Cranial nerves 1-6

Question 1

What is the function of the olfactory nerve?

Answer 1

Strictly sensory to the special sense of smell.

Question 2

How do the olfactory functions to process the smell?

Answer 2

The nerve fibers penetrate the cribriform plates and branch into the superior mucosa of the nasal cavity

• Whenever we breath in the conchae mixes around the air allowing chemical aerosols to dissolve in the mucosa. They then reach the superior zone then they bind to chemoreceptors that are associated with specific nerve endings.
• The combined message from these receptors track back to the CNS and is interpreted as an aroma.

Question 3

How can you damage the olfactory nerve?

Question 4

What is anosmia?

Answer 4

the loss of the sense of smell, either total or partial. It may be caused by head injury, infection, or blockage of the nose.
-Damage to olfactory results in anosmia.

Question 5

How does the optic nerve function in interpreting the special sense of sight?

Answer 5

it conveys sight through photoreceptors embedded in the retina.

Question 6

Whats the route of the optic nerve?

Answer 6

-It passes through the optic canal and the middle of the posterior orbit to blend with the sclera (The white of the eye) on the back of the eye.

Question 7

What is a peculiar fact about the embryology of the optic nerve?

Answer 7

• The retina is derived from the optic cup which is a part of the embryonic diencephalon which means the entire optic tract is considered to be an extension of the brain rather than a true nerve.

Question 8

What is the function of the optic chiasm?

Answer 8

connects the left and right optic nerves.

Question 9

What is decussation?

Answer 9

1 : the action of crossing (as of nerve fibers) especially in the form of an X. 2 : a crossed tract of nerve fibers passing between centers on opposite sides of the nervous system.

Question 10

Decussation of the eye is limited; how is it limited?

Answer 10

• Decussation occurs only to the axons of the medial half of each retina and not the lateral half of the retina.
• The axons of the lateral half of the retina will not decussate; they continue along the ipsilateral path to synapse on ganglia on the same side of the body.

Question 11

Why is the decussation of the eye split between the medial halves of the retina and lateral halves?

Answer 11

-Because all the objects perceived on the right visual field will be perceived by the left visual plane and vice versa.

Question 12

What results from a damage to the eye or the optic nerve anterior to the optic chiasm?

Answer 12

We would lose vision on the side where the damage occurred.

Question 13

What is the condition of bitemporal hemianopsia?

Answer 13

-Due to loss of vision in the periphery or temporal field. Th vision that results from Bitemporal hemianopsia is similar to the blinders that are used on horses to force them to look straight ahead.

Question 14

What would happen if there is a damage to optic nerve posterior to the optic chiasm?

Answer 14

-It would result in homonymous hemianopsia; this occurs from a stroke or another type of damage to the posterior of the optic tract.

Question 15

What is the pathway of the oculomotor nerve?

Answer 15

-it passes through the superior orbital fissure and splits into superior and inferior branches.

Question 16

What is the function of the oculomotor nerve?

Answer 16

=Supplies motor innervation to a majority of muscles that move the eye such as;

• levator palpebrae superiors
• superior, middle and inferior rectus
• The inferior oblique

Question 17

What is The Edinger–Westphal nucleus?

Answer 17

The Edinger–Westphal nucleus (accessory oculomotor nucleus) is the parasympathetic pre-ganglionic nucleus that innervates the iris sphincter muscle and the ciliary muscle.
- The edinger-Westphal nucleus is just above the main oculomotor nucleus

Question 18

What happens with damage to the oculomotor nerve?

Answer 18

• The superior oblique and the lateral rectus muscles are the only two muscles not supplied by the oculomotor nerve. these muscles will have a disproportionate pull on the eye.
• This results in the down and out sight.
• Also, loss of the parasympathetic will cause loss of function on the iris sphincter which will result in mydriasis (Pupillary dialation)

Question 19

What is diplopia?

Answer 19

Double vision due to inability to focus pupil on the same object.

Question 20

What is the pathway of the trochlear nerve?

Answer 20

-it passes through the superior orbital fissure and penetrates the surface of the superior oblique muscle.

Question 21

What happens when you damage trochlear nerve?

Answer 21

-Easily damage due to its long extension and small size and the only muscle damaged superior oblique muscle which causes intortion (Rotation of the eye inwards)

Question 22

What are intortion and extortion?

Answer 22

• When you lay down and watch tv sideways, your eye maintain a vertical vision and tv characters are not walking on walls due to the motion of intortion and extortion.
• intortion; superior oblique muscles rotate the superior margin of the eye towards the midline
• Extortion; inferior oblique muscle rotates the inferior margin of the eye towards the midline.

Question 23

What is the pathway of the trigeminal nerve?

Answer 23

-starts laterally from the pons and then it branches to supply sensory and motor innervation to the face.
-The three principal branches are the
ophthalmic, maxillary and mandibular branches.

Question 24

What is the pathway of V1 or the ophthalmic branch of trigeminal nerve?

Answer 24

=it enters via the superior orbital fissure and begins to branch extensively to perceive sensory information from the orbit.

Question 25

What is the final branch of V1z

Answer 25

pierces the medial orbital wall and branches into anterior and posterior ethmoidal nerves for sensation to the ethmoidal air cells.
-The anterior ethmoidal continues into the nasal cavity as the internal nasal branch which innervates the anterior aspect of the lateral nasal wall and septum

Question 26

What is the positioning of the V2 branching?

Answer 26

It goes to the external of the face underneath the zygomatic arch and underneath facial muscles.
-and goes to the lateral wall of the nasal cavity

Question 27

What is the importance of the sphenopalatine ganglion?

Answer 27

it’s the point of continuity between the external and internal branches of the V2.
-Its where numerous connections are going in and out.

Question 28

The largest and most inferior branch of the trigeminal is V3 splits into?

Answer 28

Anterior and posterior divisions

Question 29

What does the anterior division of V3 split into and supply

Answer 29

it splits immediately splits into a number of muscular branches that supply the muscles of mastication

• the first branch is to the masseteric nerve to the masseter muscle
• The deep temporal nerve supplies the temporalis mm.
• Lateral pterygoid nerve to the lateral pterygoid muscle
• Medial pterygoid nerve to medial pterygoid muscle
• Buccal branch from anterior division; sensory branch that serves the mucosa on the inside of the cheek and external surface of the cheek

Question 30

What does the posterior division of V3 split into and supply?

Answer 30

=more prominent in the infratemporal fossa;

• the inferior alveolar nerve; projects inferolateral and inter the mandible of the jaw through the mandibular foramen to enter the mandibular canal; supplies innervation to teeth and mucosa. It remerges superficially through the mental foramen and the mental nerve to supply skin around the chin.
• a small branch off the inferior alveolar nerve splits off prior to entering the mandible; it continues medial to the mandible and hypoglossal region. “its known as the nerve to mylohyoid and innervates the mylohyoid muscle and anterior belly of digastric.
• Another prominent division is the lingual nerve it courses into the hypoglossa region courses between hyoglossus and submandibular gland to supply senesory innerveation to the anterior 2/3 of tongue (Just somatic sensory taste is the facial nerve not V3)

A third branch is the auricular temporal nerve; giving a sesnory branch to parotid gland and anterior portion of the ear.

Question 31

What is trigeminal neuralgia?

Answer 31

-the onset of pain can be a gentle breeze or light touch; the pain is described as electric and stabbing in nature.

Question 32

The abducen nerve:

Answer 32

-it innervates the lateral rectus muscle to abduct the pupil when looking at something at the corner of the eye.

Question 33

Damage to the abducen nerve results in

Answer 33

-results in loss of lateral movement of the affected eye and leads to abducens nerve palsey.

Question 34

What does the frontal branch of V1 provide innervation for?

Answer 34

the frontal n branch of V1; this branches further into super trochlear n and supraorbital nerve; Thes two branches supply skin in this region

Question 35

What does the lateral division of V1 supply?

Answer 35

-Lateral division is the lacrimal nerve which innervates the lacrimal gland

Question 36

what are other divisions of V1?

Answer 36

• The nasal ciliary nerve runs towards the ethmoid making up the medial wall of the orbit. This then branches into the long ciliary nerve for general sensation to the eye.
• • also branches to infratrochlear nerve for sensation to the medial eyelid and bridge of noes