Exam 2: Ch 12 Skeletal Muscle

Question 1

Fibrous connective tissue from tendons form what

Answer 1

epimysium sheaths that extend around and into skeletal muscles

Question 2

inside the muscle fibrous connective tissue divides muscle into columns called

Answer 2

fascicles

Question 3

perimysium

Answer 3

connective tissue around fascicles

Question 4

muscle fibers are

Answer 4

muscle cells ensheated by thin connective tissue layer called endomysium

Question 5

plasma membrane is called

Answer 5

sarcolemma

Question 6

muscle fibers are similar to other cells except are

Answer 6

multinucleate and striated

Question 7

most distinctive feature of skeletal muscle is its

Answer 7

striations

Question 8

NMJ

Answer 8

• neuromuscular junction
  Includes the single synaptic ending of the motor neuron innervating each muscle fiber & underlying specializations of sarcolemma

Question 9

motor end plate

Answer 9

place on sarcolemma where NMJ occurs

Question 10

each motor neuron branches to

Answer 10

innervate a variable # of muscle fibers

Question 11

a motor unit includes

Answer 11

each motor neuron & all fibers it innervates

Question 12

when a motor neuron is activated

Answer 12

all muscle fibers in its motor unit contract

Question 13

 Number of muscle fibers in motor unit varies according to

Answer 13

degree of fine control capability of the muscle

Question 14

 Innervation ratio is

Answer 14

motor neurons : : muscle fibers; vary from 1:100 to 1:2000

Question 15

Fine movements occur when

Answer 15

motor units are small, i.e. 1 motor neuron innervates small # of fibers

Question 16

 Gross movements occur when

Answer 16

motor units are large: 1 motor neuron innervates large # of fibers

Question 17

 Q: Since individual motor units fire “all-or-none,” how do skeletal muscles perform smooth movements?

Answer 17

…

Question 18

 A:Recruitment is used

Answer 18

Brain estimates number of motor units required & stimulates them to contract;
 It keeps recruiting more units until desired movement is accomplished in smooth fashion:
• More & larger motor units are activated to produce greater strength

Question 19

 Structure of Muscle Fiber

- Each fiber is packed with

Answer 19

myofibrils

Question 20

 Structure of Muscle Fiber

- Myofibrils are

Answer 20

are 1m in diameter & extend length of fiber

• Packed with myofilaments;

Question 21

 Structure of Muscle Fiber :

myofilaments

Answer 21

composed of thick & thin filaments that give rise to bands which underlie striations

Question 22

 Structure of Muscle Fiber :

A band

Answer 22

is dark, contains thick filaments (mostly myosin);

Question 23

 Structure of Muscle Fiber :

H band

Answer 23

• Light area at center of A band

- area where actin & myosin do not overlap

Question 24

 Structure of Muscle Fiber :

I band

Answer 24

light, contains thin filaments (mostly actin);

Question 25

 Structure of Muscle Fiber :

- Z line/disc where

Answer 25

• At center of I band

- where actins attach

Question 26

 Structure of Muscle Fiber :

Sarcomeres

Answer 26

contractile units of skeletal muscle consisting of components between 2 Z discs

Question 27

 Structure of Muscle Fiber :

M lines

Answer 27

 are structural proteins that anchor myosin during contraction

Question 28

 Structure of Muscle Fiber :

Titin

Answer 28

 is elastic protein attaching myosin to Z disc that contributes to elastic recoil of muscle

Question 29

 Sliding Filament Theory of Contraction:

- Muscle contracts because

Answer 29

myofibrils get shorter

Question 30

 Muscle contracts because myofibrils get shorter and it occurs because

Answer 30

thin filaments slide over & between thick filaments towards center = shortening distance from Z disc to Z disc

Question 31

 Cross bridges are formed by

Answer 31

heads of myosin that extend toward & interact with actin

Question 32

Each myosin head contains

Answer 32

ATP-binding site which functions as an ATPase

Question 33

 Myosin can not bind to actin unless

Answer 33

unless it is “cocked” by hydrolyzing ATP;

Question 34

after binding, myosin undergoes

Answer 34

conformational change (power stroke) which exerts force on actin

Question 35

Sliding Filament Theory of Contraction

Answer 35

 1. Myosin head has hydrolyzed ATP to ADP + Pi
 2. Cross bridges are formed by heads of myosin molecules that extend toward & interact with actin
 3. Pi is released causing a conformational change in myosin head
 4. Powerstroke occurs sliding thin filament over thick and ADP is released
 Note: at this point, cross bridges are stuck….ATP is needed for detachment
 5. Myosin head binds new ATP and releases actin
 6. Myosin head hydrolyzes ATP to ADP + Pi

Question 36

Control of cross bridge attachment to actin is via

Answer 36

troponin-tropomyosin system = serves as a switch for muscle contraction & relaxation

Question 37

 The filament tropomyosin lies in

Answer 37

grove between double row of G-actins (that make up actin thin filament)

Question 38

Troponin complex is attached to

Answer 38

tropomyosin at intervals of every 7 actins

Question 39

In relaxed muscle,

Answer 39

, tropomyosin blocks binding sites on actin so cross bridges can not occur; this occurs when Ca++ levels are low (<10-6 M)

Question 40

 When Ca++ levels rise (>10-6 M),

Answer 40

Ca++ binds to troponin causing conformational change which moves tropomyosin & exposes binding sites Allowing crossbridges & contraction to occur; crossbridge cycles stop when Ca++ levels decrease (<10-6 M)

Question 41

Ca++ levels decrease because

Answer 41

because it is continually pumped back into the sarcoplasmic reticulum (SR - a calcium reservoir in muscle)

Question 42

 Most Ca++ in SR is in

Answer 42

terminal cisternae;

Question 43

running along terminal cisternae are

Answer 43

T tubules

Question 44

 Excitation-Contraction Coupling:

- Skeletal muscle sarcolemma is

Answer 44

is excitable

 Conducts APs just like axons

Question 45

 Release of ACh at NMJ causes

Answer 45

large depolarizing end-plate potentials & APs in muscle

Question 46

 APs race over

Answer 46

sarcolemma & down into muscle via T tubules

Question 47

 T tubules are extensions of

Answer 47

sarcolemma

Question 48

 Ca++ channels in SR are

Answer 48

mechanically linked to channels in T tubules

Question 49

 APs in T tubules cause release

Answer 49

of Ca++ from cisternae via V-gated Ca++ release channels

 Called electromechanical release

Question 50

 Muscle Relaxation

Answer 50

 Ca++ from SR diffuses to troponin to initiate crossbridge cycling & contraction
 When APs cease, muscle relaxes
- Because Ca++ channels close & Ca++ is pumped back into SR

Question 51

 Twitch

Answer 51

= single rapid contraction & relaxation of muscle fibers

Question 52

summation)

Answer 52

 If 2nd stimulus occurs before muscle relaxes from 1st, the 2nd twitch will be greater

Question 53

 Contractions of varying strength (graded contractions) are obtained by stimulation of

Answer 53

of varying numbers of fibers (motor unit recruitment)

Question 54

incomplete tetanus

Answer 54

If muscle is stimulated by an increasing frequency of electrical shocks, its tension will increase to a maximum

Question 55

complete tetanus

Answer 55

 If frequency is so fast no relaxation occurs, a smooth sustained contraction results

Question 56

Treppe or staircase effect

Answer 56

 If muscle is repeatedly stimulated with maximum voltage to produce individual twitches, successive twitches get larger