Chapter 5. Cranial Nerves. Main Syndromes

5.1. Cranial nerves

In the development of a clinical complex of signs and symptoms in case of damage to any cranial nerve, not only its peripheral structures, which anatomically represent the cranial nerve, are involved but also other structures in the brainstem, in the subcortical region, the cerebral hemispheres, including certain areas of the cerebral cortex.

For physicians, it is important to determine the area affected by the pathological process — from the nerve itself to its cortical representation. Thus, there is a system that provides the function of the cranial nerve.

The 12 pairs of cranial nerves (CN) (Fig. 5.1) are divided into:

• motor;
• sensory;
• mixed.

Fig. 5.1. The base of the brain with the roots of the cranial nerves: 1 — pituitary gland; 2 — olfactory nerve; 3 — optic nerve; 4 — oculomotor nerve; 5 — trochlear nerve; 6 — abducens nerve; 7 — motor root of the trigeminal nerve; 8 — sensory root of the trigeminal nerve; 9 — facial nerve; 10 — intermediate nerve; 11 — vestibulocochlear nerve; 12 — glossopharyngeal nerve; 13 — vagus nerve; 14 — accessory nerve; 15 — hypoglossal nerve; 16 — spinal roots of the accessory nerve; 17 — medulla oblongata; 18 — cerebellum; 19 — trigeminal ganglion; 20 — cerebellar peduncle; 21 — optic tract

Some of these nerves have autonomic nuclei that control vascular tone, salivation, lacrimation, and trophism. Three pairs are only sensory (I, II, VIII); five pairs are motor (III, IV, VI, XI, XII); and four pairs are mixed (V, VII, IX, X). CNs III, V, VII, IX, X have a lot of autonomic fibers.

In addition, special sensitivity analyzers are distinguished:

• olfactory (CN I);
• optic (CN II);
• auditory and vestibular (CN VIII);
• gustatory (CNs VII and IX).

The system of motor nerves is part of the pyramidal cortical-muscular tract. The nuclei of the motor cranial nerves are analogs of the anterior horns of the spinal cord. They contain the bodies of peripheral motor neurons of the corticobulbar pyramidal tract. The system of sensory nerves are a homologue of segmental sensitivity of other division of the body, providing proprioceptive and extraceptive sensitivity. The nuclei of the sensory cranial nerves are analogs of the posterior horns of the spinal cord. These nuclei contain bodies of the second neurons. In this regard, the sensory nerve system, similar to the system that provides sensitivity to any part of the body, consists of a chain of three neurons, and the motor nerve system, similar to the corticospinal tract, consists of two neurons.