PHIL 1000X Study Guide - Final Guide: Dystrophin, Unit, Motor Unit
10 May 2018
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BLOCK XC
MODULE X7 - MUSCLE PHYSIOLOGY
UNIT 2
Fatigue, Mechanics & Exercise
Unit Objectives
When you have finished this unit, you should be able to:
1. Describe the relationship between the length of a muscle fiber before contraction, and
the tension developed in it during contraction.
a. Maximum tension is going to occur if the muscle fibre is at its resting length
before contraction (that’s the optimal actin-myosin overlap)
2. Explain the summation of muscle twitches.
a. When you sum muscle twitches, you have sequential action potentials
b. Because of that, calcium builds up in the cell (because action potential is what
causes release of calcium from sarcoplasmic reticulum)
c. With all of the Ca2+ built up in the cytoplasm, then the troponin and tropomyosin
stay in the position that allows actin and myosin to bind
d. Continued actin and myosin binding means you get sustained contraction
3. Describe the recruitment of motor units.
a. If you want to generate more tension, you have to recruit more nerves
b. Each nerve will innervate several muscle cells (motor unit)
c. So as you activate more nerves, you get more motor units / muscle cells
activated, building up more tension in the muscle as a whole
d. This is the main way that more tension is generated in a muscle
4. Differentiate between isometric and isotonic contractions.
a. Isometric = muscle generates tension, but doesn’t change length (ex: if you were
to hold onto a box and keep it in one position)
b. Isotonic = muscle shortens, leading to movement of a load (ex: picking up a box
from the ground and putting it on a shelf)
5. Discuss the force (load)-velocity relationship.
https://upload.wikimedia.org/wikipedia/en/thumb/2/22/Muscle_Force_Velocity_relationshi
p.png/300px-Muscle_Force_Velocity_relationship.png
As force increases (lifting a heavier load), velocity is lower → can’t lift as quickly
The maximum efficiency (highest power) is achieved for lifting a medium load at a
medium velocity
