Exam 2- Skeletal Muscle Mechanics Flashcards
___ is the muscle’s response to a single stimulus
twitch
describe the 3 components of a twitch
1- latent period (latency)- slight delay b/w when you give the stimulus and the muscle contracts- involves AP traveling down neuron axon, transmission of AP from terminal to muscle membrane, and initiation of contraction by AP on muscle membrane itself (latency very short, only a few ms)
2- contraction phase- contraction/tension
3- relaxation phase- goes back to normal
when a muscle is responding to a series of stimuli, you get something called ___, which is the ___
tetany
the maximum sustained contraction of the muscle
with tetany, the muscle is being stimulated so rapidly that…
instead of contract & relax, it contracts and stays contracted at its maximum strength
what is the difference b/w muscle tension and load
tension: the force generated by a muscle contraction
load: the force of resistance exerted against a muscle (ex: weights; resistance of weight against gravity when walking up stairs)
what are the 2 major types of muscle contraction and what defines them
isotonic and isometric
relationship b/w tension and load defines them
describe isotonic muscle contraction
tension is greater than the load (lifting a 1 pound weight: muscles generate 1lb tension, muscles generate enough tension to overcome the resistance –> load is moved)
- once muscle tension exceeds the load, remains constant throughout the remainder of the contraction
- typical sliding filament mechanism: sarcomeres shorten, muscle contract, load is moved, then muscle realaxes, sarcomeres go back to normal length)
what is the most typical form of muscle contraction
isotonic- tension greater than load
describe isometric muscle contraction
load is greater than the max tension your muscles can generate (and can’t be moved or the muscle is held in a fixed position- either way load can’t be moved)
- as muscle tries to move the load, more and more cross-bridges form, instead of sarcomere/muscle shortening, muscle tension keeps increasing until it maxes out, sarcomeres do not really shorten
- sarcomeres stay ~ the same length, but muscle tension increases
in isotonic contraction, __ shorten and __ remains the same
sarcomeres
tension
at the cellular level, muscle contraction is ___, meaning every time you get an AP, get contraction of…
all-or-none
of the same strength
although muscle membrane produce a typical all-or-none action potential, what happens with intact muscles?
intact muscles can respond with a wide range of graded responses (diff amt of tension) depending on the degree of resistance of the load
ex: if lifting weights, generate a lot of force vs. in surgery, generate small force
muscles will generate graded responses to 2 types of stimuli:
1- change stimulus intensity –> graded response
2- change stimulus frequency –> graded response
muscles generate a graded response to changes in stimulus intensity, describe motor unit recruitment/summation
a motor unit is one motor neuron and all the muscle fibers that it innervates, motor neuron has 1 axon but multiple terminals- so can activate multiple motor cells
- motor nerve is made of many motor neurons (not all axons have the same diameter in a single motor nerve- diameter determines speed of AP AND threshold voltage as well)- threshold voltage is directly proportional to axon diameter (small diameter have the lowest threshold and will be stimulated first)
when talking about a muscles graded response to changing stimulus intensity, what directly proportional relationship is the basis of this?
axon diameter directly proportional to threshold voltage- small diameter have lowest threshold & are stimulated first
describe how different stimulus intensities change a muscles contraction
- if have low stimulus intensity –> below threshold & no firing neurons –> no muscle contraction
- intensity reaches threshold –> threshold for only the smallest diameter neurons –> get their motor fibers contracting –> very small contraction b/c only a few have been activated
- increase stimulus more –> more motor neurons firing –> more muscles contracting –> more tension
- once reach max stimulus –> all neurons firing –> max tension