Muscle of facial expression is all innervated (supplied)by facial nerve VII?
A. True***
B. False.
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The facial nerve (VII cranial nerve), is the seventh cranial nerve paired. In this article, the anatomical course of the nerve, and the motor, sensory and parasympathetic functions of its terminal branches will be examined.
The facial nerve is associated with those derived from the second pharyngeal arch.
1- Motor: It innervates the muscles of the facial expression, the posterior belly of the digastric, the hyoid style and the stapedio muscle.
2- Sensory: a small area around the shell of the atrium.
3- Special sensory: provides a special taste sensation to the previous 2/3 of the tongue.
4- Parasympathetic: supplies many of the glands of the head and neck, including:
- Submandibular and sublingual salivary glands.
- Nasal, palatine and pharyngeal mucous glands.
- and the tear glands
Anatomy of the facial nerve:
The course of the facial nerve is very complex. There are many branches, which transmit a combination of sensory, motor and parasympathetic fibers.
Anatomically, the course of the facial nerve can be divided into two parts:
+ This content may interest you: Topographic anatomy, Anatomical models, Oximeter.
- Intracranial: the course of the nerve through the cranial cavity, and the skull itself.
- Extracranial: the course of the nerve outside the skull, through the face and neck
Intracranial:
The nerve arises in the bump, an area of the brainstem. It starts as two roots; a large motor root and a small sensory root (the part of the facial nerve that arises from the sensory root is sometimes known as the intermediate nerve).
The two roots travel through the internal acoustic meatus, an opening 1cm long in the stony part of the temporal bone. Here, they are very close to the inner ear.
Still inside the temporal bone, the roots leave the internal acoustic meatus, and enter the facial canal. The channel is a "Z" shaped structure. Within the facial canal, three important events occur:
- First, the two roots fuse to form the facial nerve.
- Next, the nerve forms the geniculate ganglion (a ganglion is a collection of nerve cell bodies).
- Finally, the nerve leads to:
• Petrosal major nerve: parasympathetic fibers to the mucous and lacrimal glands.
• Stapedio nerve: motor fibers to the staped middle ear muscle.
• Eardrum cord: special sensory fibers in the anterior 2/3 tongue and parasympathetic fibers in the submandibular and sublingual glands.
The facial nerve then leaves the facial canal (and the skull) via the stylomastoid foramen. This is an exit located just behind the styloid process of the temporal bone.
Extracranial:
After leaving the skull, the facial nerve becomes superior when running just before the outer ear.
The first extracranial branch that arises is the posterior atrial nerve. It provides motor innervation to some of the muscles around the ear. Immediately distal to this, the motor branches are sent to the posterior belly of the digastric muscle and the stylohyoid muscle.
The main nerve trunk, now called the motor root of the facial nerve, continues anterior and inferior in the parotid gland (note: the facial nerve does not contribute to the innervation of the parotid gland, which is innervated by the glossopharyngeal nerve).
Within the parotid gland, the nerve ends up dividing into five branches:
- Temporary branch
- Zygomatic branch
- Buccal branch
- The marginal mandibular branch
- Cervical branch
These branches are responsible for innervating the muscles of facial expression that are: occipito-frontal, temporoparietal, orbicularis eye muscle, superciliary corrugator, procer, nasal, risorio, major and minor zygomatic, buccinator, platysma, among others.
Facial nerve functions:
Motor function:
The facial nerve branches are responsible for innervating many of the muscles of the head and neck. All these muscles are derived from the second pharyngeal arch.
The first motor branch arises within the facial canal; The stapedio nerve. The nerve passes through the pyramidal eminence to supply the stapedium muscle in the middle ear.
Between the stomaomastoid foramen and the parotid gland, three more motor branches emerge:
A. True***
B. False.
------------------------
The facial nerve (VII cranial nerve), is the seventh cranial nerve paired. In this article, the anatomical course of the nerve, and the motor, sensory and parasympathetic functions of its terminal branches will be examined.
The facial nerve is associated with those derived from the second pharyngeal arch.
1- Motor: It innervates the muscles of the facial expression, the posterior belly of the digastric, the hyoid style and the stapedio muscle.
2- Sensory: a small area around the shell of the atrium.
3- Special sensory: provides a special taste sensation to the previous 2/3 of the tongue.
4- Parasympathetic: supplies many of the glands of the head and neck, including:
- Submandibular and sublingual salivary glands.
- Nasal, palatine and pharyngeal mucous glands.
- and the tear glands
Anatomy of the facial nerve:
The course of the facial nerve is very complex. There are many branches, which transmit a combination of sensory, motor and parasympathetic fibers.
Anatomically, the course of the facial nerve can be divided into two parts:
+ This content may interest you: Topographic anatomy, Anatomical models, Oximeter.
- Intracranial: the course of the nerve through the cranial cavity, and the skull itself.
- Extracranial: the course of the nerve outside the skull, through the face and neck
Intracranial:
The nerve arises in the bump, an area of the brainstem. It starts as two roots; a large motor root and a small sensory root (the part of the facial nerve that arises from the sensory root is sometimes known as the intermediate nerve).
The two roots travel through the internal acoustic meatus, an opening 1cm long in the stony part of the temporal bone. Here, they are very close to the inner ear.
Still inside the temporal bone, the roots leave the internal acoustic meatus, and enter the facial canal. The channel is a "Z" shaped structure. Within the facial canal, three important events occur:
- First, the two roots fuse to form the facial nerve.
- Next, the nerve forms the geniculate ganglion (a ganglion is a collection of nerve cell bodies).
- Finally, the nerve leads to:
• Petrosal major nerve: parasympathetic fibers to the mucous and lacrimal glands.
• Stapedio nerve: motor fibers to the staped middle ear muscle.
• Eardrum cord: special sensory fibers in the anterior 2/3 tongue and parasympathetic fibers in the submandibular and sublingual glands.
The facial nerve then leaves the facial canal (and the skull) via the stylomastoid foramen. This is an exit located just behind the styloid process of the temporal bone.
Extracranial:
After leaving the skull, the facial nerve becomes superior when running just before the outer ear.
The first extracranial branch that arises is the posterior atrial nerve. It provides motor innervation to some of the muscles around the ear. Immediately distal to this, the motor branches are sent to the posterior belly of the digastric muscle and the stylohyoid muscle.
The main nerve trunk, now called the motor root of the facial nerve, continues anterior and inferior in the parotid gland (note: the facial nerve does not contribute to the innervation of the parotid gland, which is innervated by the glossopharyngeal nerve).
Within the parotid gland, the nerve ends up dividing into five branches:
- Temporary branch
- Zygomatic branch
- Buccal branch
- The marginal mandibular branch
- Cervical branch
These branches are responsible for innervating the muscles of facial expression that are: occipito-frontal, temporoparietal, orbicularis eye muscle, superciliary corrugator, procer, nasal, risorio, major and minor zygomatic, buccinator, platysma, among others.
Facial nerve functions:
Motor function:
The facial nerve branches are responsible for innervating many of the muscles of the head and neck. All these muscles are derived from the second pharyngeal arch.
The first motor branch arises within the facial canal; The stapedio nerve. The nerve passes through the pyramidal eminence to supply the stapedium muscle in the middle ear.
Between the stomaomastoid foramen and the parotid gland, three more motor branches emerge:
- Posterior atrial nerve: ascends in front of the mastoid process, and innervates the intrinsic and extrinsic muscles of the outer ear. It also supplies the occipital part of the Occipitofrontal muscle.
- Nerve to the posterior belly of the digastric muscle: innervates the posterior belly of the digastric muscle (a suprahyoid muscle of the neck). It is responsible for raising the hyoid bone.
- Nerve to the stylohyoid muscle: innervates the stylohyoid muscle (a suprahyoid muscle of the neck). It is responsible for raising the hyoid bone.
Within the parotid gland, the facial nerve ends up branching into five motor branches. These innervate the facial expression muscles:
- Optional branch: innervates the frontal, orbicular muscle of the eyelids and corrugators.
- Zygomatic branch: innervates the orbicularis muscle of the eye.
- The buccal branch: Innervates the orbicular, buccinator and zygomatic muscles.
- Marginal Mandibular Branch: Innervates the chin muscle.
- Cervical branch: Innervates the platysma.
Special sensory functions:
The eardrum branch of the facial nerve is responsible for innervating the anterior 2/3 of the tongue with the special sense of taste.
The nerve arises in the facial canal and travels through the bones of the middle ear, exiting through the petrotympanic fissure and entering the infratemporal fossa. Here, the tympanic branch autos hitchhiking ’with the lingual nerve.
The parasympathetic fibers of the tympanic cord remain with the lingual nerve, but the main body of the nerve stops innervating the anterior 2/3 of the tongue.
Parasympathetic functions:
The parasympathetic fibers of the facial nerve are carried by the most petrosal branches and the tympanic branches.
Petrosal major nerve:
The petrosal major nerve is immediately distal to the geniculate ganglion within the facial canal. Then it moves in the anteromedial direction, leaving the temporal bone in the middle cranial fossa. From here, it travels through (but not through) the foramen lacerum, combining with the deep petrosal nerve to form the nerve of the pterygoid canal.
The nerve of the pterygoid duct then passes through the pterygoid canal (Vidian's canal) to enter the pterygopalatine fossa and synapses with the pterygopalatine ganglion. The branches of this ganglion continue to provide parasympathetic innervation to the mucous glands of the oral cavity, the nose and the pharynx and the lacrimal gland.
Tympanic Branches:
The tympanic branches also carry some parasympathetic fibers. These combine with the lingual nerve (a branch of the trigeminal nerve) in the infratemporal fossa and form the submaxillary ganglion. The branches of this ganglion travel to the submandibular and sublingual salivary glands.
Injuries:
Facial nerve damage:
The facial nerve has a wide range of functions. Thus, nerve damage can produce a varied set of symptoms, depending on the site of the injury.
Intracranial lesions:
Intracranial lesions occur during the intracranial course of the facial nerve (near the stylomastoid hole).
Muscles of facial expression will become paralyzed or severely weakened. The other symptoms produced depend on the location of the lesion and the affected branches:
- Eardrum cord: reduced salivation and loss of flavor in 2/3 ipsilateral of the tongue.
- Stapedio nerve: ipsilateral hyperacusis (hypersensitive to sound).
- Major petrosal nerve: ipsilateral reduced tear fluid production.
The most common cause of an intracranial facial nerve injury is the pathology of the middle ear, such as a tumor or an infection. If a definitive cause cannot be found, the disease is called Bell's palsy.
Extracranial lesions:
Extracranial lesions occur during the extracranial course of the facial nerve (distal to the stylomastoid hole). Only the motor function of the facial nerve is affected, resulting in severe paralysis or weakness of the facial expression muscles.
There are several causes of extracranial facial nerve lesions:
- Pathology of the parotid glands: for example, a tumor, mumps, surgery.
Nerve infection: particularly by the herpes virus.
- Compression during delivery with forceps: the neonatal mastoid process is not - fully developed and does not provide complete nerve protection.
- Idiopathic: if a definitive cause cannot be found, the disease is called Bell's palsy.
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