What Is the Olfactory Nerve?

Olfactory nerve: The olfactory nerve is the sensory nerve, and the primary neuron is a bipolar neuron, which exists in the upper mucosa of the nasal cavity; the surrounding part penetrates the mucosa of the top of the nasal cavity, the upper part of the nasal septum and the inside of the upper nasal nail, forming a ciliated receptor, Its ascending axon forms the olfactory nerve. The first pair of brain nerves. It is composed of olfactory mucosal olfactory cells. The human olfactory nerve contains about 20 olfactory filaments. The olfactory nerve passes the olfactory impulse to the olfactory bulb, and then passes through the olfactory triangle, the anterior penetrating mass, and the transparent septum to the olfactory center.

Olfactory nerve: The olfactory nerve is the sensory nerve, and the primary neuron is a bipolar neuron, which exists in the upper mucosa of the nasal cavity; the surrounding part penetrates the mucosa of the top of the nasal cavity, the upper part of the nasal septum and the inside of the upper nasal nail, forming a ciliated receptor, Its ascending axon forms the olfactory nerve. The first pair of brain nerves. It is composed of olfactory mucosal olfactory cells. The human olfactory nerve contains about 20 olfactory filaments. The olfactory nerve passes the olfactory impulse to the olfactory bulb, and then passes through the olfactory triangle, the anterior penetrating mass, and the transparent septum to the olfactory center.

Chinese name

Olfactory nerve

Foreign name

olfactory nerves

Location

brain

Numbering

I

Overview of the olfactory nerve

The human olfactory nerve begins in the olfactory mucosa of the nasal cavity. The central processes of the olfactory cells first merge and interweave into clumps in the mucosa, and then form 15 to 20 olfactory filaments from the clumps. The olfactory filaments leave the olfactory mucosa, pass through the holes in the ethmoidal plate and enter the anterior cranial fossa, ending at the olfactory bulb. Olfactory cells are both the primary afferent neurons of the olfactory sense and the receiving cells of the olfactory receptors. The olfactory neuron myelin sheath is covered with a double-layered "sheath" formed by the dura mater and arachnoid membrane. The intracranial subarachnoid space can extend through the space under this sheath to the olfactory mucosa. Therefore, some patients with increased intracranial pressure may also experience cerebrospinal fluid leakage from the nasal cavity. When the anterior cranial fossa is broken, the olfactory wire can be torn off, causing an olfactory disorder.

Olfactory nerve anatomy

Functional special sensation (special visceral afferent)-smell. "Smell is a sense of smell that perceives odorous substances dispersed in the environment." The body of olfactory sensory neurons (also known as olfactory neurons or olfactory cells) is located on the nasal septum and the olfactory mucosa of the nasal septum and the inner wall of the upper turbinate. . The central process of bipolar olfactory neurons forms about 20 olfactory nerve fiber bundles, collectively called the olfactory nerve. The olfactory nerve passes through the sieve of the ethmoidal sieve plate, passes through the dura mater and arachnoid membrane, and enters the olfactory bulb of the anterior cranial fossa. The olfactory bulb is located below the frontal lobe or orbital surface of the cerebral hemisphere. The olfactory nerve fibers and the mitral cells of the olfactory bulb form synaptic structures. The axons of the mitral cells form an olfactory bundle, which is divided into two olfactory lines inside and outside. The lateral olfactory pattern stops at the anterior piriform cortex, and the medial olfactory pattern projects through the anterior commissure to the contralateral olfactory-related structure.

Olfactory stimuli can trigger our consciousness activities and make us appreciate the deliciousness of food. At the same time, it can trigger visceral reactions under the regulation of the autonomic nervous system, such as drooling reactions caused by the fragrance of objects.

Olfactory nerve clinical examination

Perform with the patient's cooperation, accurate answers and good nasal ventilation. Pay attention to asking the patient if there is a subjective olfactory disorder such as an olfactory hallucination. Then let the patient close his eyes, press one side of his nostril, and put a volatile substance such as camphor, clove oil or cigarettes, toothpaste, soap, etc. in the nostril of the patient to be tested, let them tell what the smell is or make a comparison. Test separately. Irritating substances such as acetic acid, alcohol, formalin, etc. can stimulate the trigeminal nerve endings, so it cannot be used for olfactory examination; this examination cannot be done if there is inflammation or obstruction in the nasal cavity. Decreased or disappeared smell can be seen in anterior cranial fossa fractures, inflammation of the skull base meninges, tumors in the forehead (such as olfactory meningiomas), and tumors in the saddle. Olfactory disorders are more common in lesions around the olfactory nerve. Central lesions on one side do not cause olfactory disturbances. Hookback irritation can cause hallucinations (hookback attacks), often a precursor to temporal lobe epilepsy.

When clinically needed, ask the patient if they have an olfactory disorder. Then plug the nostrils on one side, and use substances such as camphor, toothpaste, and soap under the nostrils on the other side. Ask them if they smell, and name them. During the examination, pay attention to the contrast between the two sides, pay attention to exclude nasal diseases such as polyps, inflammation, etc., and routine nasal examinations should be performed. Some irritating substances, such as alcohol, ammonia, and acetic acid, cannot be used for olfactory detection. It should also be noted that olfactory cortical damage on one side does not cause olfactory disturbances, as each olfactory cortex accepts olfactory nerve impulses on both sides.

Smell changes are often divided into:

(1) Diminished or disappeared.

(2) Phantom smell.

Olfactory and Olfactory Related Diseases

Olfactory disorder: the main manifestation of olfactory nerve disease. Olfactory disorders include hyposmia, loss of smell, olfactory hallucinations, olfactory allergy, and abnormal smell. Olfactory decline and olfactory loss are mainly seen when the olfactory conduction pathway is blocked; olfactory hallucinations and olfactory allergies are mainly caused by olfactory central lesions. There are many reasons for olfactory disorders. In addition to those with olfactory nervous system disease, there are many other diseases that can also produce olfactory disorders, such as certain upper respiratory tract diseases that cause loss of smell, certain brain trauma and mass lesions Vascular diseases can also be caused. Some psychiatric patients (hysteresis, etc.) can have various olfactory disorders, and some are caused by congenital deficiency. Clinically important is the olfactory disorder caused by intracranial space-occupying lesions. Early detection is important for early diagnosis.