NERVE SUPPLY TO LACRIMAL GLAND MADE EXTREMELY EASY !
SENSORY NERVE SUPPLY TO THE LACRIMAL GLAND
To kick things off, let’s start with the sensory nerve supply to the lacrimal gland. To understand this, we need to first familiarize ourselves with the fifth cranial nerve, known as the trigeminal nerve, which has three divisions.
- The ophthalmic division (V1) enters the orbit through the superior orbital fissure.
- The Maxillary Division (V2) enters through the foramen rotundum.
- The mandibular division (V3) enters through the foramen ovale.
To understand the sensory nerve supply to the lacrimal glands, we’ll focus on the ophthalmic division (V1). The sensory innervation of the lacrimal gland primarily comes from the lacrimal nerve, the smallest branch of the ophthalmic division. This lacrimal nerve has a connection with either the zygomatic nerve or the zygomaticotemporal nerve, which are branches of the maxillary division (V2) of the trigeminal nerve.
CLINICAL POINT:Â LACRIMAL NERVE FINAL COMMON PATHWAY TO LACRIMAL GLAND?
Although the lacrimal nerve individually gives the sensory innervation to the lacrimal gland, it gets involved in the parasympathetic and sympathetic nerve supply to the lacrimal gland as well due to its connection with the zygomatic nerve.
PARASYMPATHETIC NERVE SUPPLY TO THE LACRIMAL GLAND
To understand the parasympathetic nerve supply to the lacrimal gland, we need to dive deep into the basics and understand the relevant anatomy of the facial nerve.
Relevant Facial Nerve Anatomy
The facial nerve, the 7th cranial nerve, arises from the pons in the brainstem. It is a mixed cranial nerve (having both sensory and motor components).
It has three nuclei:
- MOTOR NUCLEUS
- SUPERIOR SALIVATORY NUCLEUS/ PARASYMPHATHETIC NUCLEUS
- NUCLEUS TRACTUS SOLITARIUS
The motor nucleus of the facial nerve forms a facial colliculus around the vestibulocochlear nerve, which also takes its origin from the pons. It supplies the muscles of mastication and facial expression. Therefore, these fibers coming out of the motor nucleus are known as the BRACHIAL EFFERENT FIBRES.
The parasympathetic/salivatory nucleus supplies the secretory component of innervation to the lacrimal gland, sublingual gland, submandibular gland, palatine gland, and nasal glands. Therefore, the fibers coming from the parasympathetic nucleus or secretory nucleus are called the general and visual factors.Â
The nucleus tractus solitarius is a sensory nucleus associated with receiving taste sensations from the anterior 2/3rd of the tongue and palate. Therefore, these fibers that are coming to the nucleus tractus solitarius are called SPECIAL VISCERAL AFFERENTS (remember, taste is special).
Often, books mention another nucleus—the spinal nucleus of the trigeminal nerve—when they mention the facial nerve. But it’s important not to get confused. It belongs to the trigeminal nerve and not the facial nerve. To learn more about this, you can check out the fun video on our channel.
Lacrimatory Nucleus
The journey of parasympathetic nerve supply to the lacrimal gland starts here! The superior salivatory nucleus has two parts. The superior part is called the lacrimatory nucleus since it is associated with the parasympathetic supply to the lacrimal gland. The inferior part of the superior salivatory nucleus is associated with the parasympathetic nerve supply of other salivary glands (not of importance to us here!). The fibers from the lacrimatory nucleus travel in a common sheath with the fibers of the nucleus tractus solitarius and the fibers of the spinal nucleus of the trigeminal nerve. These three together are called the NERVUS INTERMEDIUS. Note that the motor fibers from the motor nucleus of the trigeminal nerve are not a part of the nervus intermedius.
To know more about this you can check the fun video on our channel .Â
Course Of The Parasympathetic Nerve Fibres
the parasympathetic fibres that took origin from the lacrimatory nucleus, travel in nervus intermedius and now they enter the Internal acoustic meatus , an opening present in the petrous part of temporal bone. Traveling inside the petrous bone it reaches the anterior part of the medial wall of The middle ear. (Check 12:02 of the video)
From this location, it enters the bony canal or facial canal in the middle ear.
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Geniculate Ganglion
Let’s make a point that motor fibers also travel with the nervus intermedius in the same way and reach the anterior part of the medial wall of the middle ear. Just before the facial nerve enters the facial canal, it meets a ganglion there called the GENICULATE GANGLION.Â
The motor fibers travel through the geniculate ganglion, enter the facial canal, and continue on their journey to supply the facial muscles. But the parasympathetic fibers take a separate route at this point from the geniculate ganglion. Instead of traveling with the motor fibers, they separated, and now they are called the GREATER PETROSAL NERVE, which chooses to enter the cranial cavity instead of entering the middle ear.
GENICULATE GANGION is not a PARASYMPATHETIC GANGLION!! It is a sensory ganglion. Therefore the parasympathetic fibres do not relay in it !
Greater Petrosal Nerve , Deep Petrosal Nerve and Vidian Nerve
The parasympathetic nerve supply from the superior salivatory nucleus (lacrimatory nucleus) separates from the motor route at the level of the geniculate ganglion and is now renamed the greater petrosal nerve. It enters the cranial cavity through the foramen lacerum. Soon it encounters another opening in the cranial cavity to a canal called the PTERYGOID CANAL. The pterygoid canal is a canal that leads to the pterygopalatine fossa in the skull.
Quite interestingly, the greater petrosal nerve, after entering the foramen lacerum, encounters an internal carotid artery with sympathetic nerve supply to the lacrimal gland (which comes from the superior cervical ganglion) entwined around it. These sympathetic fibres are called the DEEP PETROSAL NERVE .Â
Both the parasympathetic (greater petrosal) and sympathetic nerve supply(deep petrosal) nerves ultimately have to reach the lacrimal gland. so they both join together as they enter the pterygoid canal. As they merge together, we get a NERVE TO PTERYGOID CANAL / VIDIAN NERVE.
Pterygopalatine Fossa And Pterygopalatine Ganglion
The Vidian nerve finally enters the space called the pterygopalatine fossa, a triangular space between the orbit and maxillary bone, harboring the pterygopalatine ganglion.
The pterygopalatine/sphenopalatine ganglion is the parasympathetic ganglion where the parasympathetic fibers relay.
Therefore, till now, we have discussed the preganglionic parasympathetic fibers and how they reached the ganglion. From here, we discuss the postganglionic fibers.
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Post Ganglionic Fibres And Zygomatic Nerve
The postganglionic fibers finally merge with the zygomatic nerve (a branch of the V2 division). As mentioned above, the zygomatic nerve has a connection to the lacrimal nerve, and it is through this connection that the parasympathetic fibers are going to finally reach the lacrimal nerve.
Sympathetic Nerve Supply to the Lacrimal Gland
The sympathetic innervation of the lacrimal gland starts in the superior cervical ganglion. The post-synaptic fibers travel with the internal carotid artery before joining the greater petrosal to form the vidian nerve. The sympathetic fibers do not synapse again with the sphenopalatine ganglion but continue with the parasympathetic ganglion to finally reach the lacrimal gland through the lacrimal nerve.
