Hypoglossal nerve
Encyclopedia
The hypoglossal nerve is the twelfth cranial nerve (XII), leading to the tongue
. The nerve arises from the hypoglossal nucleus
and emerges from the medulla oblongata
in the preolivary sulcus
separating the olive and the pyramid. It then passes through the hypoglossal canal
. On emerging from the hypoglossal canal, it gives off a small meningeal branch and picks up a branch from the anterior ramus
of C1. It spirals behind the vagus nerve
and passes between the internal carotid artery
and internal jugular vein
lying on the carotid sheath
. After passing deep to the posterior belly of the digastric muscle
, it passes to the submandibular region to enter the tongue
.
It supplies motor fibres to all of the muscles of the tongue
, except the palatoglossus muscle
, which is innervated by the vagus nerve
(cranial nerve X) or, according to some classifications, by fibres from the glossopharyngeal nerve
(cranial nerve IX) that "hitchhike" within the vagus.
The hypoglossal nerve is derived from the basal plate
of the embryo
nic medulla oblongata
.
. If there is a loss of function on one side (unilateral paralysis), the tongue will point toward the affected side.
The strength of the tongue can be tested by getting the person to poke the inside of his/her cheek, and feeling how strongly he/she can push a finger pushed against the cheek - a more elegant way of testing than directly touching the tongue.
The tongue can also be looked at for signs of lower motor neuron
disease, such as fasciculation
and atrophy
.
Paralysis/paresis of one side of the tongue results in ipsilateral curvature of the tongue (apex toward the impaired side of the mouth); i.e., the tongue will move toward the affected side.
Cranial Nerve XII is innervated by the contralateral cortex, so a purely upper motor neuron lesion will cause the tongue to deviate away from the cortical lesion.
Tongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
. The nerve arises from the hypoglossal nucleus
Hypoglossal nucleus
The hypoglossal nucleus is a cranial nerve nucleus, and it extends the length of the medulla, and being a motor nucleus, is close to the midline...
and emerges from the medulla oblongata
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
in the preolivary sulcus
Sulcus (anatomy)
A sulcus is a depression or fissure in the surface of an organ, especially the brain.-Elsewhere:* anterior interventricular sulcus* calcaneal sulcus* coronal sulcus* gingival sulcus* gluteal sulcus* interlabial sulci...
separating the olive and the pyramid. It then passes through the hypoglossal canal
Hypoglossal canal
The hypoglossal canal is a bony canal in the occipital bone of the skull.-Anatomy:It transmits the hypoglossal nerve from its point of entry near the medulla oblongata to its exit from the base of the skull near the jugular foramen...
. On emerging from the hypoglossal canal, it gives off a small meningeal branch and picks up a branch from the anterior ramus
Ramus
Ramus can refer to:* A branch* A portion of a bone , as in the Ramus of the mandible or Superior pubic ramus* A nerve ramus such as the Dorsal ramus of spinal nerve* Petrus Ramus...
of C1. It spirals behind the vagus nerve
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
and passes between the internal carotid artery
Internal carotid artery
In human anatomy, the internal carotid arteries are two major arteries, one on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid artery, and they supply the brain....
and internal jugular vein
Internal jugular vein
The two internal jugular veins collect the blood from the brain, the superficial parts of the face, and the neck.-Path:On both sides and at the base of the brain, the inferior petrosal sinus and the sigmoid sinus join to form the internal jugular vein...
lying on the carotid sheath
Carotid sheath
The carotid sheath is an anatomical term for the fibrous connective tissue that surrounds the vascular compartment of the neck. It is part of the deep cervical fascia of the neck, below the superficial cervical fascia meaning the subcutaneous adipose tissue immediately beneath the skin.The deep...
. After passing deep to the posterior belly of the digastric muscle
Digastric muscle
The digastric muscle is a small muscle located under the jaw. so digastric muscles are muscle fibers in ligament of treitz ,omohyoid , occipitofrontalis....
, it passes to the submandibular region to enter the tongue
Tongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
.
It supplies motor fibres to all of the muscles of the tongue
Tongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
, except the palatoglossus muscle
Palatoglossus muscle
The palatoglossus, glossopalatinus, or palatoglossal muscle is a small fleshy fasciculus, narrower in the middle than at either end, forming, with the mucous membrane covering its surface, the glossopalatine arch....
, which is innervated by the vagus nerve
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
(cranial nerve X) or, according to some classifications, by fibres from the glossopharyngeal nerve
Glossopharyngeal nerve
The glossopharyngeal nerve is the ninth of twelve pairs of cranial nerves . It exits the brainstem out from the sides of the upper medulla, just rostral to the vagus nerve...
(cranial nerve IX) that "hitchhike" within the vagus.
The hypoglossal nerve is derived from the basal plate
Basal plate (neural tube)
In the developing nervous system, the basal plate is the region of the neural tube ventral to the sulcus limitans. It extends from the rostral mesencephalon to the end of the spinal cord and contains primarily motor neurons, whereas neurons found in the alar plate are primarily associated with...
of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
nic medulla oblongata
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
.
Testing the hypoglossal nerve
To test the function of the nerve, a person is asked to poke out his/her tongueTongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
. If there is a loss of function on one side (unilateral paralysis), the tongue will point toward the affected side.
The strength of the tongue can be tested by getting the person to poke the inside of his/her cheek, and feeling how strongly he/she can push a finger pushed against the cheek - a more elegant way of testing than directly touching the tongue.
The tongue can also be looked at for signs of lower motor neuron
Lower motor neuron
Lower motor neurons are the motor neurons connecting the brainstem and spinal cord to muscle fibers, bringing the nerve impulses from the upper motor neurons out to the muscles...
disease, such as fasciculation
Fasciculation
A fasciculation , or "muscle twitch", is a small, local, involuntary muscle contraction and relaxation visible under the skin arising from the spontaneous discharge of a bundle of skeletal muscle fibers...
and atrophy
Atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...
.
Paralysis/paresis of one side of the tongue results in ipsilateral curvature of the tongue (apex toward the impaired side of the mouth); i.e., the tongue will move toward the affected side.
Cranial Nerve XII is innervated by the contralateral cortex, so a purely upper motor neuron lesion will cause the tongue to deviate away from the cortical lesion.