The submandibular ganglion is a small parasympathetic ganglion involved in regulating the autonomic functions of the submandibular and sublingual salivary glands. It is part of the parasympathetic nervous system and receives preganglionic fibers from the facial nerve (cranial nerve VII), specifically through its branch, the chorda tympani.
Location
The submandibular ganglion is located on the medial side of the mandible, suspended from the lingual nerve, a branch of the mandibular division of the trigeminal nerve (V3). It is situated near the submandibular gland, close to the posterior border of the mylohyoid muscle, and lies in proximity to both the sublingual and submandibular salivary glands. This location allows the ganglion to provide parasympathetic innervation to these glands.
Structure and Anatomy
The submandibular ganglion is an important parasympathetic ganglion that plays a crucial role in the autonomic control of the salivary glands. Below is a detailed description of its anatomy.
Structure and Composition
The submandibular ganglion is a small, oval-shaped parasympathetic ganglion. It contains the cell bodies of postganglionic parasympathetic neurons, where preganglionic parasympathetic fibers synapse. The ganglion is part of the parasympathetic nervous system and primarily serves to control the secretion of saliva from the submandibular and sublingual glands.
Relations to Other Structures
The submandibular ganglion has several important anatomical relationships with nearby structures:
- Lingual Nerve (V3): The ganglion is suspended from the lingual nerve, which carries sensory fibers from the anterior two-thirds of the tongue and provides a pathway for parasympathetic fibers to reach the submandibular and sublingual glands. While the lingual nerve itself is sensory, it serves as a conduit for parasympathetic fibers that pass through the submandibular ganglion.
- Submandibular Gland: The submandibular ganglion lies in close proximity to the submandibular gland, which is its primary target for parasympathetic innervation.
- Sublingual Gland: Although primarily associated with the submandibular gland, the submandibular ganglion also sends fibers to the sublingual gland, which is situated near the floor of the mouth.
- Mylohyoid Muscle: The ganglion is located close to the posterior border of the mylohyoid muscle, a muscle that forms the floor of the mouth and acts as an important landmark for the ganglion’s position.
Nerve Connections
The submandibular ganglion has important connections with several nerves that allow it to function as a relay station for parasympathetic fibers.
Preganglionic Parasympathetic Fibers
The preganglionic parasympathetic fibers that synapse in the submandibular ganglion arise from the superior salivatory nucleus in the brainstem. These fibers travel via the facial nerve (cranial nerve VII), specifically through its branch, the chorda tympani. The chorda tympani joins the lingual nerve (a branch of the mandibular nerve, V3) and carries the preganglionic fibers to the submandibular ganglion, where they synapse with postganglionic neurons.
Postganglionic Parasympathetic Fibers
After synapsing in the submandibular ganglion, the postganglionic parasympathetic fibers leave the ganglion and travel to the submandibular and sublingual glands, where they stimulate the secretion of saliva. These fibers reach the glands by traveling alongside the ducts that lead to the oral cavity, ensuring a direct and efficient parasympathetic response.
Sensory Fibers from the Lingual Nerve
Although the submandibular ganglion primarily functions as part of the parasympathetic system, it is anatomically connected to the lingual nerve, which carries sensory fibers from the anterior two-thirds of the tongue. The lingual nerve does not contribute sensory fibers to the ganglion, but it serves as a physical link, suspending the ganglion and providing a pathway for the parasympathetic fibers.
Sympathetic Fibers
The submandibular ganglion also receives sympathetic fibers, although they do not synapse within the ganglion. These sympathetic fibers are derived from the superior cervical ganglion and travel along the external carotid artery and its branches. The sympathetic fibers regulate blood flow to the submandibular and sublingual glands by constricting blood vessels, helping to control glandular function, particularly during stress.
Ganglionic Input and Output
- Input (Afferent): The primary afferent input to the submandibular ganglion comes from the chorda tympani, which carries preganglionic parasympathetic fibers from the facial nerve. These fibers synapse in the ganglion to relay parasympathetic signals to the salivary glands.
- Output (Efferent): The main efferent output from the submandibular ganglion is to the submandibular and sublingual glands. Postganglionic parasympathetic fibers travel to these glands to regulate salivary secretion. Additionally, sympathetic fibers pass through the ganglion but do not synapse there, as they travel to the same target glands to modulate blood flow and secretion.
Branches of the Submandibular Ganglion
The submandibular ganglion has several important branches that distribute postganglionic fibers to their target organs:
- Glandular Branches: These branches carry postganglionic parasympathetic fibers to the submandibular gland. These fibers directly stimulate the secretion of saliva from the acinar cells of the gland.
- Sublingual Branches: Additional branches extend to the sublingual gland, which lies in the floor of the mouth. These fibers help regulate saliva production from the sublingual gland.
Vascular Supply
The submandibular ganglion receives its blood supply from nearby arteries, including branches of the lingual artery and the facial artery. These arteries also supply blood to the submandibular and sublingual glands, ensuring that the ganglion and its target organs receive adequate nourishment.
Histological Structure
Microscopically, the submandibular ganglion consists of neuronal cell bodies, where synapses between preganglionic and postganglionic parasympathetic fibers occur. These neurons are supported by glial cells and a connective tissue matrix. The ganglion’s small size and close proximity to the target glands enable efficient signal transmission, ensuring timely parasympathetic control of salivary secretion.
Connections with Other Autonomic Plexuses
The submandibular ganglion is connected to the broader autonomic nervous system, particularly through its interaction with other parasympathetic and sympathetic fibers:
- Superior Cervical Ganglion: Sympathetic fibers that influence the submandibular and sublingual glands arise from the superior cervical ganglion and travel along the external carotid artery. These fibers do not synapse in the submandibular ganglion but contribute to the regulation of glandular blood flow.
- Facial Nerve (VII): The facial nerve, via its branch, the chorda tympani, provides the preganglionic parasympathetic input to the submandibular ganglion. The facial nerve’s involvement is crucial for the parasympathetic control of saliva production.
Function
The submandibular ganglion is responsible for regulating the autonomic functions of the submandibular and sublingual salivary glands, playing a key role in controlling saliva secretion. It is part of the parasympathetic nervous system, specifically under the influence of the facial nerve. Below is a detailed explanation of the submandibular ganglion’s functions.
Parasympathetic Control of Saliva Production
The primary function of the submandibular ganglion is to regulate the secretion of saliva from the submandibular and sublingual glands. This is achieved through parasympathetic fibers that originate from the facial nerve (cranial nerve VII), specifically via the chorda tympani branch.
Preganglionic Parasympathetic Innervation
The preganglionic parasympathetic fibers arise from the superior salivatory nucleus in the brainstem. These fibers travel through the facial nerve (cranial nerve VII) and then via the chorda tympani. The chorda tympani joins the lingual nerve (a branch of the mandibular division of the trigeminal nerve, V3) and carries preganglionic fibers to the submandibular ganglion.
Synapse in the Submandibular Ganglion
The preganglionic parasympathetic fibers synapse with postganglionic neurons within the submandibular ganglion. This synapse is crucial for transmitting parasympathetic signals to the target organs, the submandibular and sublingual glands.
Postganglionic Parasympathetic Fibers
After synapsing in the ganglion, the postganglionic parasympathetic fibers travel to the submandibular and sublingual glands. These fibers stimulate the acinar cells within the glands to produce and secrete saliva. In response to parasympathetic stimulation, the glands secrete watery, enzyme-rich saliva, which plays an important role in digestion and maintaining oral hygiene.
Regulation of Salivary Secretion
The submandibular ganglion ensures that the submandibular and sublingual glands secrete saliva in response to physiological needs, particularly during eating and speaking.
Increased Saliva Production
The parasympathetic stimulation mediated by the submandibular ganglion causes an increase in saliva production when needed, such as in response to taste or chewing. The increase in watery saliva helps in the lubrication of food, making it easier to chew and swallow. Saliva also contains digestive enzymes like amylase, which begin the process of carbohydrate breakdown in the mouth.
Maintenance of Oral Health
Salivary production controlled by the submandibular ganglion also plays a crucial role in maintaining oral hygiene. By constantly producing a baseline level of saliva, the salivary glands help wash away food particles and bacteria, keeping the oral cavity clean. Saliva contains enzymes and antibodies that help protect the mouth from infections.
Interaction with Sensory Inputs
The submandibular ganglion is involved in reflex responses to sensory stimuli, such as taste and smell, which affect saliva production.
Taste-Induced Salivation
The taste of food strongly influences salivation. Sensory information from the anterior two-thirds of the tongue, carried by the chorda tympani (a branch of the facial nerve), plays a significant role in triggering increased salivation. When food is tasted, parasympathetic fibers are activated, and the submandibular and sublingual glands are stimulated to secrete saliva in anticipation of digestion.
Smell-Induced Salivation
In addition to taste, the smell of food can also activate parasympathetic signals that pass through the submandibular ganglion. This reflex prepares the digestive system by increasing salivary production, even before food is ingested.
Sympathetic Modulation of Salivary Glands
Although the submandibular ganglion primarily handles parasympathetic signals, it also plays a role in the sympathetic regulation of the salivary glands.
Sympathetic Fibers Passing Through the Ganglion
Sympathetic fibers, originating from the superior cervical ganglion, pass through the submandibular ganglion without synapsing. These fibers travel along the external carotid artery and its branches to reach the salivary glands. The sympathetic fibers regulate the vascular supply to the glands, controlling blood flow to the salivary tissues.
Decreased Saliva Production
During sympathetic stimulation, such as in stressful situations, the submandibular and sublingual glands produce thicker, mucous-rich saliva rather than the watery type stimulated by parasympathetic activity. Sympathetic activity tends to decrease overall saliva production, leading to the sensation of a dry mouth, which is common in stressful or anxiety-inducing situations. This response is part of the body’s fight or flight mechanism, where digestive functions, including saliva production, are reduced to conserve energy for other immediate needs.
Role in Secretory Reflexes
The submandibular ganglion is involved in several autonomic reflexes that control salivary secretion in response to various stimuli.
Cephalic Phase of Digestion
The submandibular ganglion contributes to the cephalic phase of digestion, which refers to the anticipatory response of the digestive system to the sight, smell, or thought of food. Parasympathetic stimulation through the submandibular ganglion causes an increase in saliva production even before food enters the mouth. This reflex prepares the mouth and digestive system for food intake.
Salivation Reflex
The ganglion is also involved in the salivation reflex, triggered by food in the mouth. When food is chewed, sensory input from the tongue and oral cavity (carried by the chorda tympani and lingual nerve) activates the parasympathetic pathway via the submandibular ganglion, leading to an increase in salivary output. This reflex ensures the food is properly moistened for easier swallowing and digestion.
Coordination with the Trigeminal Nerve (V3)
The submandibular ganglion has a close anatomical and functional relationship with the lingual nerve, a branch of the mandibular division of the trigeminal nerve (V3).
Conduit for Parasympathetic Fibers
Although the lingual nerve itself is a sensory nerve, it serves as a conduit for the parasympathetic fibers of the submandibular ganglion. These fibers hitch a ride on the lingual nerve to reach the submandibular and sublingual glands. This arrangement allows for efficient communication between the parasympathetic nervous system and the salivary glands.
Sensory Integration
The lingual nerve provides sensory innervation to the anterior two-thirds of the tongue, allowing it to relay taste and tactile information. This sensory input is integrated with the autonomic function of the submandibular ganglion, enabling the glands to respond appropriately to stimuli in the mouth.
Clinical Significance
The submandibular ganglion plays a crucial role in the parasympathetic regulation of the submandibular and sublingual glands, which are responsible for producing saliva. Its dysfunction or damage can lead to several clinical conditions:
Xerostomia (Dry Mouth)
Damage to the submandibular ganglion or its parasympathetic pathways can result in xerostomia, a condition characterized by a reduction in salivary secretion. This can lead to difficulties in chewing, swallowing, and speaking, as well as an increased risk of oral infections, dental decay, and gum disease.
Sialadenitis (Salivary Gland Inflammation)
Infections or blockages of the submandibular or sublingual glands can result in sialadenitis, where inflammation leads to swelling, pain, and decreased saliva production. Parasympathetic dysfunction may exacerbate this condition by impairing the normal secretion of saliva.
Nerve Damage During Surgery
Surgical procedures in the floor of the mouth, particularly during submandibular gland removal or neck surgeries, can injure the submandibular ganglion or its parasympathetic fibers. This may result in hypofunction of the salivary glands and subsequent xerostomia.
