Logan Steele
The facial nerve, or cranial nerve 7 (CN VII), is a nerve in the human head that controls several muscles in the face, including those that help us smile, frown, wrinkle our nose, and raise our eyebrows. It is responsible for providing motor innervation to the facial muscles, enabling various facial expressions and oral communication. The facial nerve also has sensory and parasympathetic functions, such as taste sensation and tear production. It arises from the brain stem and extends posteriorly and anteriorly, branching into five terminal branches that control specific muscles and functions.
| Characteristics | Values |
|---|---|
| Nerve type | Facial nerve (CN VII) |
| Nerve composition | Motor, sensory and parasympathetic components |
| Nerve fibres | Special visceral efferent (SVE) fibres, general visceral efferent (GVE) fibres, sensory nerve fibres |
| Nerve branches | Posterior auricular nerve, nerve to the posterior belly of the digastric muscle, nerve to the stylohyoid muscle, temporal, zygomatic, buccal, marginal mandibular, cervical |
| Nerve functions | Motor innervation of facial muscles, parasympathetic innervation of glands of the oral cavity, sensory innervation of the anterior two-thirds of the tongue, taste sensation, hearing |
| Nerve damage | Bell's palsy, Ramsay Hunt syndrome, hemifacial spasm, facial nerve palsy |
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What You'll Learn
Facial nerve anatomy and functions
The facial nerve, or CN VII, is the seventh cranial nerve. It arises from the brain stem and extends posteriorly to the abducens nerve and anteriorly to the vestibulocochlear nerve. The facial nerve is comprised of three nuclei: general visceral efferent, special visceral afferent, and general somatic afferent. The upper motor neuron (UMN) of the facial nerve is located in the primary motor cortex of the frontal lobe. The facial nerve provides motor innervation of the facial muscles responsible for facial expressions, parasympathetic innervation of the glands of the oral cavity and the lacrimal gland, and sensory innervation of the anterior two-thirds of the tongue.
The nerve of the pterygoid canal passes through the pterygoid canal (Vidian canal) to enter the pterygopalatine fossa and synapses with the pterygopalatine ganglion. Branches from this ganglion provide parasympathetic innervation to the mucous glands of the oral cavity, nose, and pharynx, and the lacrimal gland. The chorda tympani also carries some parasympathetic fibres, which combine with the lingual nerve in the infratemporal fossa to form the submandibular ganglion.
The facial nerve has a complex course with many branches, which transmit a combination of sensory, motor, and parasympathetic fibres. The nerve arises in the pons, an area of the brainstem, and exits through the stylomastoid foramen, after which it divides into terminal branches at the posterior edge of the parotid gland. Within the parotid gland, the nerve terminates by splitting into five branches, which innervate the muscles of facial expression.
The facial nerve can be divided into two parts: intracranial and extracranial. The intracranial course of the nerve involves the nerve passing through the cranial cavity and the cranium. The extracranial course of the nerve involves the nerve passing through the face and neck. Lesions on the facial nerve can result in a varied set of symptoms, depending on the site of the lesion. Intracranial lesions can cause paralysis or severe weakness of the muscles of facial expression.
The facial nerve also plays a role in emotional facial expressions, which are influenced by the limbic and extrapyramidal systems.
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Facial nerve palsy
The facial nerve is the seventh cranial nerve (CN VII). It is responsible for providing motor innervation to the muscles of facial expression, as well as innervating the stapedius muscle, the stylohyoid muscle, and the posterior belly of the digastric muscle. The facial nerve also carries sensory and parasympathetic fibres, supplying the glands of the oral cavity, the lacrimal gland, and providing taste sensation to the anterior two-thirds of the tongue.
Bell's palsy is the most commonly known cause of facial paralysis, affecting 10 to 40 per 100,000 people. It is characterised by unilateral total palsy, typically presenting as a lower motor neuron lesion. The underlying cause of Bell's palsy is unknown, but it is believed to have links to viral infections. Recovery from Bell's palsy can take up to a year, and in some cases, complete recovery may not be achieved.
Ramsay Hunt syndrome, resulting from Herpes Zoster infection, is another cause of facial nerve palsy. This syndrome affects the geniculate ganglion, leading to facial paralysis and additional symptoms such as otalgia, vesicular eruptions, and vertigo. The prognosis for Ramsay Hunt syndrome is poorer compared to Bell's palsy, with only 21% of patients recovering within 12 months.
The evaluation and management of facial nerve palsy require a comprehensive approach involving healthcare professionals from various disciplines. It is crucial to distinguish between lower motor neuron palsy and upper motor neuron palsy, as the causes and treatments differ significantly. While the cause of facial nerve palsy often remains unknown, early identification and appropriate management are essential for optimising patient outcomes and improving their overall quality of life.
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Facial nerve branches
The facial nerve, also known as Cranial Nerve 7 (CN VII), is a complex structure with many branches that transmit sensory, motor, and parasympathetic fibres. The nerve arises from the brain stem and extends posteriorly to the abducens nerve and anteriorly to the vestibulocochlear nerve.
The facial nerve consists of two parts: the proper facial nerve and the intermediate nerve. The former contains a motor component and a small general somatic afferent component, while the latter carries sensory and parasympathetic visceromotor components. The facial nerve exits the brain stem from its ventrolateral surface at the cerebellopontine angle.
The nerve's course can be divided into two parts: intracranial and extracranial. The intracranial course refers to the nerve's path through the cranial cavity and the cranium, while the extracranial course refers to its path outside the cranium, through the face and neck. The nerve begins as two roots: a large motor root and a small sensory root. These roots travel through the internal acoustic meatus of the temporal bone and enter the facial canal.
The facial nerve then exits the cranium via the stylomastoid foramen and divides into terminal branches at the posterior edge of the parotid gland. These branches are responsible for innervating the muscles of facial expression. Within the parotid gland, the nerve typically terminates by bifurcating into five motor branches:
- Temporal – Controls forehead muscles and includes the frontalis, orbicularis oculi, and corrugator supercilii.
- Zygomatic – Helps close the eyes and includes the orbicularis oculi.
- Buccal – Allows movement of the nose, blinking, raising the upper lip, and smiling.
- Marginal mandibular – Draws the lower lip down and includes the depressor labii inferioris, depressor anguli oris, and mentalis.
- Cervical – Allows movement in the chin and lower lip by controlling the platysma muscle in the neck.
These branches are crucial for various facial expressions and movements, and damage to them can result in specific movement or sensory issues.
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Facial nerve development
The facial nerve, also known as the seventh cranial nerve (CN VII), is responsible for providing motor innervation to the facial muscles, enabling expressions such as smiling and frowning. This nerve develops from the facioacoustic primordium, which forms during the third week of embryonic development.
During the fourth week, the facial nerve splits into two: the chorda tympani and the caudal main trunk. The geniculate ganglion and the nervus intermedius develop at the beginning of the fifth week. The facial muscles themselves originate from the second branchial arch during the seventh and eighth weeks. The peripheral segment of the facial nerve undergoes extensive branching between the 10th and 15th weeks. Ossification of the bony canal housing the nerve occurs from the 16th week until birth.
The facial nerve arises from the brain stem and extends posteriorly to the abducens nerve and anteriorly to the vestibulocochlear nerve. It exits the brain stem from its ventrolateral surface at the cerebellopontine angle. The nerve then courses through the facial canal in the temporal bone and exits through the stylomastoid foramen, after which it divides into terminal branches at the posterior edge of the parotid gland.
The facial nerve is comprised of three nuclei: general visceral efferent, special visceral afferent, and general somatic afferent. The upper motor neuron is located in the facial motor area of the precentral gyrus, specifically in the primary motor cortex of the frontal lobe. Axons from the upper motor neuron travel along the ipsilateral corticobulbar tract to the lower pons, where they cross to the other side and synapse with the lower motor neuron. The main motor nucleus (lower motor neuron) is responsible for voluntary control of the facial muscles and divides into four subnuclei: dorsal, intermediate, lateral, and medial.
The dorsal subnucleus innervates the facial muscles of the ipsilateral upper quadrant, receiving input from both hemispheres of the brain. Conversely, the lateral subnucleus connects to contralateral corticobulbar fibres only, innervating the muscles of the ipsilateral lower quadrant of the face.
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Facial nerve and surgery
The facial nerve, or cranial nerve VII, is responsible for providing motor innervation to the muscles of facial expression. It also provides parasympathetic innervation to the glands of the oral cavity, nose, and pharynx, as well as the lacrimal gland. The facial nerve carries both motor and sensory fibres, with motor axons innervating the muscles of facial expression and the stapedius muscle.
Facial nerve surgery, or reanimation surgery, is often required when a paralysed facial nerve does not recover. This paralysis may occur due to a traumatic head injury, a stroke, or the growth of a benign tumour called a facial neuroma on the seventh cranial nerve. During reanimation surgery, healthy muscles are placed in the correct orientation to allow active facial motion, and blood vessels and nerves are connected to native vessels and healthy nerves in the face. These procedures are performed under general anaesthesia.
The recovery time for reanimation procedures varies depending on the specific procedure, the patient's age and health, and the duration of nerve and muscle paralysis. Facial nerve rehabilitation therapy is crucial for recovery after surgery. Patients may be referred to specialised facial physical therapists to aid in the recovery process. It may take more than a year for a patient to experience the full benefits of the procedure, and additional procedures may be performed concurrently to enhance patient satisfaction.
Facial nerve repair surgery carries certain risks, including injury to other facial structures such as the parotid gland and duct, as well as other facial nerve branches. The most common nerve injured during facelift surgery is the greater auricular nerve, a sensory nerve. The buccal branch of the facial nerve is also susceptible to damage during facelift procedures, but collateral innervation often results in asymptomatic outcomes.
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Frequently asked questions
The facial nerve is the seventh cranial nerve (CN VII). It arises from the brain stem and extends posteriorly to the abducens nerve and anteriorly to the vestibulocochlear nerve.
The facial nerve is responsible for providing motor innervation to the facial muscles, enabling facial expressions such as smiling and frowning. It also has sensory and parasympathetic functions, including taste sensation and tear production.
The facial nerve has five branches with distinct motor functions: Temporal, Zygomatic, Buccal, Marginal Mandibular, and Cervical.
The facial nerve innervates several muscles in the face, including the stapedius muscle, the stylohyoid muscle, the posterior belly of the digastric muscle, and the muscles of facial expression.
When the facial nerve malfunctions, it is often referred to as facial nerve palsy, which means paralysis of the facial nerve. Conditions such as Bell's palsy and Ramsay Hunt syndrome can cause temporary facial paralysis or nerve damage.
