Nerves of Head and Neck

Nerves of Head

Major nerves supplying the Head are:

• Cranial Nerve
• Nerves of Submandibular Region
• Mandibular Nerve
• Chorda Tympani Nerve
• Otic Ganglion

Cranial Nerves

Cranial nerves are the 12 nerves that emerge directly from the brain. Out of the 12 pairs of the cranial nerves, the initial 2 pairs originate from the forebrain and the next 10 pairs originate from the brainstem. They may be numbered 1 to 12 in the craniocaudal sequence of their connection on the brain. The cranial nerves are usually designated by Roman numerals.

The 12 pairs of nerves are:

Nerves of Submandibular Region

From posterior section of the mandibular nerve, the lingual nerve originates and between the ramus of the mandible and the medial pterygoid muscle it descends. By passing inferior to the lower border of the superior constrictor of the pharynx and it inclines forwards subsequently, at its connection near the posterior end of the mylohyoid line, enters the mouth. Now between medial outermost layer of the mandible and the mucus membrane of the gingiva, it enters the submandibular region by passing just behind and inferior to the third molar tooth.

In this position, it’s likely to be injured by the ungainly extraction of the adjacent tooth and is accessible to local anesthetics. In its additional course, the lingual nerve is located near the side of the tongue, crosses the styloglossus and upper part of the hyoglossus and hooks below the submandibular duct. In the process, it crosses the submandibular duct superficially and after that turns up deep to the duct (the double crossing).

Connected to the undersurface of the nerve is the submandibular ganglion, which is located on hyoglossus just above the deep part of the submandibular gland and supplies it secretomotor fibres that have synapse in the ganglion. Other postganglionic fibres reenter the lingual nerve, which carries them to the sublingual gland

The lingual nerve is itself corticoafferent to the anterior ⅔rd of the tongue and the inner (lingual) surface of the gums, but its content fibres belonging to the chorda tympani nerve carry taste sensations from the anterior ⅔rd of the tongue with the exception of from vallate papillae.

Mandibular Nerve

Among the 3 sections of the trigeminal nerve the mandibular nerve is the largest one. Being composed of both sensory and motor fibres, it’s a mixed nerve. It supplies all the structures originated from this arch because it is a nerve of the very first pharyngeal arch, example, muscles of mastication.

The origin point is in the middle cranial fossa as 2 roots: a bigger sensory root and a smaller motor root. The large sensory root instantly leaves the cranial cavity by going through foramen ovale to goes into the temple fossa and originates from lateral convex part of the trigeminal ganglion. The small motor root appears from the pons is located deep to the trigeminal ganglion and the sensory root. It also goes through foramen ovale to join the sensory root just below the foramen ovale in the infratemporal fossa, so creating the key trunk. The mandibular nerve trunk is short and after a brief course breaks up into a small anterior and large posterior section.

Chorda Tympani Nerve

It is a slim branch of facial nerve. Due to its intimate relationship to the middle ear (tympanum) it is called chorda tympani nerve.

Inside the posterior wall of the tympanic (middle ear) cavity, it appears from facial nerve in the facial canal about 6 millimeters above the stylomastoid foramen. It runs across the lateral wall (tympanic membrane), before that it enters the middle ear via the posterior canaliculus of chorda tympani in the posterior wall. Here it crosses the lateral aspect of long process of incus and medial aspect of handle of malleus. At the anterior margin of tympanic membrane it enters anterior canaliculus in the anterior wall of the middle ear goes through canaliculus and issues at the base of skull via medial end of petrotympanic fissure. It then goes medially, forwards and downwards, grooves the medial side of the spine of the sphenoid, running anteroinferiorly deep to lateral pterygoid to join the posterior aspect of the lingual nerve about 2 cm below the base of the skull.

Otic Gnaglion

It’s joined to the mandibular division of trigeminal nerve and gives a relay station to the secretomotor fibres to the parotid gland and is a small parasympathetic ganglion. It’s closely associated with the mandibular nerve but functionally it’s related to glossopharyngeal nerve, topographically.

Size: Pinhead (2-3 millimeters in size).

Location: Temple fossa, just below the foramen ovale.

Connections

• Lateral: Mandibular nerve.
• Medial: Tensor palati muscle.
• Posterior: Middle meningeal artery.
• Anterior: Medial pterygoid muscle.

Nerves of Neck

Major nerves supplying the Neck are:

• Cutaneous Nerves
• Ventral Root of Spinal Nerves
• Cervical Plexus
• Phrenic Nerve
• Cervical Part of the Symphathetic Trunk
• Spinal Cord

Cutaneous Nerves of Neck

The skin on the rear of the neck is supplied segmentally by cutaneous nerves, originated from dorsal rami of C2, C3 and C4 spinal nerves.

The skin on the front and side of the neck on every side is supplied by 4 cutaneous nerves originated from ventral rami of C2 to C4 spinal nerves via branches of the cervical plexus.

They can be called as follows:

• Lesser occipital nerve (C2).
• Great auricular nerve (C2 and C3).
• Transverse cervical nerve (C2 and C3).
• Supraclavicular nerves (C3 and C4).

Ventral Root of  Spinal Nerves

A ventral root as well as a dorsal root combines to create a spinal nerve, which travels outside from the vertebral canal via an intravertebral foramen (bone opening). The ventral root (motor root) of every single spinal nerve includes axons from motor neurons whose cell bodies are located inside the gray matter of the spinal cord.

The spinal nerves in the thoracic and lumbar zones have a fourth or visceral section, which becomes part of the autonomic nervous system. A posterior section a.k.a. posterior ramus through each spinal nerve shifts towards the posterior for stimulating muscles and the skin of the back. The primary part of the nerve, the anterior section (anterior ramus), goes on forward to innervate muscles as well as skin on the front and sides of the trunk and limbs.

The spinal cord connects with the body through the spinal nerves, which belong to the peripheral nervous system.

Cervical Plexus

The cervical plexus is also named plexus of loops because ventral ramus of C1 and branches of C2 C4 ventral rami are joined with 1 another to create 3 loops. The very first loop is directed forwards in front of the transverse process of atlas and the remaining 2 loops are directed backwards.Ventral rami of the upper 4 cervical nerves create it. The ventral rami of c2-c4 break up into upper and lower branches.

The cervical plexus is located on levator scapulae and scalenus medius muscles deep to prevertebral fascia, internal jugular vein and sternocleidomastoid. The cervical plexus supplies skin and muscles of the neck and the thoracoabdominal diaphragm. Its branches are ordered into superficial and deep groups.

Phrenic Nerve

The point of origin is from ventral rami of C3, C4 and C5 but primarily from C4.

It runs vertically downwards on the anterior surface of the scalenus anterior, which it crosses obliquely from lateral to medial side. Afterward it runs downwards on the cervical pleura to go into the thorax behind first costal cartilage.

The phrenic nerve gives:

• Single Motor Supply to the diaphragm (muscle of respiration).
• Sensory innervation to diaphragmatic pleura, pericardium and subdiaphragmatic pleura.

Crvical Part of the Sympathetic Trunk

Both sympathetic trunks (left and right) join to create ganglion impar and they both go from the base of the skull to the base of coccyx.

The cervical part of Sympathetic trunk is located in front of the transverse processes of cervical vertebrae and neck of the 1st rib behind the carotid sheaths and in front of prevertebral fascia. Location is 1 on either side of cervical part of the vertebral column.

As the internal carotid nerve accompanying the internal carotid artery, every trunk is constant upwards into the cranial cavity. It becomes constant with the thoracic part of the sympathetic chain in the neck of the 1st rib, inferiorly.

The cervical part of sympathetic trunk does give gray rami communicantes to all the cervical spinal nerves but doesn’t get the preganglionic fibres via white rami communicantes from the cervical sections of the spinal cord. Every trunk gets preganglionic fibres from lateral horn cells of T1-T4 spinal sections.

Spinal Cord

The spinal cord is the lower cylindrical part of the central nervous system inhabiting the upper two-thirds of the vertebral canal and is typically 45 cm long. It starts at the foramen magnum as the continuance of medulla oblongata and normally ends opposite the intervertebral disc between the L1 and L2 vertebrae. The spinal cord stretches up to the level of the lower border of S2 vertebra in foetus. The functions of the spinal cord are as follows:

• Transmission of info to and fro between body and brain.
• Performance of simple reflexes.

The spinal cord is cylindrical structure, somewhat flattened anteroposteriorly. Its lower end tapers into a cone creating the conus medullaris. The spinal cord supplies origin to 31 pairs of spinal nerves. The girth of spinal cord increases substantially in the regions that supply origin to large nerves of the limbs. These enlargements are called cervical and lumbar swellings/enlargements.