Medulla Oblongata: Functions, Neurons, and Medullar Pyramids

Medulla Oblongata: Functions, Regulation of Vital Functions, Neurons, and Medullar Pyramids

The medulla oblongata is the lower part of the brain and the lowest portion of the brainstem, connecting the spinal cord to the higher parts of the brain. It is a critical component of the autonomic nervous system, responsible for controlling vital functions such as heartbeat and respiration. The medulla is divided into two main parts: the ventral medulla (anterior portion) and the dorsal medulla (posterior portion).

Functions and Regulation of Vital Functions

The medulla oblongata plays a crucial role in transmitting signals between the spinal cord and the higher parts of the brain. It also controls various autonomic functions, including heartbeat and respiration. The upper portion of the dorsal medulla forms the lower region of the fourth ventricle, a fluid-filled cavity surrounded by white matter on the outside and gray matter on the inside.

Neurons and Neuronal Functions

The medulla contains both myelinated (white matter) and unmyelinated (gray matter) nerve fibers. The white matter of the medulla is intermingled with the gray matter, giving rise to part of the reticular formation, a network of interconnected neuron clusters within the brainstem. Neurons of the reticular formation play a central role in the transmission of motor and sensory impulses. They carry out complex integrative functions, specializing in the control of autonomic nervous activity, regulating respiration, heart rate, and digestive processes. Other activities of neurons in the medulla include control of movement, relay of somatic sensory information from internal organs, and control of arousal and sleep.

Medullar Pyramids

The ventral portion of the medulla oblongata contains the medullary pyramids, which are paired white matter structures that travel along the length of the medulla oblongata. These structures are bordered medially by the anterior commissure and have an anterolateral sulcus along their lateral borders, where the hypoglossal nerve emerges from. Each pyramid also has a pronounced bulge known as an olive. The medullary pyramids contain motor fibers known as the corticobulbar and corticospinal tracts. The corticospinal tracts are on the anterior surface of the pyramids and transport motor signals that originate in the precentral gyrus and travel through the internal capsule to the spinal cord.

The lower limit of the pyramids is marked when the fibers cross (decussate). About 90% of these fibers leave the pyramids in successive bundles and decussate (cross over) in the anterior median fissure, forming the pyramidal decussation or motor decussation. Having crossed over at the middle line, they pass down in the posterior part of the lateral funiculus as the lateral corticospinal tract. The other 10% of the fibers stay uncrossed in the anterior corticospinal tract. The pyramidal decussation marks the border between the spinal cord and the medulla oblongata.

Clinical Significance

Injuries or diseases affecting the medulla oblongata can have significant consequences. Medial medullary syndrome, caused by injuries or diseases in the middle portion of the medulla, is characterized by partial paralysis of the opposite side of the body, loss of the senses of touch and position, or partial paralysis of the tongue. Lateral medullary syndrome, caused by injuries or diseases in the lateral portion of the medulla, is associated with a loss of pain and temperature sensations, loss of the gag reflex, difficulty swallowing, vertigo, vomiting, or loss of coordination.

In summary, the medulla oblongata is a vital part of the brainstem that plays a crucial role in transmitting signals between the spinal cord and the higher parts of the brain, as well as regulating autonomic functions such as heartbeat and respiration. It is composed of various neurons and neural structures, including the medullary pyramids, which are essential for motor function and communication between the brain and the spinal cord. Injuries or diseases affecting the medulla can have severe consequences, highlighting the importance of understanding its structure and function.