Somatosensory Tracts: Facial Sensation Flashcards
(38 cards)
Where does the Trigeminal N emerge from?
Midpons
Location of Trigeminal Ganglion:
Middle cranial fossa
4 cranial nerve nuclei associated with the Trigeminal N:
(1) Chief Sensory Nucleus
(2) Spinal Trigeminal Nucleus
(3) Tract of V
(4) Mesencephalic
(5) Motor Nucleus of V
Chief Sensory Nucleus
- General Somatic Information
- Processes discriminative touch, pressure, vibration and conscious proprioception
- Located in midpons
Spinal Nucleus and Tract of V
Processes pain and temperature
Mesencephalic Nucleus of V
- Located in midbrain
- Processes non-conscious proprioceptive information
Motor Nucleus of V
- Special visceral efferent
- Muscles of mastication
- Derived from first branchial arch
Mesencephalic Nucleus of V receives afferents from:
Muscle spindles of muscles of mastication, periodontal ligaments of the teeth, and the TMJ
Nucleus that prevents biting down too hard:
Mesencephalic Nucleus of V
(relays non-conscious proprioceptive information about the position of the jaw)
Only structure in the CNS that contains the cells bodies of the first order sensory neurons:
Mesencephalic Nucleus
Central processes from Mesencephalic Nucleus of V travel to:
Reticular formation, cerebellum, Motor Nucleus of V
Jaw-Jerk Reflex
(1) Chin is tapped causing stimulation of proprioceptors
(2) Project to Mesencephalic Nucleus
(3) Fibers project to synapse in the Motor Nucleus of V
(4) Motor fibers innervate the muscles of mastication
(5) Occlusion of the jaw
Clinical Relevance of Jaw-Jerk Reflex
This reflex can be tested to assess the function of these brainstem nuclei (mesencephalic, motor) and the third branch of the Trigeminal N which carries these fibers
Spinal Trigeminal Nucleus / Spinal Nucleus of V
- Pain and temperature fibers from the periphery have their cell bodies in the trigeminal ganglion, and their central processes enter the brainstem thru the sensory root of V in the midpons; fibers descend into spinal trigeminal tract and synapse in the spinal nucleus of V (ONLY instance in which sensory fibers descend upon entering the brainstem)
- 2nd order neurons travel in the contralateral trigeminothalamic tract; collaterals to pain-modulating systems terminate in the VPM of the Thalamus
- VPM –> Posterior limb –> face area of primary somatosensory cortex
Corneal (Blink) Reflex: Afferent Limb
Pain and touch receptors in cornea –> opthalmic nerve –> terminate centrally in ipsilateral spinal trigeminal nucleus –> trigeminothalamic tract sends bilateral collaterals to facial motor nucleus
Cornreal (Blink) Reflex: Efferent Limb
Facial nerve fibers –> stimulate orbicularis occuli bilaterally –> eyes blink
3 Parts of the Spinal Nucleus of V:
(1) Pars Caudalis
(2) Pars Interpolarais
(3) Pars Oralis
Lateral Medullary Syndrome: Occluded Artery
PICA – sometimes due to occlusion of vertebral artery at origin of PICA
Lateral Medullary Syndrome results in damage to:
Spinal Trigeminal Tract and Nucleus
Lateral Medullary Syndrome: Symptoms
- Ipsilateral loss of pain and thermal sense on face and in oral cavity
- Contralateral loss of pain and temperature sensation from body
Proprioception is conveyed through the ____ ___ ____ and is perceived as:
- Principal Sensory Nucleus
- Pressure of displacement but not pain
Lesion of Spinothalamic Tract: Symptoms
Loss of pain and temperature sensation on contralateral side of body
Disruption of PICA: Ipsilateral Spinocerebellar Tract Lesion
- Can occur as the tract travels thru lateral medulla or as it enters the cerebellum via inferior cerebellar peduncle
- Results in gait ataxia
Horner Syndrome
- Lesion of descending sympathetic fibers that travel in lateral tegmentum of brainstem
- Ipsilateral ptosis, miosis, and anhidrosis
