Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Nervous System (General Outline of Structure and Development of the Nervous System)
Central Nervous System
Brain - Medulla Oblongata

The Medulla Oblongata is the direct continuation of the Spinal Cord. Its lower boundary is considered to be the exit point of the roots of the first cervical spinal nerve or the pyramidal decussation. The upper boundary is marked by the posterior edge of the Pons. The length of the medulla oblongata is approximately 25 mm, and its shape resembles a truncated cone with its base directed upward (anteriorly). On the surfaces of the medulla oblongata, the anterior median fissure, posterior median groove, and the anterolateral and posterolateral sulci are clearly visible as longitudinal continuations from the spinal cord; the central canal runs through its interior. The roots of Cranial Nerves IX–XII emerge from the medulla oblongata. These grooves and cranial nerve roots divide the surfaces of the medulla oblongata into funiculi and tracts.

On both sides of the anterior median fissure lie the pyramids of the medulla oblongata, formed by bundles of nerve fibers belonging to the corticospinal (pyramidal) tract. Lateral to the pyramids on both the right and left, the Hypoglossal nerve (cranial nerve XII) emerges from the anterolateral sulcus onto The surface of the medulla oblongata. An ovoid elevation, known as the olive, is located lateral to the anterolateral sulcus. Dorsal to the olive, within the posterolateral (retro-olivary) sulcus, emerge the rootlets of the glossopharyngeal (IX), vagus (X), and accessory (XI) cranial nerves. On the posterior surface of the medulla oblongata, flanking the posterior median groove, are the gracile and, lateral to it, cuneate fasciculi, which are the upward continuation of the posterior funiculus of the spinal cord. Near the inferior angle of the Rhomboid fossa, these fasciculi exhibit elevations—the gracile and cuneate tubercles—which contain the gracile and cuneate nuclei.

In transverse section, the medulla oblongata consists of gray and White matter. The fibers of the descending corticospinal tract run through its base. The Gray matter of the tegmentum of the medulla oblongata is represented by the nuclei of cranial nerves IX–XII and the nuclei of the reticular formation. The WHITE MATTER OF the tegmentum is formed by long and short fibers of ascending and descending pathways.

Structural and Functional Characteristics of the nuclei and Pathways of the medulla oblongata. The reflex Functions of the medulla oblongata are mediated by the Neurons of the tegmental gray matter and are associated with the presence of the nuclei of four pairs of cranial nerves: the hypoglossal (XII), accessory (XI), vagus (X), and glossopharyngeal (IX), as well as the reticular formation nuclei. The nuclei of the medulla oblongata provide sensory, motor, and autonomic innervation to the structures of the HEAD, neck, Thorax, and abdomen.

The axons of the nerve Cells of the Nucleus ambiguus (the motor Nucleus of the glossopharyngeal [IX] and vagus [X] nerves) innervate the musculature of the Pharynx and Larynx. The axons of the motor neurons of the Accessory nerve nucleus (XI pair) innervate the skeletal Muscles of the neck and back. The muscles of the Tongue are innervated by the hypoglossal nerve nucleus (XII pair).

Throughout almost its entire length, the medulla oblongata contains the spinal sensory nucleus of the Trigeminal nerve (V pair). Its neurons receive axons from sensory neurons of the trigeminal ganglion, which transmit impulses from facial Skin Receptors and the mucosal membranes of the nasal and oral cavities. Another source of afferent connections is provided by the ganglia of the Vagus nerve, whose sensory axons transmit impulses from receptors of the dura mater, External ear, and other Organs. Situated within the core of the medulla oblongata is The Nucleus of the solitary tract, which serves as the common sensory nucleus for the facial, glossopharyngeal, and vagus cranial nerves. Afferent impulses reach the neurons of this nucleus via Facial Nerve fibers. These sensory impulses originate from the taste buds of the anterior ²/₃ of the tongue. Sensory impulses from the taste buds of the posterior third of the tongue and the lower Regions of the pharyngeal mucosa are transmitted via the glossopharyngeal and vagus nerves.

Located between the motor and sensory nuclei in the tegmentum of the medulla oblongata are autonomic nuclei, as well as the nuclei of the reticular formation. The axons of neurons from the dorsal nucleus of the vagus nerve (X pair) travel within this nerve to peri-organ and intra-organ autonomic ganglia of the thoracic and abdominal cavities. Through these peripheral ganglia, the functions of the Internal Organs of the respiratory, digestive, and urinary (partially) systems, as well as The Heart, are regulated. Afferent impulses from organs and Tissues reach the neurons of the dorsal nucleus of the vagus nerve via viscerosensory neurons of the vagus nerve and from the nuclei of other cranial nerves. The axons of neurons from the inferior salivatory nucleus (IX pair) travel to the peripheral otic ganglion, whose postganglionic fibers innervate the Cytology/practical/97.html">Parotid salivary gland. The inferior salivatory nucleus also receives viscerosensory fibers from the nucleus of the solitary tract and the trigeminal nerve nuclei.

The reticular Formation of the tegmentum of the medulla oblongata is a collection of neurons distributed diffusely and grouped into nuclei. Among the reticular nuclei, the largest ones include the gigantocellular reticular nucleus, the parvocellular reticular nucleus, and the lateral reticular nucleus.

In the caudal third of the medulla oblongata lie the nuclei of the gracile and cuneate fasciculi—the gracile nucleus and the cuneate nucleus. These nuclei receive fibers from sensory neurons whose Cell bodies are located in the intervertebral (spinal) ganglia. These pseudounipolar neurons transmit information (nerve impulses) from tactile and proprioceptors of the upper and lower body and limbs. The axons (efferent fibers) of the gracile and cuneate nuclei project to the thalamic nuclei and olivary neurons.

The olivary nuclei form the olivary complex, located in the very Base of the tegmentum of the medulla oblongata. The olivary nuclear complex belongs to the structures that regulate motor activity. The functional role of this complex involves the execution of motor programs aimed at maintaining upright posture and body balance during locomotion.

The following ascending pathways pass through the tegmentum of the medulla oblongata: the anterior and posterior spinocerebellar tracts, the spinothalamic tract, and the fibers of the gracile and cuneate fasciculi; the descending pathways include the rubrospinal and tectospinal tracts.

The pons is located superior to the medulla oblongata, with the Cerebellum positioned dorsal to it.