6. Trigeminal

Question 1

3 functions of the trigeminal nerve

Answer 1

1. motor
2. general sensation
3. proprioception

Question 2

what is cranial nerve V?

Answer 2

trigeminal nerve

Question 3

motor function of trigeminal nerve

Answer 3

mainly to muscles of mastication

Question 4

general sensation of trigeminal nerve

Answer 4

(*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

Question 5

proprioception of trigeminal nerve

Answer 5

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

Question 6

where is motor nucleus of CN V?

(path from nucleus to muscles)

Answer 6

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

Question 7

key muscles of mastication innervated by trigeminal nerve

Answer 7

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

Question 8

3 tests for motor function of CN V

Answer 8

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)

Question 9

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

Answer 9

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

(indicates motor trigeminal lesion)

Question 10

basic organization of SENSORY trigeminal pathway

Answer 10

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)

Question 11

how many neurons and synapses in sensory trigeminal pathway?

is there decussation or no?

Answer 11

• 3 neurons
• 3 synapses
• 1 decussation

Question 12

name, cutaneous branches, and location of V1 dermatome?

Answer 12

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

Question 13

name, cutaneous branches, and location of V2 dermatome?

Answer 13

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

Question 14

name, cutaneous branches, and location of V3 dermatome?

Answer 14

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

Question 15

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

Answer 15

cell bodies of these are found in TRIGEMINAL ganglion

(aka Semilunar, Gasserian)

Question 16

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

Answer 16

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)

Question 17

1. 2 brainstem nuclei,
2. which afferents synapse in each?
3. pathway of each?

Answer 17

• 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

Question 18

when do the brainstem nuclei decussate?

chief sensory nucleus &

spinal nucleus

Answer 18

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

Question 19

2nd order neurons;

and path

Answer 19

• 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

Question 20

trigeminal path for TOUCH

Answer 20

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

Question 21

trigeminal path for PAIN & TEMPERATURE

Answer 21

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

Question 22

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

Answer 22

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

Question 23

define the path/differences of the trigeminothalamic tract at:

1. CAUDAL to midpons
2. ROSTRAL to midpons

Answer 23

• 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)

Question 24

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

Answer 24

trigeminothalamic tract at levels CAUDAL TO MIDPONS

Question 25

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

Answer 25

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**

Question 26

where in homunculus is the face represented?

Answer 26

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

Question 27

what causes the distortion of the homunculus map?

Answer 27

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

Question 28

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

Answer 28

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

Question 29

trigeminal pathway for PROPRIOCEPTION (how are these unique for sensory neurons?)

Answer 29

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

Question 30

what are the 2 limbs of the **jaw jerk reflex?**

Answer 30

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

Question 31

how to test **jaw jerk reflex?**

Answer 31

* 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

Question 32

jaw jerk reflex --\> UMN vs. LMN lesions

Answer 32

* **UMN lesion: hyperactive or repeating reflex (clonus)** * LMN lesion: absent reflex

Question 33

**corneal (blink reflex):** stimulus, sensory, & motor limbs

Answer 33

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

Question 34

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

Answer 34

then corneal reflex is ABSENT

Question 35

side of sxs for lesions to: **principal nucleus, trigeminal nerve,** or **spinal nucleus?**

Answer 35

symptoms on side of face **IPSILATERAL to lesion** **PNS (IPSILATERAL)**

Question 36

side of sxs for lesions to: * **trigeminothalamic tract,** * **VPM,** * **internal capsule, or** * **primary somatosensory cortex**

Answer 36

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)