PROTUBERANCIA (Puente) - Configuración externa, interna, fibras, núcleos, vasos

Anatomy of the Pons

Introduction to the Pons

• The speaker, Valentín Velázquez, introduces the topic of the anatomy of the pons, also known as mesencephalon or bridge.

• The pons is described as a nervous structure located between the cerebral peduncles, cerebellum, and medulla oblongata.

External Configuration

• The pons has an irregular cubic shape with six faces and is characterized by numerous transverse striations that form its transverse fibers.

• Dimensions of the pons are provided: width (35mm), length (27mm), and depth (25mm).

• The anterior face features a median groove called the basilar sulcus, often associated with the basilar artery.

Anterior Face Details

• Lateral to the basilar sulcus are rounded eminences known as pontine bulges; these are significant anatomical landmarks.

• Two roots emerge from this area: a smaller motor root and a larger sensory root for cranial nerve V (trigeminal nerve).

Posterior Face Overview

• The posterior face of the pons is covered by cerebellum tissue and forms part of the anterior boundary of the fourth ventricle.

• A conventionally defined imaginary line marks where the pons meets spinal cord structures.

Internal Structure of the Pons

Cross-sectional Anatomy

• A cross-section reveals two symmetrical lateral halves separated by a central structure called the median raphe.

• It consists of an anterior/ventral plane containing longitudinal and transverse fibers along with pontine nuclei.

White Matter Composition

• The white matter in this region includes various fiber arrangements: longitudinal, transverse, and arciform fascicles that connect different brain regions.

Relationship with Cerebellum

Acoustic Pathways and Motor Fibers

Formation of the Acoustic Pathway

• The trapezoid body originates from the anterior nuclei of the acoustic nerve, forming the acoustic pathway. This pathway is visualized in relation to Reil's band or lateral lemniscus.

• The acoustic pathway consists of fibers from both the anterior nucleus and lateral tubercle, which unite at the midline raphe.

Longitudinal Fibers and Motor Pathways

• Longitudinal fibers are categorized into primary motor pathways (corticospinal and corticonuclear) and accessory motor pathways. The main motor fibers originate from the precentral gyrus, traversing through the internal capsule to reach the pons.

• These pyramidal fibers descend caudally, recrossing laterally at various levels, constituting both anterior and lateral corticobulbar tracts.

Accessory Motor Pathways

• The accessory pyramidal tract arises from the temporal lobe cortex, reaching the pons via internal capsule; it includes aberrant fibers that form aberrant fascicles.

• Sensory fibers relate directly to cranial nuclei or anterolateral systems, ascending to sensory cortex while forming medial and lateral lemnisci as well as posterior longitudinal fasciculus.

Sensory Fiber Connections

• The lateral lemniscus is associated with auditory sensation while medial lemniscus connects with cranial nerve nuclei such as facial and trigeminal nerves. Visual representations illustrate these connections clearly within their respective pathways.

Gray Matter Structures

• Gray matter structures include those specific to pons along with bulbospinal gray matter divided into anterior (motor) and posterior (sensory) horns related to cranial nerve nuclei origins arranged in three columns: one for each cranial nerve type (motor/sensory).

Cranial Nerve Nuclei Arrangement

Overview of the Anular Protuberance and Its Vascular Supply

Vascular Branches of the Basilar Artery

• The anular protuberance's vascular supply is dependent on collateral branches from the basilar artery, which are categorized into three groups: short circumferential and long circumferential branches.

• Short circumferential branches target specific spinal segments, typically around five or six, originating from the posterior aspect of the basilar trunk.

Long Circumferential Branches

• Long circumferential branches include the middle cerebellar arteries and superior cerebellar arteries, which play a crucial role in supplying blood to cerebellar structures.

Venous Drainage Considerations

• Various types of veins are involved in venous drainage, directing blood either towards the petrosal sinus or into the basilar vein.