Cross references:
Fast vs. Slow Twitch Muscles
Motor Neuron Evolution
Amphioxus Amphioxus Motor Nerves Dorsal Motor Neurons Ventral Motor Neurons Amphioxus Locomotion New perspectives on the evolution of protochordate...(PubMed) http://www.ncbi.nlm.nih.gov/pubmed/11604123?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_SingleItemSupl.Pubmed_Discovery_RA&linkpos=4&log$=relatedreviews&logdbfrom=pubmed "Cephalochordates (i.e. amphioxus) are segmented and resemble vertebrates in having two distinct locomotory modes, slow for distance swimming and fast for escape, that depend on separate sets of motor neurons and muscle cells. The sense organs of both amphioxus and tunicate larvae serve essentially as navigational aids ..." "Similarities between amphioxus and tunicate sense organs are then most easily explained if distance swimming evolved before and escape behaviour after the two lineages diverged, leaving tunicates to adopt more passive means of avoiding predation." same article: Philos Trans R Soc Lond B Biol Sci. 2001 Oct 29;356(1414):1565-72. Review.PMID: 11604123 New perspectives on the evolution of protochordate sensory and locomotory systems, and the origin of brains and heads. Related articles Free article PDF can be read, but not copied. Below is a compilation of information about Amphioxus Fast vs. Slow Twitch Muscles extracted from more general pages. Amphioxus Motor Nerves says: "The synaptic zones in each segment consist of two distinct domains, the ventral (VC) and dorsal (DC) synaptic compartments. Both utilize acetylcholine as a transmitter. The ventral synaptic compartments are where the deep, anaerobic, fast muscle cells receive their innervation. The dorsal compartment is where the superficial, aerobic, slow muscle cells of the myomeres receive their innervation." Dorsal Motor Neurons says, referring to the Amphioxus : "Amphioxus myotomes consist of separate sets of superficial and deep muscle fibers, each with its own innervation, that are thought to be responsible for slow swimming and escape behavior, respectively." Ventral Motor Neurons says, referring to the Amphioxus : "Synaptic patterns reveal five categories of descending pathways, four of which are associated with the ventral compartment (VC) motoneurons responsible for escape swimming." Amphioxus Locomotion says: "Amphioxus has three types of motoneurons, ventral compartment (VC) motoneurons, which innervate the fast fibers of the myotome, dorsal compartment (DC) ones, which innervate the slow fibers, and visceral motoneurons, which innervate all other body muscles " "Cephalochordates (i.e. amphioxus) are segmented and resemble vertebrates in having two distinct locomotory modes, slow for distance swimming and fast for escape, that depend on separate sets of motor neurons and muscle cells." "Amphioxus myotomes consist of separate sets of superficial and deep muscle fibers, each with its own innervation, that are thought to be responsible for slow swimming and escape behavior, respectively. CotA: Amphioxus Fast-Slow Twitch
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