Muscle Physiology

Question 1

Skeletal Muscle

Answer 1

several levels of organization

Question 2

Muscle contains

Answer 2

muscle contains numerous muscle cells; also called muscle fibers (~10-80 um diameter)

each has a multiple mitochondria

Question 3

Sarcolemma

Answer 3

outer limiting membrane of fiber

Question 4

Contact area; motor end-plate

Answer 4

nerve terminal and sarcolemma

Question 5

Actin or thin filament

Answer 5

dont change in length and composed of 2 stands of actin protein + 2 strands of tropomyosin protein wound as a helix

Question 6

Myosin or thick filament

looks like a hockey stick

Answer 6

Protein helixes with intermittent cross bridge; dont change in

interacts with actin to shorten sarcomere; to get a contraction

Question 7

Sarcoplasmic reticula
(endoplasmic reticula)

Answer 7

storage site for calcium

parallel to myofibrils; goes throxughout muscle cell and goes outside cell

Question 8

sarcomere

Answer 8

basic contractile unit of muscle fiber

area between z lines

Question 9

Myofibril

Answer 9

series of repeating sarcomeres

Question 10

Transverse tubules filled with ECF allows?

Answer 10

action potential to be transmitted into interior of cell

Action potential moves along sarcolemma & down transverse tubules

Question 11

Sequence of Events - Transfer of Information

Action Potential &raquo_space;> Axon Terminal &raquo_space;> Release of?

Answer 11

which binds to muscle receptors

Question 12

Acetylcholinesterase is and does what?

Answer 12

is an enzyme that breaks down acetylcholine

Question 13

Action Potential (Na+ influx) &raquo_space;

Answer 13

Ca++ release from sarcoplasmic reticulum\
Ca++ diffuses down concentration gradient &raquo_space; sarcoplasmic fluid

Passive Process

Question 14

Contraction then occurs - if

Answer 14

if ATP is available
At rest - Ca++ pumped back into sarcoplasmic reticulum

Active Process

Question 15

Many points along actin molecule contain active sites that chemically interact with head of myosin molecule.
What happens when Ca++ is absent?
What happens when Ca++ is present?

Answer 15

If Ca++ absent - active sites covered by tropomyosin & contraction inhibited

Ca++ presence - binds with troponin &raquo_space; change in tropomyosin &raquo_space; exposure of active sites

Question 16

2 Functions of ATP

Answer 16

1. Break in actin & myosin link
   * Requires ATP
2. Cross-bridge movement
   Rigor Mortis - stiffening of skeletal muscle after death (3-4 h for start) &raquo_space; (12 h finish)

then disappears - next 48 - 60 h

Due to lack of ATP - myosin & actin are linked

Question 17

Cross Bridges

Answer 17

The myosin molecules globular heads that protrude from a thick filament within a muscle fiber and interact with the actin molecules on the thin filaments to shorten the muscle fiber during contraction

Question 18

Compounds that affect muscle transmission

Curare

Answer 18

South American Poison - binds to ACh
Receptors
Death due to inability to breath - affects skeletal
muscles responsible for breathing movement Not broken down by acetylcholinesterase

Question 19

Compounds that affect muscle transmission

Nerve Gas & certain Pesticides

Answer 19

• inhibits acetylcholinesterase
• ACh is not destroyed
• ion channels remain open
• no repolarization
• no additional action potentials
• skeletal muscle paralysis

Question 20

Compounds that affect muscle transmission

Botulinus toxin

Answer 20

produced by bacterium
Clostridium botulinum &raquo_space; blockage of ACh release from nerve terminal

VERY TOXIC - 0.0001 mg&raquo_space; death to 1 human

500 g &raquo_space; death to entire human population

Question 21

spatial summation

Answer 21

Increase number of motor units that contract at any one time

Question 22

temporal summation

Answer 22

Increase frequency of contraction within a muscle unit

due to incomplete removal of Ca++ back to resting level (temporal summation).

Question 23

Altering Force of Contraction - Skeletal Muscle

2 forms

Answer 23

1. Spatial Summation

2. Temporal Summation

Question 24

Tetany

Answer 24

contraction of whole muscle without relaxation

Question 25

Each contraction - slightly greater than last

Answer 25

Stair Case Effect

Question 26

2 Muscle Types

Answer 26

1. Red Muscle - dark meat - slow contraction (long distance) 2. White Muscle - white meat - rapid contraction (short distance)

Question 27

Red Muscle = dark meat | 4 important factors

Answer 27

1. Slow, methodical contractions 2. Relatively fatigue-resistant 3. High oxidative metabolism - uses lipids for primary energy source 4. More fat in the muscle

Question 28

White Muscle = white meat

Answer 28

1. Rapid, small bursts of contraction 2. Fatigues easily 3. Glycogen for primary energy source 4. Less fat in the muscle

Question 29

Skeletal Muscle Fiber Types | 4 Types

Answer 29

1. Fast fibers 2. Slow fibers 3. Oxidative fibers 4. Glycolytic fibers 1. Fast & slow fibers - based on maximum velocity for shortenin 2. Oxidative & glycolytic fibers - based on major pathway for ATP

Question 30

Fast Fibers:

Answer 30

Myosin with high ATPase activity

Question 31

Slow Fibers:

Answer 31

Myosin with lower ATPase activity

Question 32

Oxidative Fibers:

Answer 32

Contain numerous mitochondria with high capacity for oxidative phosphorylation Dependent on blood flow to deliver oxygen & fuel Also contains large amount - myoglobin (oxygen-binding protein) This increases oxygen diffusion rate into muscle + serves as a small oxygen store Large amount of myoglobin produces dark-red color Oxidative fibers = red muscle fibers

Question 33

Glycolytic Fibers:

Answer 33

Few mitochondria - but high concentration - glycolytic enzymes & store of glycogen Less blood flow + less myoglobin Paler in color = white muscle

Question 34

Three General Groups of Skeletal Muscle Fibers

Answer 34

1. Slow - Oxidative 2. Fast - Oxidative 3. Fast - Glycolytic

Question 35

Slow - Oxidative

Answer 35

low myosin - ATPase acitivity + high oxidative capacity (red muscle)

Question 36

Fast - Oxidative

Answer 36

high myosin - ATPase activity + high oxidative capacity (red muscle)

Question 37

Fast - Glycolytic

Answer 37

high myosin - ATPase activity + high glycolytic activity (white muscle)