Cranial Nerves - Anatomy & Physiology

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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)

A summary of the cranial nerves is shown below:

Nerve	Attatchment to brain	Exit Foramen	Fibre Type	Location of cell bodies	Distribution
I - Occulomotor	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	Dorsal oblique 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

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