Accessory & hypoglossal nerves

Белгородский государственный университетCranial Nerves Prof. Dr. A.V. Tverskoy

Prepared By :

Navdeep Gaur

Group No.091218

Cranial NervesDEFINITION : THE NERVES THAT EMERGE DIRECTLY FROM THE BRAIN, IN CONTRAST TO SPINAL NERVES, WHICH EMERGE FROM SEGMENTS OF THE SPINAL CORD.

Cranial NervesA

Cranial Nerves in Humans There are traditionally twelve pairs of cranial nerves. Only the first and the second pair emerge from the cerebrum ; the remaining ten pairs emerge from the brainstem.

About Cranial NervesThe cranial nerves are part of the peripheral nervous system (PNS) with the exception of cranial nerve II. The optic nerve, along with the retina, is not a true peripheral nerve but a tract of the diencephalon. Cranial nerve ganglia originate in the central nervous system(CNS). The remaining eleven axons extend beyond the brain and are therefore considered part of the PNS.

Cranial nerves in non-human vertebrates

Human cranial nerves are nerves similar to those found in many other vertebrates. Cranial nerves XI and XII evolved in other species to amniotes (non-amphibian tetrapods), thus totaling twelve pairs. In some primitive cartilaginous fishes, such as the spiny dogfish or mud shark (Squalus acanthias), there is a terminal nerve numbered zero, since it exits the brain before the traditionally designated first cranial nerve.

Names of Cranial Nerves

Ⅰ Olfactory nerve

Ⅱ Optic nerve

Ⅲ Oculomotor nerve

Ⅳ Trochlear nerve

Ⅴ Trigeminal nerve

Ⅵ Abducent nerve

Ⅶ Facial nerve

Ⅷ Vestibulocochlear nerve

Ⅸ Glossopharyngeal nerve

Ⅹ Vagus nerve

Ⅺ Accessory nerve

Ⅻ Hypoglos

How to memorise cranial nerves

Cranial Nerve 11Name : Accessory Nerve

Basis of Classification :

Motor Cranial Nerves

Reason for their classification :

Because they contain only efferent (Motor) fibers.

Information about Accessory NerveCranial Exit :

Jungular Foramen

Main Action :

Motor to sternocleidomastoid

and

trapezius

What is Accessory Nerve?The accessory nerve is a nerve that controls specific muscles of the shoulder and neck. As part of it was formerly believed to originate in the brain, it is considered a cranial nerve. Based on its location relative to other such nerves, it is designated the eleventh of twelve cranial nerves, and is thus abbreviated as (CN XI).

Accessory nerveMotor:

Turn head side to side

shrug shoulders with resistance

Description of Accessory NerveA

DescriptionTraditional description of the Accessory nerve divide it into 2 parts:

(a) a spinal part

and

(b) a cranial part.

But because the cranial component rapidly joins the vagus nerve and serves the same function as other vagal nerve fibers, modern descriptions often consider the cranial component part of the vagus nerve and not part of the accessory nerve proper

More DescriptionThe spinal accessory nerve provides motor innervation from the central nervous systemto two muscles of the neck: the sternocleidomastoid muscle and the trapezius muscle. The sternocleidomastoid muscle tilts and rotates the head, while the trapezius muscle has several actions on the scapula, including shoulder elevation and adduction of the scapula.

The accessory nerve is derived from the basal plate of the embryonic spinal segments C1–C6.

Origin of Accessory NerveThe fibers that form the spinal accessory nerve are formed by lower motor neurons located in the upper segments of the spinal cord. This cluster of neurons, called the spinal accessory nucleus, is located in the lateral horn of the spinal cord. This is in contrast to most other motor neurons, whose cell bodies are found in the spinal cord's anterior horn. The lateral horn of high cervical segments appears to be continuous with the nucleus ambiguus of the medulla oblongata, from which the cranial component of the accessory nerve is derived.

ClassificationAmong investigators there is disagreement regarding the terminology used to describe the type of information carried by the accessory nerve. As the trapezius and sternocleidomastoid muscles are derived from the branchial arches, some investigators believe the spinal accessory nerve that innervates them must carry branchiomeric (special visceral efferent, SVE) information. This is in line with the observation that the spinal accessory nucleus appears to be continuous with the nucleus ambiguus of the medulla. Others, notably Haines, consider the spinal accessory nerve to carry general somatic efferent (GSE) information. Still others believe it is reasonable to conclude that the spinal accessory nerve contains both SVE and GSE components.

FunctionThe Accessory Nerve functions as to control the sternocleidomastoid and trapezius muscles. The thoracic branches of the spinal accessory nerve are matched to vagal innervation in early embyrologic development of the mammalian heart.

Clinical Relevance

Injury :

Accessory nerve disorder :

Injury to the spinal accessory nerve can cause an accessory nerve disorder or spinal accessory nerve palsy, which results in diminished or absent function of thesternocleidomastoid muscle and upper portion of the trapezius muscle.

Accessory Nerve DisorderPresentation :

Patients with spinal accessory nerve palsy often exhibit signs of lower motor neuron disease such as diminished muscle mass,fasciculations, and partial paralysis of the sternocleidomastoid and trapezius muscles. Interruption of the nerve supply to the sternocleidomastoid muscle results in an asymmetric neckline, while weakness of the trapezius muscle can produce a drooping shoulder, winged scapula, and a weakness of forward elevation of the shoulder.

Causes of Accessory Nerve Disorder

Medical procedures are the most common cause of injury to the spinal accessory nerve.In particular, radical neck dissection and cervical lymph node biopsy are among the most common surgical procedures that result in spinal accessory nerve damage.London notes that a failure to rapidly identify spinal accessory nerve damage may exacerbate the problem, as early intervention leads to improved outcomes.

TreatmentThere are several options of treatment when iatrogenic (i.e., caused by the surgeon) spinal accessory nerve damage is noted during surgery. For example, during a functional neck dissection that injures the spinal accessory nerve, injury prompts the surgeon to cautiously preserve branches of C2, C3, and C4 spinal nerves that provide supplemental innervation to the trapezius muscle.Alternatively, or in addition to intraoperative procedures, postoperative procedures can also help in recovering the function of a damaged spinal accessory nerve. For example, the Eden-Lange procedure, in which remaining functional shoulder muscles are surgically repositioned, may be useful for treating trapezius muscle palsy.

Hypoglossal Nerve :

is the twelfth cranial nerve (XII),

Leading to muscles of the tongue.

It is called hypoglossal nerve because it is below the tongue.

It controls tongue movements of speech, food manipulation, and swallowing.

Cranial Nerve XII

Name :

Hypoglossal Nerve.

TrajectoryThe nerve arises from the hypoglossal nucleus and emerges from the medulla oblongatain the preolivary sulcus separating the olive and the pyramid. It then passes through thehypoglossal 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 veinlying on the carotid sheath. After passing deep to the posterior belly of the digastric muscle, it passes to the submandibular region, passes lateral to the Hyoglossus muscle, and inferior to the lingual nerve to reach and efferently innervate 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 embryonic medulla oblongata.

Hypoglossal nerveMotor:

Turn head side to side

Shrug shoulders with resistance

Function:

Tongue movements of speech, food manipulation, and swallowing

Clinical test:

Tongue function

Effects of damage:

Difficulty in speech and swallowing; atrophy of tongue; inability to stick out (protrude) tongue

Uses in nerve repairFacial nerve paralysis is a difficult situation to fix, but new cranial nerve substitution techniques allow for some usage to be restored, to include hypoglossal-facial anastomosis.

This procedure is considered the standard for reanimating the face when the proximal end of the facial nerve is not available, but the peripheral system is still viable. There are two options:

Hypoglossal nerve completely transected and connected to facial nerve.

Hypoglossal nerve partially transected and connected to facial nerve. This may be accomplished with interposition cable grafts or jump grafts. An advantage of partial transection is minimizing tongue weakness and purported decrease in synkinesis. There are disadvantages though since there are then fewer nerve cells to drive the movement of features in the face.

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