Cranial Nerve XI: The Spinal Accessory Nerve (2023)


This nerve supplies the sternocleidomastoid and trapezius muscles,which have the following functions:

  1. Rotationof head away from the side of the contracting sternocleidomastoid muscle.

  2. Tilting of the head toward the contracting sternocleidomastoidmuscle.

  3. Flexion of the neck by both sternocleidomastoidmuscles.

  4. Elevation of the shoulder by thetrapezius.

  5. Drawing the head back so the face is upward bythe trapezius muscles.

With weakness or paralysis these functions aredecreased or absent. When the lesion is nuclear or infranuclear, there is associated muscle atrophyand fasciculations.


Observe the volume and contour of the sternocleidomastoid muscles as the patient looks ahead. Test the right sternocleidomastoid muscle by facing the patient and placing your right palm laterally on the patient's left cheek. Ask the patient to turn the head to the left, resisting the pressure you are exerting in the opposite direction. At the same time, observe and palpate the right sternocleidomastoid with your left hand. Then reverse the procedure to test the left sternocleidomastoid.

Continue to test the sternocleidomastoid by placing your hand on the patient's forehead and pushing backward as the patient pushes forward. Observe and palpate the sternocleidomastoid muscles.

Now test the trapezius. Ask the patient to face away from you and observe the shoulder contour for hollowing, displacement, or winging of the scapula. Observe for drooping of the shoulder. Place your hands on the patient's shoulders and press down as the patient elevates or shrugs the shoulders and then retracts the shoulders.

Basic Science

The eleventh nerve has two parts. The smaller cranial part arises from cells in the nucleus ambiguus and ultimately is distributed with the vagus nerve. This portion innervates the pharyngeal muscles. The main part, the spinal portion, arises from a long column of nuclei situated in the ventral part of the medulla and extending to the fifth cervical segment or lower. Supranuclear innervation is not well known. It has been characterized by authors as being ipsilateral, contralateral, or bilateral. It begins in the precentral gyri and descends in the corticobulbar tract. As the fibers leave the cord they join together and ascend through the foramen magnum, then leave through the jugular foramen with the vagus nerve. The nerve descends in the neck near the jugular vein and supplies the sternocleidomastoid and trapezius muscles, joined by motor or sensory contributions from the upper cervical nerves. Some recent insights into the supranuclear contributions are discussed in the Clinical Significance section below.

The sternocleidomastoid muscles originate from the sternum and clavicle and insert on the mastoid process. Each one (1) rotates the head to the opposite side of the body, that is, away from the side of the muscle; (2) tilts the head to the same side of the body. Acting together the sternocleidomastoid muscles flex the neck and bring the head forward and down.

The trapezius muscle originates on the occiput and the spinous processes of the cervical and thoracic vertebrae and inserts on the clavicle and scapula. Some controversy centers on whether all or part of the muscle is supplied by the spinal accessory nerve; many believe only its upper portion is supplied by the eleventh nerve. When the head is fixed, the trapezius elevates the shoulders. When the scapula is fixed, it draws the head ipsilaterally; jointly the trapezii pull the head back so the face is upward.

Clinical Significance

Supranuclear lesions of the eleventh nerve cause moderate, often transient, impairment of function of the sternocleidomastoid and trapezius muscles, due to the bilateral innervation. In the spinal cord the nuclei can be involved in amyotrophic lateral sclerosis, syringomyelia, polio, and intraspinal tumors. Occlusion of the vertebral or posterior inferior cerebellar artery produces infarction of the medullary tegmentum, with deficits of V, IX, X, and XI (Wallenberg's syndrome).

Nerves IX, X, and XI travel together in the jugular foramen. They may be compressed by tumors and aneurysms (Vernet's syndrome). The XII nerve may also be involved in more extensive lesions occurring in the posterior later-ocondylar space (syndrome of Collet-Sicard); causes include parotid tumors, carotid body tumors, adenopathy of whatever cause, and tuberculosis involving the lymph nodes. Sarcoidosis is another cause. A similar set of etiologies can damage the same four nerves (IX, X, XI, XII) in the posterior retroparotid space (Villaret's syndrome).

Isolated lesions of the spinal accessory nerve are rare. Surgical injury is one cause. The eleventh nerve crosses the posterior triangle of the neck lying on the levator scapulae, and it is quite vulnerable to surgical procedures in that area, such as biopsy or exploration. Involvement can occur some time following surgery, suggesting entrapment by scar tissue. An idiopathic mononeuropathy manifested by pain along the posterior border of the sternocleidomastoid muscle followed by weakness has been reported. Radiation can cause injury, with or without involvement of other nerves. Some unusual causes have been reported: injury during attempted hanging; love-play bites during sex.

A recent report of three cases of dissociated weakness of the sternocleidomastoid and trapezius muscles has provided insight into the neuroanatomy of the spinal accessory nerve (Manon-Espaillat and Ruff, 1988). The following comments are based upon these cases in addition to previous anatomical findings. The nuclei to the sternocleidomastoid and trapezius muscles appear to be somatotopically arranged in the cervical cord. Motor neurons at C1–2 innervate the sternocleidomastoid, while neurons at C3–4 innervate the trapezius. This innervational pattern can account for isolated weakness of one muscle or the other.

The supranuclear innervation to motor neurons for each of the muscles appears to take different courses. Supranuclear fibers from the precentral gyrus destined for the sternocleidomastoid descend in the brainstem tegmentum, while fibers going to the trapezius motor neurons are in the ventral brainstem. Consequently, restricted lesions in these locations can produced dissociated weakness of the two muscles.

The supranuclear fibers to the sternocleidomastoid appear to have a double decussation in the brainstem. The first occurs caudal to the oculomotor complex in the pontine tegmentum, and the second at the cervicomedullary junction (Bender, Shanzer and Wagman, 1964). Therefore at this level a single lesion can produce an ipsilateral sternocleidomastoid weakness and contralateral trapezius weakness.

These findings lead to the following clinical generalizations with reference to localization (Manon-Espaillat and Ruff, 1988):

  • Trapezius weakness on one side and sternocleidomastoid weakness on the contralateral side indicate an upper motor neuron lesion ipsilateral to the involved sternocleidomastoid and above the oculomotor nerve nucleus

  • Trapezius muscle weakness with sparing of the sternocleidomastoid points to a lesion in the ventral brainstem, lower cervical cord, or lower spinal accessory roots

  • Sternocleidomastoid weakness alone indicates a brainstem tegmentum or upper cervical accessory root lesion

  • Weakness of both muscles ipsilaterally can be produced by a lesion in the contralateral brainstem, ipsilateral high cervical cord, or an accessory nerve lesion peripherally before the nerve bifurcates to both muscles

  • A peripheral lesion distal to the bifurcation also produces weakness involving only one muscle

Detailed discussions and further sources may be found in the References.


  1. Adams RD, Victor M. Principles of neurology. 3rd ed. New York: McGraw-Hill, 1985.

  2. Bender MB, Shanzer S, Wagman IH. On the physiologic decussation concerned with head turning. Confin Neurol. 1964;24:169–81. [PubMed: 14154331]

  3. Brodal A. Neurological anatomy in relation to clinical medicine. 3rd ed. New York: Oxford University Press, 1981.

  4. DeJong RN. The neurologic examination. 4th ed. New York: Harper & Row, 1979;225–40.

  5. Haymaker W, Kuhlenbeck H. Disorders of the brainstem and its cranial nerves. In: Baker AB, Joynt RF, eds. Clinical neurology. Philadelphia: Lippincott, 1985;vol 3.

  6. Manon-Espaillat R, Ruff RL. Dissociated weakness of sternocleidomastoid and trapezius muscles with lesions in the CNS. Neurology. 1988;38:796–97. [PubMed: 3362378]

  7. Newsom-Davis J, Thomas PK, Spalding JMK. Diseases of the ninth, tenth and eleventh cranial nerves. In: Dyck PJ, Thomas PK, Lambert EH, Bunge R, eds. Peripheral neuropathy. 2nd ed. Philadelphia: W.B. Saunders, 1984; 2: 1337–50.

  8. Olarte M, Adams D. Accessory nerve palsy. J Neurol Neurosurg Psychiatry. 1977;40:1113–16. [PMC free article: PMC492910] [PubMed: 202681]

  9. Willoughby EW, Anderson NE. Lower cranial nerve motor function in unilateral vascular lesions of the cerebral hemisphere. Br Med J. 1984;289:791–94. [PMC free article: PMC1442928] [PubMed: 6434083]


What is the accessory nerve cranial nerve XI responsible for? ›

This nerve supplies the sternocleidomastoid and trapezius muscles, which have the following functions: Rotation of head away from the side of the contracting sternocleidomastoid muscle. Tilting of the head toward the contracting sternocleidomastoid muscle. Flexion of the neck by both sternocleidomastoid muscles.

What is the function of cranial nerve XI quizlet? ›

The accessory nerve is also referred to as cranial nerve XI, the eleventh cranial nerve, or just CN XI. Two muscles necessary for the movement of the neck and shoulder are given motor function by the accessory nerve. The sternocleidomastoid and trapezius muscles are innervated, and their only motor function is somatic.

How do you assess the spinal accessory nerve CN XI? ›

Clinical relevance: assessing the accessory nerve

When assessing the sternocleidomastoid, ask the patient to turn their head as far to the left as they can. With your left hand bracing their left shoulder, pull their chin forward. Weakness or no resistance to your pull suggests accessory nerve weakness.

What is the primary function of the accessory XI cranial nerve ___________________ sensory or motor or both? ›

The accessory nerve is the eleventh paired cranial nerve. It has a purely somatic motor function, innervating the sternocleidomastoid and trapezius muscles. In this article, the anatomical course, motor functions and clinical relevance of the nerve will be examined.

What is the function of the accessory nerve quizlet? ›

The accessory nerve is responsible for swallowing, head, neck and shoulder movements.

What happens if the spinal accessory nerve is damaged? ›

Spinal Accessory Nerve Injury

The spinal accessory nerve can be damaged during trauma or even during surgery when surgeons are operating on lymph nodes or on the jugular vein in the neck. The symptoms are shoulder pain, outward “winging” of the shoulder blades, and weakness or atrophy of the trapezius muscle.

What is cranial nerve XI called and how is it tested? ›

The 11th (spinal accessory) cranial nerve is evaluated by testing the muscles it supplies: For the sternocleidomastoid, the patient is asked to turn the head against resistance supplied by the examiner's hand while the examiner palpates the active muscle (opposite the turned head).

Is cranial nerve XI a sensory motor or mixed nerve? ›

Cranial nerves III, IV, VI, XI, and XII are pure motor nerves. Cranial nerves V, VII, IX, and X are mixed sensory and motor nerves. The olfactory nerve (CN I) contains special sensory neurons concerned with smell. The optic nerve (CN II) contains sensory neurons dedicated to vision.

What is the function of the cranial and spinal nerves? ›

For example, cranial nerves help you make facial expressions, move your eyes and process smells. Spinal nerves: You have 31 pairs of spinal nerves branching out from your spinal cord. These nerves can provide sensory function, motor function or both.

Which of the following may be a symptom of damage to the accessory nerve XI? ›

Signs. Limited or loss of sustained abduction of the shoulder is the most common sign. A full passive range of motion may eventually progress to decreased passive range of motion due to adhesive capsulitis (frozen shoulder). The ipsilateral shoulder may droop.

How should the nurse test cranial nerve XI? ›

Cranial Nerve XI – Spinal Accessory

Ask the patient to turn their head to the left while resisting the pressure you are exerting in the opposite direction. At the same time, observe and palpate the right sternocleidomastoid with your left hand.

What is the accessory nerve number 11? ›

Description. The Spinal Accessory Nerve (SAN) or Cranial Nerve 11 is termed a cranial nerve as it was originally believed to originate in the brain. It has both a cranial and a spinal part, though debate still rages regarding if the cranial part is really a part of the SAN or part of the vagus nerve.

What type of nerve is the accessory XI nerve? ›

The accessory nerve, also known as the eleventh cranial nerve, cranial nerve XI, or simply CN XI, is a cranial nerve that supplies the sternocleidomastoid and trapezius muscles. It is classified as the eleventh of twelve pairs of cranial nerves because part of it was formerly believed to originate in the brain.

What cranial nerve is responsible for Bell's palsy? ›

Bell palsy is a disorder of the nerve that controls movement of the muscles in the face. This nerve is called the facial or seventh cranial nerve. Damage to this nerve causes weakness or paralysis of these muscles.

Which cranial nerve has the action of speech and swallowing? ›

Vagus nerve This nerve is responsible for the muscles involved in swallowing, voice and resonance.

What are the symptoms of accessory nerve damage? ›

A patient with an injury to the SAN may present with neck pain, asymmetrical shoulders, inability to shrug the shoulder, or weakness in the neck area. The patients can also have complications secondary to treatment.

Is cranial nerve 11 motor or sensory? ›

Table of cranial nerves
No.NameSensory, motor, or both
VIIIVestibulocochlear In older texts: auditory, acoustic.Mostly sensory
IXGlossopharyngealBoth sensory and motor
XVagusBoth sensory and motor
XIAccessory Sometimes: cranial accessory, spinal accessory.Mainly motor
9 more rows

What is cranial nerve IX? ›

Introduction. The glossopharyngeal nerve is the 9th cranial nerve (CN IX). It is one of the four cranial nerves that has sensory, motor, and parasympathetic functions. It originates from the medulla oblongata and terminates in the pharynx.

What cranial nerve is responsible for eye movement? ›

The oculomotor nerve is the third cranial nerve (CN III). It allows movement of the eye muscles, constriction of the pupil, focusing the eyes and the position of the upper eyelid. Cranial nerve III works with other cranial nerves to control eye movements and support sensory functioning.

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