Lecture 5: Skeletal muscle contraction

Question 1

Epimysium

Answer 1

Connective tissue surrounding entire muscle

Question 2

Muscle

Answer 2

Made up of multiple fascicles

Question 3

Perimysium

Answer 3

Connective tissue surrounding each fascicle

Question 4

Fascicle

Answer 4

A bundle of myofibers

Question 5

Endomysium

Answer 5

Delicate connective tissue surrounding each myofiber

Question 6

Sarcolemma

Answer 6

Cell membrane of muscle fiber

Question 7

Myofiber

Answer 7

Individual multinucleated muscle cell

Question 8

Myofibril

Answer 8

A chain of sarcomeres within a myofiber

Question 9

Myofilament

Answer 9

Actin and myosin filaments that make up a sarcomere

Question 10

T-tubule

Answer 10

Invagination of sarcolemma that lie close to cisternae of the sarcoplasmic reticulum
Form triads with cisternae
Two per sarcomere

Question 11

Z-discs (Z-lines)

Answer 11

Anchor actin filaments

Located at each end of sarcomere

Question 12

I -bands

Answer 12

Composed entirely of actin

Width changes during contraction

Question 13

A-bands

Answer 13

Composed of Actin and myosin

Width does not change during contraction

Question 14

H-bands

Answer 14

Composed entirely of Myosin

Width changes during contraction

Question 15

During contraction, Actin filaments:

Answer 15

Form the I-bands which become narrower in width

Question 16

During contraction, A-bands:

Answer 16

Are equivalent to the length of the myosin filaments and do not change width

Question 17

During contraction, H-bands:

Answer 17

Are the part of the A band that is not overlapped by actin filaments and becomes narrower

Question 18

DHP receptors

Answer 18

Voltage-sensitive calcium channels located on sarcolemma T-tubules
Causes conformation change in ryanodine receptors
Minute amount of calcium flows into cytosol via these channels

Question 19

Ryanodine receptors

Answer 19

Located on cisternae of sarcoplasmic reticulum
Open in response to DHP conformation change
Allow calcium into cytosol from SR

Question 20

SERCA

Answer 20

Sarcoplasmic reticulum calcium ATPase

Uses ATP to pump calcium back into the SR

Question 21

Calsequestrin

Answer 21

In the SR, it maintains an optimum calcium concentration gradient to facilitate the return of calcium to SR

Question 22

Preload

Answer 22

Load on a muscle in the relaxed state (prior to contraction)

Question 23

Preload results

Answer 23

Stretches the muscle which stretches the sarcomere
Preload generate passive tension in the muscle
Muscle resists the tension applied to it
Force of resistance is measured as passive tension
The greater the preload, the greater the passive tension

Question 24

Afterload

Answer 24

The load the muscle works against

Question 25

Isotonic contraction occurs when

Answer 25

The muscle generates more force than the afterload

Question 26

Isometric contraction occurs when

Answer 26

The muscle generates less force than the afterload

Question 27

Cross-bridge cycling starts when

Answer 27

When free calcium is available and binds to troponin

Question 28

Continuous cycling of cross-bridges is

Answer 28

Contraction

Question 29

ATP role in cross-bridging

Answer 29

ATP is required to break the link with actin

Question 30

Cross-bridge cycling continues until

Answer 30

Withdrawal of calcium ion | ATP is depleted

Question 31

Sarcomere 3.5um

Answer 31

0 tension

Question 32

Sarcomere 2.2um

Answer 32

100% tension

Question 33

Sarcomere 1.65um

Answer 33

100% tension

Question 34

Sarcomere <1.65um

Answer 34

Tension drops towards 0

Question 35

Where is ATP required for muscle contraction

Answer 35

Most is used for sliding filament mechanism Pumping calcium back into the SR (using SERCA) Pumping sodium/potassium ions through the sarcolemma to re-establish resting potential

Question 36

Phosphocreatine

Answer 36

Releases energy rapidly Reconstitutes ATP ATP+phosphocreatine allows energy for 5-8 seconds contraction

Question 37

Glycolysis

Answer 37

Lactic acid buildup | Can sustain contraction for 1 minute

Question 38

Oxidative phosphorylation

Answer 38

Provides more than 95% of all ATP needed for long term contraction

Question 39

Characteristics of fast fibers

Answer 39

``` Light/white fibers Fewer mitochondria Primarily use glycolysis or anaerobic respiration resulting in buildup of pyruvic and lactic acid Little myoglobin Larger concentration of ATPase ```

Question 40

Characteristics of slow fibers

Answer 40

``` Dark/red fibers More mitochondria Primarily use aerobic respiration More myoglobin Smaller concentration of ATPase ```

Question 41

T or F: The numbers of myofibers can be increased after brith

Answer 41

False. Only the number of myofibrils can be increased, which increases mass of myofibers

Question 42

Motor unit

Answer 42

A neuron and the myofibers it innervates | All-or-none system

Question 43

A nerve cell may innervate how many myofibers

Answer 43

Anywhere from a few to several hundred

Question 44

Summation

Answer 44

An additional spike can occur before previous calcium ions have been returned to the SR This increases the total amount of calcium ion in the cytosol and increases the rate of cross-bridge cycling This increases muscle tension

Question 45

Tetany

Answer 45

If the frequency of spikes is fast enough, there is no time for relaxation between spikes. The muscle remains at maximum contraction

Question 46

First class lever system

Answer 46

Fulcrum is in the middle | i.e., raising chin using sternocleidomastoid

Question 47

Second class

Answer 47

Resistance (out-force) is in the middle | i.e., raising the body on the ball of the foot

Question 48

Third class

Answer 48

Effort (in-force) is in the middle i.e., Both in and out forces are on the same side of the fulcrum Both forces move in same direction