HYPOGLOSSAL NERVE

· It is the 12th Cranial Nerve
· Motor Nerve
· Supplies all the intrinsic muscles of the tongue, and the

Styloglossus, Geniglossus, Hyoglossus.

FUNCTIONAL COMPONENTS

Somatic Efferent Nuclei

Hypoglossal nucleus lies in the medulla in the floor of the fourth ventricle deep to the hypoglossal triangle.

ORIGIN:
It emerges as a no of rootlets on anterior surface of Medulla Oblongata b/w pyramid & the olive.

COURSE:
Runs laterally in the post cranial fossa & leaves the skull through Hypoglossal Canal.
Now comes in close contact with 9th, 10th, 11th CN, ICA & IJV. Descends b/w ICA & IJV until it reaches the lower border of posterior belly of digastric where it runs forward & medially. It then curves forward crossing the loop of lingual artery just above the tip of greater cornu of hyoid bone. It runs forward lateral to hyoglossus & medial to mylohyoid. (Lies below the deep part of submandibular gland, submandibular duct & lingual nerve. It ends by curving up to the tip of the tongue supplying branches to the muscles.

In the upper part of its course it is joined by small branch from cervical plexus
(C1 & C2)
The branch later leaves the nerve as its
Descending branch
Nerve to thyrhyoid
Nerve to Genihyoid

BRANCHES:

Meningeal Branch:

Supply meningies in posterior cranial fossa.

Descending Branch:

Composed of C1 fibers, descends in front of carotid sheath joined by C2 & C3 from cervical plexus to form a loop called Ansa Cervicalis. Branches from this loop supply omohyoid, Sternohyoid, Sternothyroid

Nerve to Thyrohyoid
It is composed of C 1 fibers. It supplies the thyrohyoid muscle.

Nerve to Genihyoid:
It is composed of C1 fibers. It supplies the genihyoid muscle.

Muscular Branches:
All intrinsic muscles of tongue along with Styloglossus, Hyoglossus, Geniglossus
Except Palatoglossus supplied by pharyngeal plexus.

Communicating Branch:
Hypoglossal nerve communicates with the lingual nerve at the side of the tongue.

TESTING THE INTEGRITY OF HYPOGLOSSAL NERVE

EXAMINATION

Inspection
Ask the patient to open the mouth, inspect the tongue, as it lies on the floor of mouth for its
· Size
· Shape
· Wasting
· Fasciculations

Ask the patient to protrude the tongue
If lesion of the nerve is present tongue deviates towards paralyzed side.
The normal muscle pulls the unaffected side of tongue forward leaving the paralyzed side stationary. The tip of the tongue thus deviates to paralyzed side.

Ask the patient to press tongue against cheek while you resist with finger pressure on outside of cheek.
In unilateral paralysis movements towards normal side will be weak.

INTERPRETATION

In Bilateral Upper Motor Neuron Lesions (e.g. pseudobulbar palsy)
Tongue looks small, conical and is immobile

In Unilateral Upper Motor Neuron Lesion, the tongue may sometimes deviates towards paralyzed side when protruded. There is no wasting. It is usually seen in acute stroke and disappears over days.

In Bilateral Lower Motor Neuron Lesions (e.g. bulbar palsy), there is generalized wasting with Fasciculations.

In Unilateral Lower Motor Neuron Lesions, wasting and Fasciculations are present on the affected side only.

In Bilateral tongue paralysis there is dysarthria