The nerve of the pterygoid canal, also known as Vidian nerve, is formed by the union of two nerves: the greater petrosal nerve (a parasympathetic nerve) and the deep petrosal nerve (a sympathetic nerve). It carries both parasympathetic and sympathetic fibers to the pterygopalatine ganglion, which innervates structures such as the lacrimal gland and nasal mucosa.
Location
The nerve of the pterygoid canal is located in the pterygoid canal, which lies within the base of the sphenoid bone. It originates at the junction of the foramen lacerum and the petrous portion of the temporal bone and travels anteriorly through the pterygoid canal towards the pterygopalatine fossa, where it connects to the pterygopalatine ganglion.
Structure and Anatomy
The nerve of the pterygoid canal, also known as the Vidian nerve, is a mixed autonomic nerve that plays an important role in supplying both sympathetic and parasympathetic fibers to the structures of the head and face, including the lacrimal gland and nasal mucosa. Below is a detailed description of its anatomy.
Formation
The nerve of the pterygoid canal is formed by the convergence of two nerves:
- Greater Petrosal Nerve: This nerve carries preganglionic parasympathetic fibers from the facial nerve (cranial nerve VII). It arises from the geniculate ganglion in the facial nerve and travels toward the foramen lacerum.
- Deep Petrosal Nerve: This nerve carries postganglionic sympathetic fibers that originate from the superior cervical ganglion and travel along the internal carotid artery’s plexus. It reaches the foramen lacerum where it joins the greater petrosal nerve.
The union of the greater petrosal nerve and the deep petrosal nerve forms the nerve of the pterygoid canal.
Course
- Origin: The nerve originates at the junction of the greater petrosal nerve and the deep petrosal nerve, which occurs near the foramen lacerum, a structure located at the base of the skull.
- Passage Through the Pterygoid Canal: After its formation, the nerve enters the pterygoid canal, which is located within the sphenoid bone. The pterygoid canal is also known as the Vidian canal and lies medial to the pterygoid plates of the sphenoid bone.
- Exit and Termination: The nerve exits the pterygoid canal at the anterior end and enters the pterygopalatine fossa, where it communicates with the pterygopalatine ganglion. This ganglion lies just below the maxillary nerve (V2) and is a major relay center for autonomic fibers destined for various facial structures.
Nerve Components
The nerve of the pterygoid canal carries both parasympathetic and sympathetic fibers:
- Parasympathetic Fibers: These originate from the greater petrosal nerve, a branch of the facial nerve. They are preganglionic fibers that synapse in the pterygopalatine ganglion before continuing to their target organs.
- Sympathetic Fibers: These come from the deep petrosal nerve, which originates from the sympathetic plexus around the internal carotid artery. The sympathetic fibers are postganglionic and pass through the pterygopalatine ganglion without synapsing, continuing to their target tissues.
Relations to Other Structures
The nerve of the pterygoid canal is situated near several important anatomical structures:
- Foramen Lacerum: The nerve begins its course near the foramen lacerum, a gap at the base of the skull through which the greater petrosal nerve travels. Although the foramen lacerum is closed by cartilage in living individuals, it serves as a landmark for the origin of the nerve of the pterygoid canal.
- Pterygoid Canal: The nerve travels through the pterygoid canal, a bony passage located within the sphenoid bone, medial to the medial pterygoid plate.
- Pterygopalatine Fossa: After exiting the pterygoid canal, the nerve enters the pterygopalatine fossa, a space located between the pterygoid process of the sphenoid bone and the maxilla. This fossa contains the pterygopalatine ganglion and is a hub for the distribution of autonomic and sensory fibers to the face.
- Pterygopalatine Ganglion: The nerve of the pterygoid canal reaches the pterygopalatine ganglion, where the parasympathetic fibers synapse. The sympathetic fibers pass through this ganglion without synapsing and continue to their target tissues.
Connections
The nerve of the pterygoid canal connects with several key structures as part of the autonomic supply to the head:
- Pterygopalatine Ganglion: The parasympathetic fibers synapse in the pterygopalatine ganglion, while the sympathetic fibers pass through without synapsing. The ganglion then distributes autonomic fibers to the lacrimal glands, nasal mucosa, palate, and pharynx.
- Maxillary Nerve (V2): The pterygopalatine ganglion lies just below the maxillary nerve, and some of the autonomic fibers from the pterygopalatine ganglion hitch a ride with branches of the maxillary nerve to reach their target tissues.
- Greater Palatine Nerve: Some fibers from the nerve of the pterygoid canal travel with the greater palatine nerve to supply the palate and the nasal cavity.
- Zygomatic Nerve: Fibers destined for the lacrimal gland pass through the zygomatic nerve and then transfer to the lacrimal nerve (a branch of the ophthalmic division of the trigeminal nerve, V1) to provide secretomotor innervation to the gland.
Branches and Distribution
The nerve of the pterygoid canal distributes both parasympathetic and sympathetic fibers to various structures:
- Lacrimal Gland: Parasympathetic fibers synapse in the pterygopalatine ganglion and travel to the lacrimal gland via branches of the maxillary and ophthalmic nerves. Sympathetic fibers pass through the pterygopalatine ganglion without synapsing and follow the same pathway to regulate blood flow in the gland.
- Nasal Mucosa: The nerve supplies autonomic fibers to the nasal mucosa, aiding in the regulation of mucus production and vascular tone.
- Palate: Fibers from the nerve of the pterygoid canal reach the palate, helping regulate glandular secretions in the oral cavity.
- Pharynx: The nerve also sends fibers to the pharynx, where it participates in controlling the mucosal secretions and blood vessels.
Vascular Supply
The nerve of the pterygoid canal is closely related to the internal carotid artery, as the deep petrosal nerve arises from the sympathetic plexus that surrounds the internal carotid artery. The pterygopalatine fossa, where the nerve terminates, receives blood supply from branches of the maxillary artery.
Histological Structure
Microscopically, the nerve of the pterygoid canal consists of both myelinated and unmyelinated fibers. The parasympathetic fibers from the greater petrosal nerve are preganglionic and myelinated, while the sympathetic fibers from the deep petrosal nerve are postganglionic and unmyelinated.
Function
The nerve of the pterygoid canal (Vidian nerve) carries both parasympathetic and sympathetic fibers, making it a key player in autonomic innervation to several facial and cranial structures. It regulates secretory functions in the lacrimal glands, nasal mucosa, and palate, as well as vascular tone. Below is a detailed explanation of the nerve’s functions based on its parasympathetic and sympathetic components.
Parasympathetic Functions
The parasympathetic component of the nerve of the pterygoid canal originates from the greater petrosal nerve, a branch of the facial nerve (cranial nerve VII). These preganglionic parasympathetic fibers synapse in the pterygopalatine ganglion before innervating their target structures.
Lacrimal Gland Stimulation
The parasympathetic fibers of the nerve of the pterygoid canal play a critical role in stimulating tear production by the lacrimal gland. After synapsing in the pterygopalatine ganglion, postganglionic fibers travel via the zygomatic nerve (a branch of the maxillary nerve, V2) and the lacrimal nerve (a branch of the ophthalmic nerve, V1) to reach the lacrimal gland. Activation of these fibers leads to tear secretion, which helps to maintain moisture on the surface of the eye and protects the cornea from irritation and infection.
Nasal Gland Secretion
The parasympathetic fibers also innervate the glands of the nasal mucosa, promoting the secretion of mucus. This is crucial for maintaining the moisture and function of the nasal passages. Increased parasympathetic activity, mediated through the nerve of the pterygoid canal, leads to enhanced mucus production, helping to humidify inhaled air and trap particulate matter. The fibers reach the nasal mucosa via branches from the pterygopalatine ganglion that follow the greater palatine nerve and other branches of the maxillary nerve (V2).
Palatal Gland Secretion
The parasympathetic component of the nerve of the pterygoid canal also provides innervation to the palatal glands. These glands, located in the hard and soft palate, secrete mucus to help lubricate the oral cavity and facilitate swallowing. This innervation ensures that the mucosal surfaces of the palate remain moist, contributing to oral health and comfort during speech and eating.
Pharyngeal Gland Secretion
Parasympathetic fibers also reach the pharyngeal mucosa, where they stimulate the secretion of mucus, helping to maintain the moisture of the pharynx and facilitate the passage of food during swallowing. These fibers travel via the pharyngeal branch of the pterygopalatine ganglion to reach the pharynx.
Sympathetic Functions
The sympathetic fibers in the nerve of the pterygoid canal originate from the deep petrosal nerve, which carries postganglionic sympathetic fibers from the superior cervical ganglion. These fibers do not synapse in the pterygopalatine ganglion; instead, they pass through the ganglion and continue to their target tissues, where they regulate vascular tone.
Vasoconstriction in the Lacrimal Gland
The sympathetic fibers innervating the lacrimal gland regulate the blood vessels supplying the gland. Sympathetic activation causes vasoconstriction, reducing blood flow to the gland, which in turn reduces tear production. This response is typically seen in stressful situations, where sympathetic activity increases, causing a decrease in fluid secretion.
Vasoconstriction in the Nasal Mucosa
In the nasal mucosa, the sympathetic fibers control the vasoconstriction of blood vessels. This reduces the blood flow to the nasal glands, leading to decreased mucus production. The sympathetic response can be observed in situations such as stress or cold exposure, where reduced nasal secretions result in a dry nasal passage.
Vasoconstriction in the Palatal and Pharyngeal Mucosa
Sympathetic fibers passing through the pterygopalatine ganglion also regulate blood flow to the palatal and pharyngeal glands. When these fibers are activated, vasoconstriction occurs, reducing glandular secretion and contributing to a dry mouth or throat during stress or dehydration. This is part of the body’s overall fight or flight response, conserving fluids and reducing non-essential secretions.
Regulation of Glandular Secretions
The nerve of the pterygoid canal provides a balance between parasympathetic stimulation, which promotes glandular secretion, and sympathetic stimulation, which inhibits secretion and constricts blood vessels. This dynamic regulation ensures that the mucosal surfaces of the eye, nose, palate, and pharynx remain well-hydrated during rest and are appropriately modulated during stress or increased sympathetic activity.
Balance Between Parasympathetic and Sympathetic Functions
The balance between the parasympathetic and sympathetic innervation via the nerve of the pterygoid canal allows for precise control over secretions in response to the body’s needs. For instance, during eating or exposure to irritants, parasympathetic activity increases to enhance tear and mucus production, protecting the mucosal surfaces. Conversely, during stress or cold conditions, sympathetic activity predominates, reducing secretions to conserve fluids and maintain normal function.
Role in Reflex Pathways
The nerve of the pterygoid canal participates in reflex pathways that control glandular secretions in response to sensory stimuli such as taste, smell, and irritants.
Taste and Smell-Induced Salivation
When food is tasted or smelled, parasympathetic signals are sent through the nerve of the pterygoid canal to increase salivary, nasal, and lacrimal secretions. This reflex is part of the cephalic phase of digestion, preparing the body for food intake by increasing glandular secretions in the mouth, nose, and eyes.
Protective Reflexes
The parasympathetic fibers within the nerve of the pterygoid canal also help facilitate protective reflexes, such as tearing and increased nasal secretions in response to irritants like smoke or allergens. This enhances the clearance of particles from the eye and nasal passages.
Connections with the Pterygopalatine Ganglion
The pterygopalatine ganglion serves as the relay station for parasympathetic fibers carried by the nerve of the pterygoid canal. The parasympathetic fibers synapse in the ganglion, while the sympathetic fibers pass through without synapsing.
Distribution to Facial Structures
After synapsing in the pterygopalatine ganglion, the parasympathetic fibers are distributed to target organs such as the lacrimal gland, nasal mucosa, palate, and pharynx. The sympathetic fibers follow the same pathways, regulating vascular tone in these structures.
Clinical Significance
The nerve of the pterygoid canal (Vidian nerve) plays a critical role in autonomic regulation of the lacrimal glands, nasal mucosa, and palate through its parasympathetic and sympathetic fibers. Dysfunction or damage to the nerve can lead to several clinical conditions:
Vidian Neuralgia
This rare condition involves severe facial pain along the distribution of the nerve. It may be triggered by inflammation, trauma, or compression of the nerve, causing intense discomfort around the nose, eyes, and upper palate.
Dry Eye and Dry Nose
Damage to the parasympathetic fibers of the nerve can result in decreased tear production (dry eye) and reduced mucus secretion in the nasal passages (dry nose). This can occur due to surgery, trauma, or inflammatory conditions affecting the pterygoid canal or pterygopalatine fossa.
Surgical Considerations
The nerve of the pterygoid canal is important in procedures involving the pterygopalatine fossa or sinonasal surgeries. Care must be taken to avoid injury to the nerve, which could result in autonomic dysfunction such as reduced tear production or nasal dryness.
