Physiology Lecture 5 Flashcards
general movement of AP to muscle cell
L5S4
-Presynaptic nerve cell synapses with a muscle cell
-ACh is released and binds with receptors on motor end plate of muscle cell
-AP propogates down t-tubule
-Binds to a receptor in the tubule that induces the release of calcium from the sarcoplasmic reticulum
-Calcium seeks binding sites on thin filaments
Crossbridges can now bind to the thin filaments
What reabsorbs calcium so crossbridges can relax?
Sarcoplasmic reticulum
What is a motor unit?
Single alpha motor neuron and all the muscle fibers it innervates
They fire all at once
Is each muscle fiber within a motor unit the same fiber type?
Yes
Recruiting more motor units results in what?
Greater number of crossbridges
Motor units are generally recruited in order from _____ to ______.
Smallest to largest
This minimizes the amount of fatigue
Fatigue can be caused by a decrease in production of what?
ATP
Difference between muscle tension and load?
Muscle tension is the force exerted on an object
Load is the force exerted on the muscle by the object
When muscle tension is greater we see what type of contraction?
Isotonic concentric
When the load is greater than the muscle tension we see what type of contraction?
Isotonic eccentric
What does the force velocity curve show?
As force needed increases, velocity goes down.
When velocity is 0 we have what type of contraction?
Isometric
Having a negative velocity is what?
Eccentric
What is a tetanic contraction?
Muscle is unable to relax and stays maximally contracted
What is summation?
increase in muscle tension from successive action potentials occurring during the phase of mechanical activity
When do we have the most force production?
When out muscles are halfway because this is when the maximum amount of crossbringing is occuring.
What is active insufficiency?
Example
When a multi joint muscle reaches a length so short it can no longer generate effective force.
Making a fist with the wrist extended is stronger than with the wrist flexed.
What is passive insufficiency?
Example
Occurs when a multi joint muscle is passively elongated such that it cannot allow full ROM at both joints simultaneously
difficult to reach the toes with the knee extended as compared to that with the knee flexed
What is muscle strength influenced by?
- Number of MU/fibers recruited
- Frequency of fiber stimlation
- Initial length of fiber at rest
What is muscle pennation?
Describes the orientation of muscle fibers relatively to the load axis of the muscle
With pennation, do we get more or less fibers in the same amount of area?
More
The greater the angle of pennation, the more ________ in the same area which results in ___________.
muscle (crossbridges)
more force production
Why would we want smaller pennation angles in some instances?
Smaller angle of pennation means more velocity but less force
Muscle that generate force have _______ cells while muscles that generate velocity have _______ cells.
shorter, longer
