The human nervous system. Sky blue is PNS; yellow is CNS.
Left View of the human brain from below, showing origins of cranial nerves. Right Juxtaposed skull base with foramina in which many nerves exit the skull.
3D Medical Animation still shot of Lumbosacral Plexus
The oculomotor (III), troclear (IV) and abducens (VI) nerves supply the muscle of the eye. Damage will affect the movement of the eye in various ways, shown here.
The facial nerve (VII) supplies the muscles of facial expression. Damage to the nerve causes a lack of muscle tone on the affected side, as can be seen on the right side of the face here.
A damaged glossopharyngeal nerve (IX) may cause the uvula to deviate to the affected side.
The cranial nerves in the horse.
Ventral view of a sheep's brain. The exits of the various cranial nerves are marked with red.

In the somatic nervous system, the cranial nerves are part of the PNS with the exception of the optic nerve (cranial nerve II), along with the retina.

- Peripheral nervous system

The cranial nerves are considered components of the peripheral nervous system (PNS), although on a structural level the olfactory (I), optic (II), and trigeminal (V) nerves are more accurately considered part of the central nervous system (CNS).

- Cranial nerves
The human nervous system. Sky blue is PNS; yellow is CNS.

4 related topics

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Schematic diagram showing the central nervous system in yellow, peripheral in orange

Central nervous system

Part of the nervous system consisting primarily of the brain and spinal cord.

Part of the nervous system consisting primarily of the brain and spinal cord.

Schematic diagram showing the central nervous system in yellow, peripheral in orange
Dissection of a human brain with labels showing the clear division between white and gray matter.
Diagram of the columns and of the course of the fibers in the spinal cord. Sensory synapses occur in the dorsal spinal cord (above in this image), and motor nerves leave through the ventral (as well as lateral) horns of the spinal cord as seen below in the image.
Different ways in which the CNS can be activated without engaging the cortex, and making us aware of the actions. The above example shows the process in which the pupil dilates during dim light, activating neurons in the spinal cord. The second example shows the constriction of the pupil as a result of the activation of the Eddinger-Westphal nucleus (a cerebral ganglion).
A map over the different structures of the nervous systems in the body, showing the CNS, PNS, autonomic nervous system, and enteric nervous system.
Schematic image showing the locations of a few tracts of the spinal cord.
Reflexes may also occur without engaging more than one neuron of the CNS as in the below example of a short reflex.
Diagram depicting the main subdivisions of the embryonic vertebrate brain, later forming forebrain, midbrain and hindbrain.
Development of the neural tube

In vertebrates the CNS also includes the retina and the optic nerve (cranial nerve II), as well as the olfactory nerves and olfactory epithelium.

Microscopically, there are differences between the neurons and tissue of the CNS and the peripheral nervous system (PNS).

Nerves (yellow) in the arm

Nerve

Nerves (yellow) in the arm
Cross-section of a nerve
Micrograph demonstrating perineural invasion of prostate cancer. H&E stain.

A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system.

Cranial nerves innervate parts of the head, and connect directly to the brain (especially to the brainstem). They are typically assigned Roman numerals from 1 to 12, although cranial nerve zero is sometimes included. In addition, cranial nerves have descriptive names.

The left optic nerve and the optic tracts.

Optic nerve

The left optic nerve and the optic tracts.
A fundus photograph showing the back of the retina. The white circle is the beginning of the optical nerve.
MRI scan of human eye showing optic nerve.
The ophthalmic artery derived from internal carotid artery and its branches. (optic nerve is yellow)
Superficial dissection of brain-stem. Lateral view.
Dissection of brain-stem. Lateral view.
Scheme showing central connections of the optic nerves and optic tracts.
Nerves of the orbit. Seen from above.
Nerves of the orbit, and the ciliary ganglion. Side view.
The terminal portion of the optic nerve and its entrance into the eyeball, in horizontal section.
Structures of the eye labeled
This image shows another labeled view of the structures of the eye
Optic nerve.Deep dissection.Inferior view.
Optic nerve.Deep dissection.Inferior view.
Optic nerve
Optic nerve
Human brain dura mater (reflections)
Optic nerve
Optic nerve
Optic nerve
Cerebrum.Inferior view.Deep dissection
Cerebral peduncle, optic chasm, cerebral aqueduct. Inferior view. Deep dissection.

The optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain.

The optic nerve has been classified as the second of twelve paired cranial nerves, but it is technically part of the central nervous system, rather than the peripheral nervous system because it is derived from an out-pouching of the diencephalon (optic stalks) during embryonic development.

Autonomic nervous system innervation, showing the parasympathetic (craniosacral) systems in blue.

Parasympathetic nervous system

One of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system.

One of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system.

Autonomic nervous system innervation, showing the parasympathetic (craniosacral) systems in blue.

Specific nerves include several cranial nerves, specifically the oculomotor nerve, facial nerve, glossopharyngeal nerve, and vagus nerve.

The parasympathetic nerves are autonomic or visceral branches of the peripheral nervous system (PNS).