Introduction to botulinum toxin
Michael Parker, Charlie James in Fundamentals for Cosmetic Practice, 2022
Once the primary motor neurones have exited the medulla oblongata inferiorly, they form the anterior and posterior corticospinal tracts (Figure 8.4). These tracts start in the cerebral cortex and travel through the spinal cord until they synapse with lower motor neurons responsible for trunk and limb movement. The anterior corticospinal tracts are made of primary motor neurons which do not decussate in the medulla oblongata and subsequently cross the midline in the spinal cord at the level they innervate. These tracts are responsible for the controlling movement of muscles of the trunk. The lateral cortico-spinal tracts make up more than 90% of the motor neurons within the spinal cord. Unlike the anterior corticospinal tracts, these tracts decussate within the medulla oblongata as opposed to the spinal cord. Due to this decussation, they innervate the contralateral side of the body from the cerebral hemisphere, which initiated a specific movement. The lateral corticospinal tracts are responsible for controlling the movement of the limbs and digits. Both the anterior and lateral corticospinal tracts synapse with lower motor neurons via the anterior horns of the spinal cord.
Clinical Neuroanatomy
John C Watkinson, Raymond W Clarke, Christopher P Aldren, Doris-Eva Bamiou, Raymond W Clarke, Richard M Irving, Haytham Kubba, Shakeel R Saeed in Paediatrics, The Ear, Skull Base, 2018
The sensory nucleus is very extensive. The cell bodies of the sensory fibres lie in the gasserian ganglion overlying the petrous apex. At least 50% of the fibres do not enter the main sensory nucleus but are concerned solely with stretch reflex activity. The other fibres form ascending and descending branches. The ascending fibres enter the mesencephalic nucleus of the Vth nerve. Their subsequent course and exact function is not understood. The descending fibres convey pain and temperature sensation and synapse in the nucleus of the descending tract of the Vth nerve, which lies adjacent to the descending tract itself and extends as low as C2 cord level. The sensory fibres derived from the facial, glossopharyngeal and vagus nerves all join the same tract and relay in the same nucleus. The secondary ascending pathway fibres swing across the brainstem, ventral to the central canal to become the secondary ascending tract of the Vth nerve, which is adjacent to the medial lemniscus, adding sensation derived from the face to that of the arm and leg in the latter pathway. In the decussation, these fibres are very vulnerable to damage by midline lesions, such as syringomyelia and syringobulbia, producing a classical sensory deficit, typically extending forwards from the back of the head. This is the so-called ‘onion peel’ or ‘balaclava’ sensory deficit, which may leave sensation intact only over the nose and central face in the final stages of its development.
Discussions (D)
Terence R. Anthoney in Neuroanatomy and the Neurologic Exam, 2017
A detailed look at the derivation of the optic chiasm demonstrates quite clearly how use of the same terms to describe embryologic and mature regions of the brain breeds confusion. First of all, the embryologic optic chiasm is typically assigned to the telencephalon, not the diencephalon (e.g., W&W, p. 170). At this stage, the chiasm does not contain-any sensory nerve fibers. Much of the mature optic chiasm, however, is made up of axons from ganglion cells whose cell bodies reside in the visual retinae. In fact, the decussation there of many such “optic” axons is what gives the “chiasm” its name. Since the visual retinae, including their ganglion cells, are usually considered to be diencephalic derivatives (e.g., W&W, p. 169), the ganglion cell axons in the optic chiasm can also be considered diencephalic. In brief, then, the mature optic chiasm probably contains both telencephalic and diencephalic derivatives—the telencephalic probably including at least glial cells which did not migrate out of the embryologic chiasm, and the diencephalic including portions of axons from retinal ganglion cells.
Horizontal Gaze Palsy and Progressive Scoliosis in Dizygotic Twins
Published in Journal of Binocular Vision and Ocular Motility, 2022
Catarina Xavier, Miguel Vieira, Ana Filipa Duarte, Ana Xavier, Eduardo D. Silva
Brain MRI of our patients demonstrates the typical features of the disease showing a normal appearing brain, corpus callosum and cerebellum, in contrast with a brainstem malformation consisting of abnormal flattening of dorsal pons and medulla with deep anterior and posterior midline clefts with a butterfly-like bifid appearance.3,10 These MRI features likely result from the absence of normal decussation of the descending cortical spinal tracts and the ascending somatosensory tracts.3,6 As shown in previous studies,7,15 on our patients the brain MRI showed no changes of the extraocular muscles and their motor nerves, supporting the causal inter and supranuclear mechanism of the horizontal gaze palsy that is probably caused by aberrant supranuclear input onto the abducens motoneurons and hypoplasia and disruption of decussating projections in the medial longitudinal fasciculus.4,6,11
Aplasia of the Optic Nerve: A Report of Seven Cases
Published in Neuro-Ophthalmology, 2020
Yujia Zhou, Maura E. Ryan, Marilyn B. Mets, Hawke H. Yoon, Bahram Rahmani, Sudhi P. Kurup
MRI confirms the diagnosis and can provide information on other CNS abnormalities (Figure 2). In our review, the contralateral optic nerve appears unremarkable in unilateral ONA. The optic chiasm is either abnormal or hypoplastic in all cases (n = 7, 100%). The measurements of the optic canal and optic tracts are shown in Table 1. There may be small margins of error when measuring these small structures, as the MRI slice thickness is 2–3 mm, even though dedicated orbital images were used. In unilateral ONA, the ipsilaterally involved optic canal is smaller. The optic tracts are not detectable in bilateral ONA and are asymmetric in unilateral ONA. Interestingly in all cases of unilateral ONA (3 of 3, 100%), the optic tracts are larger on the side ipsilateral to the ONA. Such asymmetry was also reported in one previous study.5 On the other hand, the patient from another case report of unilateral ONA had symmetrical optic tracts.15 Due to the small sample size of our study and previous studies, it is difficult to conclude whether and how the size of the optic tract is related to the laterality of ONA, especially considering that there is partial decussation of the contralateral optic nerve at the optic chiasm.
Spatial hearing processing: electrophysiological documentation at subcortical and cortical levels
Published in International Journal of Neuroscience, 2019
Nematollah Rouhbakhsh, John Mahdi, Jacob Hwo, Baran Nobel, Fati Mousave
In spatial conditions being tested in this study, two possible processing mechanisms were in progress. In co-located condition, due to periodic entity of the target and aperiodic entity of the distractors, the target stimuli relatively became augmented and therefore relatively unaffected by inhibition neural networks and unlike to the target stimuli, the distractors, in contrast, became squelched [57,58]. In the separated condition, removing the distractors from the target spatially results in augmenting of the target energy, thus making the neural cue detectors more accessible to spatial cues. At the IC level, the encoded signals receive an extra level of refinement through the lateral lemniscus neural networks whereas decussating to the opposite side of the auditory pathways [59]. This decussation could be used to establish another contrast and then converge information coming up at the level of the IC from inferior auditory pathways [60].
Related Knowledge Centers
- Anatomy
- Central Nervous System
- Neuroanatomy
- Peripheral Nervous System
- Brain
- Optic Chiasm
- Chiasm
- Medullary Pyramids
- Sensory Decussation
- Basil