Muscles pt. 2

Question 1

Describe how muscle function gets complicated in life-like scenarios in terms of residual force enhancement (rFE)

Answer 1

Experimental setup: Isometric contraction
1. Muscle is set up at peak length -> force ramps up due to latency, and then plateaus at a consistent level of peak force.
2. Take the same muscle and shorten it. Force ramps up due to latency, but then plateaus at a smaller force (due to force-length curve)
3. Take muscle and stretch it back to peak length.
Expectation: same force as trial 1
Real result: Increase in force (rFE)
Mechanism: maybe titin? But we don’t really know what’s going on which this

Question 2

Describe how muscle function gets complicated in life-like scenarios in terms of tendon/latch mechanisms

Answer 2

The frog ankle illustrates how tendon/latch mechanisms bypass muscle’s force-velocity relationship (explains how a frog jumps - generates a lot of force and quickly)
- There is a mechanism in frogs that is locking the ankle in place (the ankle can’t rotate) -> mechanics of leg act as the latch
- Muscle shortens but ankle can’t rotate, so applying force to stretch a tendon (tendon=elastic like a rubber band; energy stored as stretched)
- Tendon snap back when latch released and we get high force and velocity at the same time (at some point, the mechanics of the leg are going to change and release the latch)
- Stored energy released all at once
- Rapid ankle rotation and high force delivered to ground for hopping

Question 3

Work general definition, formula and units

Answer 3

Energy used to do stuff, or force (F) applied to move something a distance (d)
- W = Fxd (if direction of force and movement are aligned)
- Units: Nm = Joules (J)

Question 4

Are you doing mechanical work if you’re pushing on a heavy box that’s not moving?

Answer 4

No

Question 5

What kind of contraction are you performing while holding a plank? Are you doing work?

Answer 5

Isometric, no

Question 6

Power definition, formula and units

Answer 6

The rate energy is used to do stuff, or work (W) over time
P=W/t=(Fxd)/t=Fxv where v=shortening velocity
Units: Watts (W) = J/t = (Nxm)/t

Question 7

Draw the force-velocity curve and the power-velocity curve for a single myofibril, a single fiber and a constant number of fibers. Where is peak power?

Answer 7

Peak power: 20-40% of Vmax

Question 8

Assume you are operating at peak power on flat ground. Describe what happens to force and power once you hit a hill and you don’t shift gears

Answer 8

Pedaling is harder at the hill, so need more force. Power decreases because we’re moving at a slower velocity (P=F x v) and as force increases, power decreases

Question 9

If you were to bike up a hill at a lower gear than before, is your leg moving slower or faster than before? is your muscle shortening slower or faster?

Answer 9

You’re moving faster cause it’s easier to pedal

Question 10

If you were to bike up a hill at a lower gear than before, is your muscle producing as much force as before? How does power change?

Answer 10

Less force is being produced (because legs are moving faster - force-velocity relationship)
Power increase compared to before because velocity is greater

Question 11

A muscle fiber has enough ATP for ~3 sec of activity at max power. What are the 3 energy sources for contraction

Answer 11

1. Phosphocreatine-creatine system
2. Oxidative phosphorylation
3. Glycolysis-lactic acid system

Question 12

Describe how the phosphocreatine-creatine system replenishes the muscle fiber’s energy for contraction

Answer 12

Phosphocreatine reacts with ADP to form Cr + ATP
- Fast: 4 mol ATP/min, but Cr-Pi is depleted in 5-8 sec

Question 13

Describe how oxidative phosphorylation replenishes the muscle fiber’s energy for contraction

Answer 13

• Replenishes muscle’s energy at <70% of muscle’s max intensity
• Supplies 95% of all long-term contraction energy
• Muscle glycogen supplies glucose for 5-10 mins for oxidative phosphorylation
• To sustain energy for hours: up to 1/2 of fuel is glucose from the blood for 2-4 hours. Then, fatty acids (less efficient fuel source)
• Slow to start, and slow ATP supply (1 mol ATP/min)

Question 14

Why do runners “hit the wall” when running?

Answer 14

There is a fuel change from blood glucose to fatty acids. Since fatty acids are a less efficient fuel source, runners experience exhaustion and pain.

Question 15

Describe how the glycolysis-lactic acid system replenishes the muscle fiber’s energy for contraction

Answer 15

• Fills time between the phosphocreatine-creatine system and oxidative phosphorylation when <70% of muscle’s max intensity is being used
• primary energy source at >70% max
• intermediate speed - 2.5 mol ATP/min
• uses muscle glycogen to make ATP faster than oxidative phosphorylation
• consumed supply in ~1.5 mins (much faster than oxidative phosphorylation, makes ATP much faster)
• End products (lactic acid) may impact contraction?

Question 16

What are two ATP uses in muscle?

Answer 16

1. Myosin head (Cross-bridges)
2. Ca2+ pumps on the SR

Question 17

Only the ATP use at the myosin head can count toward…

Answer 17

Useful, mechanical work
- the myosin head is the only thing that’s tagging on something and moving a certain distance in the muscle

Question 18

Max energetic efficiency of human muscle and what this means

Answer 18

25%
- that means, at max, 25% of muscle energy goes to useful mechanical work.
- The rest is converted to heat (Ca2+ pump is counted as heat)

Question 19

True or false: the muscle is usually much less efficient than 25% (max energetic efficiency of human muscle)

Answer 19

True
- we don’t use muscle optimally

Question 20

How efficient is an isometric contraction?

Answer 20

0% efficient because work isn’t being done at all (no energy is going to useful mechanical work)

Question 21

Why do your muscles get warm during use?

Answer 21

Our muscles are poorly efficient -> a lot of our energy ends up producing heat.

Question 22

Some individuals have genetic mutations affecting DHPRs and RyRs. When exposed to certain anesthetics, these abnormal receptors stop regulating Ca2+ release, leading to constant, high levels of Ca2+ in the cytoplasm.
- how might this affect the cross-bridge cycle?

Answer 22

Cross-bridge cycle just keeps going

Question 23

Some individuals have genetic mutations affecting DHPRs and RyRs. When exposed to certain anesthetics, these abnormal receptors stop regulating Ca2+ release, leading to constant, high levels of Ca2+ in the cytoplasm.
-What impact does this have on muscle energy use?

Answer 23

Use lots of energy

Question 24

Some individuals have genetic mutations affecting DHPRs and RyRs. When exposed to certain anesthetics, these abnormal receptors stop regulating Ca2+ release, leading to constant, high levels of Ca2+ in the cytoplasm.
- What symptoms do you think you would see in an affected individual? (4)

Answer 24

• Muscle rigidity (due to continuous contractions)
• Stop breathing (all muscles are tensed up)
• Heat up
• Depleted glycogen stores

Question 25

Describe slow oxidative vertebrate muscle fibers in terms of the following: - Speed of MHC ATPase and Ca2+ pump in SR - Max power - Metabolism - Aerobic support (mitochondria, blood supply, myoglobin) - Glycogen stores - Fatiguability - Use

Answer 25

- Speed of MHC ATPase and Ca2+ pump in SR: Slow - Max power: good - Metabolism: oxidative (aerobic) - Aerobic support (mitochondria, blood supply, myoglobin): High (red) - Glycogen stores: Low - Fatiguability: Fatigue resistance (oxidative metabolism can run for hours) - Use: Posture, slow walk

Question 26

Describe fast oxidative glycolytic vertebrate muscle fibers in terms of the following: - Speed of MHC ATPase and Ca2+ pump in SR - Max power - Metabolism - Aerobic support (mitochondria, blood supply, myoglobin) - Glycogen stores - Fatiguability - Use

Answer 26

- Speed of MHC ATPase and Ca2+ pump in SR: Fast - Max power: High - Metabolism: Primarily oxidative, but also glycolytic (anaerobic) - Aerobic support (mitochondria, blood supply, myoglobin): Good (pink) - Glycogen stores: medium - Fatiguability: Fatigue resistance (because they primarily use oxidative phosphorylation) - Use: Rapid but sustained (e.g. fast walking)

Question 27

Describe fast glycolytic vertebrate muscle fibers in terms of the following: - Speed of MHC ATPase and Ca2+ pump in SR - Max power - Metabolism - Aerobic support (mitochondria, blood supply, myoglobin) - Glycogen stores - Fatiguability - Use

Answer 27

- Speed of MHC ATPase and Ca2+ pump in SR: Fast - Max power: Very high - Metabolism: Glycolytic (anaerobic) - Aerobic support (mitochondria, blood supply, myoglobin): Low (white) - Glycogen stores: high (supporting glycolytic-lactic acid system) - Fatiguability: Rapidly fatigued - Use: Sprint

Question 28

True or false: fiber types have different force- and power-velocity curves - If true, draw them

Answer 28

True - Same general relationship, but shape is slightly different

Question 29

If fast glycolytic fibers can achieve more force at slow velocities, why use slow oxidative fibers? Give 2 answers and use the power-shortening velocity curve in one of them.

Answer 29

1. Slow oxidative fibers are fatigue resistant. 2. Slow oxidative fibers have a higher peak power at a slower speed _. deliver force and energy at a higher rate at slower velocities

Question 30

Why do you run a marathon slower than a 50m dash?

Answer 30

Need to provide energy for many hours -> need to use oxidative metabolism -> provide energy slower so we have a limit to our speed

Question 31

Describe how fiber type location differs across vertebrate muscle

Answer 31

Fishes: separated Other vertabrates: mixed within muscle (different types of fibers all in one muscle)

Question 32

Describe the impact of athletic training on the following: - The number of myofibrils - The ATP and Cr-Pi stores - The glycogen stores in muscle and liver - The number of mitochondria (SO, FOG) - Converting fibers

Answer 32

- Increase the number of myofibrils (but not the number of cells) - Increase ATP and Cr-Pi stores - Increase glycogen stores in muscle and liver - Increase number of mitochondria in slow oxidative and fast oxidative glycolytic fibers - <10% of fast-twitch fibers can change to slow-twitch (but most of our fibers stay the same identity) - Some fast glycolytic fibers convert to fast oxidative glycolytic fibers

Question 33

What are 4 purposes of skeletal muscle control systems?

Answer 33

1. Voluntary motion 2. Coordination of multiple muscles 3. Get graded levels of force (so we're not producing max force all the time, e.g. contracting gravity) 4. Provide some automatic systems (don't think about which muscles to contract when doing certain things like walking)

Question 34

Where do signals for voluntary motion originate?

Answer 34

The motor cortex

Question 35

Cerebellum function

Answer 35

Coordinates timing of complex motions

Question 36

Where is the origin of central pattern generators (big patterned signals that coordinate different muscle movements) and reflex arcs?

Answer 36

The spinal cord

Question 37

Describe the arrangement of motor control neurons

Answer 37

Sensory neuron and axons in descending pathway from motor cortex synapse at interneuron in spinal cord. Interneuron in spinal cord synapses onto alpha motor neuron which synapses to a muscle. Ascending axons are also present, bringing sensory info to the brain.

Question 38

What do temporal and spatial summation allow for in general?

Answer 38

Summation lets us modulate the level of force produced by a muscle - Graded levels of force are achieved through summation: control force over time (scale=fractions of second) and control force over space

Question 39

Describe temporal summation in muscles and what causes it

Answer 39

Temporal summation occurs when the frequency of twitches is so high that subsequent twitches occur when all the previous Ca2+ hasn't been sequestered into the SR yet and cross bridges are still occurring upon the second stimulation. - More Ca2+ is released -> even more cross bridges

Question 40

Difference between incomplete tetanus and fused tetanus

Answer 40

Fused tetanus: can no longer see individual twitches anymore Incomplete twitches: can still kind of see individual twitches

Question 41

What is a motor unit?

Answer 41

An alpha motor neuron and all fibers it connects to; only have 1 type of fiber within unit

Question 42

Describe the variation in motor units

Answer 42

More and smaller motor units in areas where we need fine control

Question 43

Where might you find large motor units?

Answer 43

Big muscles that you need a lot of force for, e.g. quads, hamstring, etc.

Question 44

Where might you find small motor units?

Answer 44

Muscles required for fine control (e.g. hands, face, eyes, etc).

Question 45

We have 1000s of motor units, which is too many for the brain to individually control. How do we deal with this?

Answer 45

The brain has a single axon that innervates different cell body sizes - Alpha motor neurons with smallest cell bodies are innervated first, which innervate slow oxidative (SO) fibers. - Alpha motor neurons with medium-sized cell bodies are innervated second, which innervate fast oxidative glycolytic (FOG) fibers - Alpha motor neurons with largest cell bodies are innervated last, whcih innervate fast glycolytic fibers. *Increase stimulation rate of brain on alpha motor neurons to recruit faster fibers

Question 46

Describe the force- stimulation rate of SO, FOG and FG fibers

Answer 46

SO recruited first, then FOG, then FG. - All forces plateau due to tetanus - SO has smallest force plateau, then FOG, then FG

Question 47

What are the 5 elements of reflex arcs?

Answer 47

1. Sensor 2. Sensory neuron 3. Interneuron 4. Alpha motor neuron 5. Muscle

Question 48

What advantage is there to bypassing the brain through a reflex arc?

Answer 48

Fewer steps, so takes less time for muscle action - Prevents tissue damage, for example

Question 49

True or false: the information involved in a reflex arc never reaches the brain

Answer 49

False - There are ascending axons bringing sensory info to the brain, so we will eventually process the stimulus

Question 50

Describe and draw the diagram of the withdrawal reflex/flexor reflex (6 steps) - Describe reciprocal innervation

Answer 50

Pulls the limb back in response to pain 1. Sensor detects pain 2. AP in sensory neuron goes to spinal cord 3. Excites IN1 and sends signal to brain 4. Branch 1.1 excites alpha neuron to flexor (e.g. hamstring- bends knee to lift lower leg) 5. Branch 1.2 excites IN2 6. Inhibits alpha motor neuron to extensor (e.g. quads) Reciprocal innervation: one signal excites one muscle and inhibits its opposition at the same time

Question 51

Describe and draw the cross-extensor reflex (6 steps)

Answer 51

Withdrawal reflex plus keep the other leg straight (helps us stay upright so that we lift up our foot but we don't want to fall over and hurt ourselves even more) 1. Signal to spinal cord like before 2. Excite first interneuron and signal to brain 3. Finish withdrawal reflex with reciprocal innervation in pain leg 4. Third branch from first interneuron crosses to the other side of the spinal cord and excites a third interneuron 5. First branch from third interneuron excites an alpha motor neuron of the extensor (quad) -> extends quad which prevents us from falling over 6. Second branch from third interneuron excites fourth interneuron, which inhibits alpha motor neuron to flexor (hamstring) - Opposite of withdrawal reflex

Question 52

Some neurons have tone. What is tone?

Answer 52

Always active, and we change the level of activity

Question 53

Neural tone

Answer 53

Stimulating (sending APs) all the time, but pacing changes

Question 54

Less tone vs. default tone vs. more tone

Answer 54

Less tone: APs are being sent slower Default tone: normal level of tone More tone: APs are being sent faster

Question 55

Muscle response to increase in tone

Answer 55

Increased tone -> increased stimulation -> more signals to contract -> more contraction

Question 56

Muscle response to decrease in tone

Answer 56

Decreased tone -> decreased stimulation -> fewer signals to contract -> less contraction

Question 57

What allows for the stretch (myotactic) reflex?

Answer 57

Muscle spindles

Question 58

Muscle spindle

Answer 58

Special muscle fiber wrapped by stretch-sensitive neuron

Question 59

On a muscle spindle, the ends of the muscle fiber have...

Answer 59

Contractile filaments innervated by gamma motor neurons (but center doesn't have any myofibrils)

Question 60

Describe a stretch neuron's tone

Answer 60

Always firing

Question 61

What changes the AP firing rate in a muscle spindle? Be specific

Answer 61

Stretch - Stretching increases tone, and compression decreases tone

Question 62

Where do signals from the muscle spindle go to?

Answer 62

Goes to spinal cord and synapses directly on alpha motor neurons for the same muscle

Question 63

Describe and draw the stretch (myotactic) reflex (6 steps)

Answer 63

1. Whole muscle stretches, and spindle stretches too 2. Increase firing rate of stretch neuron (i.e. increase its tone) 3. Excites alpha motorneuron to same muscle that the spindle is embedded in 4. Muscle contracts and shortens 5. Spindle length is reduced, which decreases the tone of the stretch neuron 6. Decrease in tone reduces the firing rate of the stretch neuron

Question 64

True or false: if the whole muscle is stretched, this allows the spindle muscle to also stretch

Answer 64

True

Question 65

Give two examples of a stretch (myotactic) reflex

Answer 65

1. Knee-jerk reflex (hit causes a momentary stretch in the quad muscle) 2. Holding position (e.g. carrying a box and don't want our arms to drop -> myotactic reflex is keeping you from dropping your arms without thinking if yourarm slightly shifts while holding the box)

Question 66

What do gamma motor neurons do to the set point of the muscle spindle?

Answer 66

Gamma motor neurons change the "set point" of the muscle spindle - Ex: let's say we've shortened the whole muscle. This makes it so we hav slack, so we can't detect small length changes. Solution: gamma motor neurons control spindle length to let stretch neurons work effectively (gamma motor neurons fire on the ends of the spindle and do contraction-coupling to lengthen it out)

Question 67

Describe smooth muscle structure

Answer 67

- Smaller, spindle-shaped cells (not long rope-like fibers like skeletal muscle)

Question 68

Smooth muscle cells are (uninucleate/multinucleate)

Answer 68

Uninucleate

Question 69

Describe smooth muscle tissue

Answer 69

Very stretchy

Question 70

True or false: smooth muscle cells are striated

Answer 70

False - Because thin and thick filaments are not arranged in sarcomeres

Question 71

True or false: smooth muscle cells have T-tubules, DHPRs and RyRs

Answer 71

False

Question 72

Describe how sliding filaments are arranged in smooth muscle

Answer 72

Filaments in lattice arrangement throughout cell, and are held together by dense bodies on the cytoskeleton.

Question 73

What are attachment plaques in the sliding filaments?

Answer 73

They attach filaments to the cell membrane in smooth muscle

Question 74

What way do thin filaments slide during smooth muscle contraction?

Answer 74

In opposite directions

Question 75

True or false: Thick filaments in smooth muscle have bare zones

Answer 75

False

Question 76

Describe what it means to say that smooth muscle filaments experience "change of partners" during stretch

Answer 76

After smooth muscle cell is stretched, the cell is longer and thinner so original filament sets no longer overlap with their original thick filaments, but they overlap with neighbouring thick filaments (different thin filaments are nearby, cross-bridges move to these)

Question 77

Why does change of partners occur in smooth muscle but not skeletal muscle?

Answer 77

Possible in smooth muscle because all myosin heads point the same way in smooth muscle

Question 78

Why is the process of "change of partners" useful in the bladder?

Answer 78

Bladder stretches when filled with pee, need to be able to contract the bladder to pee

Question 79

Describe the stress-relaxation property in smooth muscle that results from change of partners

Answer 79

- As length of muscle initially increases, so does the force; this is due to the resistance from cross-bridges that haven't detached from the original filament yet and the elasticity of the myosin neck - Decrease in force aka "stress-relaxation" occurs as myosin heads move to new, closer thin filaments (so smooth muscle cell isn't being stretched anymore)

Question 80

True or false: there is a defined length-tension relationship in smooth muscle, similar to skeletal muscle

Answer 80

False

Question 81

True or false: the number of cross-bridges before and after a smooth muscle cell is stretched is the same due to the "change of partners"

Answer 81

True

Question 82

Describe single vs. multi-unit smooth muscle

Answer 82

Single-unit: electrical synapses are connecting together through gap junctions and cells are being excited together as one - postganglionic axon of the autonomic nervous system doesn't connect to every cell due to presence of gap junctions Multi-unit: No gap junctions, cells are acting separately - postganglionic axon of the autonomic nervous system connects to every cell

Question 83

Describe phasic vs tonic smooth muscle

Answer 83

Phasic: Rhythmic contractions Tonic: Muscle has tone - it is always on, it's just a matter of "what degree of on it is"

Question 84

Myogenic vs neurogenic excitation

Answer 84

Myogenic: Contraction originates in the muscle itself Neurogenic: Contraction originates in the neuron

Question 85

What 2 smooth muscle classifications are common? Give examples for each

Answer 85

1. Single unit, phasic and myogenic: gut, urinary bladder 2. Multiunit, tonic and neurogenic: blood vessels, hair, iris

Question 86

In late pregnancy, smooth muscle in the uterus changes from multiunit to single unit. Why might this be important?

Answer 86

Ensures uterine muscle cells contract simultaneously.

Question 87

What are the two forms of myogenic excitation? What do both forms ensure?

Answer 87

1. Pacemaker potential 2. Slow wave potential In both, the ANS modifies contraction by moving baseline potential closer to/farther from AP threshold (changes baseline potential by changing the ion fluxes across the membrane)

Question 88

Describe pacemaker potential - Draw it

Answer 88

Potential starts with a drift, due to leaky ion channels in the membrane which leads to slow depolarization in the membrane over time. Once drift reaches AP threshold, single AP fires. - Spikes come from Ca2+ influx, not Na+

Question 89

Describe slow wave potential and give an example of an organ where this is seen - Draw it

Answer 89

Potential starts with a random drift, that comes from the following: - Leaking across the cell membrane - Random speeding up/slowing down of ion channels, especially Na+ channels (greatest contribution) - Random speeding up/slowing down of ion pumps Then, once AP threshold is met, there is a burst of APS before the potential goes back down.

Question 90

Varicosity and orientation relative to muscle cells

Answer 90

Swellings along long ANS axon. - Each swelling is near a smooth fiber cell, but not as close as synapses

Question 91

Describe the interactions between varicosities and smooth muscle fibers

Answer 91

Diffuse "shower" of neurotransmitter over the smooth muscle fiber - more room for diffusion of neurotransmitters compared to synapse

Question 92

True or false: there are junctional folds in the smooth muscle fiber - Explain a consequence of the answer

Answer 92

False - There are neurotransmitter receptors all over the fiber - Receptors all over means that muscle sensitive to hormones and compounds in the blood (i.e. stuff outside of the junction)

Question 93

What are the 3 pathways that can connect excitation to an increase in cytoplasmic Ca2+ in smooth muscle?

Answer 93

1. Sarcolemma, voltage-gated Ca2+ channels opened by AP 2. SR, triggered by second messenger 3. Sarcolemma, Ca2+ channel opened by second messenger

Question 94

Describe how Ca2+ comes from the SR, triggered by a second messenger (4 steps)

Answer 94

1. neurotransmitter binds to GPCR on cell membrane 2. G-protein activates enzymes 3. Enzymes make inositol triphosphate (IP3) 4. IP3 opens Ca2+ channel on SR

Question 95

Kinases

Answer 95

Enzymes that split ATP and phosphorylate stuff to activate things

Question 96

Phosphatases

Answer 96

Enzymes that remove Pi from stuff to deactivate things

Question 97

What turns the ATPase in the myosin head on/off?

Answer 97

Regulatory myosin light chain (MLC) - depends on phosphorylation state of MLC

Question 98

What controls the phosphorylation state of MLC?

Answer 98

MLC kinase (MLCK) and MLC phosphatase (MLCP) control whether MLC is phosphorylated

Question 99

MLCK and MLCP (are/are not) always present and operating, so smooth muscle is (always/sometimes) on - Explain why

Answer 99

MLCK and MLCP are always present and operating, so smooth muscle is always on (always have some phosphorylated MLC)

Question 100

What does the "degree of on" of a smooth muscle depend on?

Answer 100

Which enzyme (MLCK or MLCP) is currently working faster

Question 101

Describe how ATPase is switched on, increasing contraction (control at the thick filament) (4 steps)

Answer 101

1. Ca2+ binds to a protein called calmodulin (CaM) 2. Ca2+-CaM complex activates MLCK 3. MLCK phosphorylates MLC, which swithces the ATPase on 4. Cross-bridge cycle runs = contraction

Question 102

Describe how ATPase is switched off, decreasing contraction (control at the thick filament) (6 steps)

Answer 102

1. Ca2+ is removed from cytoplasm through several pumps 2. Low Ca2+ concentration promotes unbinding of Ca2+ from CaM 3. So, MLCK deactivated 4. MLCP dephosphorylates MLC 5. So, ATPase switched off 6, Cross-bridge cycle stops = relaxation

Question 103

True or false: Troponin and tropomyosin are present in both smooth and skeletal muscle

Answer 103

False - it's only present in skeletal muscle

Question 104

Describe the control at the thin filament by Ca2+-CaM

Answer 104

1. Myosin binding site on g-actin is blocked by caldesmon (instead of tropomyosin) 2. Ca2+-CaM also binds to caldesmon, removing it 3. And other enzymes can phosphorylate caldesmon, which also removes it from the thin filament.

Question 105

What 4 things promote smooth muscle contraction?

Answer 105

1. Stimulation from the parasympathetic autonomic nervous system (uses Ach) 2. Stimulation by the sympathetic autonomic nervous system (uses norepinephrine + epinephrine, which also influence contractino if they come from somewhere other than the sympathetic nervous system) -> binds to α1 receptors 3. Serotonin slows down MLCP 4. Stretch

Question 106

What 2 things promotes relaxation/decreases contraction in smooth muscle?

Answer 106

1. Sympathetic autonomic nervous system (norepinephrine + epinephrine) - binds β2 receptors -> inhibits MLCK 2. Hormones from the blood

Question 107

What are 5 other things that influence contraction?

Answer 107

1. O2 2. CO2 3. pH 4. Nitric oxide (NO) 5. Heat