Anatomy of the Vessels and Nerves of the Head and Neck (Angioneurology) - Chornokulskyi S.T. 2009

Nerves of the Head and Neck
Optic nerve

[II] (N. opticus) Fig. 27, 28, 31

It is a collection of axons from the ganglion Cells of the retina. It pierces the fibrous tunic of the Eyeball, the adipose body of the Orbit, and enters the cranial cavity through the optic canal. Here, a partial decussation (of medial fibers only) of both optic nerves takes place, followed by The formation of the optic tracts.

Neural Pathways of the visual analyzer

The Cell bodies of the first-order Neurons are photoreceptor cells—rods and cones—which are capable of sinking into the pigmented layer of the retina under very bright illumination.

The Nerve Impulse is transmitted to bipolar neurons (second-order neuron), and from there to ganglion (node) neurons (third-order neuron). Each axon of a ganglion cell (there are 1 million of them in the optic nerve) conducts an impulse from many photoreceptors (130 million). The axons of the ganglion cells converge at the optic disc (discus n. optici), which marks the Water/144.html">Origin of the n. opticus.

Topographically, four parts are distinguished: intraocular, orbital, canalicular, and intracranial. The optic nerve is considered a pseudo-cranial nerve (cranial nerve II) because it contains neither a ganglion nor a Nucleus, and is thus a part of the Brain. The optic nerve is enclosed by two sheaths: the external sheath (Vagina externa), which is a continuation of the dura mater encephali, and the internal sheath (vagina interna), a continuation of the arachnoid and pia mater encephali, with intersheath spaces (spatia intervaginalia) located between them.

The optic nerve contains visual and reflex (pupillary reflex) fibers. The intracranial part of the optic nerve forms an incomplete decussation of nerve fibers (the fibers of the medial PARTS OF THE nerve cross)—the optic chiasm (chiasma opticum). The optic tracts are formed after the decussation. Each optic tract (tractus opticus) contains nerve fibers from the lateral half of the retina of its own eye and the medial half of the retina of the opposite eye.

The nerve fibers of the optic tract reach three subcortical visual centers: the nuclei of the lateral geniculate bodies, the pulvinar of the thalamus, and the gray layer of the superior colliculi of the tectum of the mesencephalon. The majority of visual fibers synapse in the nuclei of the lateral geniculate bodies (fourth-order neuron). The axons of the fourth-order neurons form the optic radiation (radiatio optica), which passes through the posterior limb of the internal capsule to the cortical center of the visual analyzer (the gyri bordering the calcarine sulcus). The reflex fibers of the optic tract synapse on the neurons of the gray layer of the mesencephalic tectum. From here, the axons of the gray layer of the tectum extend to the nuclei of the Oculomotor nerve (including parasympathetic ones) of the same and opposite sides, to the somatic motor nuclei of the Brainstem (tractus tectobulbaris), to the anterior horn nuclei of the Spinal Cord (tractus tectospinalis), and to the medial longitudinal fasciculus. These pathways mediate protective unconditioned motor reactions in response to unexpected light stimuli (flashes of light).

Efferent limb of the pupillary reflex arc

The axons of the parasympathetic nuclei of the third pair of Cranial Nerves (the Edinger-Westphal nucleus — center for pupillary constriction, and The Nucleus of Perlia — center for accommodation) travel within the oculomotor nerve to reach the neurons of the ciliary ganglion. Postganglionic parasympathetic fibers innervate the sphincter pupillae Muscle and the ciliary muscle. The dilator pupillae muscle is innervated by sympathocytes from the ciliospinal center (preganglionic fibers) and neurons of the superior cervical ganglion of the Sympathetic trunk (postganglionic fibers).

Fig. 31. Neural pathway of the visual analyzer (by neuron)

1 - eyeball (bulbus oculi);

2 - retina: a - rod and cone epitheliocytes (first-order neuron);

b - bipolar neuron (second-order neuron); c - multipolar neuron (third-order neuron);

3 - optic nerve (n. opticus);

4 - optic chiasm (chiasma opticum);

5 - optic tract (tractus opticus);

6 - subcortical visual centers: 6a - lateral geniculate body (corpus geniculatum laterale); 6b - pulvinar of the thalamus; 6c - superior colliculus of the Midbrain tectum (colliculus superior tecti mesencephali);

7 - axons of the fourth-order neurons (of the geniculate body and thalamic pulvinar);

8 - calcarine sulcus (sulcus calcarinus);

9 - spinal cord (medulla spinalis);

10 - Pons;

11 - tectospinal tract (tractus tectospinalis);

12 - medial longitudinal fasciculus (fasciculus longitudinalis medialis);

13 - Nucleus of the medial longitudinal fasciculus (nucleus of Darkschewitsch);

14 - ventral ROOT of spinal nerve;

15 - Skeletal Muscle