PMC:6610326 / 17321-18914
Annnotations
{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/6610326","sourcedb":"PMC","sourceid":"6610326","source_url":"https://www.ncbi.nlm.nih.gov/pmc/6610326","text":"α-motor units can be subdivided according to their contractile properties, into fast-twitch (F) and slow-twitch (S) fatigue-resistant types (Table 3) (Burke et al., 1973). In addition, fast-twitch α-motor units can be further categorized into fast-twitch fatigable [FF] and fast-twitch fatigue-resistant [FR] types, based on the length of time they sustain contraction. The basis of this classification is the duration of the twitch contraction time (Burke et al., 1973). F- and S-MNs also exhibit different afterhyperpolarization duration (AHP) properties. AHP is the phenomenon by which the membrane potential undershoots the resting potential following an action potential. S-MNs have a longer AHP than F-MNs, indicating that S-MNs have a longer “waiting period” before they can be stimulated by an action potential. Thus, they cannot fire at the same frequency as F-MNs (Eccles et al., 1957), so the larger FF-MNs take longer to reach an activation threshold. Similarly, other electrical properties differ between S- and F-MNs (Table 3), including their input resistance (a measure of resistance over the plasma membrane) and rheobase (a measure of the current needed to generate an action potential). S-MNs have a higher input resistance than F-MNs, underlying Hennenman’s size principle which postulates that S-motor units are the first to be recruited during movement, followed by FR and then FF units (Henneman, 1957; Mendell, 2005). Hence, a slow movement generating a small force will only recruit S-MNs, whereas a quick and strong movement will also recruit F-MNs, as well as S-MNs.","tracks":[{"project":"2_test","denotations":[{"id":"31316328-4148752-38515343","span":{"begin":165,"end":169},"obj":"4148752"},{"id":"31316328-4148752-38515344","span":{"begin":465,"end":469},"obj":"4148752"},{"id":"31316328-13430719-38515345","span":{"begin":890,"end":894},"obj":"13430719"},{"id":"31316328-13495469-38515346","span":{"begin":1420,"end":1424},"obj":"13495469"},{"id":"31316328-15914463-38515347","span":{"begin":1435,"end":1439},"obj":"15914463"}],"attributes":[{"subj":"31316328-4148752-38515343","pred":"source","obj":"2_test"},{"subj":"31316328-4148752-38515344","pred":"source","obj":"2_test"},{"subj":"31316328-13430719-38515345","pred":"source","obj":"2_test"},{"subj":"31316328-13495469-38515346","pred":"source","obj":"2_test"},{"subj":"31316328-15914463-38515347","pred":"source","obj":"2_test"}]},{"project":"0_colil","denotations":[{"id":"31316328-4148752-630800","span":{"begin":165,"end":169},"obj":"4148752"},{"id":"31316328-4148752-630801","span":{"begin":465,"end":469},"obj":"4148752"},{"id":"31316328-13430719-630802","span":{"begin":890,"end":894},"obj":"13430719"},{"id":"31316328-13495469-630803","span":{"begin":1420,"end":1424},"obj":"13495469"},{"id":"31316328-15914463-630804","span":{"begin":1435,"end":1439},"obj":"15914463"}],"attributes":[{"subj":"31316328-4148752-630800","pred":"source","obj":"0_colil"},{"subj":"31316328-4148752-630801","pred":"source","obj":"0_colil"},{"subj":"31316328-13430719-630802","pred":"source","obj":"0_colil"},{"subj":"31316328-13495469-630803","pred":"source","obj":"0_colil"},{"subj":"31316328-15914463-630804","pred":"source","obj":"0_colil"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"2_test","color":"#93a0ec","default":true},{"id":"0_colil","color":"#baec93"}]}]}}