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Neuroanatomy II > 17 - Cranial Nerves III > Flashcards

17 - Cranial Nerves III Flashcards

1
Q

CN V

A

Trigeminal nerve

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2
Q

CN V function

A

The trigeminal nerve provides:

  • sensory innervation to the face and underlying mucous membranes
  • motor innervation to the muscles of mastication
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3
Q

Describe the general sensation component of CN V

A

GSA:

General sensation from the scalp, cranial dura, major intracranial blood
vessels, face, cornea, conjuctiva, lacrimal gland, mucous membrane of the: paranasal sinuses, nasal cavity, and oral cavity; teeth, gums, and hard palate

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4
Q

Describe the general proprioception component of CN V

A

GP:

General proprioception
extraocular muscles, TMJ, muscles of mastication, and periodontal ligament (PDL) surrounding roots of teeth.

Proprioceptive sense helps us so that we can chew better and not bite our tongue when we are eating or when we are speaking

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5
Q

Describe the skeletal motor component of CN V

A

SVE:

Skeletal motor (BranchioMOTOR) to the muscles of mastication and a
few other muscles (the trigeminal nerve is the nerve of the 1st branchial / pharyngeal arch). The muscles of mastication include the temporalis, masseter, and the medial and lateral pterygoids), also innervates the mylohyoid, anterior belly of the digastric, tensor tympani, and tensor veli palatini
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6
Q

Describe the funciton of the tensor tympani

A

The tensor tympani attaches to the malleus and the malleus attaches to the inner surface of the tympanic membrane. When the TT contracts,
it tenses the tympanic membrane (becomes stiffer), preventing it from vibrating, therefore does not move the malleus.

This tiny muscle protects the eardrum from loud sounds and diminishes the transmission of sound vibrations from the eardrum to the inner ear (via the 3 ossicles: malleus – incus, stapes).

When chewing is initiated (by motor fibers of V), TT contracts.

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7
Q

What is UNIQUE about CN V?

A

in addition to carrying its own fibers, the trigeminal nerve is the only cranial nerve that carries parasympathetic “hitch-hickers” of other cranial nerves and sympathetic fibers from the internal carotic plexus, in its own branches.

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8
Q

Which three nerves does it carry parasympathetics for?

A

Oculomotor
Facial
Glosopharyngeal

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9
Q

Parasympathetic “hitch-hikers” of the oculomotor nerve

A

oculomotor nerve: parasympathetic fibers leave the ciliary ganglion via the ophthalmic division (V1) to terminate in the sphincter pupillae and ciliary muscles

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10
Q

Parasympathetic “hitch-hikers” of the facial

A

There are TWO sets of fibers

1 - facial nerve: parasympathetic fibers leave the pterygopalatine ganglion via the maxillary division (V2) to terminate in the lacrimal, nasal and palatine glands

2 - facial nerve: parasympathetic fibers leave the submandibular ganglion via the mandibular division (V3) to terminate in the sublingual and submandibular glands

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11
Q

Parasympathetic “hitch-hikers” of the glossopharyngeal nerve

A

glossopharyngeal nerve:

parasympathetic fibers leave the otic ganglion via the mandibular division (V3) to terminate in the parotid gland

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12
Q

What other “hitch-hikers” does CN V carry?

A

Sympathetic “hitch-hikers” from the internal carotid plexus are carried by the ophthalmic division (V1) to the dilator pupillae muscle

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13
Q

Three divisions of CN V

A

1 - ophthalmic division (sensory)
2 - maxillary division (sensory)
3 - mandibular division (mixed: sensory and motor)

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14
Q

Three sensory nuclei of CN V

A

1 - Mesencephalic nucleus
2 - Principal (main, chief) sensory nucleus
3 - Spinal nucleus

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15
Q

Mesencephalic sensory nucleus of CN V

A

mesencephalic nucleus of the trigeminal

Location: in midbrain

Function: general proprioception from muscles innervated by the trigeminal nerve, and the periodontal ligament (PDL).

The muscles of mastication, and PDL contain nerve receptors that convey information to the brain about the position of the jaw

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16
Q

Principal (main, cheif) sensory nucleus of CN V

A

principal (main, chief) sensory nucleus of the trigeminal

Location: in midpons

Function: discriminatory (fine, detailed) touch and pressure sensation from orofacial structures, GP from extraocular muscles and TMJ.

Sensory input is relayed to the principal nucleus by the central processes of sensory neurons located in the V ganglion

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17
Q

What do the mesencephalic and principal nuclei have in common?

A

The above 2 nuclei are similar to / are the head counterpart of the dorsal column nuclei (“nucleus gracilis” and “nucleus cuneatus”)

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18
Q

Spinal nucleus of the trigeminal

A

Spinal nucleus of the trigeminal

Location: in pons, medulla, extends to spinal cord levels of C1 – C2

It is sitting on top of the substantia gelatinosa of the spinal cord; it resembles the substantia gelatinosa structurally and functionally

Function: nociceptive and thermal sensation and some tactile sense from orofacial structures

Note: the trigeminal nerve is the only cranial nerve that has a “pain nucleus”.

19
Q

Describe the one motor nucleus of the trigeminal

A

Motor nucleus of the trigeminal

Location: in midpons
Function: contains the cell bodies of motor neurons whose axons gather to form the motor root of the trigeminal nerve.

These neurons innervate the muscles of mastication and a few other muscles

20
Q

Four tracts of trigeminal nerve

A

spinal tract of trigeminal
ventral trigeminal lemniscus
dorsal trigeminal lemniscus
trigeminoreticular fibers

21
Q

Spinal tract of trigeminal (origin, course, termination, function)

A

origin:
pons, near sensory root of V

course:
descends in pons, through medulla, to C1 or C2

termination:
spinal nucleus of trigeminal (in pons, medulla, C1-C2)

function:
pain, temperature, some tactile sense

  • merges with Lissauer’s tract at upper cervical levels
22
Q

Ventral trigeminal lemniscus (origin, course, termination, function)

A

AKA ventral trigeminothalamic tract

origin:
spinal nucleus of V

course:
ascends to the thalamus

termination:
VPM nucleus of the thalamus

function:
pain, temperature, tactile sensation

  • is similar to the “spinothalamic tract” of the anterolateral system (ALS)
23
Q

(origin, course, termination, function)

A

AKA dorsal trigeminothalamic tract

origin:
main sensory nucleus of V

course:
ascends to the thalamus

termination:
VPM nucleus of the thalamus

function:
discriminative (fine, detailed) touch, proprioception

*Is similar to the “medial lemniscus” (of the DC-ML pathway)

24
Q

(origin, course, termination, function)

A

trigeminoreticular fibers

origin:
main sensory nucleus
spinal nucleus of V

course:
project to nearby brainstem reticular formation, bilaterally

termination:
reticular formation

function:
arousal, produced by stroking or slapping the face, or “smelling salts” (containing ammonia)

  • similar to / counterparts of the “spinoreticular tract”
25
Q

Four pathways of trigeminal nerve

A

1 - discriminatory (fine) touch and pressure sensation
2 - pain and temperature sensation
3 - motor pathway
4 - general proprioception pathway

26
Q

Discriminatory (fine) touch and pressure sensation from the orofacial region

A

a. 1st order neuron cell bodies are located in the trigeminal ganglion
b. their central processes terminate in the main sensory nucleus of V
c. 2nd order neurons are located in the main sensory nucleus of V
d. 2nd order neuron axons join the dorsal trigeminal lemniscus to ascend to the VPM nucleus of the thalamus
e. 3rd order neurons in VPM project to the postcentral gyrus (representing the orofacial region)

27
Q

Pain and temperature sensation from the orofacial region

A

a. 1st order neuron cell bodies are located in the trigeminal ganglion
b. their central processes descend in the spinal tract of V
c. they terminate in spinal nucleus of V
d. 2nd order neurons located in the spinal nucleus of V join the ventral trigeminal lemniscus to ascend to the VPM
e. 3rd order neurons in the VPM project to the postcentral gyrus, as well as the anterior cingulate and anterior insular cortices. The cingulate and insular cortices process the affective (emotional) component of pain

28
Q

Motor pathway of the trigeminal nerve

A

a. lower motor neuron cell bodies are located in the motor nucleus of V
b. their axons exit the brainstem at midpontine level as the motor root of V
c. axons join the mandibular division of the trigeminal to distribute to all the muscles innervated by the trigeminal

29
Q
  1. general proprioception (GP) pathway of the trigeminal nerve
A

a. 1st order neuron cell bodies are located in the mesencephalic nucleus
Note that this is an unusual nucleus because it contains pseudounipolar neurons instead of multipolar neurons enclosed in other nuclei. Pseudounipolar neurons are typically found in the peripheral nervous system and are enclosed in sensory ganglia such as the trigeminal and DRG and not in nuclei. These pseudounipolar neurons though, are the only primary afferents whose cell bodies are located within the CNS

b. their peripheral processes distribute with branches of the trigeminal nerve
c. their central processes terminate in the main sensory nucleus of V (for sensation) and the motor nucleus of V (for reflex movement of the jaw)

30
Q

What is the role of the trigeminal nerve in the corneal blink reflex?

A
  1. the ophthalmic division of the trigeminal nerve forms the afferent (sensory) limb of the corneal blink reflex arc
  2. the facial nerve forms the efferent (motor) limb of the reflex arc
31
Q

Damage to ophthalmic division, will:

A
  1. reduce sensation over the V1 zone

2. inhibit the corneal blink reflex

32
Q

Damage to the maxillary division, will:

A

reduce or inhibit sensation over the V2 zone

33
Q

Damage to the mandibular division, will:

A
  1. reduce or inhibit sensation over the V3 zone
  2. may cause paralysis of the muscles of mastication,
    resulting in the jaw to deviate to the side of the lesion
34
Q

Trigeminal neuralgia characteristics

A

Is characterized by sharp, excruciating, intermittent pain on one side of the face.

Spontaneous onset.

Each attack lasts for only a few seconds, but individual feels fine between attacks.

The excruciating pain is triggered by touching of the affected side of the face, brushing teeth, or moving the mouth while talking, or chewing.

35
Q

Two possible causes

A
  1. demyelination of the trigeminal nerve (resulting from demyelinating disease) as it enters the pons of the brain stem.
  2. vascular structures or “loops” may develop next to, or surround (compressing) one of the divisions of the trigeminal nerve (ophthalmic or maxillary). The compression results in demyelination
36
Q

Ephaptic transmission

A

Demyelination results in ephaptic transmission of nerve impulses (“short
circuiting” or “cross-talk” between adjacent fibers).

37
Q

Severity of pain

A

The pain may be so excruciating, that it may cause the patient to contemplate
suicide. Thus this condition should be taken seriously by the physician.

38
Q

SUMMARY - the trigeminal nerve is the only cranial nerve that…

A

1 - carries “hitch-hikers”
2 - has 4 parasympathetic ganglia suspended from its three divisions
3 - has a pain nucleus

39
Q

“Hitch-hikers” review

A

Parasympathetic fibers belonging to other cranial nerves

i. oculomotor
ii. facial
iii. glossopharyngeal

Sympathetic fibers from the internal carotid plexus

40
Q

4 parasympathetic ganglia in three divisions review

A

1 - ophthalmic division — suspends ciliary ganglion (of CN III)

2 - maxillary division — suspends pterygopalatine ganglion (of CN VII)

3 - mandibular division — suspends otic and submandibular ganglia
(of CN IX and CN VII, respectively)

41
Q

Pain nucleus review

A

Since the following nerves do not have a pain nucleus of their own, they pick up nociception from their territories and then “dump” nociception in the trigeminal system for further processing

a. facial nerve
b. glossopharyngeal nerve
c. vagus nerve

42
Q

Where else does the trigeminal nerve process nociception from?

A

Note that the trigeminal nerve also processes nociception from the sensory territory of the dorsal rami of the upper (1-2) cervical nerves.

43
Q

Lesion in trigeminal nerve review

A

A lesion to the trigeminal motor root will result in deviation of the jaw to the side of the lesion (upon protrusion of the jaw)

Neuroanatomy II (10 decks)

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