Today people were tweeting about the Calyx of Held. It sounds like a potentate in medieval times, but this is what Google says."The Calyx of Held is a particularly large synapse in the mammalian auditory central nervous system, so named by Hans Held in his 1893 article Die centrale Gehörleitung because of its resemblance to the calyx of a flower. Globular bushy cells in the anteroventral cochlear nucleus (AVCN) send axons to the contralateral medial nucleus of the trapezoid body (MNTB), where they synapse via these calyces on MNTB principal cells. These principal cells then project to the ipsilateral lateral superior olive (LSO), where they inhibit postsynaptic neurons and provide a basis for interaural level detection (ILD), required for high frequency sound localization. This synapse has been described as the largest in the brain."
I've never heard of this brain blob. Now to figure out the definition given above.
Synapse: that little electrical jump of space between the ends of two nerve cells. I always imagine a teeny bolt of lightning crossing. Three kinds are described according to the elements involved, but never mind. Also, they can send the jump to muscles and organs.
Mammalian means something has changed or been added since reptiles.
Globular bushy cells. Cells are often "named" by saying what they look like. These are obviously bushy globs. Evidently in this context "olive" is the shape, not the color.
lateral superior olive (LSO) "Thus, the LSO receives excitatory input from the ipsilateral [same side] ear and inhibitory input from the contralateral [other side] ear. ... Ipsilateral projections are primarily inhibitory (glycinergic), and the contralateral projections are excitatory." In other words, this is how you triangulate distance to tell where a sound is coming from.
To understand them, you have to know about them. "The superior olivary complex (or SOC or superior olive) is a collection of brainstem nuclei that functions in multiple aspects of hearing and is an important component of the ascending and descending auditory pathways of the auditory system."
"The mammalian cochlear nucleus (CN) consists of a diverse set of neurons both physiologically and morphologically that are involved in processing different aspects of the sound signal. One class of CN neurons that is located near the entrance of the auditory nerve (AN) to the CN has an oval soma with an eccentric nucleus and a short-bushy dendritic tree and is called a globular/bushy cell (GBC). They contact the principal cells of the medial nucleus of the trapezoid body (MNTB) with the very large calyx of Held that is one of the most secure synapses in the brain. Because MNTB cells provide an inhibitory input to the lateral superior olive, a structure purported to play a role in lateralizing high frequency sounds, GBC physiology is of great interest."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2518325/
When you consider how poorly I'm grasping all this stuff, please take into consideration that the phone rang twice with a wrong number dialed by a drunk demanding to know where I am, one kitten has just thrust his nose into my coffee cup which luckily is cool rather than hot -- his sister burned her nose yesterday. One of the two bachelor male cats just beat up on that kitten and had to be chased outside by making terrible sounds and thumping my feet hard. Household commotion is a continuing hazard for bloggers.
This is what I get out this news about yet another brain part that's barely distinguishable from the mush around it except by shape and location. Too bad brain parts are not color-coded like those brilliant computer depictions of brain systems we call "the connectome."
This bit is called a "calyx" because it is a cup-shaped structure like that in a flower. It's kind of a reservoir where things are held. I looked for a definition of the MNTB and got "Merchant Navy Training Board" so I guess the acronym is rather for the preceding phrase in the paragraph: "medial nucleus of the trapezoid body." Acronyms do not help explain this stuff. GBC may refer to "gall bladder cancer" but that doesn't usually happen in the ears. In this case, it seems to mean "globular bushy cells."
That this complex of the Calyx of Held is so stable and large means that it's not a surprise that Hans discovered it at the end of the 19th century, but also means that it has been conserved and replicated over the millennia since the beginning in early mammals, who evidently survived by listening more than reptiles did. Good hearing is crucial for both predator and prey, a whole world of meaning for those dependent on it. Humans ordinarily get deaf in old age, but that doesn't mean much to the species since they are no longer breeding. That aspect of survival is gone for them except in protecting the young. Human survival is often due to wisdom accumulated by the old which can be read rather than heard. This has changed: loud music is destroying hearing in the young, cultural revolution has discredited whatever is old. No doubt our survival both as individuals and groups is damaged.
Neither do the young read very much, but turn to the mechanism of sight which is much managed with optical devices, color, flickering, and many other devices. However, more than ever, the human young are both predators and prey. I haven't thought about this except for noting the evidence which is extensive and pervasive, mediated by sex, drugs, and family breakdown.
I'm nearing the end of Joseph LeDoux's "The Deep History of Ourselves". He defines the amygdala as something like the Calyx of Held except in terms of survival reflexes, an unconscious, well-conserved reservoir of information about danger that operates as reflex rather than reflection. It is not receptive of theories, depending entirely on what has meant survival. These reflexive salvific impulses are not named or numbered, so far as I know. They are behavioral rather than structures, so they come and go before anyone can say, "Oh, that reminds me of a . . ." What? A boomerang? A square dance? Lemmings?
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