30 Muscle Motor Unit - Motor Unit PSL302: Lecture 30, by...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Muscle Motor Unit Motor Unit - Def’n: a motoneuron + all the muscle fbers that it innervates - The muscle fbers oF a motor unit all contract together - Motoneuron in ventral horn (or motor nucleus in medulla) -> axon thru ventral root -> specifc muscle -> terminate on diFF muscle fbers = contract together - Jxn bwn terminal + muscle fber: terminal is broken up, parallel along same muscle fber = large synaptic summation automatically = a.p. guaranteed in post-jxnal fbre - Neuromuscular jxn very diFF From normal synapses Motor Unit Type - The muscle fbers oF a motor unit are all same type - There are 3 broad categories of muscle Fbers , and hence oF motor units 1. Slow oxidative - Slow twitch (long rise-time oF Force): build-up oF Force relatively long (in ms) - “Twitch”: contraction caused by 1 a.p. - Rich in myoglobin : dark red colour - Stores oxygen (muscle version oF hemoglobin) - Many mitochondria: “oxidative” -> aerobic metabolism : Krebs cycle - Non-fatiguing : eFfcient generation oF ATP; oxygen doesn’t run out - Used in postural support: sustains contraction For hours on end - Small maximal force : enough For antigravity, but not enough to get you out oF chair 2. ±ast oxidative/glycolytic - Intermediate twitch & rise-time - Moderate maximal Force - Some myoglobin: lighter colour - Moderate number oF mitochondria - ±atigues slowly (over several minutes) - Mixed glycolytic/oxidative metabolism 3. ±ast glycolytic - ±ast twitch & rise-time - Large maximal force + large Fber size , i.e. get out oF chair - Little or no myoglobin: pale Fbers - ±ew mitochondria: glycolytic metabolism - ±atigues rapidly (in 1 min) due to lactic acid accumulation Diagram: comparing categories of muscle Fbers - Twitch tension: size oF maximal Force - ±ibers in muscles not same across species - Chickens: dark meat -> entire muscle is slow oxidative (unlike us: postural support) - In humans: we mix all muscle fbers together, although in diFF combos throughout body PSL302: Lecture 30, by ProF. MacKay ±riday, Nov. 26, 2010 1 oF 4
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Motoneuron - muscle fber relationship - Small diameter motoneurons innervate
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

30 Muscle Motor Unit - Motor Unit PSL302: Lecture 30, by...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online