Conduction Functions
Nerve fibers connecting different parts of the nervous system pass through the medulla oblongata and pons. They can be divided into three groups:
- Transit pathways. Pass straight through. These include ascending and descending spinal tracts, the pyramidal, rubrospinal, and spinothalamic tracts.
- Terminating pathways. End within the brainstem structures, such as the fasciculus gracilis and fasciculus cuneatus (gracile and cuneate tracts).
- Originating pathways. Originate within the medulla oblongata itself: vestibulospinal, reticulospinal, and olivospinal tracts.
Role of the Reticular Formation (RF)
The reticular formation of the brainstem exerts a marked influence on motor activity and reflexes. The effect depends on which part of the RF is activated:
- Ventromedial regions: stimulation leads to inhibition of the knee-jerk reflex, suppression of movements initiated by the cortex, and blockade of impulse transmission along $\gamma$-afferent fibers.
- Dorsolateral regions: stimulation causes facilitation of the knee-jerk reflex and cortically induced movements, and increases muscle tone (both flexors and extensors).
Intrinsic Functions and Reflex Activity
These structures house cranial nerve (CN) nuclei and centers for somatic and autonomic reflexes. The medulla oblongata contains the nuclei of CN VII, IX, X, XI, and XII, while the pons contains CN V and VI.
Neurons perform primary analysis of sensory information: vestibular, tactile, auditory, and gustatory. Bulbar centers are under the descending control of the cerebellum and the red nuclei of the midbrain.
Reflexes feature complex coordination and often include both somatic and autonomic components. The main groups are:
- Nutritive: motor (sucking, chewing, swallowing) and secretory (salivation and gastric juice secretion).
- Protective: coughing, sneezing, vomiting, blinking, lacrimation.
Each reflex is strictly specific and is triggered from a specific reflexogenic zone. An interesting example: mechanical stimulation of the pharynx induces vomiting, whereas the entry of food into the same zone initiates swallowing.
Autonomic and Metabolic Functions
The medulla oblongata is responsible for regulating vital processes.
- Respiratory center: paired and consists of inspiratory (inspiration) and expiratory (expiration) compartments. Respiratory neurons are capable of automatism—the independent generation of action potentials. This automatism depends on the humoral influence of $CO_2$ and signals from the vagus nerves.
- Vasomotor center: maintains blood vessel tone.
- Cardiac center: includes the nucleus of the vagus nerve (N. vagus), which exerts an inhibitory effect on the heart, and neurons connected to spinal centers that produce an excitatory effect.
和其他 — The brainstem also participates in the regulation of metabolism, as proven by Claude Bernard's classic experiment ("sugar puncture").