Cranial nerves: Overview

Cranial nerves: OverviewComponents and types of cranial nerves. Cranial nerve nuclei
~ 5 min

The peripheral nervous system is the part of the nervous system located outside the brain and spinal cord. It regulates the functions of our body.

The peripheral nervous system has two functional units: afferent (or sensory) and efferent (or motor).

Here, based on the principle of functional autonomy, we can distinguish two more divisions of the PNS:

  • Somatic nervous system (that controls voluntary actions and conveys sensory information from the skin, skeletal muscles and joints)
  • And the autonomic nervous system (that controls the involuntary activities within the body, as the work of our stomach, for instance).

The anatomical components of the PNS are ganglia (which are the groups of cell bodies) and nerves (which are the bundles of axons running together).

The latter include 31 pairs of spinal nerves (that arise from the spinal cord) and 12 pairs of cranial nerves (that arise from the brain).

Cranial nerves

In this note, we will briefly discuss the cranial nerves (nervi craniales)

Cranial nerves (nervi craniales)
Cranial nerves (nervi craniales)

To get familiar with these nerves, let’s list all of them in one place.

  • The first cranial nerve (CN I), the olfactory nerve (nervus olfactorius) is responsible for olfaction (or the sense of smell)
Olfactory nerve (nervus olfactorius)
Olfactory nerve (nervus olfactorius)
Olfactory nerve (nervus olfactorius)
Olfactory nerve (nervus olfactorius)
  • The second cranial nerve (CN II), the optic nerve (nervus opticus) is responsible for vision
Optic nerve (nervus opticus)
Optic nerve (nervus opticus)
Optic nerve (nervus opticus)
Optic nerve (nervus opticus)

There are three cranial nerves in charge of eye movement:

  • The third cranial nerve (CN III), the oculomotor nerve (nervus oculomotorius)
Oculomotor nerve (nervus oculomotorius)
Oculomotor nerve  (nervus oculomotorius)
Oculomotor nerve (nervus oculomotorius)
Oculomotor nerve  (nervus oculomotorius)
  • The fourth cranial nerve (CN IV), the trochlear nerve (nervus trochlearis)
Trochlear nerve (nervus trochlearis)
Trochlear nerve (nervus trochlearis)
Trochlear nerve (nervus trochlearis)
Trochlear nerve (nervus trochlearis)
  • The sixth cranial nerve (CN VI), the abducens nerve (nervus abducens)
Abducens nerve (nervus abducens)
Abducens nerve (nervus abducens)
Abducens nerve (nervus abducens)
Abducens nerve (nervus abducens)
  • The fifth cranial nerve (CN V), the trigeminal nerve (nervus trigeminus) is responsible for mastication and sensation of the facial area
Trigeminal nerve (nervus trigeminus)
Trigeminal nerve (nervus trigeminus)
  • The seventh cranial nerve (CN VII), the facial nerve (nervus facialis), in charge of facial expressions, sensory innervation to the taste buds of the anterior ⅔ of the tongue, salivation, and lacrimation.
nerve (nervus facialis)
 nerve (nervus facialis)
nerve (nervus facialis)
 nerve (nervus facialis)
  • The eighth cranial nerve (CN VIII), the vestibulocochlear nerve (nervus vestibulocochlearis), supplies the hearing and equilibrium receptors
Vestibulocochlear nerve (nervus vestibulocochlearis)
Vestibulocochlear nerve (nervus vestibulocochlearis)
Vestibulocochlear nerve (nervus vestibulocochlearis)
Vestibulocochlear nerve (nervus vestibulocochlearis)
  • The ninth cranial nerve (CN IX), the glossopharyngeal nerve (nervus glossopharyngeus) is responsible for multiple functions. These include speech, swallowing, salivation, sensory innervation of the pharynx and some other structures, sensory innervation to the taste buds of the posterior ⅓ of the tongue, and salivation. It also receives signals from chemoreceptors in the carotid bodies, which help regulate respiration and baroreceptors of the carotid sinus, which help monitor blood pressure.
Glossopharyngeal nerve (nervus glossopharyngeus)
Glossopharyngeal nerve (nervus glossopharyngeus)
Glossopharyngeal nerve (nervus glossopharyngeus)
Glossopharyngeal nerve (nervus glossopharyngeus)
  • The tenth cranial nerve (CN X), the vagus nerve (nervus vagus), is responsible for swallowing, speech, sensory innervation of the pharynx, larynx, thoracic and abdominal organs, as well as the baroreceptors of the aortic arch, chemoreceptors in the carotid and aortic bodies, and from taste buds of the epiglottis.
Vagus nerve (nervus vagus)
Vagus nerve (nervus vagus)
Vagus nerve (nervus vagus)
Vagus nerve (nervus vagus)
  • The eleventh cranial nerve (CN XI), the accessory nerve (nervus accessorius) innervates the trapezius and sternocleidomastoid muscles, which together move head and neck, and the nerve carries sensory proprioceptive information from these muscles.
Accessory nerve (nervus accessorius)
Accessory nerve (nervus accessorius)
Accessory nerve (nervus accessorius)
Accessory nerve (nervus accessorius)
  • The twelfth cranial nerve (CN XII), the hypoglossal nerve (nervus hypoglossus) sends fibers to the muscles of the tongue, providing its movement.
Hypoglossal nerve (nervus hypoglossus)
Hypoglossal nerve (nervus hypoglossus)
Hypoglossal nerve (nervus hypoglossus)
Hypoglossal nerve (nervus hypoglossus)

If we take the first letter of each nerve, we can build a mnemonic to help remember the cranial nerve names:

Only One Of The Two Athletes Felt Very Good, Victorious, And Healthy

Now let’s discuss the terms special, general, somatic and visceral. The information is considered special if it’s related to our special senses (vision, smell, taste, hearing and balance), while general is referred to information from everywhere else. The information carried by a nerve is called somatic if it goes to or from the skeletal muscles and skin, or visceral if it travels to or from our internal organs.

Broadly speaking, the cranial nerve consists of four components:

  • Somatic motor component
  • Visceral motor component
  • Visceral sensory component
  • Somatic sensory component

Further, these components can be classified in a more comprehensive manner, but we will discuss this in greater detail in subsequent videos.

Now let’s take a look at the diagram. As we can see, some nerves have only a sensory component, others have only a motor component, and others have both. Thus, all cranial nerves can be divided into purely sensory, purely motor, while most nerves are mixed.

The easiest way to remember if a nerve is sensory, motor or both, is to use this mnemonic trick:

“Some say money matters, but my brother says big brains matter most”

Cranial nerve nuclei

If the cranial nerve has a sensory component (whether visceral or somatic), then it has a sensory nucleus. If it has a motor component, then it has a motor nucleus. Finally, if it has a visceral component (the motor part, specifically), then it has an autonomic (or visceral) nucleus.

The names of the nuclei are not crucial for now. What we should really pay attention to at this point is the distribution of the nuclei in the brain stem. The midbrain contains the nuclei of the 3rd and 4th cranial nerves, the pons contains nuclei of the 5th, 6th, 7th, and 8th cranial nerves, and the medulla oblongata contains the nuclei of the 9th, 10th, 11th, and 12th cranial nerves (this is the Rule of Fours if we conditionally consider the 1st and 2nd cranial nerves also to be part of the midbrain)

There are several exceptions to this rule, which we will discuss in greater detail in subsequent videos.

Dictionary

Cranial nerves: Overview

Peripheral nervous system
systema nervosum periphericum
Cranial nerves
nervi craniales
Olfactory nerve
nervus olfactorius
Optic nerve
nervus opticus
Oculomotor nerve
nervus oculomotorius
Trochlear nerve
nervus trochlearis
Abducens nerve
nervus abducens
Trigeminal nerve
nervus trigeminus
Facial nerve
nervus facialis
Vestibulocochlear nerve
nervus vestibulocochlearis
Glossopharyngeal nerve
nervus glossopharyngeus
Vagus nerve
nervus vagus
Accessory nerve
nervus accessorius
Hypoglossal nerve
nervus hypoglossus
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