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

The Nervous System (general structural and developmental plan of the nervous system)
Central Nervous System
Limbic System and Reticular Formation

The limbic system is defined as a morphofunctional complex of Brain structures responsible for the emotional coloring of behavior. In 1878, the anatomist P. Broca first used this term to designate the "marginal" or "limbic" lobe—a region of the Telencephalon bordering the Brainstem. The so-called "marginal lobe" on the Medial surface of the hemispheres consists of the cingulate and hippocampal gyri.

The inclusion of these brain structures in the limbic system is based on their close functional connection with the Hypothalamus and their role in organizing motivational and emotional behavior. In addition to hypothalamic structures, the system comprises the hippocampus, amygdala, limbic cortex, anterior and posteromedial thalamic nuclei, and the septum pellucidum. A distinctive feature of the limbic cortex is its connectivity with the frontal lobe areas, which provide conscious regulation of emotional appraisals of external stimuli. All Components of the limbic system are integrated by reciprocal pathways into a cohesive functional entity.

The limbic system is also characterized by an Abundance of reciprocal connections with other brain regions as well as within its own structures. It features complex recurrent pathways that facilitate the Propagation of Excitation along intricate circular circuits. A prime example of such a circular pathway is the Papez circuit, which runs from the hippocampus via the fornix, mamillary bodies, anterior thalamic Nucleus, and cingulate cortex, back to the hippocampus.

By altering the hormonal balance, these structures participate in generating behavioral drives (motivation) and regulate the actions themselves by intensifying or dampening the emotional component of behavior.

The Functions of the limbic system extend far beyond emotional reactions. They also maintain Homeostasis, regulate the Sleep-wake cycle, and play a crucial role in Learning and Memory processes.

The reticular formation plays a vital role in maintaining wakefulness, acting alongside the limbic system. This system encompasses a wide array of structures, extending from the Spinal Cord (the Gray matter between the anterior and posterior horns) up to the diencephalic structures. Structurally, the reticular formation is characterized by a specific type of neuron (reticular neuron) and a distinct pattern of connectivity. It features polysynaptic chains of short-axon Neurons, as well as neurons with numerous collaterals. Due to this Organization, a single reticular neuron exerts a direct influence on approximately 30,000 other reticular neurons.

Structurally, the reticular formation is divided into three zones: the median, medial, and lateral zones. The median zone lies along the brain's midline; the medial zone occupies the medial Regions of the brainstem; and the lateral zone is situated adjacent to the sensory nuclei of the brainstem.

Positioned along the pathways of all incoming and outgoing nerve impulses (information streams) of the Central Nervous system, the reticular formation, together with the limbic system, acts as one of the brain's primary activating systems.