Lab 6: Somatosensory Systems II Flashcards
Marginal Zone
Thin rim of cells dorsal to the size able substantia gelatinosa
Substantia Gelatinosa
(Rexed’s lamina II)
Receives terminations of first order pain and temperature neurons
Ventral (anterior) White Commissure
Crossing of the axons from pain/temperature projection neurons to reach the lateral funiculus of the opposite side
Anterolateral System
Consists of the crossed pain/temperature fibers that ascend to the brain stem and thalamus on the opposite (contralateral to) the stimulated receptors.
Reticular Formation
Receives some fibers of the ALS that take a multisynaptic course to terminate in the intralaminar nuclei of the thalamus (slow pain pathway)
Raphe Nuclei
Pale nuclei near that midline that:
- receive descending fibers from the periaqueductal gray of the midbrain
- project fibers to the dorsal horn of the spinal cord for inhibition of ascending pain transmission
Dissociated Sensory Loss
-a small stroke in the medulla can affect one sensory system but not the other
-the ALS is in the posterolateral vascular territory (ventrolateral tegmentum) and the medial lemniscus is in the paramedian zone (close to the midline)
This occurs in Wallenberg (lateral medullary) Syndrome which results from an infarct in the vascular territory of PICA
Caudal Pons
The Medial Lemniscus has begun to move laterally towards the ALS
Rostral Pons
The medial lemniscus meets the ALS in the lateral tegmentum at this level and they travel adjacent to each other en route to the thalamus
Periaqueductal Gray Nuclei of the Midbrain
- receive fibers from ALS
- send descending fibers to raphe nuclei of brainstem for inhibition of pain transmission
Ventral Posterolateral (VPL) Nucleus of the Thalamus
Synapse site of fibers of the ALS
Posterior limb of internal capsule
Path of fibers from the VPL to the somatosensory cortex
Internal Medullary Lamina
Sheet of fibers in thalamus
Intralaminar nuclei
Nuclei in internal medullary lamina that:
- receive pain/temperature fibers from the reticular formation
- send axons to widespread areas of cortex
Posterior Limb, internal capsule
Contains fibers (thalamic radiations) from the VPLs to the somatosensory cortex (postcentral gyrus and posterior paracentral gyrus, Brodmann Areas 3,1,2)
Postcentral Gyrus and Posterior part of Paracentral Lobule
Where sensations of discriminative touch/pressure (medial lemniscus) and pain/temperature (ALS) are detected
Posterior Parietal Cortex
Where sensations are recognized
Ophthalmic and maxillary divisions of Trigeminal Nerve
- course in the wall of the cavernous sinus
- contain sensory fibers only
Mandibular Division of Trigeminal Nerve
-contains sensory and motor fibers
Trigeminal Ganglion
Consists of cell bodies of sensory fibers from face, ear, orbit, oral cavity, nasal cavity, paranasal sinuses meninges
Trigeminal Nerve Roots
Located in the lateral tegmentum, between the motor and main sensory nucleus of V
Motor Nucleus (V)
Medial to the trigeminal nerve roots; supplies the muscles of mastication
Main Sensory Nucleus (V)
Lateral to the trigeminal nerve roots
Properties of Main Sensory Nucleus (V)
- receive axons from large-fiber neurons of trigeminal ganglion
- are comparable to dorsal column nuclei in that they’re involved in discriminative touch
- send axons across the midline (decussation not visible) to joint the ventral trigeminothalamic tract
Mid Pons
Main sensory and motor nuclei of the trigeminal nerve (V): in the dorsolateral tegmentum of the pons
Trigeminal nerve roots: easy to see between the main sensory and motor nuclei in the slice on the left
Spinal Trigeminal Tract
The pain/temperature neurons in the trigeminal ganglion from the anterior head have central processes that enter the pons and descend into the medulla and rostral spinal cord
Caudal Medulla
Spinal Trigeminal Tract: central processes of neurons for pain/temperature from the ipsilateral face and teeth
Spinal Trigeminal Nucleus: medial to the spinal trigeminal tract; receives fibers from the spinal Trigeminal tract; contains neurons that process pain and temperature information from the face and send axons across the midline to become the VENTRAL TRIGEMINOTHALAMIC TRACT (VTTT)
Spinal Trigeminal Nucleus and Substantia Gelatinosa
The spinal trigeminal nucleus is continuous caudally with the substantia gelatinosa of the dorsal horn of the spinal cord. Neither of these structures are visible in a clinical scan, but the general position can be determined because both are located in the lateral tegmentum, with the tract being peripheral to the nucleus
Mid/Rostral Medulla
Spinal Trigeminal tract: lateral to spinal trigeminal nucleus
Spinal trigeminal nucleus: has cells whose axons cross (crossing not visible) and ascend as the ventral trigeminothalamic tract to the thalamus
VTTT Fiber Organization
They’re not gathered into a discrete bundle in the medulla, but in the caudal Pons they are found dorsal to the medial Lemniscus
Mid Pons (trigeminal nerve system locations)
Ventral Trigeminothalamic Tract (VTTT):
-has fibers from the contralateral spinal Nucleus of V plus some from the contralateral main sensory nucleus of V
-travels dorsal to the medial lemniscus
-projects to the ventral posterior medial (VPM) nucleus of the thalamus
Main sensory nucleus of V:
Receives input from discriminative touch and vibration receptors via fibers of the trigeminal nerve
Motor Nucleus of V: BE motor nucleus to the muscles of mastication
Trigeminal Nerve Roots: pass between the main sensory and motor nuclei of V
Midbrain
VTTT: dorsal to the medial lemniscus: carries sensory information from contralateral face
Medial Lemniscus: carries discriminative touch sensation from the contralateral trunk and limbs
ALS: carriers pain and temperature sensation from the contralateral trunk and limbs
Ventral Posterior Medial (VPM) Nucleus of the Thalamus
- synapse for fibers of the VTTT
- located medial to the VPL nucleus
- is a sensory relay nucleus of the thalamus for general sensations from the face and for taste
Posterior Limb of Internal Capsule
Lateral to the thalamus; has fibers from the VPM and VPL en route to the postcentral gyrus and posterior paracentral gyrus
