2 - Green - Muscle Physiology II

Question 1

Active Tension

Answer 1

Force generation by formation of actin-myosin crossbridges

Question 2

Cachexia

Answer 2

Dramatic muscle atrophy seen in patients with chronic illness

“wasting syndrome”

AIDS, cancer, diabetes, MS

Question 3

Isometric Contraction

Answer 3

length constant, tension changes

Object too heavy to pickup

Question 4

Isotonic Contraction

Answer 4

Tension constant, length changes

Bicep curls for the girls

Question 5

Motor Unit

Answer 5

Single Motor neuron and all muscle fibers it innervates

Question 6

Myopathy

Answer 6

Disease of skeletal muscle not caused by nerve disorders

Congenital, genetic abnormalities in Mt, glucose/glycogen metabolism defects

Question 7

Myositis

Answer 7

Inflammation of skeletal muscles

Muscles closest to trunk

Causes: Injury, infection, autoimmune disease

Question 8

Rhabdomyolysis

Answer 8

Rapid destruction of muscle cells

Muscle proteins in urine–very dark urine

Question 9

Sarcopenia

Answer 9

Age-related reduction in skeletal muscle mass and strength

normal , not disease related

Question 10

Total Tension

Answer 10

Force generated by cross bridge formation and stretching muscle tension

Question 11

Concentric

v

Eccentric

Answer 11

Concentric - muscle decreasing in length against opposing load–lifting weight up

Eccentric - muscle increasing in length as it resists load–pushing weight down

Question 12

Optimal Length (L_o)

Answer 12

Length of muscle where maimum force is generated

Question 13

What occurs if muscle is stretch too far?

Too close?

Answer 13

Little actin/myosin overlap, few corssbridges–low tension

Too much overlap, crowded, cross bridges weakened–low tension

Question 14

What is the majority of tension in the normal working range of muscle?

Answer 14

Majority from active tension–actin/myosin crossbridges

Question 15

Passive Tension

Answer 15

Inherent property of muscle fiber, generated by stretching muscle to different lengths

not caused by actin-myosin crossbridges

Question 16

What is the mechanical advantage gained by muscular attachment points?

Answer 16

Fulcrum advantage, joint moves small compared to distal end of moment arm

Question 17

Force-Velocity Relationship of Muscle

Answer 17

More load, slower velocity.

Vmax when load = 0

Question 18

Load Velocity is Directly Proportional to what?

Answer 18

Number of crossbridges formed

Question 19

Type I Fibers:

AKA

Mitochondria?

Source of Energy?

Color?

Fatigue?

Motor Neuron Size?

Uses?

Answer 19

Slow-Twitch

Slow myosin ATPase

High Mitochondria

Cellular Respiration (Aerobic)

Red (high myoglobin)

Resistant to fatigue

Small, slow conductiong motor neurons

Running marathons

Question 20

Type IIa Fibers:

AKA

Mitochondria?

Source of Energy?

Color?

Fatigue?

Motor Neuron Size?

Uses?

Answer 20

Fast Twitch

Fast myosin ATPase

High mitochondria

Cellular respiration, low glycolysis

Red-Pink (high myoglobin)

Semi fatigue resistant

Intermediate, fast-conducting motor neurons

Sprinting, walking

Question 21

Type IIb Fibers:

AKA

Mitochondria?

Source of Energy?

Color?

Fatigue?

Motor Neuron Size?

Uses?

Answer 21

Fast Twitch

Fast myosin ATPase

Low Mitochondria

Rich in Glycogen

Glycolysis

White (low myoglobin)

Fatigue Easily

Large, fast-conducting motor neurons

Hitting a baseball

Question 22

Innervation Ratio

Answer 22

Number of fibers innervated by motor unit

Question 23

Type I Motor Units

Answer 23

Few fibers innervated – small ratio

Slow conducting

Fine, graded movements

Question 24

Type II Motor Units

Answer 24

Large diameter, large ratio

Faster-conducting

Coarse movements

Question 25

What two ways can tension be increased in muscle?

Answer 25

Recruitment - increasing motor units contracting Summation - Increasing frequency of individuals motor unit firing

Question 26

In what order are muscle fibers recruited?

Answer 26

Type I (slow) first Type II (fast) second

Question 27

What are some proposed causes for muscular fatigue

Answer 27

Glycogen / creatine phosphate depleted **ATP levels do NOT decrease substantially** decreased motor neuron firing decreased O2 impaired Ca²⁺ release

Question 28

Muscle Cells in Aging Motor Units in Aging

Answer 28

Atrophy Fewer satellite cells reduced mitocondria - - - Reduced number Increase in number of fibers/motor unit (motor neuron loss)

Question 29

Muscular Dystrophy

Answer 29

Progressive skeletal muscle weakness, defect in muscle proteins, death of muscle cells and tissues ## Footnote **Duchenne / Becker** **Mutation in dystrophin gene** **Instability of sarcolemma--damage during contractions**

Question 30

Malignant Hyperthermia

Answer 30

Defect in RYR1 Channel Open easily, close slowly **Anesthetics, muscle relaxers** **Uncontrolled Ca²⁺ release** **Rigidity / Heat production**