|Brain: Cranial nerves|
Cranial nerves as they pass through the skull base to the brain.
(pl: nervi craniales)
|Overview - Table|
Cranial nerves (sometimes termed cerebral nerves), are nerves that emerge directly from the brain and the brainstem, in contrast to spinal nerves (which emerge from various segments of the spinal cord). Information is exchanged between the brain and various regions, primarily of the head and neck, via the cranial nerves.
Spinal nerves reach as far as the first cervical vertebra, and the cranial nerves fill a corresponding role above this level. Each cranial nerve is paired and is present on both sides. Depending on source there are in humans twelve or thirteen pairs of cranial nerves, which are assigned Roman numerals I-XII, and zero assigned to cranial nerve zero, according to the order in which they originate from the forebrain to the back of the brain and the brainstem.
The cranial nerves are components of the peripheral nervous system, with the exception of cranial nerve II (the optic nerve), which is not a true peripheral nerve but a neural tract of the diencephalon connecting the retina with the lateral geniculate nucleus; hence both the optic nerve and the retina are part of the central nervous system (CNS). The axons of the remaining twelve nerves extend beyond the brain and are considered part of the PNS. The central ganglia of the cranial nerves or cranial nerve nuclei originate in the CNS, preferentially from the brainstem.
- 1 Anatomy
- 2 Function
- 3 Clinical significance
- 4 History
- 5 Other animals
- 6 See also
- 7 References
- 8 External links
Traditionally, in humans there are considered to be twelve cranial nerves, all of which are paired, and numbered I-XII or 1-12. The nerves are: the olfactory nerves (I), the optic nerves (II), the oculomotor nerves (III), the trochlear nerves (IV), the trigeminal nerves (V), the abducens nerves (VI), the facial nerves (VII), the vestibulocochlear nerves (VIII), the glossopharyngeal nerves (IX), the vagus nerves (X), the accessory nerves (XI), and the hypoglossal nerves (XII).
Nerves are generally named according to their structure or function. For example, the olfactory nerve (I) supplies smell, and the facial nerve (VII) supplies sensation to the face. As Latin was the lingua franca of the study of Anatomy when the nerves were first documented, recorded, and discussed, many nerves hold Latin, including the trochlear nerve (IV), named according to its structure, as it supplies a muscle that attaches to a pulley (Latin: trochlea), the trigeminal nerve (V) named according to its three heads (Latin: tri-geminus), and the vagus nerve (X), named for its wandering course (Latin: vagus).
Cranial nerves are numbered based on their rostral-caudal orientation, as, when viewing the brain and brainstem from below, they are often visible in their numeric order. For example, the olfactory nerves (I) and optic nerves (II) arise from the base of the forebrain, and the other nerves, III to XII, arise from the brainstem.
Unique anatomical terminology is used to describe the course of the cranial nerves. Like all nerves, the nerves have a nucleus, and a course within and outside of the brain. The course within the brain is known as the central course of the nerve, and the course after it has emerged from the brain as the peripheral course. The nerves are paired, which means that they occur on both the right and left sides. Some nerves cross from the right side to the left side, and this is known anatomically as decussating. If a nerve supplies a muscle, skin, or has another function on the same side of the body as where it originates, this is called an ipsilateral course. If the course is opposite to the nucleus of the nerve, this is known as a contralateral course.
Grossly, all cranial nerves have a nucleus. With the exception of the olfactory nerve (I) and optic nerve (II), all the nuclei are present in the brainstem. In general, motor nuclei are present ventrally, and sensory nuclei are present dorsally.
Specifically, the midbrain of the brainstem has the nuclei of the oculomotor nerve (III) and trochlear nerve (IV); the pons has the nuclei of the trigeminal nerve (V), abducens nerve (VI), facial nerve (VII) and vestibulocochlear nerve (VIII); and the medulla has the nuclei of the glossopharyngeal nerve (IX), vagus nerve (X), accessory nerve (XI) and hypoglossal nerve (XII). The olfactory nerve (I) emerges from the olfactory bulb, and depending slightly on division the optic nerve (II) is deemed to emerge from the lateral geniculate nuclei.
Because each nerve may have several functions, the nerve fibres that make up the nerve may collect in more than one nucleus. For example, the trigeminal nerve (V), which has a sensory and a motor role, has at least four nuclei.
Exiting the brainstem
With the exception of the olfactory nerve (I) and optic nerve (II), the cranial nerves emerge from the brainstem. The oculomotor nerve (III) and trochlear nerve (IV) emerge from the midbrain, the trigeminal (V), abducens (VI), facial (VII) and vestibulocochlea (VIII) from the pons, and the glossopharyngeal (IX), vagus (X), accessory (XI) and hypoglossal (XII) emerge from the medulla.
The olfactory nerve (I) and optic nerve (II) emerge separately. The olfactory nerves emerge from the olfactory bulbs on either side of the crista galli, a bony projection below the frontal lobe, and the optic nerves (II) emerge from the lateral colliculus, swellings on either side of the temporal lobes of the brain.
Similar to the dorsal root ganglia of the spinal nerves and parasympathetic ganglia of the sacral parasympathetic system, the sensory cranial nerves have a number of ganglia outside the central nervous system. The sensory ganglia are directly correspondent to dorsal root ganglia and are as known as cranial sensory ganglia, and found along the course of the cranial nerves, outside the brain and skull. Sensory ganglia exist for nerves with sensory function; V, VII, VIII, IX, X. There are also a number of parasympathetic cranial nerve ganglia, while sympathetic ganglia innervating the head and neck reside in the upper regions of the sympathetic trunk, and do not belong to the cranial nerves.
- The trigeminal ganglia of the trigeminal nerve (V), which occupies a space in the dura mater called Meckel's cave. This ganglion contains only the sensory fibres of the trigeminal nerve.
- The geniculate ganglion of the facial nerve (VII), which occurs just after the nerve enters the facial canal.
- A superior and inferior ganglia of the glossopharyngeal nerve (IX), which occurs just after it passes through the jugular foramen.
Additional ganglia for nerves with parasympathetic function exist, and include the Ciliary ganglion of the oculomotor nerve (III), the pterygopalatine ganglion of the maxillary nerve (V2), the submandibular ganglion of the lingual nerve, a branch of the facial nerve (VII), and the otic ganglion of the glossopharyngeal nerve (IX).
Exiting the skull
|cribiform plate||Olfactory nerve (I)|
|optic foramen||Optic nerve (II)|
|superior orbital fissure||Oculomotor (III)
|round foramen||Trigeminal V2
|oval foramen||Trigeminal V3
|internal auditory canal||Facial (VII)
|jugular foramen||Glossopharyngeal (IX)
|hypoglossal canal||Hypoglossal (XII)|
After emerging from the brainstem, the cranial nerves travel within the skull, but must leave this bony compartment in order to reach their destinations. Some nerves pass through holes in the skull, called foramina, as they travel to their destination. Other nerves pass through bony canals, longer pathways enclosed by bone. These foramina and canals may contain more than one cranial nerve, and may also contain additional blood vessels.
- The olfactory nerve (I) passes through the cribiform plate, many small perforations in the part of the ethmoid bone.
- The optic nerve (II) passes through the optic foramen as it travels to the eye.
- The oculomotor nerve (III), trochlear nerve (IV), abducens nerve (VI) and the opthalamic branch of the trigeminal nerve (V1) travel through the cavernous sinus into the superior orbital fissure, passing out of the skull into the orbit.
- The maxillary division of the trigeminal nerve (V2) passes through the round foramen
- The mandibular division of the trigeminal nerve (V3) passes through the oval foramen
- The facial nerve (VII) and vestibulocochlear nerve (VIII) both pass through the internal auditory canal
The facial nerve enters the temporal bone at the internal acoustic meatus but exits the skull via the stylomastoid foramen while the vestibulocochlear nerve never actually exits the skull.
The following images show the cranial nerves schematically showing their respective exits from the CNS or brain-stem (not including the optic nerve, which, being part of the CNS, does not leave it), and their path, as well as conceptual innervation targets.
3 The oculomotor controls a number of motor function of the eye, both somatic and autonomic.
5 The trigeminal innervates a large number of structures, both motor and sensory.
7 The facial nerve stands for innervation of a large number of structures both motor and sensory.
9 The glossopharyngeal innervates a number of motor and sensory structures of the tongue and pharynx.
12 The hypoglossal nerve innervates the musculature of the tongue and pharynx.
Brainstem nuclei with associated functions are often found in similar areas of the brainstem. These are also known as functional columns. Functional columns are a result of the development of the spinal cord. Four columns of gray matter are present in the spinal cord during embryological development. Each column represents a different function, and contributes neurons to different nerves. Each nerve is innervated by neurons from one or more of the columns.
As the spinal cord develops, there are four columns. These are the general somatic efferent column, the general visceral efferent column, the general visceral afferent column and general somatic afferent column. These columns also extend into the brainstem, but are divided into smaller pieces. In the brainstem there are six columns.
Four 'general' columns contain fibres that supply sensation or control muscles:
- The general somatic efferent column controls voluntary movement of skeletal muscles of the eye and tongue, and contains fibres of the oculomotor nerve (III), trochlear nerve (IV), abducens nerve (VI) and hypoglossal nerve (XII).
- The general visceral efferent column supply parasympathetic innervation to cranial structures, and contain fibres from the oculomotor nerve (III), facial nerve (VII), glossopharyngeal nerve (IX) and vagus nerve (X).
- The general somatic afferent column carries the sensation of touch, pain and temperature from the face and mucous membranes of the mouth chiefly. It contains fibres from the trigemintal nerve (V), facial nerve (VII), and vagus nerve (X).
- The general visceral afferent column contains sensory fibres from the glossopharyngeal (IX) and vagus nerve (X).
- Special visceral (branchial) efferent columninnervates striated musculature of the branchial arches in; pharynx, larynx, roof of the mouth, jaw, and face; via nerves, V, VII, IX, X, XI.
- Special visceral afferent column innervates taste-buds developed from the endodermal regions of the branchial arches.
- Special sense afferent column innervates the vestibulocochlear system.
The cranial nerves innervate the head and neck area, including both somatic and autonomic motor innervation as well as sensory innervation. Together the cranial nerves supply sensory innervation of the special senses such as taste, vision; smell; hearing. They also supply afferents of the somatic senses: visceral sensation of the head and neck; balance, and proprioception combining vestibular perception with proprioceptive information from the head and neck.
Two nerves, the glossopharyngeal nerve (IX) and vagus nerve (X), innervate innervate both motor and sensory synapses pertaining to abdominal organs (though not pelvic), as well as structures of the neck and chest.
Differentiating the cranial nerves from spinal nerves, the cranial nerves are not strictly bound to certain segments of the body (as in dermatomes), but rather organize after function, hence the innervated areas overlap significantly more than those of spinal nerves.
The olfactory nerve (I) conveys the sense of smell.
Damage: Damage to the olfactory nerve (I) can cause an inability to smell (anosmia), a distortion in the sense of smell (parosmia), or a distortion or lack of taste. Specific testing is performed when an individual perceives lack of taste or affected taste. The smell from each nostril is tested individually, and with consideration of airflow. Different substances are used, and these include coffee or soap. Using stronger smelling substances, for example ammonia, may lead to the activation of nociceptors of the trigeminal nerve.
The optic nerve (II) transmits visual information.
Damage: Damage to the optic nerve (II) affects vision. Vision is affected depending on the location of the lesion. A person may not be able to see things on their left or right side (homonymous hemianopsia), or may have difficulty seeing things on their outer visual fields (bitemporal hemianopsia) if the optic chiasm is involved.:82 Vision may be tested using a number of different tests, examining the visual field, or by examining the cornea with a ophthalmoscope, using a process known as funduscopy. Visual field testing may be used to pin-point structural lesions in optic nerve, or further along the visual pathways.
Eye movement (III, IV, VI)
The oculomotor nerve (III), trochlear nerve (IV) and abducens nerve (VI) coordinate eye movement.
Damage: Damage or lesion of nerves III, IV, or VI may affect the movement of the eye or pupil. Either both or one eye may be affected, and if both eyes are affected no double vision (diplopia) will occur. These nerves might be examined by observing how the eye follows an object in different directions. This object may be a finger or a pin, and may be moved at different directions to test for pursuit velocity. If the eyes do not work together, the most likely cause is damage to a specific cranial nerve or nuclei.
Damage to the oculomotor nerve (III), such as from a palsy can cause double vision (diplopia) with lateral strabismus, and also ptosis and mydriasis.:84 All but specific deviations may be due to damage in this nerve or any of the muscles it innervated, (though not internuclear ophthalmoplegia). Lesion may also lead to inability to open the eye, due to disrupted innervation of the levator palpebrae (unlike in Horner syndrome, which only results in a droopy eyelid). Individuals suffering from lesion or damage to the oculomotor nerve may compensate by tilting their heads to alleviate symptoms due to lack of control from oblique muscles when the eye is not adducted.
Damage to the trochlear nerve (IV) can also cause diplopia with the eye adducted and elevated.:84 The result will be an eye which can not move downwards or inwards properly (especially downwards when in an inward position). This is due to impairment in the superior oblique muscle innervated by the trochlear nerve.
Facial sensation (V)
Conditions affecting the trigeminal nerve (V) include trigeminal neuralgia, cluster headache, and trigeminal zoster. Trigeminal neuraliga occurs later in life, from middle age onwards, most often after an age of 60; and is a condition associated with very strong pain distributed over the area innervated by the trigeminal nerve. Often the pain follows the distribution of the maxillary or mandibular nerve, (branches V2 and V3. The trigeminal nerve is also present in the tendon reflexive jaw jerk. A reflex involving an induced twitch in muscles involved in closing the jaw when upon tapping on the jaw. A stronger reflex may be present if there is a supranuclear lesion of the trigeminal nerves motor nucleus, for example in pseudobulbar palsy. In Parkinson's disease the trigeminal nerve is involved in the glabellar reflex which causes involuntary eye-blinking.
Facial expression (VII)
Damage: Lesions of the facial nerve (VII) may manifest as facial palsy. This is where a person is unable to move the muscles on one or both sites of their face. If only the peripheral nerve itself is affected, this may cause Bell's palsy. Palsy that occurs is on the same side of the affected nerve. Central facial palsy will manifest in a similar fashion. If the nerve is damaged only on one side, a person will still be able to raise the eyebrows and crease the forehead on that side. That is because the frontalis muscle is innervated by both the left and the right cranial nerve. The effect is most often unilateral, and indicates contralateral damage or engagement of the cerebrum.
Hearing and balance (VIII)
The vestibulocochlear nerve (VIII) splits into the vestibular and cochlear nerve. The vestibular part is responsible for innervating the vestibules and semicircular canal of the inner ear, which transmits information about balance, and is an important component of the vestibuloocular reflex, which keeps the head stable and allows the eyes to track moving objects. The cochlear nerve transmits information from the cochlea, allowing sound to be heard.
Damage: When damaged, the vestibular nerve may give rise to the sensation of spinning and dizziness, and may cause rotatory nystagmus. Function of the vestibular nerve may be tested through caloric stimulation. Damage to the vestibulocochlear nerve can also present as repetitive and involuntary eye movements (nystagmus), particularly when looking in a horizontal plane. The cochlear nerve will cause partial or complete deafness in the affected ear.
Oral sensation and taste (IX)
The glossopharyngeal nerve (IX) is almost exclusively sensory in supplying five afferent nuclei of the brainstem, covering the oropharynx and back of the tongue with innervation.
Damage: Damage may result in difficulties swallowing.
Vagus nerve (X)
Loss of function of the vagus nerve (X) will lead to a loss of parasympathetic innervation to a very large number of structures. Of the major effects a rise in blood pressure and heart rate may occur. Isolated dysfunction of only the vagus nerve is rare, but can be diagnosed by a hoarse voice, due to dysfunction of the superior laryngeal nerve
Testing of function may be performed by assessing ability to drink liquids. Choking on either saliva or liquids may indicated neurological damage to the vagus nerve (X).
Damage to the glossopharyngeal nerve (IX) can be assessed by asking the subject to say "Ah" during phonation inspect to see if the uvula deviates. Positive sign indicative of unilateral damage occurs with finding of asymmetrically deviating uvula, towards the side with an intact or healthy nerve.
Shoulder elevation and head-turning (XI)
Damage: Damage to the accessory nerve (XI) may lead to contralateral weakness in the trapezius, which can be tested by asking the subject to raise their shoulders or shrug, upon which the scapula will move out into a winged position if the nerve is damaged. Weakness or an inability to elevate the scapula may be present, since the levator scapulae is alone in providing this function.
Tongue movement (XII)
The hypoglossal nerve (XII) is unique in that it is innervated bilaterally from both hemispheres motor cortex. Damage to the nerve at lower motor neuron level may lead to fascinations of atrophy of the musculature of the tongue. The fasciculations of the tongue are sometimes said to look like a "bag of worms". Upper motor neuron damage will not lead to atrophy or fasciculations, but only weakness of the innervated muscles.
When the nerve is damaged it will lead to unilateral weakness, and the tongue will upon being stuck out move towards the weaker or damaged side, as shown in the image.
Doctors, neurologists and other medical professionals may conduct a cranial nerve examination as part of a neurological examination to examine the cranial nerves. This is a highly formalised series of steps involving specific tests for each nerve, testing the function of the olfactory nerve (I) first, and progressing sequentially for each nerve. Knowledge of cranial nerve function is an important, as it may indicate which portion of the brainstem is damaged. It is of clinical importance to know the path and origin of the cranial nerves, both intracranially as well as extracranially.
A cranial nerve exam starts with observation of the patient, as some cranial nerve lesions may affect the symmetry of the eyes or face. The eyes are examined and the visual acuity is tested through reading a Snellen chart. The visual fields are tested, and specific movements of the eyes requested to test for nerve lesions or nystagmus. The sensation of the face is tested, and patients are asked to perform different movements with their face, such as puffing out of the cheeks. Hearing is checked, by voice and tuning forks. The patient's uvula is examined, and finally the patient is asked to shrug, turn their head, and tongue function assessed by various tongue movements.
The cranial nerves are often the first structures to be affected by different forms of brain injury such as hemorrhaging or tumors, partly because they are sensitive to compression. Mononeuropathy of a cranial nerve may sometimes be the first symptom of an intracranial or skull base cancer.
Stroke may damage the blood supply to areas of the nerves. It may also damage the areas of the brain that control the nerves. If there is a stroke of the midbrain, pons or medulla, various cranial nerves may be damaged, resulting in dysfunction and symptoms of a number of different syndromes.
Nerves may be compressed because of increased intercranial pressure or tumour masses that presses against the nerves. For example, an optic glioma may impact on the optic nerve (II), and an acoustic neuroma may compress the facial nerve (VII) and vestibulocochlear nerve (VIII)
Inflammation can be a result of infection, such as viral causes, or can occur spontaneously. Inflammation is more common in some nerves than others. Spontaneous inflammation may result in a palsy of a nerve that self-resolves, such as Trochlea palsy. Inflammation of the facial nerve (VII) may result in Bell's palsy. Inflammation of the trigeminal nerve (V) may result in Trigeminal neuralgia, a phenominon in which the face is exquisitely tender.
Terminal nerve controversy
The terminal nerve, often called cranial nerve zero, CN 0 (or cranial nerve nulla or N, since there is no Roman numeral for zero), has been largely neglected from textbooks, even though it was first clearly identified over a century ago. It was first shown to be present in the shark, but its presence in humans (and other mammals) remained somewhat controversial. More recent studies have shown the nerve to be quite distinct in human fetuses and infants, and has also regularly been seen in the adult brain. The nerve axons are unmyelinated and arise from ganglia. The terminal nerve has also been shown to release luteinising hormone. Another study has shown the terminal nerve to be a microscopic plexus of unmyelinated fibres in the frontal lobes. It was concluded in the study, confirming earlier findings by light microscope, that this nerve is a common finding in the human brain.
Cranial nerves are also present in other non-human vertebrates. Other amniotes (non-amphibian tetrapods) have cranial nerves similar to those of humans. In anamniotes (fishes and amphibians), in contrast, the accessory nerve (XI) and hypoglossal nerve (XII) in humans does not exist, with the accessory nerve (XI) being an integral part of the vagus nerve (X) and the hypoglossal nerve (XII) being represented by a variable number of spinal nerves emerging from vertebral segments fused into the occiput; these two nerves only became discrete nerves in the ancestors of amniotes (non-amphibian tetrapods).
- Neil Norton; ill. by Frank H. Netter; contrib. ill.: John A. Craig ... [et al.] (2007). Netter's head and neck anatomy for dentistry. Philadelphia, Pa.: Saunders Elsevier. ISBN 978-1-929007-88-2.:78
- Susan Standring, Neil R. Borley [et al.] (2008). "OVERVIEW OF CRANIAL NERVES AND CRANIAL NERVE NUCLEI". Gray's anatomy: the anatomical basis of clinical practice (40th ed.). [Edinburgh]: Churchill Livingstone/Elsevier. ISBN 978-0-443-06684-9.
- Kandel, Eric R. (2013). Principles of neural science (5. ed. ed.). Appleton and Lange: McGraw Hill. pp. 1019–1036. ISBN 978-0-07-139011-8.
- Whitlock, KE (2004). "Development of the nervus terminalis: origin and migration". Microscopy research and technique 65 (1-2): 2–12. PMID 15570589.
- Board Review Series – Neuroanatomy, Fourth Edition, Lippincott Williams & Wilkins, Maryland 2008, p. 177. ISBN 978-0-7817-7245-7.
- James S. White (21 March 2008). Neuroscience. McGraw-Hill Professional. pp. 1–. ISBN 978-0-07-149623-0. Retrieved 17 November 2010.
- Mallatt, Elaine N. Marieb, Patricia Brady Wilhelm, Jon (2012). Human anatomy (6th ed. media update. ed.). Boston: Benjamin Cummings. pp. 431–432. ISBN 978-0-321-75327-4.
- Clinically oriented anatomy (6th ed., [International ed.]. ed.). Philadelphia [etc.]: Lippincott Williams & Wilkins, Wolters Kluwer. 2010. pp. 1055–1082. ISBN 978-1-60547-652-0.
- Ober, Frederic H. Martini ; with William C.; coordinator, art; photographer, illustrator, Claire W. Garrison, illustrator, Kathleen Welch, clinical consultant, Ralph T. Hutchings, biomedical (1998). Fundamentals of anatomy and physiology (4th ed.; interactive ed. ed.). London: Prentice Hall International. pp. 474–485. ISBN 978-0-13-010436-6.
- Drake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell ; illustrations by Richard; Richardson, Paul (2005). Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone. pp. 800–807. ISBN 978-0-8089-2306-0.
- Purves, Dale, George J. Augustine, David Fitzpatrick, William C. Hall, Anthony-Samuel LaMantia, James O. McNamara, and Leonard E. White (2008). Neuroscience. 4th ed. Sinauer Associates. pp. 12–13. ISBN 978-0-87893-697-7.
- Mtui, M.J. Turlough FitzGerald, Gregory Gruener, Estomih (2012). Clinical neuroanatomy and neuroscience (6th ed. ed.). [Edinburgh?]: Saunders/Elsevier. p. 198. ISBN 978-0-7020-3738-2.
- Kandel, Eric R. (2013). Principles of neural science (5. ed. ed.). Appleton and Lange: McGraw Hill. pp. 1533–1549. ISBN 978-0-07-139011-8.
- Nesbitt AD, Goadsby PJ (Apr 11, 2012). "Cluster headache". BMJ (Clinical research ed.) (Review) 344: e2407. PMID 22496300.
- Fitzgerald, M.J. Turlough FitzGerald, Gregory Gruener, Estomih Mtui (2012). Clinical neuroanatomy and neuroscience (6th ed. ed.). [Edinburgh?]: Saunders/Elsevier. p. 235. ISBN 978-0-7020-3738-2.
- Mtui, M.J. Turlough FitzGerald, Gregory Gruener, Estomih (2012). Clinical neuroanatomy and neuroscience (6th ed. ed.). [Edinburgh?]: Saunders/Elsevier. pp. 220–222. ISBN 978-0-7020-3738-2.
- O'Connor, Nicholas J. Talley, Simon (2009). Clinical examination : a systematic guide to physical diagnosis (6th ed. ed.). Chatswood, N.S.W.: Elsevier Australia. pp. 330–352. ISBN 978-0-7295-3905-0.
- Kumar (et al.), Vinay (2010). Robbins and Cotran pathologic basis of disease. (8th ed. ed.). Philadelphia, PA: Saunders/Elsevier. p. 1266. ISBN 978-1-4160-3121-5.
- Paradiso, Mark F. Bear, Barry W. Connors, Michael A. (2007). Neuroscience : exploring the brain (3rd ed. ed.). Philadelphia, PA: Lippincott Williams & Wilkins. p. 173. ISBN 978-0-7817-6003-4.
- Vilensky JA, The neglected cranial nerve: nerves terminus (Cranial nerve N). Clin Anat. 2014 Jan;27(1) PMID 22836597
- Fuller GN and Burger PC, Nervus terminals (cranial nerve zero) in the adult human. Clin Neuropathol.1990 Nov-Dec;9(6) PMID 2286018
- Quiring, Daniel Paul (1950). Functional anatomy of the vertebrates.. New York: McGraw-Hill. p. 249.
|Wikimedia Commons has media related to Cranial nerves.|
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- Cranial nerve animations (University of Liverpool Veterinary School).