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ZOOL 461 > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

1
Q

What are the two different types of muscle?

A

Smooth muscle (no banding patterns) and striated muscle

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2
Q

What kinds of muscles are made from striated muscle?

A

Skeletal muscle (voluntary muscle), cardiac muscle. This is where we see striations and banding patterns. We see banding patterns due to the different densities of the filaments and zones.

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3
Q

Where do you find single unit smooth muscle?

A

In tubular organs like the digestive system, uterus, and the urinary tract

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4
Q

Where do you find multiunit unit smooth muscle?

A

Find this where we want fine, discrete control of contraction - blood vessels, iris (controls size of the pupil). This muscle causes hairs to stand erect

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5
Q

What percentage of mass does skeletal muscle generally take up in the human body?

A

30-40%

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6
Q

What are other words for muscle cells?

A

Myocytes, muscle fibres

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7
Q

What are two general characteristics of muscle cells?

A
  • long and cylindrical –> 5-100um in length

- multinucleate

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8
Q

How is a multinucleate muscle cell formed?

A

Mononucleate cells called myoblasts (undifferentiated cells) congregate together into a tubular structure. This tubular structure is called a myotubule. All of the myoblasts then fuse together to form a single cell with multiple nuclei

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9
Q

Why is having multiple nuclei important for muscle cells?

A

They are relatively large cells with a lot of protein turnover and therefore need to regulate a lot of protein expression (what the nuclei do)

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10
Q

Myofibrils

A

thin, ribbon-like structures that run the length of the muscle cell. They are about 1 um in width. Made up by a series of sarcomeres.

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11
Q

A-band

A

Region of the sarcomere occupied by the thick filaments. The length of the A -band does not change during muscle contraction. This region is anisotropic. Dark region

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12
Q

I-band

A

The region between the adjacent A-bands. Half is on what side of the Z-line and half is on the other side of the Z-line. The I-band does get smaller during muscle shortening. Isotropic. Light region. Spans two sarcomeres

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13
Q

Anisotropic

A

Polarizes light. Characteristic of the A-band which forms the dark region

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14
Q

Isotropic

A

Does not polarize light. Characteristic of the I-band, or light region.

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15
Q

H-zone

A

This zone consist only of thick filaments. It runs down the centre of the A-band. It shows up slightly lighter in a scan as it only has think filaments and no thin filaments. Gets smaller when muscle shortens

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16
Q

M-line

A

band down the middle of the A-band –> consists of structural proteins which help hold the A-band together.

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17
Q

titin

A

largest protein ever described. Associates with myosin and actin filaments. Roles: elasticity, holding myosin in a plane

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18
Q

nebulin

A

associates only with the thin filaments,

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19
Q

thin filaments

A

Attached to the Z-discs. Purely thin filaments within the I band. They are made of actin (cytoskeletal element). Microfilament. Actin is made up of a bunch of monomers of actin called g actin. 2 sets of f actin intertwine to form actin filament. Length = 1 um

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20
Q

thick filaments

A

Made from myosin. Each thick filament consists of about 200 - 400 myosin assemblies. Two S1 fragments from each assembly extending out from the backbone of tails. about 1.6 um in length

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21
Q

What kind of arrangements do we see in the sarcomere cross section?

A
  • outside of H-zone within the A-band (where there is overlap between thick and thin filaments): See hexagonal arrangement of 6 thin filaments surrounding 1 thick filaments and 3 thick filaments around every thin filament –> gives a 2:1 ratio of thin to thick filaments.
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22
Q

Myosin molecule

A

150 nm in length. Has myosin light chain and myosin heavy chain. Tail and head regions are made up of the myosin heavy chain. Myosin light chains wrap around neck region and sit within the head regions. One myosin assembly has 2 MHC intertwined with two head groups sticking out as well as 4 MLC

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23
Q

What is the tail of the myosin made up of?

A

light meromyosin

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24
Q

What is the head and neck region of the myosin made up of?

A

heavy meromyosin

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25
Q

What proteolytic enzyme splits the myosin heavy chain into light meromyosin and heavy meromyosin ?

A

trypsin

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26
Q

What proteolytic enzyme splits the heavy meromyosin into its s1 and s2 fragments?

A

papain

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27
Q

What is the S2 fragment? Associated light myosin?

A

The part of the heavy meromyosin that forms the neck or hinge region. The regulatory myosin light chain wraps around and associates with it

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28
Q

What is the S1 fragment? Associated light myosin?

A

The part of the heavy meromyosin that forms the head region -globular region. The essential myosin light chain sits in the base of this globular region. This head region has an actin binding site as well as an ATPase on it which can bind and hydrolyze ATP. This is the most functionally important component of the myosin filament, the other parts are structural

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29
Q

Distance between S1 fragments

  • within the same row of heads
  • within different rows
A

3 rows of heads spiraling total
43 nm for the same row of heads
14.3 nm for different rows of heads - so a myosin head will have the same orientation upwards every 14.3 nm.
- See a myosin head sticking up every 14.3 nm

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30
Q

bare zone

A

region of the thick filament that does have any myosin heads sticking out from it. 0.2um wide

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31
Q

g actin

A

globular actin - 5 nm in diameter. These g-actins self polymerize into f-actin chain

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32
Q

f actin

A

filamentous actin - 2 sets of these spiral together to form actin filament. Like two spiraled chains of beads. Formed from self polymerized g actin

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33
Q

tropomyosin

A

regulatory protein that runs the length of the actin filament and lies within the groove of the 2 chains of beads.

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34
Q

troponin

A

regulatory globular protein that sits on the actin periodically along the actin filament.

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35
Q

Native actin

A

actin + the regulatory proteins associated with it. This is the form of actin the way it is found in the muscle

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36
Q

Pure actin

A

just f actin without w/o the regulatory proteins

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37
Q

Independent force generator

A

Cross bridges! The myosin heads attaching to the actin filaments act independently of other myosin heads attaching to actin filaments. So they generate force independently.

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38
Q

Force - Tension relationship

A

Relationship between the length of the sarcomere and the amount of force that sarcomere is able to generate

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39
Q

3.65 um long sarcomere. Can this sarcomere generate any force?

A

No. There is no overlap of the thin and filaments at this length and thus no cross bridges can be formed. With no cross bridges being formed, no force can be generated

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40
Q

2.25 um long sarcomere. Can this sarcomere generate any force?

A

Yes. Maximum force is generated at this sarcomere length because there is full overlap between the heads of the of the myosin assemblies and the thin filaments (max # of X bridges being formed). Thin filaments come so close together that only the length of the bare zone separates them.

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41
Q

2.05 um long sarcomere. How much force can this sarcomere generate?

A

Maximum force is still generated at this length of sarcomere because there is still the maximum amount of cross bridges being formed even though there is more overlap. The thin filaments meet together, almost touching but not overlapping at this length.

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42
Q

Plateau of the length-tension relationship

A

Between 2.05 um and 2.25 um sarcomere length. There is maximum force being generated in this range of sarcomere lengths because there is maximum over lap giving maximum amount of cross bridges being made, while also not having any thin filament interference

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43
Q

Thin filament interference

A

Begins when the sarcomere length is shorter than 2.05 um. This is because the thin filaments extending into the opposite side of the sarcomere begin to interfere with the ability of cross bridges to form because the actin has polarity. If less than maximum amount of cross bridges form, the force generated will be less.

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44
Q

Isometric contraction

A

The muscle/sarcomere length is not changing. We stretch the muscle to a certain length, experimentally, and then hold it there - see how hard the sarcomere can pull at the given length. Like pushing against the wall with a straight arm.

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45
Q

What happens with the sarcomere length is below 2.05 um?

A

-thin filament interference
-reduced calcium released
-reduced calcium affinity to the troponin c protein
Ca must bind to the actin (regulatory proteins) before before the binding see for the myosin head can be exposed. Thus, when there is less calcium present, or the proteins which bind it have less affinity for it, less force will be generated as less cross bridges can form.

46
Q

A-band compression

A

When a sarcomere is so short that the A-band/thick filaments would have to be crushed by the Z-lines if the sarcomere was to get any shorter. When the A-band is compressed (sarcomere lengths less than 1.65 um), the force generated is drastically reduced and we see a very steep decline in force generated

47
Q

pure actin + myosin —> ____? Why?

A

cross bridge formation

48
Q

pure actin + myosin + ATP —> what happens, why?

A

cross bridges dissociate because the binding of ATP results in the dissociated of the myosin head from the actin filament

49
Q

native actin + myosin –> ____? Why?

A

No cross bridges form because calcium is not present

50
Q

native actin + myosin + calcium —> ____? why?

A

cross bridges can form because the binding of calcium to troponin results in the dissociation of tropomyosin from the myosin binding site on the actin, allowing cross bridges to form

51
Q

native actin + myosin + calcium +ATP –> ___? Why?

A

The cross bridges dissociate because the binding of ATP results in the myosin head detaching from the actin filament.

52
Q

What elements form a weakly bound cross bridge?

A

actomyosin - ADP - Pi. This is a weakly bound cross bridge as there is no pulling occurring yet. Reversible.

53
Q

What makes a weakly bound cross bridge turn into a strongly bound cross bridge?

A

The spontaneous departure of the inorganic phosphate from actomyosin bound to ADP. This strongly bound cross bridge is now force generating and is irreversibly bound.

54
Q

What causes the rigor state in muscles?

A

During the cross bridge cycle, if the strongly bound actomyosin -ADP segment has ADP, the muscle will go into a state of rigor or stiffness when the ADP molecule detaches (muscle is locked in position). This muscle can only exit this state once a fresh ATP molecule binds to myosin which results in the detachment of actin from myosin.

55
Q

What nervous system controls skeletal muscle?

A

The somatic part of the peripheral nervous system. This is voluntary control - we are conscious of controlling our skeletal muscle.

56
Q

What type of receptor is on the cell membrane of a skeletal muscle cell? What does it do?

A

Nicotinic acetylcholine receptor (ion channel). It responds to acetylcholine released into the neuromuscular junction by the motor neuron. The acetylcholine results in the nicotinic ACh receptor to change conformation and allow sodium to flow in to the muscle cell through these receptors. This causes action potential propagation within the muscle cell.

57
Q

What are terminal cisternae?

A

Swellings of the SR on either side of t-tubule projections of the muscle cell membrane. They are also called lateral sacs. They have ryanodine receptors embedded within them

58
Q

What is the role of the dihydropuridine receptors in skeletal muscle cells?

A

These are receptors found on the T-tubules. They are L-type voltage gated calcium channels. Because of their VG properties, they change conformation when action potentials propagate depolarizations down the t-tubule. This change in configuration results in the ‘unplugging’ of a segment of the dihydropuridine receptor from the ryanodine receptor which allows calcium to be released from the sarcoplasmic reticulum and into the intracellular space.

59
Q

How is a skeletal muscle cell turned off?

A

Intracellular calcium is removed.

60
Q

parvalbumin

A

calcium binding protein that helps reduce the abundance of calcium in the intracellular space of skeletal muscle cells. The higher the amount of free calcium, the higher the tendency for calcium to bind to parvalbumin

61
Q

What are the pumps that move calcium back into the sarcoplasmic reticulum?

A

A certain type of calcium ATPase pump called SERCA pumps. Sarcoendoplasmic reticulum calcium ATPase. They pump calcium from very low concentrations to relatively high concentrations into the SR using ATP. These pumps are always on.

62
Q

calsequestrin

A

Acts as a calcium buffer in the SR. It lowers the extreme concentration difference between the SR and the intracellular space, making it easier for the SERCA pumps to pump Ca back into the SR.

63
Q

What does the origin of the muscle refer to?

A

the part of the muscle attaching to the more medial part of the body

64
Q

What does the insertion of the muscle refer to?

A

Distal connection of the muscle to the skeleton. most distant from the torso of the body.

65
Q

Series elasticity

A

In series with the contractile elements within a muscle. The SE bears the same amount of force as the CE. The SE will change length in proportion to the force generated by the CE. The SE only bears force when there is contraction occurring in the CE (X bridges attached)
Largest sources of SE:
- the neck region of myosin heads
- tendons

66
Q

parallel elasticity

A

is in parallel with the CE. It does NOT bear the same force as the CE (and thus SE). However, the forces exerted by the PE sum together with the CE to get the total force produced by a muscle
- the more you stretch a muscle, the more the PE will pull back, and this occurs even if there is no muscle contraction occurring

67
Q

What is a shortening contraction?

A

concentric contraction

68
Q

What is a lengthening contraction?

A

eccentric contraction

69
Q

How is muscle strength increased?

A

Muscle hypertrophy. Exerting forces on muscles stimulates the growth of myofibrils within the muscle cell. Making muscle cells larger + adding more sarcomeres in parallel to one another.

70
Q

How do you increase the speed of muscle shortening?

A

Add sarcomeres in series. Having longer filament lengths does NOT increase the speed of shortening. If the load that the muscle has to lift is less, the speed will be faster!

71
Q

How do you calculate the speed of sarcomere shortening?

A

Speed of half a sarcomere shortening (1 Z-line moving in) x 2 ( 2 Z-lines in each sarcomere) x # of sarcomeres in series

72
Q

How does the force generated relate to the velocity of shortening?

A

The force generated by a muscle decreases as the speed of shortening increases.

73
Q

Why do higher shortening velocities give less force generation?

A
  • Lower number of cross bridges able to be formed when the filaments are sliding at higher velocities
  • Average force produced by each cross bridge decreases bc the avg position of a given cross bridge is further along through the pulling cycle so the avg force produced by each cross bridge will begin to decrease
74
Q

What is work?

A

Force exerted times the distance it was moved (if vectors are parallel)

75
Q

What is power?

A

the rate of doing work. Force multiplied by velocity
J/s = Watts
The power output is higher when the same amount of force is put in but the time it took to move the thing decreased.

76
Q

Is glycolysis an anaerobic or aerobic source of energy?

A

anaerobic - not sustainable. Can provide ATP rapidly but this is not sustainable for long periods of time

77
Q

Is oxidative phosphorylation an anaerobic or aerobic source of energy?

A

aerobic - sustainable but slow in producing ATP

78
Q

What concentration of ATP is skeletal muscle always buffered at? What molecule ensures this?

A

5 mM. Creatine phosphate phosphorylates ADP to ATP
There is 20-40 mM of creatine phosphate present when at rest. Oxidative phosphorylation adds inorganic phosphate to creatine during rest to replenish the stores.

79
Q

How does a twitch fibre differ from a tonic fibre?

A

A twitch fibre gives an all or nothing response when stimulated by an action potential. It is either stimulated or not.
A tonic fibre gives a graded response to different depolarization stimuli. It will give a small contraction in response to less depolarization but will give a larger contraction when there is a greater depolarization. There is no firing of action potentials here (normally)

80
Q

tonic muscle fibres

A

slow contractile speed. They still respond to neurostimulation but they don’t fire action potentials. You instead get a graded depolarization.

81
Q

Multiterminal innervation

A

Because there is no longer an action potential being propagated along the muscle cell, you need a mechanism so that the entire muscle cell can still experience a graded depolarization. Multiple synapses along the length of the muscle cell. Get a release of calcium in response to the graded depolarization.

82
Q

Where do we find tonic muscle fibres?

A

muscle spindles (stretch receptors), muscle fibres controlling our eyes (extraocular muscles). These muscle fibres give really fine control of musle contraction (because of the graded response)

83
Q

Characteristics of slow twitch muscle fibres

A

Type l myosin heavy chain. Slow in terms of contraction. consume ATP slowly, highly oxidative and fatigue resistant. Highly sustainable. Produces low power output. These tend to have a very good blood supply - lots of myoglobin. Dark. Good for repetitive movements like walking.

84
Q

myoglobin

A

It is a hemoglobin type protein found in muscles. It binds to and carries oxygen. It is quite dark in colour. increasing ability of a muscle to be supplied with oxygen. Muscles with a lot of myoglobin are typically associated with being slow and oxidative.

85
Q

What are the different types of fast twitch muscle fibre types?

A

lla, llb, llx/lld

86
Q

lla muscle fibre

A

fast twitch oxidative/glycolytic fibre. type 2a myosin heavy chain. Has a high vMax and a gives a high power output. They are oxidative but they also have substantial glycolytic capacities. Good blood supply. good for supplying atp and also being quite fast (consume ATP fast) and sustaining this for long periods of time. Jogging

87
Q

llb muscle fibre

A

type 2b myosin heavy chain. This is very fast and highly anaerobic. Has a very poor blood supply and low myoglobin. Is it the fastest muscle fibre in the vertebrate muscle system. Highly fatiguable but they produce a very high power output because of their speed.

88
Q

llx or lld

A

Is intermediate of lla and llb in terms of speed, contractile properties, anaerobic vs aerobic properties, and fatiguability. This is the fastest muscle fibre we find in humans.

89
Q

Hennemen’s Size principle

A

Motor axons with small cell bodies (which innervate slower muscle fibres) need less excitation to be stimulated and motor axons with larger cell bodies (which innervate faster muscle fibres) need more excitation to be stimulated. Brain does not need to send separate signals to different motor units. It will just increase the amount of excitation sent if it wants more.

90
Q

monosynaptic reflex

A

Has a single synapse and has no interneurons. The connection between the afferent and efferent neurons is made within the CNS

91
Q

afferent neuron

A

Neurons that relay sensory signals to integrative centers of the central nervous system. Sensory receptor —> CNS

92
Q

presynaptic

A

typically where neuronal output occurs. At the end of a neuron. Where the neuron forms a synapse with another neuron or muscle fibre which has a physiological effect

93
Q

efferent neuron

A

relay control signals from the CNS to target cells. Like alpha motor neurons

94
Q

polysynaptic reflex

A

reflex that involves more than one synapse and therefore must have interneurons involved.

95
Q

simple neural networks

A

DO NOT involve the brain. These are involuntary reflexes which only involve the spinal cord in the CNS. Because the brain is not involved, these responses are very rapid. Use reflexes where we need quick reactions or a “ pre planned response “

96
Q

acquired reflex

A

these types of reflexes do involve the brain. They tend to be involuntary but they are actions we learn and practice

97
Q

simple reflex

A

unlearned, hardwired. The brain is NOT involved. The spinal cord does the thinking. They are very predictable. i.e. what happens when you ring a doorbell?

98
Q

pain/withdrawal reflex

A

instinct that is designed to prevent as much damage as possible. uses reciprocal innervation
The afferent neuron synapses on:
- an interneuron which has an excitatory synapse to the efferent alpha motor neuron which innervates the muscle that causes withdrawal
- an interneuron which has an inhibitory synapse on alpha motor unit of the antagonist muscle. Turns off the muscle that put the body part there in the first place
- a neuron that sends the signals up to the brain

99
Q

crossed extensor reflex

A

reflex causes stimulus to cross from one side of the body to the other side. This is an example of reciprocal innervation
afferent neuron synapses on:
- interneuron which has an excitatory synapse on the efferent alpha motor neuron which innervates the opposite leg’s extensors (bear weight on opposite leg)
-interneuron which has an inhibitory synapse onto the efferent alpha motor unit of the extensors of the pained leg (remove pressure off of that leg)

100
Q

reciprocal innervation

A

This mechanism/dual action of turning on one neuron an inhibiting another through one afferent neuron or within the same reflex arc

101
Q

gamma motor neurons

A

coactivate with alpha motor neurons to ensure that the intrafusal muscle fibres remain under tension and do not become slack when muscles contract so that stretch sensitivity is maintained during movements

102
Q

parasympathetic

A

cholinergic - involved with acetylcholine and second messenger systems

103
Q

sympathetic

A

adrenergic response - norepinephrine and epinephrine activating alpha and beta adrenergic receptors. The same NT can stimulate a different response in different muscle cells, just due to the presence of different receptors

104
Q

alpha 1 adrenergic receptors

A

involved in the sympathetic part of the autonomic nervous system. These receptors have similar affinities/ sensitivities to both epinephrine and norepinephrine. Activation of these receptors tends to cause contraction

105
Q

beta 2 adrenergic receptors

A

involved in the sympathetic response of the autonomic nervous system. Is more sensitive to epinephrine than to norepinephrine. Activation of receptors in smooth muscle cells that have these tends to result in relaxation of the muscle

106
Q

myosin light chain kinase

A

an enzyme that phosphorylates regulatory MLC. Phosphorylated MLC enhances the the ATPase activity of the myosin head group and triggers them to bind to actin filaments to form force generating cross bridges. thick filament regulation. Needs to be active for cross bridges to form. Inactivated when phosphorylated.

107
Q

calmodulin

A

Calcium bind to calmodulin and this complex then binds to MLCK which activates it. So when calcium is present, this complex can be made and MLC can be phosphorylated so that cross bridges can form

108
Q

rhokinase

A

activated indirectly by serotonin. Rhokinases inhibit MLC phosphatases

109
Q

PKA

A

cAMP production by various pathways (incl b2 receptors and E) activate protein kinase A –> PKA phosphorylates MLCK which inactivates it

110
Q

caldesmen

A

involved in thin filament in smooth muscle. similar to tropomyosin-troponin regulatory proteins. It binds to myosin binding site on actin filaments to prevent myosin from binding. Ca and calmodulin complex can bind to caldesmen which prevents it from binding to actin. Caldesmens activity is also inhibited when it is phosphorylated

111
Q

PKC

A

phosphorylated caldesmen which allows cross bridges to form – excitatory

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