intro to Skeletal Muscle Structure, Function & Metabolism

Question 1

what are the three types of muscle tissue

Answer 1

• skeletal
• cardiac
• smooth

Question 2

what are 4 features of skeletal muscle

##

think:
- locomotion,
- body weight,
- multinucleate cells and what they have
- willingness of contraction

Answer 2

• attach to and move skeleton
• 40% of body weight
• there are multinucleate cells with ovbious striations
• contraction of this musle is voluntary

Question 3

what are 2 features of cardiac muscle other than being only found in the heart

Think about visibility of the cells and willingness of contraction

Answer 3

• cells are striated
• contractions are involuntary

Question 4

what are 2 features of smooth muscles other than them being in the walls of hollow organs

Answer 4

• lack striations
• contractions are involuntary

Question 5

skeletal muscle tissue

what are the 3 functions of skeletal muscle

Think shivering, storage and mobility

Answer 5

• heat generation (shivering and involuntary contractions)
• nitrogen store/metabolism (CHO/PRO)
• locomotion/external movement

Question 6

skeletal muscle

what attaches skeletal muscle to the skeleton

Answer 6

tendons

Question 7

skeletal muscle

what is the site at which skeletal muscle is attached to an immobile bone at one end called?

Answer 7

the origin

Question 8

skeeletal muscle

what is the site at which skeletal muscle attaches to a bone and moves it called?

Answer 8

the insertion

Question 9

what needs to occur before tension at the muscle attachement sites occur?

Answer 9

stretch of the elastic/non-contractile parts of the muscle

Question 10

skeletal muscle ultrastructure

what are 2 features of myofibres (muscle cells)

Answer 10

• elongated cells
• arranged parallel to one another and bundled by connnective tissue into fascicles

Question 11

skeletal muscle ultrastructure

what is the sarcolemma

Answer 11

muscle cells’ cell membrane

Question 12

SKM connective tissue

what is:

• superficial fascia
• deep fascia

Answer 12

superficial fascia:
- loose connective tissue underlying skin

Deep fascia:
- dense connective tissue around muscle

Question 13

SKM connective tissue

what are the 3 components of connective tissue and where are they found

Answer 13

Epimysium: surrounds whole muscle

Perimysium: surrounds bundles (fascicles) of muscle cells

Endomysium: separates individual muscle cells

Question 14

myofibrils

what are myofibrils

Answer 14

long bundles of protein made up of thick and thin filaments

Question 15

myofibrils

how are myofilaments arranged

Answer 15

• arranged in sarcomeres from one Z-disc to the next

Question 16

the proteins of muscle

what 3 types of protein make up myofibrils and give 2 examples of each

Answer 16

1. contractile proteins:

• myosin and actin

2. Regulatory proteins that turn contraction on and off

• troponin and tropomyosin

3. structural proteins which provide proper alignment, elasticty and extensibility:

• titin, myomesin, nebulin and dystrophin

Question 17

Protein in muscles - Myosin

what are the thick filaments of myofibrils composed of

Answer 17

myosin

Question 18

what do M line proteins do?

Answer 18

hold myosin filaments in place

Question 19

proteins of the muscles - actin

what 3 things are the thin filaments of myofibrils made out of

Answer 19

• actin
• troponin
• tropomyosin

Question 20

what holds thin filaments together

Answer 20

Z-lines

Question 21

Does the length of filaments change?

Answer 21

No

Question 22

nerve muscle anatomy

what specialized nerve cells are associated with muscles

Answer 22

motor neurons

Question 23

excitation-contraction coupling

outline excitation contraction coupling

Answer 23

1. action potential propagates down sarcolemma
2. Transverse tubules conduct AP to cell’s interior
3. Ca2+ release channels open in Sarcoplasmic reticulum, allowing for Ca2+ to enter the sarcoplasm

Question 24

activation of muscle contraction by action potentials: OUTLINE the 3 steps

Answer 24

1. action potenital induce release of Ca2+ into sarcoplasm
2. Ca2+ binds to troponin C on thin filament, changing the troponin
3. this shifts tropomyosin off myosin binding sites, enabling myosin to bind to actin

Question 25

outline the 7 steps of cross-bridge cycling ## Footnote this occurs after excitation-contraction coupling

Answer 25

1. myosin head binds to actin forming cross bridge 2. Pi is released from myosin head, causing conformational change in myosin 3. power stroke occurs, where myosin head bends towards centre of sarcomere, sliding thin filaments towards the centre too. 4. ADP is released 5. New ATP molecule binds to myosin head, allowing for the head to release from actin 6. ATP is hydrolysed, causing the myosin head to return to its original orientation 7. this repeats, however the **sarcomere's length** has **shortened**

Question 26

# contractile properties what is "Twitch"

Answer 26

- single contraction and relaxation of a muscle in response to a single brief stimulus

Question 27

# contractile properties what is henneman's size principle

Answer 27

motor units are generally recruited in order of smallest to largest (or *Fewest* to *most fibres*) as contraction increases

Question 28

what is the importance of normal resting length for skeletal muscles?

Answer 28

- it is the optimal resting length for generation of max tension

Question 29

Sarcomere length at muscle's optimal resting length?

Answer 29

~2.0 µm

Question 30

if length of skeletal muscle is increased, why is tension reduced

Answer 30

- because overlap between thick and thin filaments decreases

Question 31

if skeletal muscle length decreases, why does tension decrease?

Answer 31

because fluid **pressure** **builds** and **thin** **filaments** from either end of the **sacromere** **collide**.

Question 32

# types of mucles contraction what is summation

Answer 32

when a muscle is stimulated multiple times in rapid succession so strength of contraction increases

Question 33

# types of muscle contraction what is incomplete tetanus

Answer 33

muscles stimulated at high enough rate so that muscle does not fully relax between contractions

Question 34

# types of muscle contraction what is complete tetanus

Answer 34

muscle stimulated at high frequency so that NO relaxation occurs (steady state of tension)

Question 35

# types of muscle contraction give 1 in vitro example of complete tetanus and 1 in vivo example

Answer 35

In vitro: - high rate of stimulation prevents muscle fibres from relaxing In vivo: - different motor units acitvated in rapid succession to generate sustained contraction