Cranial Nerves - Anatomy & Physiology

Introduction

The brainstem, cranial nerves and pyramids. © BioMed Archive.

Cranial nerves are those nerves which arise from the brain and brain stem rather than the spinal cord. Nerves arising from the spinal cord are the peripheral nerves. There are 12 cranial nerves, although the trigeminal nerve (V) has 3 branches. These are:

Opthalmic (V1)

Maxillary (V2)

Mandibular (V3)

Cranial Nerve Location and Routes

A summary of the cranial nerves is shown below:

Nerve	Attatchment to brain	Exit Foramen	Fibre Type	Location of cell bodies	Distribution
I - Olfactory	Olfactory bulb	Cribriform plate	SVS	Olfactory epithelium	Olfactory epithelium
II - Optic	Optic chiasma	Optic canal	SSS	Retina	Retina
III - Occulomotor	Midbrain	Orbital fissure and Round Foramen	GSM + GVM	Nuculi III parasympathetic nuculi III	Extraoccular mm. Constrictor pupulli
IV - Trochlear	Midbrain (dorsal)	Round Foramen	GSM	Nuc IV	Dorsal oblique mm.
V - Trigeminal	Pons	V1 - Orbital fissure V2 - Round Foramen and Orbital Fissure V3 - Oval Foramen	V1 - GSS V2 - GSS V3 - SVM	V1 - Trigeminal gangion V2 - Trigeminal ganglion V3 - Nuculi V	V1 - Eye region V2 - Upper jaw inc. teeth V3 - mm. of arch 1
VI - Abducens	Medulla oblongata	Orbital fissure	GSM	Nuc IV	Lateral rectus and retractor bulbi mm.
VII - Facial	Medulla oblongata	Stylomastoid foramen	SVM + GVM + SVS	Nuc III (Taste - gleniailate ganglion)	mm. of arch 2 Submaxillary and sublingual glands Rostral 2/3 taste
VIII - Vestibulocochlear	Medulla oblongata	Inner accoustic meatus	SSS	Vestibular ganglion	Maculae and cristae
IX - Glossopharyngeal	Medulla oblongata	Jugular foramen	G/S V M/S	Ganglia IX - SVM Nuculi ambiguous - mm. arch 3	Carotid gland Caudal 1/3 taste mm. of arch 3 Carotid body
X - Vagus	Medulla oblongata	Jugular foramen	GVM + SUM + GVS + GSS	Ganglion X - (amongst others)	Thoracic and abdominal organs mm. of arches 4-6 Pharynx and larynx External ear
XI - Accessory	Medulla oblongata	Jugular foramen	GSM	Cervical spinal cord	Trapezius m. etc
XII - Hypoglossal	Medulla oblongata	Hypoglossal canal	GSM	Medulla nuculi XII	Tongue mm.

Cranial Nerve Fibre Types

Cranial nerves are best explained by function:

• General Somatic Motor (GSM)

Motor cortex —→ Motor nuculi —→ Muscle

• General Visceral Motor (GVM)

Brainstem —→ Parasympathetic nuculi —→ Parasympathetic ganglion —→ Gland etc

• "Branchial motor" - Special Visceral Motor (SVM)

Motor cortex —→ Motor nuculi —→ Muscle

• General Somatic Sensory (GSS) and General Visceral Sensory (GVS)

Sensory cortex —→ Thalamus —→ Trigeminal nuculi —→ Trigeminal ganglion —→ Skin etc

Special sensory fibres (SSS + SVS):

Smell SVS

Priform cortex —→ Olfactory tubercle —→ Olfactory Bulb —→ SMELL

Vision SSS

Occipital cortex —→ Thalamus MGN —→ Rostral colliculus/Retinal ganglion cell —→ Bipolar cell —→ VISION

Hearing/Balance SSS

Temporal cortex —→ Thalamus MGN —→ Caudal colliculus and hindbrain —→ Spiral ganglion —→ HEARING

Taste SVS

Sensory cortex —→ Thalamus —→ Hindbrain (VII, IX, X) —→ Ganglion —→ TASTE

Cranial Nerves and their Functions

#	Name	Nuclei	Function
I	Olfactory nerve	Anterior olfactory nucleus	Transmits the sense of smell
II	Optic nerve	Lateral geniculate nucleus	Transmits visual information to the brain
III	Oculomotor nerve	Oculomotor nucleus, Edinger-Westphal nucleus	Innervates the dorsal rectus, medial rectus, ventral rectus, and ventral oblique, which collectively perform most eye movements
IV	Trochlear nerve	Trochlear nucleus	Innervates the superior oblique muscle, which depresses, pulls laterally, and intorts the eyeball
V	Trigeminal nerve	Principal sensory trigeminal nucleus, Spinal trigeminal nucleus, Mesencephalic trigeminal nucleus, Trigeminal motor nucleus	Receives sensation from the face and innervates the muscles of mastication
VI	Abducens nerve	Abducens nucleus	Innervates the lateral rectus, which abducts the eye and the retractor bulbi which forces the third eyelid across the surface of the cornea as a protective mechanism.
VII	Facial nerve	Facial nucleus, Solitary nucleus, Superior salivary nucleus	Provides motor innervation to the muscles of facial expression and stapedius, receives the special sense of taste from the anterior 2/3 of the tongue, and provides secretomotor innervation to the salivary glands (except parotid) and the lacrimal gland
VIII	Vestibulocochlear nerve	Vestibular nuclei, Cochlear nuclei	Senses sound, rotation and gravity (essential for balance & movement)
IX	Glossopharyngeal nerve	Nucleus ambiguus, Inferior salivary nucleus, Solitary nucleus	Receives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus
X	Vagus nerve	Nucleus ambiguus, Dorsal motor vagal nucleus, Solitary nucleus	Supplies branchiomotor innervation to most laryngeal and pharyngeal muscles; provides parasympathetic fibers to nearly all thoracic and abdominal viscera down to the splenic flexure; and receives the special sense of taste from the epiglottis
XI	Accessory nerve	Nucleus ambiguus, Spinal accessory nucleus	Controls muscles of the neck and overlaps with functions of the vagus
XII	Hypoglossal nerve	Hypoglossal nucleus	Provides motor innervation to the intrinsic muscles of the tongue and other glossal muscles