where Rolandic fissure meets Sylvian fissure, curving transversely backward towards the external parieto-occipital sulcus.

• This segment divides into a superior parietal lobule and an inferior parietal lobule through its transverse segment.

Characteristics of Intraparietal Sulcus

• Notable features include interruptions by Gromier's folds; additionally, a descending branch called Jensen's intermediary sulcus divides the inferior parietal lobule into supramarginal (anterior) and angular (posterior) gyri.

Occipital Lobe Insights

• The occipital lobe has a pyramidal shape with two incisures radiating from its vertex. These are identified as superior and inferior occipital incisures.

• Within these incisures lie occipital threads that relate sequentially to various gyri in adjacent regions.

Temporal Lobe Features

• Four incisures and five gyri are identified in the temporal lobe; significant structures include superior temporal sulcus, inferior temporal sulcus, along with their corresponding gyri.

• A notable structure within this area is the transverse temporal gyrus or Gesel found in part of the superior temporal gyrus.

Internal Surface Anatomy

• Three main interlobar fissures are discussed: cingulate sulcus, internal parieto-occipital sulcus, and calcarine sulcus. Each plays a role in defining brain anatomy.

• The cingulate sulcus follows a path similar to that of corpus callosum before branching off as subparietal sulcus.

Summary of Internal Gyri Delimitation

• All mentioned structures help define several gyri on the internal surface including portions of superior frontal gyrus above sympathetic sulcus.

Brain Anatomy Overview

Central Lobule and Surrounding Structures

• The central lobule, also known as the superior frontoparietal operculum, is identified as a communication fold between the central group and the precentral gyrus on the dorsal face of the hemisphere.

• This structure is bordered posteriorly by the cingulate sulcus and anteriorly by the pre-oval sulcus, surrounding the central or Rolandic sulcus.

Division of Lower Face of Hemisphere

• The lower face of the hemisphere is divided into an anterior (orbital) portion featuring structures like the H sulcus, and a posterior (occipitotemporal) portion containing lateral and medial temporo-occipital sulci.

• The anterior part of the medial occipitotemporal gyrus continues with the parahippocampal gyrus, which forms a hook or uncus at its posterior termination.

Insula of Rehus

• The fifth lobe of the brain, known as the insula of Rehus, is not visible from superficial observation due to its location within the depth of the Sylvian fissure.

• This triangular-shaped lobe has an apex called insular pole directed anteriorly and inferiorly, separated from adjacent lobes by circular sulcus.

Insular Convolutions

• From its pole radiate four sulci that delineate five insular convolutions or gyri, numbered sequentially.