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Brain Motor Centers and Pathways
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
The tectospinal tract (Figure 11.3), also known as the colliculospinal tract, is an extrapyramidal motor tract that coordinates head, neck, and eye movements. The tract originates in the superior colliculus, which is situated rostrally, just below the thalamus (Figure 12.17). The superior colliculus, together with the inferior colliculus, comprise the tectum, or roof of the midbrain, in humans. The part of the midbrain between the tectum and tegmentum constitutes the midbrain tegmentum. The two colliculi on each side form four prominences referred to as the corpora quadrigemina.
Spine
Published in Bobby Krishnachetty, Abdul Syed, Harriet Scott, Applied Anatomy for the FRCA, 2020
Bobby Krishnachetty, Abdul Syed, Harriet Scott
Descending tracts (motor)Lateral corticospinal tract (crossed pyramidal tract): fibres carry voluntary motor activity from cortex, decussate in the medulla and descend the spinal cord on the contralateral side.Anterior corticospinal tract (uncrossed pyramidal tract): voluntary motor activity from the cortex reaches the spinal cord without decussation.Tecto spinal tract: this extrapyramidal tract causes movement of the head in response to visual and auditory stimuli from the midbrain tectum to the contralateral spinal cord.Rubro spinal tract: this extrapyramidal tract regulates voluntary movements and reflexes. Fibres originate from the red nucleus of midbrain, cross to the opposite midbrain and then descend down the spinal cord.
The Evolution of Consciousness
Published in Max R. Bennett, The Idea of Consciousness, 2020
Figure 6.15 shows a frog’s brain in dorsal (C) and lateral (B) view, together with a diagram (A) of the projection of the optic tract to the principal areas of the brain subserving vision. The large size of the optic tectum of the frog, compared with that of the cerebral hemispheres (Figures 6.15A, B and C), reflects the fact that it receives the entire retinal input to the brain, whereas in mammals the optic tectum, or superior colliculus as it is called for these species, receives only part of the retinal projection. It is therefore appropriate to inquire as to whether frogs are conscious of a visual perception in the tectum rather than the telencephalon. This optic tectum has been a source of modelling of neural networks for the reflex control of eye position in the frog. From the tectum, projections occur to motor neurons that control the left medial and right lateral rectus muscles of die eyes as well as to those controlling vertical movement. This tectum has also been subjected to a control system analysis of the process of eye movement involved in saccades (Figure 6.16). According to this theory, a retinotopic mapper occurs in the tectum which projects to a saccade burst generator in the brain stem. This then receives a code for target position as determined by the position of a peak of activity in a neural map. However, all of these considerations of the functioning of the tectum emphasize Dennett’s claim1 that ‘the toad’s status falls to “mere automaton” ‘. The question being asked is: does the tectum give rise to consciousness?
The utility of quantitative MRI parameters in discriminating progressive supranuclear palsy from Parkinson’s disease
Published in Neurological Research, 2023
Halil Onder, Bilge Gonenli Kocer, Aynur Turan, Selcuk Comoglu
The crucial point was that we found a PPV of 100% in case of both high P/M and 3rd/bifrontal ventricle rates for the diagnosis of PSP. The gross examination of the brain in PSP often reveals distinctive features. The atrophy in the midbrain, especially the tectum, is the most characteristic finding [24]. However, the subthalamic nucleus atrophy as well as the dilatation of the third ventricle atrophy is also frequently observed in pathology examinations [24]. We think that the existence of the neuroradiological evidence of the atrophy of both of these two regions (mesencephalon and third ventricle) might provide a more reliable and comprehensive finding regarding the underlying PSP pathology. Therefore, instead of the use of complicated parameters such as MRPI and MRPI-2 the scopes of which are limited to the anatomy of the brain stem, we suggest searching for both of these two distinct regions (brainstem, third ventricle) to increase the diagnostic reliability of PSP subjects.
Optimizing assays of zebrafish larvae swimming performance for drug discovery
Published in Expert Opinion on Drug Discovery, 2023
Jeffrey J. Widrick, Matthias R. Lambert, Louis M. Kunkel, Alan H. Beggs
Larvae use escape or startle responses to avoid potentially harmful situations and environments. Escape responses are an early behavior, appearing as soon as 2 days post-fertilization [38,55]. While several neurons play a role in the response [56], much attention has focused on two reticulospinal neurons, or Mauthner cells, due to their large size, accessibility, and key role in triggering the escape response. The Mauthner cell bodies synapse with neurons originating in the optic tectum, spinal cord, inner ear, and lateral line and their axons synapse with motor neurons that innervate the trunk and tail muscles [57]. Consequently, tactile, visual, auditory, or vibrational stimuli can depolarize the Mauthner cell and trigger the muscular activity that initiates an all-or-none locomotor response [12,13,15,36,39]. The duration of the latency period between the stimulus and when movement begins is <10 ms, giving rise to a so-called short-latency escape response [13]. Short-latency escape responses can also be experimentally evoked by the direct depolarization of a Mauthner cell using field stimulation [39,58].
Post‐stroke visual midline shift syndrome
Published in Clinical and Experimental Optometry, 2020
Tammy Labreche, Benjamin Wild, Kristine Dalton, Susan J Leat
The alternative suggestion is that a shift of midline is independent of neglect, but may reinforce neglect. Padula et al.13 described a bimodal visual processing system composed of both focal and ambient vision. It is suggested that ‘focal’ vision contributes to detail discrimination while ‘ambient’ vision is concerned with spatial orientation. The ambient vision system is thought to consist of approximately 20 per cent of the retinal fibres that travel the retinal‐tectal pathway and synapse in the midbrain where information from proprioceptive, kinaesthetic and vestibular systems are integrated and communicate in a feed forward mechanism to other areas of the cortex (including the posterior parietal cortex and dorsal pathway).1993 Hemiparetic events disrupt the information received from one half of the body causing a mismatch between the sensorimotor information and the visual‐spatial process. This creates a distortion in the ambient visual process resulting in an ipsilesional visual midline shift with a subsequent lean away from the affected side.2009 It is not solely then a right brain lesion phenomenon. Bansal et al.2014 agrees with this theory, but suggests that it occurs in the absence of neglect and/or visual field defects. Imaging studies demonstrating that the angular gyrus (area 39), which lies adjacent to the area thought to be damaged in neglect,2002 may be responsible for the determination of midline, also support this suggestion.