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Cranial Nerves (Part 1)





Cranial Nerves (Part 1)


Chapter 7.4: Cranial Nerves (Part 1)

1. Olfactory Nerve (I)
  • Structure:
    • Origin: From olfactory receptor cells in the upper part of the nasal mucosa.
    • Pathway:
      • Central process: Axons of the receptor cells pass through the cribriform plate to the olfactory bulb.
      • Olfactory bulb: Connects to the olfactory tract.
      • Olfactory tract: Connects to the olfactory cortex.
    • Termination: In the olfactory cortex of the temporal lobe.
  • Note:
    • The olfactory nerve is a sensory nerve responsible for the sense of smell.
    • It is the only cranial nerve that does not pass through the brainstem.
2. The olfactory nerve (I) goes from:
  • Olfactory bulb => Olfactory tract.
3. The olfactory nerve (I) ends in:
  • The temporal lobe.
4. Optic Nerve (II)
  • Structure:
    • Origin: From photoreceptor cells in the retina.
    • Pathway:
      • Crossing fibers: Fibers from the nasal retina cross at the optic chiasm.
      • Non-crossing fibers: Fibers from the temporal retina continue straight.
      • Then: Both crossing and non-crossing fibers travel to the lateral geniculate nucleus and superior colliculus.
      • Lateral geniculate nucleus: Sends fibers to the visual cortex of the calcarine sulcus (occipital lobe).
    • Termination: In the visual cortex of the calcarine sulcus in the occipital lobe.
  • Note:
    • The optic nerve is a sensory nerve responsible for the sense of sight.
    • The optic chiasm is where the two optic nerves from each eye meet.
    • The visual center is located in the occipital lobe.
5. Optic Nerve (II): The fibers that cross at the optic chiasm are from:
  • The nasal retina.
6. Optic Nerve (II): The fibers that go to the lateral geniculate nucleus and superior colliculus after the optic chiasm are from:
  • The nasal retina (crossed) and temporal retina (uncrossed).
7. Optic Nerve (II): The visual center:
  • The occipital lobe.
8. Optic Nerve (II): From front to back:
  • Optic nerve => Optic tract => Lateral geniculate nucleus => Optic radiation.
9. Oculomotor Nerve (III)
  • Structure:
    • Motor nerve: Controls the extraocular muscles.
    • Origin: Oculomotor nucleus in the midbrain.
    • Autonomic fibers: Preganglionic parasympathetic fibers from autonomic nuclei within the midbrain.
    • Exit: From the anterior surface of the midbrain, runs forward through the lateral wall of the cavernous sinus.
  • Note:
    • The oculomotor nerve is a motor nerve that controls the levator palpebrae superioris muscle and some of the extraocular muscles.
    • The oculomotor nerve also has a function in regulating pupil constriction through its parasympathetic autonomic fibers.
10. Oculomotor Nerve (III): Origin:
  • Midbrain.
11. Oculomotor Nerve (III): Autonomic nucleus:
  • Parasympathetic nucleus.
12. Oculomotor Nerve (III): Autonomic fibers:
  • Preganglionic parasympathetic fibers.
13. Oculomotor Nerve (III) exits from:
  • The anterior surface of the midbrain.
14. Oculomotor Nerve (III) runs through:
  • The lateral wall of the cavernous sinus.
15. Oculomotor Nerve (III) enters the orbit through:
  • The superior orbital fissure.
16. Oculomotor Nerve (III): Motor innervation:
  • Levator palpebrae superioris muscle
  • 3 extraocular muscles (superior rectus, inferior rectus, medial rectus)
17. Oculomotor Nerve (III): Motor innervation, EXCEPT:
  • Superior oblique muscle.
18. Oculomotor Nerve (III): Motor innervation, EXCEPT:
  • Lateral rectus muscle.
19. Oculomotor Nerve (III): Autonomic innervation:
  • Ciliary muscle and sphincter pupillae muscle.
20. Trochlear Nerve (IV): Origin:
  • Midbrain.
21. Trochlear Nerve (IV): Origin:
  • Posterior surface of the midbrain.
22. Trochlear Nerve (IV): Motor innervation:
  • Superior oblique muscle.
23. Abducens Nerve (VI): Origin:
  • Pons.
24. Abducens Nerve (VI): Origin is in the pontine tegmentum, near the floor of the fourth ventricle:
  • Correct.
25. Abducens Nerve (VI) exits the brainstem at:
  • The pontomedullary junction.
26. Abducens Nerve (VI): Motor innervation:
  • Lateral rectus muscle.
27. Trigeminal Nerve (V)
  • Structure:
    • Mixed nerve: Contains a large sensory root and a small motor root.
    • Sensory root: Connects the trigeminal ganglion to the anterolateral surface of the pons.
    • Motor root: Originates in the pons, travels with the sensory root, and separates to innervate the muscles of mastication.
    • Function:
      • Sensory: Provides sensation to the face.
      • Motor: Controls the muscles of mastication.
  • Note:
    • The trigeminal nerve is the largest and most complex cranial nerve.
    • The trigeminal nerve divides into three branches:
      • Ophthalmic branch (V1): Provides sensation to the forehead, eyelids, nose.
      • Maxillary branch (V2): Provides sensation to the cheek, upper teeth, nose.
      • Mandibular branch (V3): Provides sensation to the chin, lower teeth, and motor innervation to the muscles of mastication.
28. Trigeminal Nerve (V) is formed by:
  • Large sensory root + small motor root.
29. Trigeminal Nerve (V): The sensory root connects the trigeminal ganglion to:
  • The anterolateral surface of the pons.
30. Trigeminal Nerve (V): Motor root origin:
  • Pons.
31. Trigeminal Nerve (V): The origin of the trigeminal nerve is:
  • The anterolateral surface of the pons.
32. Trigeminal Nerve (V): Ophthalmic branch (V1) – Sensory innervation:
  • Eyeball
  • Anterior nasal mucosa
  • Upper eyelid, skin of the forehead and vertex
  • Some paranasal sinuses
33. Trigeminal Nerve (V): Ophthalmic branch (V1) – Pathway:
  • Passes through the lateral wall of the cavernous sinus
  • Below CN 3, 4
  • Reaches the superior orbital fissure, divides into terminal branches
  • Lateral branch: Tentorial branch
34. Trigeminal Nerve (V): Ophthalmic branch (V1) – Pathway:
  • Passes through the lateral wall of the cavernous sinus.
35. Trigeminal Nerve (V): Ophthalmic branch (V1) – Pathway:
  • Passes through the lateral wall of the cavernous sinus.
36. Trigeminal Nerve (V): Ophthalmic branch (V1) is located below:
  • CN 3, 4.
37. Trigeminal Nerve (V): Ophthalmic branch (V1) – Lateral branch:
  • Tentorial branch.
38. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches, EXCEPT:
  • Tentorial branch.
39. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Lacrimal nerve:
  • Runs along the superior border of the lateral rectus muscle to the lacrimal gland.
  • Branches into the conjunctiva of the upper eyelid and the lateral upper corner of the eye.
  • Continues with the zygomatic branch of the maxillary nerve.
40. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Lacrimal nerve:
  • Runs along the superior border of the lateral rectus muscle to the lacrimal gland.
41. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Lacrimal nerve:
  • Runs along the superior border of the lateral rectus muscle to the lacrimal gland.
42. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Lacrimal nerve branches into:
  • Conjunctiva of the upper eyelid and the lateral upper corner of the eye.
43. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Lacrimal nerve branches into:
  • Conjunctiva of the upper eyelid and the lateral upper corner of the eye.
44. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Lacrimal nerve continues with:
  • The zygomatic branch of the maxillary nerve.
45. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Frontal nerve:
  • Runs under the roof of the orbit.
  • Divides into the supratrochlear nerve and supraorbital nerve.
  • All 3 nerves loop around the superior border of the orbit to innervate the skin of the upper eyelid and forehead.
46. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Frontal nerve:
  • Runs under the roof of the orbit.
46. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Frontal nerve divides into:
  • The supratrochlear nerve and supraorbital nerve.
47. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Frontal nerve innervates:
  • The skin of the upper eyelid and forehead.
48. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Nasociliary nerve:
  • Crosses over the optic nerve.
49. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Nasociliary nerve – branches:
  • Branch to the ciliary ganglion and long ciliary nerves enter the eyeball.
  • Posterior ethmoidal nerve to the sphenoid sinus and posterior ethmoid sinuses.
  • Anterior ethmoidal nerve to the nasal mucosa, nasal bridge.
  • Infratrochlear nerve to the medial corner of the eye and the upper part of the nasal bridge.
50. Trigeminal Nerve (V): Ophthalmic branch (V1) – Terminal branches – Nasociliary nerve – branches – Branch to the ciliary ganglion and long ciliary nerves:
  • Enter the eyeball.
General Notes:
  • This article focuses on the structure and function of the first 5 cranial nerves: Olfactory (I), Optic (II), Oculomotor (III), Trochlear (IV), and Abducens (VI).
  • In addition to the information listed, each cranial nerve has unique characteristics that require further study.
  • To better understand the structure and function of cranial nerves, consult additional professional resources on neuroanatomy.


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