Oral Neurophysiology: Trigeminal System Flashcards
The Trigeminal Sensory Nuclei spans which area’s of the brainstem?
- Midbrain = Mesencephalic nucleus
- Pons = Pontine trigeminal (chief sensory nucleus) and Motor (masticator) nucleus
- Medulla = Spinal nucleus of trigeminal nerve (V spinal nucleus)
The Main Sensory Nucleus is located in the Pons, what are the characteristics of the primary afferent fibres which terminate here and where do they originate?
- Large diameter, myelanated afferent fibres (Mechano-proprioception fibres)
- From Ophthalmic, Maxillary and Mandibular branches (V1,2,3)
Once the primary afferent fibres reach the Main Sensory Nucleus, where do the Second order neurons ascend/branch to?
Second order neurons:
1. Cross midbrain and join the VENTRAL TRIGEMINOTHALMIC TRACT (VTTT) and terminate in VENTRAL POSTEROMEDIAL NUCLEUS (VPN) of the Thalamus
- Don’t cross the midbrain, join the DORSAL TRIGEMINOTHALMIC TRACT (DTTT) and terminate in VPM of Thalamus
What’s the function of the Main Sensory Nucleus?
- Processing dicriminative tactile
- Processing proprioceptive sensation
Outline the discriminative touch pathway from the head
- Primary afferent fibres (primary order sensory neurons) travel through the trigeminal ganglion and into the Pons
- Primary afferent fibres in the pons synapse within the Pontine Trigeminal nucleus (PTS) - from here 2nd order sensory neurons ascend and cross the midline via the Medial Lemniscus pathway
- The Lemniscus pathway synapses in the Ventral Posterior Thalamic Nucleus in the Thalamus
- 3rd order sensory neurons ascend from the thalamus, pass through the internal capsule and synapse to neurons in the face region of the sensory cortex
Where is the V Spinal Trigeminal Nucleus located in relation to the Main Sensory Nucleus and what are its subdivisions?
Inferior to the Main Sensory Nucleus
- Extends caudally to the 3rd cervical segment of the spinal cord
- V Nucleus Oralis
- V Nucleus Interpolaris
- V Nucleus Caudalis
The V Nucleus Caudalis is the most caudal part of the V Spinal Trigeminal Nucleus, what are the characteristics of its primary afferent fibres?
- Small-diameter fibres (pain & temperature)
- From the trigeminal ganglion they turn caudally and join the spinal trigeminal tract and descend
Does the 2nd order neurons of V Nucleus Caudalis cross the midline?
Yes
- Join the Trigeminothalmic Tract (TTTT) and terminate in the VPM of the Thalamus
What’s the function of the V Nucleus Caudalis?
- Processes pain and temperature information from the face, mouth and nose
Outline the pain and temperature pathway from the head
- Small diameter fibres (1st order sensory neurons) travel through trigeminal ganglion and then descend in the brain stem via the tract of the Spinal Trigeminal Nucleus
- 1st order sensory neurons synapse at the spinal trigeminal nucleus
- 2nd order sensory neurons cross midline, ascend via Spinal Lemniscus to the reticular formation in brain stem
- 2nd order sensory neurons synapse in the thalamus; specifically the Ventral Posterior thalamic nucleus
- 3rd order sensory neurons in the Ventral Posterior Thalamic Nucleus ascend to the Sensory cortex
What are the primary afferent fibres for the V Nucleus Oralis and Interpolaris? and where do the 2nd order neurons go?
- Small-diameter fibres
- Turn caudally and join the spinal trigeminal tract
- 2nd order neurons - some go to contralateral VPM (tactile information)
What’s the function of V Nucleus Oralis and Interpolaris?
- Tactile information
- Processing of pain and temperature information from teeth and other intraoral structures
- Possible function = reflexes
What’s the Trigeminal Mesencephalic Nucleus?
- Most rostral part of the Trigeminal Sensory Nuclei
What’s significant about the Trigeminal Mesencephalic Nucleus?
- There are synapses in this area - only cell bodies for:
1. Jaw muscle spindles afferents
2. Some mechanoreceptive afferents from the PDL - Cell bodies in the CNS is unique
Where are the synapses for the Trigeminal Mesencephalic Nucleus?
- Trigeminal (V) Motor Nucleus
