Excitable Tissue : Muscle

Question 1

Tendons

Answer 1

Where most skeletal muscles begin and end.

Question 2

Muscle Fibre Morphology

Answer 2

• begin and end in tendons
• each muscle fibre is a single multinucleated cell
• no communication between muscle fibres ( it can’t take a signal and recruit other cells to participate)
• each muscle fibre is conmprosed of multiple filaments which execute contraction

Question 3

Sliding filament theory

Answer 3

still just a theory, best information we have to date about muscle contractions.
- has a handful of different proteins but MYOCIN generates contraction

Question 4

all or nothing muscle contraction

Answer 4

we do not want this and our muscles are not designed for this. we don’t want to use max energy when we want to sharpen a pencil or do accupuncture. We have a graded muscle response.

Question 5

Actin

Answer 5

Contractile Protein

Polymerizes to form a thin filament. (gives structure)

Question 6

Tropomysosin

Answer 6

Contractile Protein
Binds to the thin filament.
Additional structural protein

Question 7

Myosin 2

Answer 7

Contractile Protein
Globular motor protein that has the ability to create tension and allow for contraction.
- thought of as little elastics that stretch and snap back

Question 8

Troponin

Answer 8

3 Subunits :

Troponin I :
Inhibitory
Binds actin and prevents actin/myosin association at rest.
Makes sure that they do not touch

Troponin T :
provides stability - allows binding to create an environment where contraction is possible
binds tropomyosin and helps position it on actin.

Troponin C:
calcium binding site
on/off switch. When Ca2+ is around , it binds to Troponin C and muscle wants to contact
If Ca2+ is not bound/present the relaxed strate is reinforced

Question 9

Calcium (Storage in Muscle contractions)

Answer 9

Stored in the T-tubules. When the fibres need more Ca2+, it is released to create contraction.

Important to have storage for calcium b/c free calcium may cause harm.

Question 10

Excitation Contraction Coupling

Answer 10

(Dihydropyridine DHPR receptor voltage gated) (red tube)
- physically or spatialling linked to the ryanodine receptor (RyR) in the sarcoplasmic reticulum (Pink tube)

Activation of DHPR causes conformational change in RyR causing Ca2+ release from the SR

Contrast to calcium induced / calicum release in cardiac muscle

Question 11

T/F :

Is there a change in length of individual thin or thick filaments?

Answer 11

False : no change in length. Increased amount of overlap within the cell.

Question 12

At rest, where are myocin heads?

Answer 12

Myocin heads bound to ADP and in relaxed position relative to the thin filament. No Ca2+ bound.

Question 13

Where does Ca2+ bind when it gets into the cytoplasm?

Answer 13

Binds to troponin C which induces a confirmational change , and exposes myosin binding sites on actin.

Question 14

Power stroke

Answer 14

Myosin heads move into position to bind actin and “flex” , which shortens the muscle fibre releasing ADP in the process.

Question 15

How does ATP detach from actin?

Answer 15

ATP binds the empty site where ADP was released.

Question 16

What does ATP hydrolization cause?

Answer 16

Causes myosin to return to the relaxed position.

Question 17

When do muscle contractions repeat?

Answer 17

If there is sufficient calcium and ATP present, the process repeats.

Question 18

Muscle Contaction Steps :

Answer 18

1) Myocin heads bound to ADP and in relaxed position relative to the thin filament. No Ca2+ bound.
2) Influx of calcium Binds to troponin C which induces a confirmational change , and exposes myosin binding sites on actin.
3) Powerstroke : Myosin heads move into position to bind actin and “flex” , which shortens the muscle fibre releasing ADP in the process.
4) ATP binds the empty site where ADP was released and causes detachment from actin
5) ATP hydrolization Causes myosin to return to the relaxed position.
6) If there is sufficient calcium and ATP present, the process repeats.

Question 19

ABCDE picture process

Answer 19

A ) Tropomyocin is wrapped around actin. Myocin has a molecule of ADP attached to it
B) tropomyosin is twisted to show myocin binding sites in the presence of calcium
C) myosin hitsw actin which causes the tension generation and slides the fliaments closer together. ADP gets the boot “powerstroke”
D) Wth ADP gone, there is an open binding site which ATP binds to while there is contraction
E) As soon as myosin and ATP bind, it uses energy (hydrolizes ATP) to stretch itself back out - releases from actin

Question 20

Rigor Mortis

Answer 20

ATP needs to be hydrolyzed to get into a relaxed state. When ATP runs out, we stay contracted for a few hours.

Question 21

T/F Ca2+ binds to troponin which moves tropomyocin

Answer 21

T : Troponin is the boss

Ca2+ is bound to troponin at rest/ neutral state.

Question 22

What happens as Calcium is pumped out of the cytoplasm?

Answer 22

Ca2+ dissociates from troponin.

• due to a function of Ca- ATPase, Calcium is pumped back into the sarcoplasmic reticulum or cisterns of T-tubules
• conformational change brings troponin back to neutral , hiding myosin binding sites.

Question 23

Tetanus

Answer 23

Continous muscle contraction : we use this all of the time to keep us upright. Ie) posture muscles.

Question 24

Muscle Twitch

Answer 24

• occurs when a muscle fiber is stimulated to contract by a single action potential . (one very quick action potential).
• twitch begins after depolarization, but before repolarization is complete. * important for the summation of contractions.
  duration of the twitch dependent on the muscle fiber (fast for fine motor movements or slow for sustained gross movements)

twitch occurs in approx 5ms while full relaxation takes 25ms

Question 25

Summation of muscle contraction

Answer 25

length of depolarization is shorter than duration of contraction
contractile mechanism does not have a refractory period
repeated stimulation before contraction causes a additive/summation effect (which has greater tension than a single twitch)

• if it happens fast enough, individual responses fuse and go from single contractions to tetanus.

Question 26

When is the muscle the longest? Relation to tension

Answer 26

Longest at rest

• tension proportional to the number of actin-myosin crossbridges formed
• fewer actin-myosin associations available when the muscle is stretched.
• less capacity for filament movement if the muscle is already contracted. ( no where for it to go, already overlapped)

Question 27

Types of Muscle Tissues

Answer 27

Skeletal : Striated , voluntary , attached to bone, innervated, troponin present.

Cardiac : Striated , involuntary, heart, no innervation needed for contraction, troponin present

Smooth Muscle : non-striated , involuntary, inside walls of tubular organs, most are innervated but not needed for unit smooth muscle, troponin does not exist in smooth muscle.

Question 28

Skeletal Muscle

Answer 28

Skeletal : Striated , voluntary , attached to bone, innervated, troponin present.

Question 29

Cardiac Muscle

Answer 29

Cardiac : Striated , involuntary, heart, no innervation needed for contraction, troponin present

Question 30

Smooth Muscle

Answer 30

Smooth Muscle : non-striated , involuntary, inside walls of tubular organs, most are innervated but not needed for unit smooth muscle, troponin does not exist in smooth muscle.

Question 31

Smooth Muscle contraction differs from other muscle contraction because :

Answer 31

• lack of troponin
  Ca2+ still released
• influx of calcium sue to voltage gated/ligand membrane channels.
  -effluc of Sarcoplasmic reticulum stores through Ryanodine Receptor or IP3 receptor.

Question 32

Smooth Muscle Contraction

Answer 32

Myosin needs to be phosphorylated to activate myosin ATPase.
Ca2+ binds to calmodulin which activates myosin light chain kinase (MLCK)
Process of muscle contraction is then similar to that of other muscle tissue.

Question 33

Smooth Muscle Relaxation

Answer 33

Myosin is dephosphorylated via myosin light chain phosphatase (MLCP)
- which is regulated via GRCR and cGMP pathways
Removal of intracellular Ca2+ results in dissassociation of the Ca2+ - calmodulin complex which triggers relaxation

Question 34

Plasticity of Smooth Muscle

Answer 34

Force/tension different in smooth muscle
Initial stretch of unitary smooth muscle is met with an increase in tension
If stretch is maintained, smooth muscle becomes tolerant to it and tension decreases

• smooth muscle is resistant to change but doesn’t do a lot about it. ie_ bladder sends signals (via nerves) that it is stretching, but you can override it until it reaches a certain capacity. eventually ceiling will be hit cusing involuntary contraction

Question 35

Phosphocreatine

Answer 35

Used for the first split second of muscle contraction. The rest comes from ATP

Question 36

ADP energy

Answer 36

ADP powers the first few seconds of muscle contraction through anerobic phosphrylation of ADP

Question 37

ATP energy in contraction

Answer 37

During rest or low muscular effort, excess ATP is used to restore CrP stores

Question 38

Lipids and Fatty acids

Answer 38

primary source of energy during low to moderate intensity exercise.
uses beta oxidation for <60% max

Question 39

Carbohydrates and muscle contraction

Answer 39

primary source of energy for moderate to high intensity exercise. (above 60% man)
Most of the energy for CrP and ATP resynthesis provided by glucose

Question 40

Oxygen debt

Answer 40

Metabolic needs of the muscle are on (need energy) of off (at rest).
Compensatory ventilation responses take time. ex) increased rate of respiration after you are climbing the stairs.

This happens when we are more metaboliccaly active and don’t have enough O2

We have evolved to preemtively increase our breathing to increase 02 consumption to offset the O2 debt

Question 41

Oxygen debt when muscular exertion is high

Answer 41

Aerobic resynthesis of ATP cannot keep up with the ATP utilization.
Phosphocreatine used to resynthesize ATP via creatine kinase
Fastest system : (Phosphagen > Glycolysis > Mito CHO >Mito FFA

Question 42

LActate and Oxygen Debt

Answer 42

Anerobic breakdown of glucose to lactate occurs during all intensities of exercise.
- overall contrubution to ATP decreases as level of intensity increases

Question 43

Factors that limit physical exertion

Answer 43

• Low O2 availability via the blood
• low number of mitochondria
  -Cardiovascular system is the more limiting in a vacuum.
  Respiratory is theroretically not limiting , but we must account for pollution, smoking, respiratory diseases etc.

Question 44

Temperature Regulation during exercise exertion

Answer 44

Heat is released during exertion which is challenging for homeostasis
1) sweating evaporative cooling.
iss ) dehydration and reduced blood volume.

2) Increased cutaneous blood flow promotes heat loss via convection
issues : decrease in peripheral resistance and diversion of blood away from muscle
- fall in venous BP may decrease blood flow to the brain

3) adaptation - body adjusts to a hot climate over time.