Lecture 9

Question 1

Total whole muscle force during contraction is determined by the number of recruited ____ ____. Keep in mind they are recruited in _____ (ascending or descending?) order of component fiber size. Thus Type ___ (slow-twitch) is recruited first, Type ___ (intermediate) is recruited second, and Type ___ (fast-twitch) is recruited last. Also keep in mind the size of the motorneuron is proportional to the size of the fibers (large innervates large.)

Answer 1

Motor Units

Ascending

Type I

Type IIa

Type IIb

Question 2

The force of muscle contraction is proportional to the number of ____-____ formed.

Answer 2

Cross-Bridges

Question 3

Describe the relationship between length and tension as it pertains to sarcomere length and ability of the muscle to generate force via cross-bridge formation.

Answer 3

There is an optimal length for maximum number of cross-bridges to form. The more cross-bridges form, the greater the tension/force of contraction of the muscle. For skeletal muscle, this optimal length is a resting sarcomere, which is about 2-2.2 microns.

Question 4

With Power = Force x Velocity, the maximum power of skeletal muscle is at about ____ (what fraction?) of maximal force.

Answer 4

1/3

Question 5

ALS and MS are neuromuscular diseases that affect the ______ of neurons. Both are demyelinating diseases, but which one is an autoimmune disease?

Answer 5

Axons

MS is autoimmune

Question 6

Lambert-Eaton and Myasthenia Gravis are both autoimmune neuromuscular disease that affect the ______. Lambert-Eaton decreases the number of _____ channels on the _____ side, while Myasthenia Gravis reduces the number of available ______ receptors of the ______ side.

Answer 6

Synapse

Ca++ channels

Presynaptic

Acetylcholin (ACh) Receptors

Postsynaptic

Question 7

Malignant hyperthermia is a disease that affects people undergoing _____ _____. It occurs as a result of a mutation in the RyR1 receptor that makes it “leaky,” allowing Ca++ to leak into the cytosol of muscle cells –> Ca++ ATPases respond by pumping the Ca++ into the SR, and the overuse of these ATPases overheats the body.

Answer 7

General Anesthesia

Question 8

Myotonia Congenita arises from a mutation in ____ channels, which causes muscle to remain contracted for longer than normal (Fainting Goat syndrome).

Answer 8

Cl- channels

Question 9

Cardiac myocytes are striated like skeletal muscle cells, but they typically only have ____ (how many?) nuclei. The Nuclei can be more centrally located in cardiomyocytes. Cardiomyocytes are also very rich in ______ (accounts for 1/3 of their volume), and they are connected by _____ junctions to form a syncitium. They have a less developed _____ than skeletal muscle cells, and they can branch, unlike skeletal muscle cells.

Answer 9

2

Mitochondria

Gap junctions

SR

Question 10

Unlike skeletal muscle cells, cardiomyocytes use 2 modes of removing Ca++ from the cytosol during relaxation. First, they use SERCA (as do skeletal muscle cells), but they also use ___-___ exchangers that move Ca++ to the extracellular space.

Answer 10

Na+ - Ca++ exchanger

Question 11

What is different about the interaction between DHP and Ryanodine receptors in cardiomyocytes vs skeletal muscle?

Answer 11

These receptors do not physically interact between neurons and cardiomyocytes, which means they react to Ca++ influx (the synapse is about 15nm, larger than the 10nm in skeletal muscle - motor neuron synapses.)

Question 12

Cardiomyocytes have a ______ (longer or shorter?) resting length than skeletal muscle cells. This means they are not optimized for maximal force at their resting length. Thus, a slight _____ (increase or decrease?) in sarcomere length greatly increases the force of contraction.

Answer 12

Shorter (about 1.8nm as opposed to 2-2.2nm)

Increase