The 12 Cranial Nerves

The nervous system is composed of 12 pairs of cranial nerves that controls all our body processes, motor and sensory. These cranial nerves are located at the bottom portion of the brain distributed into the four main parts: Diencephalon, Midbrain, Pons, and Medulla.

CRANIAL NERVES:

I           –      Olfactory

II          –      Optic

III         –       Oculomotor

IV         –      Trochlear

V          –      Trigeminal

VI         –      Abducens

VII        –       Facial

VIII       –       Auditory

IX         –       Glossopharyngeal

X          –       Vagus

XI         –       Accessory

XII        –       Hypoglossal    

*Note: The cranial nerves are named in order of their arrangement.  The  Olfactory nerve located at the topmost portion appointed the label  I while the Hypoglossal located at the bottom is XII.  This way, it is  easier to remember each nerves’ location according to their number.

General Information:

  • There are 12 pairs of Cranial Nerves
  • All nuclei are located at the brainstem (except I, II, XI)
  • I and II – not real nerves, they are fiber tracts of the brain (CNS), thus they should not be considered a part of the Peripheral nervous system (PNS)
  • I, II, and VIII – purely sensory nerves
  • III, IV, VI, XI, and XII – purely motor nerves
  • V, VII, IX, and X – mixed nerves. They have nuclei at the sensory portion and at the motor portion of the brainstem
  • III, IV, and VI – are responsible for eye movement and pupillary constriction
  • III, VII, IX, and X – are parasympathetic fibers (attached to glands)

Location:

CN I and II   –   Diencephalon

CN III and IV    –      Midbrain

CN VVIII      –        Pons

CN IXXII       –       Medulla

Location of Nuclei:

Sensory            –           Side

Motor              –           Middle

Mixed              –           Both sides

Somatic afferent         –           Periphery

Somatic Efferent         –           Middle portion

Functional Components:

1. Somatic Efferent (striated muscles)   – III, IV, VI

2. Branchial Efferent/Special Visceral    – V, VII, IX, X, XI

3. Visceral Efferent (Parasympathetic) – III, VII, IX, X

4. Visceral Afferent

a. General Visceral Afferent (GVA) – IX, X

b. Special Visceral Afferent (SVA) – VII, IX, X

 5. Somatic Afferent                                     – V, VII, IX, X

 6. Special Sensory Afferent                      – I, II, VIII

            Motor

           Sensory

  • Bigger
  • Lesser in number
  • Smaller
  • Numerous