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Lecture 11

Lecture 11 - Comparative Skeletal Muscle Physiology

9 Pages
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Department
Biological Sciences
Course Code
BIOC32H3
Professor
Kenneth Welch

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The Lecture 11
Chapter 10 Muscles and Animal Movement
Section Insect Asynchronous Flight Muscles P. 408 411.
Section Motor Control in Arthropods P. 413 414.
Phasic twitch
Twitch kinetics:
The AP wave on the membrane of the muscle cell must travel along the whole length
of the fibre causing the sarcomeres along the entire length causing tension if it
doesnt go through the muscle as a whole, then it will cause the muscle to stretch
APs are required to come in rapid succession and result in temporal summation (a
single fibre with summation)
Isometric: less than full production
(A tetanic contraction (or tetanized state) occurs when a motor unit has been maximally stimulated by its motor neuron.
This occurs when a muscle's motor unit is stimulated at a sufficiently high frequency of multiple impulses. Each stimulus
causes a twitch. If stimuli is delivered slow enough, the tension in the muscle will relax between successive twitches. If
stimuli are delivered at high frequency, then the twitches will add up, resulting in tetanic contraction.)
Force production modulation:
Depends on units of muscle function activated at a time and how long they remain
activated
Vertebrate motor units contains 1000s of fibres that have 100s neurons innervating
it
The motor unit: a motor neuron fires and causes twitches in all fibres that it
innervates (everything it is talking to twitches)
3 types of motor neurons:
oType I, type IIa and type IIb
oType I:
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Slow, red fibres dont contract rapidly and dont generate as much
force
Red = mitochondria
Lots of vasculature
Good at using oxidative phosphorylation as an energy source = fatigue
resistant!
Development of tension though = slow
oType IIa:
Relatively faster than slow types
Are fast rich oxidative phosphorylation
More maximum force per cross-sectional area of the muscle
Rise and relaxation times are faster
Still a little resistant to fatigue because it does use mitochondria too
A lot of vasculature relies on mitochondria
Anaerobic
Burst performance by tapping into their anaerobic store
Duck = type IIa = red
oType IIb:
White fibres like chicken breast fully type 2 fibres
Chickens can fly ground up in BURSTS of energy and muscle
contraction
Chicken can have enough burst power but cannot have sustained flight
Fast glycolytic fibres develop tension and relax relatively rapidly can
produce a lot of power a lot of force per unit of cross-section area
They dont spend energy in vasculature but cant rely on oxidative
phosphorylation but on glycolysis and fatigues fast
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Dont memorize MAT
Twitch rise and relaxation times are rapid! Because the room they might have spent
on mitochondria and vascular arent there and they have -
A lot of mitochondria and vasculature in the fast fibres!
White muscle fibres type 2 b fibres! Fatigues (cannot sustain flight in chicken);
rely on glycolysis and fatigue; anaerobic; larger than type 1
Red muscle fibres type 2 A fibres
Increase the signalling and not recruiting just red fibre types but also the other
types (when needed a burst of energy for force production)
Motor neurons are different
oSoma of type 1 is relatively small typ2A+B are larger corresponds to how
easily those motor neurons are activated; different amount of activation
signal coming from CNS
oLarger neuron bodies with less dentritic input are less apt to be recruited
First motor units to get activated by that signal are the slow (and less powerful)
Only when you need to ramp up performance, you increase amount of stimulation
from CNS and you recruit both the slow and the faster fibre types
The amount of force I need to produce, occurs in a graded fashion with the number I
need to recruit
Still recruiting the same ones that you are using at the lower force production levels
but adding on to that
Tonic muscle
Contrast that with tonic muscle: at the fibre level there are some recruited
Some vertebrate muscle fibres are not twitch at all they are tonic muscle fibres
No rapidity but need to be sustained over a long period of time
In the intrinsic eye muscle moves that dont have to occur with any rapidity at all
An iguana relying on postural muscles population of red fibres = tonic fibres
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Description
The Lecture 11 Chapter 10 Muscles and Animal Movement Section Insect Asynchronous Flight Muscles P. 408 411. Section Motor Control in Arthropods P. 413 414. Phasic twitch Twitch kinetics: The AP wave on the membrane of the muscle cell must travel along the whole length of the fibre causing the sarcomeres along the entire length causing tension if it doesnt go through the muscle as a whole, then it will cause the muscle to stretch APs are required to come in rapid succession and result in temporal summation (a single fibre with summation) Isometric: less than full production (A tetanic contraction (or tetanized state) occurs when a motor unit has been maximally stimulated by its motor neuron. This occurs when a muscles motor unit is stimulated at a sufficiently high frequency of multiple impulses. Each stimulus causes a twitch. If stimuli is delivered slow enough, the tension in the muscle will relax between successive twitches. If stimuli are delivered at high frequency, then the twitches will add up, resulting in tetanic contraction.) Force production modulation: Depends on units of muscle function activated at a time and how long they remain activated Vertebrate motor units contains 1000s of fibres that have 100s neurons innervating it The motor unit: a motor neuron fires and causes twitches in all fibres that it innervates (everything it is talking to twitches) 3 types of motor neurons: o Type I, type IIa and type IIb o Type I: www.notesolution.com
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