Septal nuclei: nerve functions and connections

Over the past century, knowledge about the anatomy and functions of different regions of the brain has increased dramatically. Scientific research has enabled us today to have at least some clues about the functioning of our brain and, consequently, about our cognitive and physiological processes.

In this article we will talk about the functions and nerve connections of the septal nuclei, A part of the brain that is essential for memory, emotional expression, pleasure, and other processes characteristic of humans and many different animals.

    What are Septal Nuclei

    The septal nuclei are a set of subcortical structures located between the hypothalamus, corpus callosum and septum pellucidum, A membrane that separates the left and right lateral ventricles of the brain. It is also possible to find references to this brain region with the terms “septal zone” and “medial olfactory zone”.

    This concept is used not only to refer to the nuclei themselves, but also a number of closely interconnected regions morphologically and functionally: the nucleus accumbens (which plays a key role in the activity of the neurotransmitter dopamine), the nucleus terminal striations and the diagonal band of Broca.

    The septal nuclei connect the limbic system to the subcortical structures of the diencephalon region, thus they allow an exchange of nerve impulses between them. Specifically, the subcortical areas we are referring to are the hippocampus, amygdala, and hypothalamus.

    When lesions appear in the septal nuclei, symptoms of excessive reactivity to food and sexual stimuli appear. This is associated with the connections of this structure with the hypothalamus, which we will discuss in the following sections.

    Connections with other areas of the brain

    The septal nuclei they receive afferents from many different areas of the brain. One of the most important connections is that which occurs with the prefrontal cortex; of this region depend on higher cognitive functions, such as working memory, inhibition of inappropriate behavior, moral thinking, planning and creation of expectations.

    The arch-shaped structure known as the fornix connects the septal nuclei with the hippocampus, a core of gray matter essential for the consolidation and retrieval of memories, as well as for the perception of space.

    Medial olfactory streaks, a collection of nerve fibers, act as a link between the septal nuclei and the olfactory bulb, which receives olfactory information from sensory receptors located in the olfactory lining.

    The septal nuclei are also connected to the amygdala, A structure of the limbic system on which emotional learning and memory depend. In this case, the grouping of axons connecting the two regions is called the “terminal striae”.

    On the other hand, this structure is also linked to the hypothalamus, which controls the release of hormones, And in the epithelium or pineal gland, which produces melatonin. Unlike other pathways of which the septal nuclei are a part, in this one the connection is bidirectional, since there are afferents and efferents in both directions.

    The efferents of the septal nuclei

    The pathways that start from the septal nuclei and project to the hypothalamus and epithelium have differentiated characteristics, despite the anatomical proximity of the two structures.

    The efferences on the hypothalamus take place through the medial telencephalic fascicle, A set of fibers with a low degree of myelination that reaches the roof of the brainstem. Myelin is a substance that covers the axons of many neurons, protects them from the extracellular environment and promotes the transmission of electrochemical impulses.

    On the other hand, the projections in the epithelium are made through the medullary striae of the thalamus. When they reach the nucleus of the habenula, there is relief from neuronal transmission; from there the efferents pass through the habenointerpedoncular tract to reach the interpeduncular nucleus and the brainstem.

    Functions of this structure

    Research suggests that the septal nuclei perform a wide variety of functions. Two of the main ones appear to be expression of pleasurable responses, including those related to sexuality, And the inhibition of feelings of fear, which depend on the amygdala.

    It is believed that the septal nuclei are involved in regulation of limbic system activity, As well as in that of the cerebral alert. In this sense its function would allow mental preparation before the expectation that a determined significant event takes place, favoring the execution of responses before the appearance of this one.

    On the other hand, this set of cores is very important for encoding new information, and therefore for long-term learning and memory. This function is associated with the connections that hold the septal nuclei with the hippocampus.

    It has generally been stated that the septal nuclei act by filling a role of the integration of different physiological and cognitive processes, Such as emotion, memory, pleasure, alertness, attention and responsiveness to external stimuli. This is due to the multiple afferents that this structure receives from other regions of the brain.

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