11.26.13 Skeletal Muscle Excitation-Contraction Coupling

Question 1

Disorders causing muscle weakness, motor neuron, ALS, (Lou Gehrig’s Disease)

Answer 1

degeneration of motor neurons

A defect on chromosome 21, which codes for superoxide dismutase,

Question 2

Lambert-Eaton syndrome

Answer 2

caused by autoantibodies against Calcium channels in motor neurons resulting in an inability to release acetylcholine. Affecting motor neurons. Need calcium to release Ach. Muscle is fine.

Question 3

Botulism

Answer 3

prevents acetylcholine release by cleaving synaptic associated proteins (SNAPs) can help with muscle spasms.

Question 4

Disorders causing muscle weakness with nicotinic receptor. Myasthenia gravis …

Answer 4

caused by autoantibodies against nicotinic receptors in skeletal muscle, less likely to muscle contract

Question 5

Disorders causing muscle weakness with Ryanodine receptors ….. Malignant hyperthermia ….

Answer 5

(Calcium-induced calcium release channels)

caused by a mutation of the ryanodine receptor allowing excessive release of calcium, usually triggered by anesthetics

Question 6

Duchenne’s muscular dystrophy

Answer 6

A mutation in dystrophin, a skeletal muscle support protein

Question 7

Length-Tension relationships in skeletal muscle

Answer 7

The amount of force generated by a muscle is directly proportional to the number of actin-myosin crossbridges per cross-sectional area. force decreases when stretched.

Question 8

Slow twitch fibers are type I

Answer 8

a slower myosin ATPase enzyme, high proportions in distance runners. a lot of myoglobin, resulting in the designation “red fibers”. need alot of oxygen. turkey legs are red.

Question 9

Fast twitch fibers are type II

Answer 9

have a faster myosin ATPase
white fibers (less myoglobin)
adapted for anaerobic metabolism

Question 10

Types of contractions, concentric

Answer 10

Muscle contracts resulting in shortening

Typical biceps curl in weightlifting

Question 11

Eccentric

Answer 11

Muscle lengthens while attempting to shorten
Run down a hill
Much more damage to muscle with this type of contraction (really sore afterwards

Question 12

types of muscle, Cardiac…

Answer 12

striated, Cardiac muscle has autorhythmicity
has a greater requirement for extracellular Ca+
Cardiac muscle has longer action potential due to longer opening of Ca+ muscle.

Question 13

Smooth Muscle

Answer 13

not striated, Contraction is not controlled by troponin or tropomyosin. Frequently contractions controlled by nerve or hormonal factors. ex. blood vessels. is initiated by calcium interacting with a calcium-dependent myosin light chain kinase

Question 14

Summary (Excitation-contraction signaling cont)

Answer 14

Calcium entry into muscle releases calcium from intacellular storage sites (sarcoplasmic reticulum) via calcium-induced calcium release (ryanodine receptors)
Elevated intracellular calcium concentrations result in calcium binding to troponin C
Calcium binding to troponin C releases inhibition of actin-myosin interactions
Myosin heads then contact actin to create muscle shortening and force generation, provided energy in the form of ATP is present

Question 15

Summary (cont

Answer 15

Force generation is dependent on the number of actin-myosin crossbridges formed per cross-sectional area
Speed of muscle contraction is dependent on myosin ATPase activity

Question 16

More Summary

Answer 16

Myosin works by binding to actin when ADP and P are bound to myosin
Release of Phosphate causes a conformational change in myosin, generating force (shortening)
This is called the power stroke
ADP is released when the myosin head is in this “cocked” position
ATP is bound, causing a dissociation from actin
Cleavage of the ATP to ADP and P allows the myosin to bind to actin

Question 17

More summary

Answer 17

Shortening of muscle results in truncation of the “I” zone of each sarcomere- be able to explain this
Disorders of motor neuron include
Amyotrophic lateral sclerosis
Lambert Eaton Syndrome
Botulism
Disorders of skeletal muscle include
Myasthenia gravis
Malignant hyperthermia
Muscular dystrophy

Question 18

objectives

Answer 18

Mechanism of contraction
Relationship between actin, myosin, tropomyosin and troponin
Calcium binding to troponin C allows actin and myosin contact
Interaction between actin and myosin crossbridges
Alterations in the striated appearance of skeletal muscle in relaxed and contracted states
Relaxation