Muscle Structure

Question 1

What is the term given to skeletal muscle due to the presence of multiple nuclei within a single cytoplasm?

Answer 1

syncytia

Question 2

Thick filaments of skeletal muscle are called ____

Answer 2

myosin

Question 3

Thin filaments of skeletal muscle are called ____

Answer 3

actin

Question 4

Actin filaments are aligned and connected to the Z-line by ____

Answer 4

Nebulin (guidewire for actin)

Question 5

Myosin filaments are connected to the Z-line by ____

Answer 5

Titin (tightens myosin)

Question 6

What are extrafusal fibers responsible for?

Answer 6

movement (contraction)

Question 7

What are intrafusal fibers responsible for?

Answer 7

stretch reception (ie., proprioception) by muscle spindles

Question 8

Extrafusal fibers contain (sensory/motor/both) neurons

Answer 8

motor neurons

Question 9

Intrafusal fibers contain (sensory/motor/both) neurons

Answer 9

motor AND sensory neurons

Question 10

The fascial layer covering the entire skeletal muscle is called ____

Answer 10

epimysium

Question 11

A skeletal muscle is composed of multiple ____

Answer 11

fascicles

Question 12

The fascial layer surrounding each fascicle is called ____

Answer 12

perimysium

Question 13

A fascicle is composed of multiple ____

Answer 13

muscle fibers (muscle cells)

Question 14

The fascial layer surrounding each muscle fiber is called ____

Answer 14

endomysium

Question 15

A muscle fiber is composed of multiple ____

Answer 15

myofibrils

Question 16

A myofibril is a bundle of ____

Answer 16

myofilaments (myosin & actin)

Question 17

What part of skeletal muscle is involved in compartment syndrome?

Answer 17

epimysium
(treatment = fasciotomy)

Question 18

When at rest, the myosin binding site on thin filaments is physically blocked by the ____

Answer 18

troponin-tropomyosin complex

Question 19

What event unblocks the binding sites on actin?

Answer 19

Ca2+ binds to troponin

Question 20

What is the function of the sarcoplasmic reticulum?

Answer 20

Ca2+ storage (relaxation) & release (contraction)

Question 21

What travels through the sarcoplasmic reticulum to trigger calcium release?

Answer 21

Na+

Question 22

What is the functional unit of a muscle fiber?

Answer 22

sarcomere

Question 23

What defines the length of a sarcomere?

Answer 23

Z-line to Z-line

Question 24

What is the Z-line/band?

Answer 24

electron dense band that anchors thin actin filaments
(ends of sarcomere)

Question 25

What is the I-band?

Answer 25

actin filaments extend from Z-band to A-band

Question 26

What is the A-band?

Answer 26

composed of entire length of myosin filaments + overlapping actin filaments

Question 27

____ filaments form a hexagonal array around each ____ filament

Answer 27

thin; thick

Question 28

What is the H-zone?

Answer 28

pale region in midportion of A band where actin filaments end (ONLY contains myosin)

Question 29

What is the M-line?

Answer 29

zone of intermolecular bridging & thickening of myosin at the midline of the A band, which forms a thin, slightly darker electron-dense band

Question 30

Each thin filament is equidistant from how many thick filaments?

Answer 30

3

Question 31

What happens to Ca2+ with cessation of neural activity?

Answer 31

SR **actively** transports Ca2+ back into terminal cisternae

Question 32

What happens to Ca2+ with depolarization of a muscle cell?

Answer 32

SR **passively** releases Ca2+ into muscle cell --> binds to troponin

Question 33

A muscle fiber is innervated by a single ____

Answer 33

LMN ending

Question 34

What is a motor unit?

Answer 34

a single motor neuron and all the muscle fibers it innervates

Question 35

What determines muscle fiber type?

Answer 35

LMN conduction speed

Question 36

T/F: muscle fibers in a motor unit are a combination of type I and type II fibers

Answer 36

FALSE all fibers in a MU are same type

Question 37

Type I fibers are ____ twitch

Answer 37

slow

Question 38

Type II fibers are ____ twitch

Answer 38

fast

Question 39

T/F: In humans, all muscles consist of a combination of type I and type II fibers

Answer 39

TRUE i.e., postural muscles (eg. soleus) still have fast twitch; fast twitch muscles (eg. gastrocs, EDL) still have slow twitch

Question 40

What muscle fiber type are red/dark?

Answer 40

type I

Question 41

What muscle fiber type are white?

Answer 41

type II

Question 42

Postural muscles contain mostly type ____ fibers

Answer 42

I

Question 43

Describe the properties of motor neurons innervating type I fibers.

Answer 43

Alpha 2 motor neuron - low threshold - slower conduction velocity

Question 44

Describe the properties of motor neurons innervating type II fibers.

Answer 44

Alpha 1 motor neuron - high threshold - faster conduction velocity

Question 45

Describe the metabolic properties of type I fibers

Answer 45

Aerobic - ^myoglobin - ^mitochondria

Question 46

Describe the metabolic properties of type II fibers

Answer 46

Anaerobic - less myoglobin - less mitochondria

Question 47

What is the endurance level of type I and II fibers?

Answer 47

type I = high type II = low

Question 48

What would happen to muscle fibers if innervation were crossed between soleus (type I) and EDL (type II)?

Answer 48

Fiber types would switch over time (innervation determines fiber type)

Question 49

What happens to type I fibers with training?

Answer 49

- no hypertrophy due to endurance training - ^mitochondria

Question 50

What happens to type II fibers with training?

Answer 50

hypertrophy with strength training