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Y1 - Neuroanatomy - Exam 2 > 6. Trigeminal > Flashcards

6. Trigeminal Flashcards

1
Q

3 functions of the trigeminal nerve

A
  1. motor
  2. general sensation
  3. proprioception
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2
Q

what is cranial nerve V?

A

trigeminal nerve

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3
Q

motor function of trigeminal nerve

A

mainly to muscles of mastication

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4
Q

general sensation of trigeminal nerve

A

(*touch, pain, temperature)

  • skin of face and anterior scalp
  • orbit
  • oral cavity & anterior 2/3 of tongue
  • nasal cavity and sinuses
  • maxillary and mandibular teeth
  • surpatentorial dura
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5
Q

proprioception of trigeminal nerve

A
  1. extraocular muscles
  2. muscles of mastication
  3. temporalmandibular joint (TMJ)
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6
Q

where is motor nucleus of CN V?

(path from nucleus to muscles)

A
  1. motor nucleus is w/in mid pons –>
  2. axons enter trigeminal nerve –>
  3. innervate muscles of mastication
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7
Q

key muscles of mastication innervated by trigeminal nerve

A
  1. lateral pterygoid
  2. medial pterygoid
  3. masseter (superficial)
  4. temporalis (superficial)
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8
Q

3 tests for motor function of CN V

A
  1. clenching teeth & palpating contraction of superficial muscles of mastication (masseter & temporalis)
  2. observing symmetry of lateral face (look for atrophy of muscle mass)
  3. opening jaw & looking for deviation of chin (towards side of lesion –> tests lateral pterygoid muscle)
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9
Q

which is the only muscle of mastication involved in opening mouth/deviating chin?

A

lateral pterygoid muscle –> jaw would deviate towards side of lesion, e.g. right lesion –> jaw deviates to right

(indicates motor trigeminal lesion)

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10
Q

basic organization of SENSORY trigeminal pathway

A
  1. dermatome of face –>
  2. 1st order neuron (cell bodies in sensory trigeminal ganglion); primary afferent –>
  3. 2nd order neuron (principal/spinal trigeminal nucleus) –> *decussation occurs/crosses midline –>
  4. 3rd order neuron (terminates in VPM nucleus of thalamus ) –> thru internal capsule to ascend –>
  5. post-central gyrus (of somatosensory cortex)
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11
Q

how many neurons and synapses in sensory trigeminal pathway?

is there decussation or no?

A
  • 3 neurons
  • 3 synapses
  • 1 decussation
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12
Q

name, cutaneous branches, and location of V1 dermatome?

A
  1. ophthalmic (corneal blink reflex)
  2. supraorbital
  3. forehead/nose/ area above eyes
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13
Q

name, cutaneous branches, and location of V2 dermatome?

A
  1. maxillary
  2. infraorbital nerves
  3. cheek (blush region); upper lip; up to hairline
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14
Q

name, cutaneous branches, and location of V3 dermatome?

A
  1. maxillary
  2. mental, buccal branch, and auriculotemporal nerves
    1. chin, lower lip, to ear; up to hairline
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15
Q

where are most of the trigeminal primary sensory neurons (touch/pain/temp) located?

A

cell bodies of these are found in TRIGEMINAL ganglion

(aka Semilunar, Gasserian)

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16
Q

path of trigeminal primary sensory neurons from the cell body in trigeminal ganglion?

A
  1. from trigeminal ganglion –>
  2. the incoming axons divide by modality –>
  3. project into the pons
  4. synapses in one of the following nuclei in the brainstem (chief sensory OR spinal nucleus)
17
Q
  1. 2 brainstem nuclei,
  2. which afferents synapse in each?
  3. pathway of each?
A
  • CHIEF SENSORY (CS) NUCLEUS of trigeminal: touch afferents
    1. trigeminal ganglion –>
    2. synapse in CS nucleus –>
    3. cross midline/decussate –>
    4. ascend up to ventral posteromedial (VPM) nucleus
  • SPINAL NUCLEUS of trigeminal: pain and temperature
    1. trigeminal ganglion –>
    2. descend in spinal tract of trigeminal –>
    3. synapse in spinal nucleus –>
    4. THEN cross midline and ascend to VPM of thalamus
18
Q

when do the brainstem nuclei decussate?

chief sensory nucleus &

spinal nucleus

A

they both decussate AFTER synapsing with the brainstem nuclei

  • chief sensory: trigem ganglion –> synapses on CS nucleus –> decussates –> ascends to VPM nucleus of thalamus
  • spinal nucleus: trigem ganlgion –> descends via spinal tract of trigem –> synapses on SN –> ascends to VPM nucleus
19
Q

2nd order neurons;

and path

A
  • 2 types of 2nd order neurons
    • chief sensory nucleus (touch)
    • spinal nucleus (pain and temp)
  • Path
    • send axons MEDIALLY to CROSS MIDLNE; and synapse in ventral posterior medial nucleus (VPM) of thalamus
20
Q

trigeminal path for TOUCH

A
  1. 1st order neurons: trigeminal ganglion cells
  2. 2nd order neurons:
    • principal (main, chief) nucleus
    • fibers cross midline & form trigeminothalamic tract (trigeminal lemniscus)
  3. 3rd order neurons:
    • VPM of thalamus
    • axons enter internal capsule –> and project into primary somatosensory cortex
21
Q

trigeminal path for PAIN & TEMPERATURE

A
  1. 1st order neurons:
    • trigeminal ganglion cells
    • *FIBERS DESCEND IN SPINAL TRIGEMINAL TRACT
  2. 2nd order neurons:
    • *SPINAL NUCLEUS (MEDULLA - C2)
    • fibers cross midline & form trigeminothalamic tract (trigeminal lemniscus)
  3. 3rd order neurons:
    • VPM of thalamus
    • axons enter internal capsule –> and project into primary somatosensory cortex
22
Q

what are the differences in the trigeminal pathway for TOUCH versus that for PAIN & TEMPERATURE?

A
  1. Difference in 2nd order neurons
    • TOUCH: principal (main, chief) nucleus, versus
    • PAIN/TEMP: spinal nucleus (medulla- C2)
  2. PAIN/TEMP path fibers DESCEND IN SPINAL TRIGEMINAL TRACT, whereas touch pathway does not
23
Q

define the path/differences of the trigeminothalamic tract at:

  1. CAUDAL to midpons
  2. ROSTRAL to midpons
A
  • At levels caudal to midpons: contains ONLY axons from 2nd order neurons in spinal nucleus of V (just pain/temp)
  • At levels rostral to midpons: contains axons from 2nd order neurons in BOTH spinal nucleus and chief sensory nucleus (pain/temp AND touch)
24
Q

which aspect of trigeminothalamic tract contains ONLY pain/temp neurons?

A

trigeminothalamic tract at levels CAUDAL TO MIDPONS

25
Q

Path of neurons from ventral posteromedial nucleus (VPM) of thalamus

A
  1. neurons in VPM –>
  2. send axons into posterior limb of internal capsule –>
  3. ascend to primary somatosensory cortex in postcentral gyrus –>
  4. in homunculus, the face is the most lateral part of postcentral gyrys
26
Q

where in homunculus is the face represented?

A

in homunculus, the face is the most lateral part of postcentral gyrus

27
Q

what causes the distortion of the homunculus map?

A

represents the greater area of the primary somatosensory cortex (SI) devoted to representation or periphery, with greater density of receptors

28
Q

blood supply of the lateral part of post-central gyrus? what feature does this area of the homunculus does this represent?

A
  1. middle cerebral artery (from circle of willis)
  2. face is represented by most lateral part of postcentral gyrus
29
Q

trigeminal pathway for PROPRIOCEPTION

(how are these unique for sensory neurons?)

A
  1. unipolar morphology
  2. cell bodies in CNS (rather than peripheral ganglion); specifically in mesencephalic nucleus of trigeminal complex
30
Q

what are the 2 limbs of the jaw jerk reflex?

A
  1. afferent limb = mesencephalic nucleus neurons, axons in mandibular division of V
  2. efferent limb = trigeminal motor nucleus neurons, axons in mandibular division of V
31
Q

how to test jaw jerk reflex?

A
  • gently tap on middle of chin w/ mouth slightly open –>
    • Normal: causes contraction of muscles of mastication & jaw closing
    • Abnormal
      • UMN lesion: hyperactive or repeating reflex (clonus)
      • LMN lesion: absent reflex
32
Q

jaw jerk reflex –> UMN vs. LMN lesions

A
  • UMN lesion: hyperactive or repeating reflex (clonus)
  • LMN lesion: absent reflex
33
Q

corneal (blink reflex):

stimulus, sensory, & motor limbs

A
  • stimulus = touch or irritation or cornea
  • sensory limb = ophthalmic division of trigeminal (V1), zygomatic branch
  • motor limb = facial nerve (VII)
34
Q

what happens if sensory or motor limb of corneal (blink) reflex is damaged?

A

then corneal reflex is ABSENT

35
Q

side of sxs for lesions to:

principal nucleus, trigeminal nerve, or spinal nucleus?

A

symptoms on side of face IPSILATERAL to lesion

PNS (IPSILATERAL)

36
Q

side of sxs for lesions to:

  • trigeminothalamic tract,
  • VPM,
  • internal capsule, or
  • primary somatosensory cortex
A

Sxs on side of face CONTRALATERAL to lesion; because once the axons have crossed the midline, if there is a lesion, you are interrupting info coming from the contralateral side of the face

(T.VIP = CONTRAlateral)

Y1 - Neuroanatomy - Exam 2 (12 decks)

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