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*MOTOR NEURONS*
*SENSORY NEURONS*
*INTER-NEURONS*
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/ˈnjʊərɒn/
(nyewr-on)
OR
/ˈnʊərɒn/
(newr-on)
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*AKA* –>
“neurone”
“nerve cell”
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*a ‘neuron’ is an ‘electrically excitable cell’ that ‘processes’ + ‘transmits’ information through ‘electrical’ + ‘chemical’ signals*
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(these signals between ‘neurons’ occur via ‘synapses’)
(which are ‘specialized connections’ with other ‘cells’)
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(‘neurons’ can connect to each other to form ‘neural networks’)
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[‘neurons’ are the core components of the…]
‘brain’ + ‘spinal cord’
(of the ‘central nervous system’ (CNS))
*the ‘ganglia’*
(of the ‘peripheral nervous system’ (PNS))
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*there are several types of specialized ‘neurons’*
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(‘sensory neurons’ respond to ‘stimuli’, such as…)
‘touch’
‘sound’
‘light’
(…and all other ‘stimuli’ affecting the cells of the ‘sensory organs’ that then send signals to the ‘spinal cord’ + ‘brain’)
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(‘motor neurons’ receive ‘signals’ from the ‘brain’ + ‘spinal cord’ to cause ‘muscle contractions’ + affect ‘glandular outputs’)
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(‘inter-neurons’ connect ‘neurons’ to other ‘neurons’ within the same region of the ‘brain’ or ‘spinal cord’ in ‘neural networks’)
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(a typical ‘neuron’ consists of…)
*a ‘cell body’*
(‘soma’)
*’dendrites’*
*an ‘axon’*
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(the term ‘neurite’ is used to describe either a ‘dendrite’ or an ‘axon’, particularly in its ‘undifferentiated stage’)
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(‘dendrites’ are ‘thin structures’ that arise from the ‘cell body’, often extending for hundreds of ‘micrometers’ + branching multiple times, giving rise to a complex ‘dendritic tree’)
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(an ‘axon’ (also called a ‘nerve fiber’ when ‘myelinated’) is a ‘special cellular extension’ (or ‘process’) that arises from the ‘cell body’ at a site called the ‘axon hillock’ + travels for a distance, as far as ‘1 meter’ in ‘humans’ or even more in other ‘species’)
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(‘nerve fibers’ are often bundled into ‘fascicles’, and in the ‘peripheral nervous system’, bundles of ‘fascicles’ make up ‘nerves’ (like strands of wire make up ‘cables’))
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(the cell body of a ‘neuron’ frequently gives rise to multiple ‘dendrites’, but never to more than 1 ‘axon’, although the ‘axon’ may branch hundreds of times before it ‘terminates’)
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(at the majority of ‘synapses’, signals are sent from the ‘axon’ of 1 ‘neuron’ to a ‘dendrite’ of another)
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…there are, however, many exceptions to these rules…
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…for example…
*’neurons’ can lack ‘dendrites’*
*’neurons’ can lack an ‘axon’*
*’synapses’ can connect an ‘axon’ to another ‘axon’ or a ‘dendrite’ to another ‘dendrite’*
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(all ‘neurons’ are ‘electrically excitable’, maintaining ‘voltage gradients’ across their ‘membranes’ by means of metabolically driven ‘ion pumps’, which combine with ‘ion channels’ embedded in the membrane to generate ‘intracellular-versus-extracellular concentration differences’ of ‘ions’ such as…)
‘sodium’
‘potassium’
‘chloride’
‘calcium’
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(changes in the ‘cross-membrane voltage’ can alter the function of ‘voltage-dependent ion channels’)
(if the ‘voltage’ changes by a large enough amount, an ‘all-or-none electro-chemical pulse’ (called an ‘action potential’) is generated, which travels rapidly along the cell’s ‘axon’ + activates ‘synaptic connections’ with other cells when it arrives)
(in most cases, ‘neurons’ are generated by special types of ‘stem cells’)
(‘neurons’ in the ‘adult brain’ generally do not undergo ‘cell division’)
(‘astrocytes’ are ‘star-shaped glial cells’ that have also been observed to turn into ‘neurons’ by virtue of the stem cell characteristic ‘pluri-potency’)
(‘neuro-genesis’ largely ceases during ‘adulthood’ in most areas of the ‘brain’)
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[however, there is strong evidence for generation of substantial numbers of new ‘neurons’ in 2 brain areas…]
*the ‘hippocampus’*
*the ‘olfactory bulb’*
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👈👈👈☜*“THE HUMAN NERVOUS SYSTEM”* ☞ 👉👉👉
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💕💝💖💓🖤💙🖤💙🖤💙🖤❤️💚💛🧡❣️💞💔💘❣️🧡💛💚❤️🖤💜🖤💙🖤💙🖤💗💖💝💘
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*🌈✨ *TABLE OF CONTENTS* ✨🌷*
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🔥🔥🔥🔥🔥🔥*we won the war* 🔥🔥🔥🔥🔥🔥