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Neurons
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Most neurons are multipolar having one axon and one or more dendritic trees, or main dendritic trunks, leaving the cell body. Neurons are divided into Golgi I and Golgi II neurons. Golgi I neurons, also known as principal neurons, usually have axons that project outside the region of gray matter in which their cell bodies and dendrites are located, the axons providing the major neuronal output from the given region. Whereas most principal neurons are excitatory, such as motoneurons (Figure 1.4) and pyramidal cells (Figure 7.1c), some are inhibitory, like cerebellar Purkinje cells (Figure 7.1d), which have the most elaborate dendritic tree of all neurons. On the other hand, multipolar Golgi II neurons, also referred to as interneurons or association neurons, have axons that are restricted to the gray matter in which their cell bodies and dendrites are located. Some interneurons are excitatory, like cerebellar granule cells (Figure 7.1e), but most are inhibitory, like the Renshaw cells (Figure 1.5).
Computational Neuroscience and Compartmental Modeling
Published in Bahman Zohuri, Patrick J. McDaniel, Electrical Brain Stimulation for the Treatment of Neurological Disorders, 2019
Bahman Zohuri, Patrick J. McDaniel
Note that, Pyramidal neurons (pyramidal cells) are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal neurons are the primary excitation units of the mammalian prefrontal cortex and the corticospinal tract. Pyramidal neurons are also one of two cell types where the characteristic sign, Negri bodies, are found in post-mortem rabies infection. Pyramidal neurons were first discovered and studied by Santiago Ramón y Cajal. Since then, studies on pyramidal neurons have focused on topics ranging from neuroplasticity to cognition.
Gangliocytoma and Lhermitte–Duclos Disease
Published in Dongyou Liu, Tumors and Cancers, 2017
Neuron is the basic cell of the nervous system that contains a nucleus within a cell body (perikaryon) and extends one or more processes (usually an axon and one or more dendrites). A neuron with an axon only is classified as unipolar neuron, that with an axon and a dendrite is classified as bipolar neuron, and that with an axon and two or more dendrites is classified as multipolar neuron, which is the most common type and widely distributed in the CNS. The axon conducts the impulses to the dendrite of another neuron or to an effector organ. The dendrites receive stimuli from a receptor organ or other nerves and transmit through the neuron to the axon. According to the direction in which they conduct impulses, neurons are categorized into three groups: (i) afferent or sensory neurons (which conduct impulses from a receptor to a center), (ii) efferent or motor neurons (which carry impulses away from a center to an organ of response), and (iii) interneurons (which conduct impulses from afferent to efferent neurons). The point at which an impulse is transmitted from one neuron to another is known as synapse.
Down regulation of DNA topoisomerase IIβ exerts neurodegeneration like effect through Rho GTPases in cellular model of Parkinson’s disease by Down regulating tyrosine hydroxylase
Published in Neurological Research, 2021
Kiyak Bercem Yeman, Sevim Isik
First, SH-SY5Y cells were differentiated into neural cells by minor changes in protocol of Encinas et al.’s study [23]. According to this protocol, cells were differentiated into neuronal cells in fibronectin-coated culture plates for 14 days. Cells were first morphologically assessed using phase contrast microscope throughout neural differentiation for 2 weeks. According to morphological observations, cell bodies enlarged during the initial stages of differentiation, but as cells began to extend more neurites, they shrank in size. After BDNF addition, number of neurites increased, and starting from day 9, cells started to show a neuronal morphology with extensive neurite outgrowth and long bipolar or multipolar processes with a fine network (Figure 1(a)). When the neuronal network almost perfectly formed, IF staining of neural-differentiated cells was performed to study the expression of Tau and NF following 2 weeks of differentiation. Cells expressed high levels of mature neuronal markers Tau and NF and were thus proven to be successfully differentiated into neuronal cells (Figure 1(b)).
Percutaneous pedestals in cochlear implantation
Published in Cochlear Implants International, 2018
Alistair Mitchell-Innes, Richard Irving, Robert Briggs
Aside from commercial products, however, the greatest contribution from percutaneous pedestals to the evolution of cochlear implants has arisen from their crucial role in many research projects. For example, the continuous interleaved sampling (CIS) and fine structure processing strategies were likely developed as a direct result of research carried out by Wilson and others on Ineraid patients with the pedestal (Dorman and Parkin, 2015). A group in Switzerland at a similar time also chose Ineraid devices to pursue their clinical and research interests, culminating in the production of 70 portable processors incorporating Wilson's CIS design. Long-term results with the CIS portable processor matched those of results achieved in the laboratory (Pelizzone et al., 1999). Importantly, percutaneous pedestals continue to be used in research today; in Melbourne, we recently used a percutaneous connector to allow simultaneous activation of individual electrodes using independent current sources (Marozeau et al., 2015). As previously discussed this is not possible via implanted devices. Specifically, the study was assessing whether all polar or multipolar versus monopolar stimulation offered a more focused electrical field. Results showed all polar stimulation produced less current spread, but did not lead to a significant advantage. Finally, the only fMRI studies in cochlear implant patients have arisen from patients with percutaneous pedestals as it is possible to safely study cortical activity in response to electrode stimulation without the speech signal being degraded (Melcher, 1998).
Objective evaluation of binaural summation through acoustic reflex measures
Published in International Journal of Audiology, 2018
Vishakha W. Rawool, Madaline Parrill
Binaural summation occurs in the auditory system due to convergence of neural impulses generated by sounds presented to the two ears, primarily at the level of the superior olivary complex (SOC). The SOC includes a collection of brainstem nuclei that serves several functions including localisation, temporal coding of complex sounds and efferent modulation of the cochlear nucleus and cochlea. The two major nuclei in the SOC are referred to as the medial superior olive (MSO) and lateral superior olive (LSO), with approximately 15,500 neurons in the MSO and 5600 neurons in the LSO in humans (Kulesza 2007). Afferents from the ventral cochlear nucleus (VCN) of the same side project on the lateral aspect of the MSO and the afferents from the contralateral VCN project on the medial side of the MSO. MSO receives both excitatory and inhibitory inputs (reviewed in Grothe et al. 2010). The LSO receives direct excitatory input from the ipsilateral anteroventral cochlear nucleus (AVCN) and indirect, inhibitory input from the contralateral AVCN through the medial nucleus of the trapezoid body (MNTB) ipsilateral to the LSO (reviewed in Phillips 2001). Efferent fibres arriving from the LSO and MSO enter the cochlea to form direct or indirect connections with the sensory hair cells. This olivo-cochlear bundle is activated during binaural stimulation and has an inhibitory influence on the cochlear response. In addition, type II multipolar cells within each cochlear nucleus project inhibitory fibres to the contralateral cochlear nuclei (Cant and Gaston 1982). The various inhibitory influences within the auditory brainstem can lead to less than perfect binaural summation.