6. Trigeminal Flashcards
3 functions of the trigeminal nerve
- motor
- general sensation
- proprioception
what is cranial nerve V?
trigeminal nerve
motor function of trigeminal nerve
mainly to muscles of mastication
general sensation of trigeminal nerve
(*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
proprioception of trigeminal nerve
- extraocular muscles
- muscles of mastication
- temporalmandibular joint (TMJ)
where is motor nucleus of CN V?
(path from nucleus to muscles)
- motor nucleus is w/in mid pons –>
- axons enter trigeminal nerve –>
- innervate muscles of mastication
key muscles of mastication innervated by trigeminal nerve
- lateral pterygoid
- medial pterygoid
- masseter (superficial)
- temporalis (superficial)
3 tests for motor function of CN V
- clenching teeth & palpating contraction of superficial muscles of mastication (masseter & temporalis)
- observing symmetry of lateral face (look for atrophy of muscle mass)
- opening jaw & looking for deviation of chin (towards side of lesion –> tests lateral pterygoid muscle)
which is the only muscle of mastication involved in opening mouth/deviating chin?
lateral pterygoid muscle –> jaw would deviate towards side of lesion, e.g. right lesion –> jaw deviates to right
(indicates motor trigeminal lesion)
basic organization of SENSORY trigeminal pathway
- dermatome of face –>
- 1st order neuron (cell bodies in sensory trigeminal ganglion); primary afferent –>
- 2nd order neuron (principal/spinal trigeminal nucleus) –> *decussation occurs/crosses midline –>
- 3rd order neuron (terminates in VPM nucleus of thalamus ) –> thru internal capsule to ascend –>
- post-central gyrus (of somatosensory cortex)
how many neurons and synapses in sensory trigeminal pathway?
is there decussation or no?
- 3 neurons
- 3 synapses
- 1 decussation
name, cutaneous branches, and location of V1 dermatome?
- ophthalmic (corneal blink reflex)
- supraorbital
- forehead/nose/ area above eyes
name, cutaneous branches, and location of V2 dermatome?
- maxillary
- infraorbital nerves
- cheek (blush region); upper lip; up to hairline
name, cutaneous branches, and location of V3 dermatome?
- maxillary
-
mental, buccal branch, and auriculotemporal nerves
- chin, lower lip, to ear; up to hairline
where are most of the trigeminal primary sensory neurons (touch/pain/temp) located?
cell bodies of these are found in TRIGEMINAL ganglion
(aka Semilunar, Gasserian)
path of trigeminal primary sensory neurons from the cell body in trigeminal ganglion?
- from trigeminal ganglion –>
- the incoming axons divide by modality –>
- project into the pons
- synapses in one of the following nuclei in the brainstem (chief sensory OR spinal nucleus)
- 2 brainstem nuclei,
- which afferents synapse in each?
- pathway of each?
-
CHIEF SENSORY (CS) NUCLEUS of trigeminal: touch afferents
- trigeminal ganglion –>
- synapse in CS nucleus –>
- cross midline/decussate –>
- ascend up to ventral posteromedial (VPM) nucleus
-
SPINAL NUCLEUS of trigeminal: pain and temperature
- trigeminal ganglion –>
- descend in spinal tract of trigeminal –>
- synapse in spinal nucleus –>
- THEN cross midline and ascend to VPM of thalamus
when do the brainstem nuclei decussate?
chief sensory nucleus &
spinal nucleus
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
2nd order neurons;
and path
- 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
trigeminal path for TOUCH
- 1st order neurons: trigeminal ganglion cells
- 2nd order neurons:
- principal (main, chief) nucleus
- fibers cross midline & form trigeminothalamic tract (trigeminal lemniscus)
- 3rd order neurons:
- VPM of thalamus
- axons enter internal capsule –> and project into primary somatosensory cortex
trigeminal path for PAIN & TEMPERATURE
- 1st order neurons:
- trigeminal ganglion cells
- *FIBERS DESCEND IN SPINAL TRIGEMINAL TRACT
- 2nd order neurons:
- *SPINAL NUCLEUS (MEDULLA - C2)
- fibers cross midline & form trigeminothalamic tract (trigeminal lemniscus)
- 3rd order neurons:
- VPM of thalamus
- axons enter internal capsule –> and project into primary somatosensory cortex
what are the differences in the trigeminal pathway for TOUCH versus that for PAIN & TEMPERATURE?
- Difference in 2nd order neurons
- TOUCH: principal (main, chief) nucleus, versus
- PAIN/TEMP: spinal nucleus (medulla- C2)
- PAIN/TEMP path fibers DESCEND IN SPINAL TRIGEMINAL TRACT, whereas touch pathway does not
define the path/differences of the trigeminothalamic tract at:
- CAUDAL to midpons
- ROSTRAL to midpons
- 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)
which aspect of trigeminothalamic tract contains ONLY pain/temp neurons?
trigeminothalamic tract at levels CAUDAL TO MIDPONS
Path of neurons from ventral posteromedial nucleus (VPM) of thalamus
- neurons in VPM –>
- send axons into posterior limb of internal capsule –>
- ascend to primary somatosensory cortex in postcentral gyrus –>
- in homunculus, the face is the most lateral part of postcentral gyrys
where in homunculus is the face represented?
in homunculus, the face is the most lateral part of postcentral gyrus
what causes the distortion of the homunculus map?
represents the greater area of the primary somatosensory cortex (SI) devoted to representation or periphery, with greater density of receptors
blood supply of the lateral part of post-central gyrus? what feature does this area of the homunculus does this represent?
- middle cerebral artery (from circle of willis)
- face is represented by most lateral part of postcentral gyrus
trigeminal pathway for PROPRIOCEPTION
(how are these unique for sensory neurons?)
- unipolar morphology
- cell bodies in CNS (rather than peripheral ganglion); specifically in mesencephalic nucleus of trigeminal complex
what are the 2 limbs of the jaw jerk reflex?
- afferent limb = mesencephalic nucleus neurons, axons in mandibular division of V
- efferent limb = trigeminal motor nucleus neurons, axons in mandibular division of V
how to test jaw jerk reflex?
- 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
jaw jerk reflex –> UMN vs. LMN lesions
- UMN lesion: hyperactive or repeating reflex (clonus)
- LMN lesion: absent reflex
corneal (blink reflex):
stimulus, sensory, & motor limbs
- stimulus = touch or irritation or cornea
- sensory limb = ophthalmic division of trigeminal (V1), zygomatic branch
- motor limb = facial nerve (VII)
what happens if sensory or motor limb of corneal (blink) reflex is damaged?
then corneal reflex is ABSENT
side of sxs for lesions to:
principal nucleus, trigeminal nerve, or spinal nucleus?
symptoms on side of face IPSILATERAL to lesion
PNS (IPSILATERAL)
side of sxs for lesions to:
- trigeminothalamic tract,
- VPM,
- internal capsule, or
- primary somatosensory cortex
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)
