Central nervous system

Anatomical and topographical division

Nervous tissue, in combination with other bodily tissues, forms a unified nervous system. According to the topographical-anatomical principle, it is divided into two major divisions:

• Central nervous system (CNS). Includes the brain and spinal cord. These vital structures are securely protected by a bony framework: they are located within the cranial cavity and the vertebral canal, respectively.
• Peripheral nervous system (PNS). Combines all nervous structures located outside the brain and spinal cord. It includes ganglia, nerve trunks (or simply nerves), and various nerve endings.

Structural components: gray and white matter

To describe the structures of the nervous system, specific terminology is used to reflect clusters of neuronal cell bodies and their processes.

In the central nervous system, pathways (tracts) have an important feature: a single pathway typically contains nerve fibers of only one type. They can be either exclusively afferent (transmitting sensory signals) or exclusively efferent (transmitting motor commands). In contrast, peripheral nerves are often mixed, combining different types of fibers.

Functional morphology and reflex arcs

In addition to the anatomical division, there is a functional division of the nervous system. It is divided into the somatic and autonomic nervous systems. These two systems differ fundamentally in their functions, internal structure, organization of nerve nuclei, ganglia, and trunks, as well as the type of reflex arcs they form.

The main task of the central nervous system is to evaluate all received information in fractions of a second and make an adequate decision. This process relies on the brain's ability to store and, if necessary, reproduce previously received information. The complex analysis and synthesis of nerve impulses that occurs in the higher centers of the brain forms the basis of higher nervous activity.

Any typical body response to a specific external or internal stimulus is carried out via a reflex arc. This is a specialized chain of neurons that sequentially includes:

1. Sensory neuron.
2. Association neuron (there may be one in the arc, several, or it may be absent altogether).
3. Effector neuron.

Clinical significance: requirements for elective surgery

Surgical interventions on the central nervous system and brain are classified as high-bleeding-risk procedures (probability of complications exceeds 1.5%).

When preparing patients with liver cirrhosis for elective surgery, it is extremely critical to consider blood coagulation parameters. The target minimum threshold platelet concentration for CNS interventions is ≥100 × 10⁹/L.

The same strict platelet concentration threshold applies to other high-bleeding-risk surgeries in the anatomical regions of the head, neck, and thorax. These include:

• Septoplasty and nasal bone reposition;
• Thyroid surgery;
• Submucosal vasotomy of the inferior nasal turbinates;
• All variants of neck lymph node dissection;
• Tonsillectomy and open maxillary sinusotomy;
• Ophthalmologic surgeries;
• Thymectomy and video-assisted mediastinal procedures.

Class and exam questions

What else to study on this topic

• Functional division: somatic and autonomic nervous systems
• Structure of the peripheral nervous system: ganglia, nerve trunks, and endings
• Features of mixed nerves and their difference from CNS pathways
• The role of association neurons in forming complex reflex arcs
• High-bleeding-risk surgical interventions in the head and neck region

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.