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VAP II > Muscle physiology and microanatomy > Flashcards

Muscle physiology and microanatomy Flashcards

1
Q

Complete this table on the anatomy and functions of the various dfferent muscle types.

A
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2
Q

What structure attaches muscles to bones?

A

Tendons

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3
Q

Groups of muscle fibres are bundled together to form ______.

A

Groups of muscle fibres are bundled together to form fascicles.

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4
Q

Muscle ______ is another name for a muscle cell.

A

Muscle fibre is another name for a muscle cell.

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5
Q

The epimysium surrounds _________.

A

The epimysium surrounds the whole muscle.

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6
Q

The perimysium surrounds ________.

A

The perimysium surrounds fascicles (bundles of muscle fibres).

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7
Q

The endomysium surrounds __________.

A

The endomysium surrounds individual muscle fibres.

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8
Q

Muscle fibres are _______nucleate - formed by fusion of individual embryonic __________.
Muscle fibres range from ___ - ____μm diameter and up to ___ m in length.

A

Muscle fibres are multinucleate - formed by fusion of individual embryonic myoblasts.
Muscle fibres range from 10-100μm diameter and up to 0.3m in length.

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9
Q

Each muscle fibre is comprised of 100s-1000s of _____.

A

Each muscle fibre is comprised of 100s-1000s of myofibrils.

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10
Q

Label the following diagram:

A
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11
Q

Label the following diagram of part of a muscle cell.

A
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12
Q

Label the following diagram of a muscle cell. Note the components that make up the traid.

A
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13
Q

Each myofibril is made up of ________, consisting of contractile proteins. These (_____) are arranged into repeating units called ________ . These are the functional unit of the contractile process.

A

Each myofibril is made up of myofilaments, consisting of contractile proteins. These myofilaments are arranged into repeating units calle sarcomeres. These are the functional unit of the contractile process.

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14
Q

Label these parts of a sarcomere.

A
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15
Q

This is a longitudinal section of ___________.

A

skeletal muscle

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16
Q

Label these parts of the ultrastructure of muscle.

A
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17
Q

Thick filaments are:

  • Composed of the protein _______
  • Confined to ____ band (dark)
  • Each thick filament is composed of 200 to 400 _______ molecules
A

Thick filaments are:

  • Composed of the protein myosin
  • Confined to A band (dark)
  • Each thick filament is composed of 200 to 400 myosin molecules
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18
Q

Thin filaments are:

  • Composed primarily of the protein ______
  • Anchored to proteins in the ___ line and extend into ___ band (interdigitate with thick filaments).
A

Thin filaments are:

  • Composed primarily of the protein actin
  • Anchored to proteins in the Z line and extend into A band (interdigitate with thick filaments).
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19
Q

Name these other components of myofilaments

A
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20
Q

Each myosin molecule contains 2 _____ chains of amino acids which are coiled around each other.

  • 2 smaller ____ chains are associated with each head.
  • Head regions have ____ and ____ binding sites.
  • The ATP binding site also serves as an enzyme (______ that hydrolyses bound ATP).

Label the following diagram.

A

Each myosin molecule contains 2 heavy chains of amino acids which are coiled around each other.

  • 2 smaller light chains are associated with each head.
  • Head regions have ATP and actin binding sites.
  • The ATP binding site also serves as an enzyme (ATPase that hydrolyses bound ATP).
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21
Q

Thin filaments: The interaction between the myosin globular heads and actin is regulated by proteins _______ and ______.

Label the following diagram.

A

The interaction between the myosin globular heads and actin is regulated by proteins tropomyosin and troponin.

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22
Q

_____ & ______ (structural proteins) help align the contractile proteins (actin & myosin):

  • ____ (by thick filaments) = elastic & helps sarcomeres spring back when stretched.
  • ____ (thin filaments) = inelastic, stabilises actin.

Label them on the following diagram.

A

Titin & Nebulin (structural proteins) help align the contractile proteins (actin & myosin):

  • Titin (by thick filaments) = elastic & helps sarcomeres spring back when stretched.
  • Nebulin (thin filaments) = inelastic, stabilises actin.
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23
Q

The molecular basis of muscle contraction is called ______ _____ theory.

A

The molecular basis of muscle contraction is called sliding filament theory.

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24
Q

What are cross-bridges?

A

Cross-bridges are formed when heads of the thick filaments attach to the thin filaments and pull them towards the centre of the sarcomere.

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25
Q

Describe what is going on at each of the four stages of the crossbridge cycle.

A
  1. Binding of ATP to myosin head breaks cross-bridge
  2. Degradation of ATP straightens myosin head (cocking)
  3. Myosin head binds to actin
  4. Myosin head swivels = power stroke; pulls actin towards the centre of the sarcomere. ADP & Pi are released.
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26
Q

What are the two roles of ATP in the crossbridge cycle?

  1. ____ Source
  2. ____ regulator

How many ATP are used in each cycle?

A
  1. Energy Source: ATP hydrolysis provides the energy for cross-bridge movement – enables myosin head to become cocked.
  2. Allosteric regulator: binding of ATP to myosin breaks the link between actin & myosin. This allows the cycle to be repeated.

How many ATP are used in each cycle? one

27
Q

How does the crossbridge cycle relate to the onset of rigor mortis after death and why is this relevant to the meat industry?

A
  • Absence of ATP in death – muscles are fixed in place
  • because myosin is unable to unbind from actin.
  • Stiffness disappears after a few days when proteolytic enzymes in cells break down muscle fibres.
  • Onset & resolution of rigor mortis partially determines tenderness of meat
28
Q

What are the roles of calcium ions, troponin, and tropomyosin in the regulation of muscle contraction?

A

Calcium & regulatory proteins tropomyosin & troponin control muscle contractions.

In resting muscle binding sites for myosin are masked by tropomyosin.

When Ca2+ binds to troponin its conformation is altered causing tropomyosin to change position & expose the binding sites for myosin.

29
Q

Large stores of Ca2+ in __________ are released in response to the arrival of an action potential.

A

Large stores of Ca2+ in the sarcoplasmic reticulum (SR) are released in response to the arrival of an action potential.

30
Q

Excitation-contraction coupling describes the relationship between d______ and c_______. Action potentials (AP) trigger muscle contraction.

A

Excitation-contraction coupling describes the relationship between depolarisation and contraction. Action potentials (AP) trigger muscle contraction.

31
Q

How does the action potential trigger muscle contraction?

A

Excitation at the motor end plate initiates the propagation of electrical impulse / action potential (AP) down the sarcolemma and T-tubular system, triggering the release of Ca2+ into sarcoplasm from the terminal cisternae of the saroplasmic reticulum.

Calcium plays an important role in the regulation of muscle contraction

32
Q

Each skeletal muscle fibre is innervated by a ________ neuron.
Motor unit = _______ & ____________.
__________________ comprises:

  • Enlarged nerve terminal
  • Synaptic cleft
  • Motor end plate
A

Each skeletal muscle fibre is innervated by a motor
neuron.
Motor unit = motor neuron & muscle fibres it innervates.
Neuromuscular junction comprises:

  • Enlarged nerve terminal
  • Synaptic cleft
  • Motor end plate
33
Q

Complete these steps involved in skeletal muscle action potential generation:

At rest:

  • Many K+ channels [open/closed], Na+ channels [open/closed].
  • Tendency for K+ to [enter/leave] cell, therefore membrane is ______ (-ve inside).
  • Resting membrane potential ≈ -___ to - ___mV
  • AP is created when cell is _________ (less –ve inside).

When neural action potential is received:

  • Binding of _________ (ACh) results in [opening/closing] of Na+ channels, which leads to depolarisation of motor end plate.
  • Depolarisation of motor endplate results in depolarisation of adjacent regions of the membrane through activation of _______ channels. This allows rapid [influx/efflux] of Na+ .
  • Na+ channels are rapidly inactivated and the cell ______ towards resting membrane potential.
  • Repolarisation is promoted by opening of additional _____ channels.
  • Arrival of AP in skeletal muscle causes release of ______ from the sarcoplasmic reticulum (SR), which initiates contraction.
A

At rest:

  • Many K+ channels open, Na+ closed.
  • Tendency for K+ to leave cell, therefore membrane is polarised (-ve inside).
  • Resting membrane potential ≈ -70 to -85mV
  • AP is created when cell is depolarised (less –ve inside).

When neural action potential is received:

  • Binding of acetylcholine (ACh) results in opening of Na+ channels, which leads to depolarisation of motor end plate.
  • Depolarisation of motor endplate results in depolarisation of adjacent regions of the membrane through activation of voltage gated Na+ channels. This allows rapid influx of Na+ .
  • Na+ channels are rapidly inactivated and the cell repolarises towards resting membrane potential.
  • Repolarisation is promoted by opening of additional K+ channels.
  • Arrival of AP in skeletal muscle causes release of Ca2+ from the sarcoplasmic reticulum (SR), which initiates contraction.
34
Q

ACh binds to _______ receptors in the endplate and causes opening of ion channels in the post synaptic membrane.

A

ACh binds to nicotinic receptors in the endplate and causes opening of ion channels in the post synaptic membrane.

35
Q

From the motor endplate in the muscle, an action potential is transmitted down _______ and causes release of Ca2+ from the sarcoplasmic reticulum.

A

From the motor endplate in the muscle, an action potential is transmitted down transverse (T) tubules and causes release of Ca2+ from the sarcoplasmic reticulum.

36
Q

Complete this diagram:

A
37
Q

Complete this diagram:

A
38
Q

What are the names and functions of the two receptor types at the Sarcoplasmic reticulum?

Complete this diagram:

A
  1. Dihydropyridin (DHP) receptor functions as a voltage sensor so detects the arrival of the AP.
  2. Ryanodine receptor detects DHP activity and functions as a calcium release channel.
39
Q

Describe what happens to calcium ions and what the role of ATP is during muscle relaxation.

A

When the AP is terminated, release of Ca2+ from
SR also ceases. Ca2+ is pumped back into the SR (10-100ms to return to low level).

Low Ca2+ and ATP regeneration allows opposite conformational change in troponin so that tropomyosin covers the myosin binding sites on actin, so inducing relaxation.

Both contraction and relaxation require ATP. During relaxation, ATP is required to pump Ca2+ back into SR.

40
Q

Clinical roles: what are three ways that ACh function can be disrupted at the neuromuscular junction? What are some examples?

A
  1. Substances that inhibit release of ACh, eg. Botulinum toxin
  2. Substances that reduce action of ACh by binding to post synaptic receptor – eg. Curare, snake α neurotoxin
  3. Acetylcholinesterase inhibitors – prevent breakdown of ACh. eg. Organophosphate-containing insecticides, nerve gases
41
Q

Complete the following information about the condition myasthenia gravis:

  • Rare condition in dogs (& v rarely cats)
  • 2 forms:
    • ______ : lack of Ach receptors
    • ______ : Autoantibodies produced against Ach receptors, which leads to decrease in numbers
  • Results in muscle __________
  • Treatment is with ___________ inhibitors which potentiate the effect of the released Ach.
A

Myasthenia gravis:

  • Rare condition in dogs (& v rarely cats)
  • 2 forms:
    • Congenital: lack of Ach receptors
    • Acquired: Autoantibodies produced against Ach receptors, which leads to decrease in numbers
  • Results in muscle weakness
  • Treatment is with anticholinesterase inhibitors which potentiate the effect of the released Ach.
42
Q

Complete the following information about hypocalcaemia (milk fever) in cows:

  • May occur following _________.
  • Hypocalcaemia affects muscle _______ due to the requirement for Ca2+ for membrane stabilisation in peripheral nerves, release of _______ at the neuromuscular junction and _______ of muscle cells.
  • Results in flaccid paresis of skeletal muscle leading to recumbency
  • Also affects _____ & ______ muscle
  • Treatment is with injection of ______ ________
A

Hypocalcaemia (milk fever) in cows:

  • May occur following calving.
  • Hypocalcaemia affects muscle contraction due to the requirement for Ca2+ for membrane stabilisation in peripheral nerves, release of ACh at the neuromuscular junction and contraction of muscle cells.
  • Results in flaccid paresis of skeletal muscle leading to recumbency
  • Also affects smooth & cardiac muscle
  • Treatment is with injection of calcium borogluconate
43
Q

Elastic elements assist muscles by storing energy and are present in:

  1. individual ________
  2. _______ tissue of muscle
  3. in the _____ & _______

Give an example of a ligament that assists muscles by storing elastic energy.

A

Elastic elements are present in:

  1. individual muscle fibres
  2. connective tissue of muscle
  3. in the tendons & ligaments

Stored energy in the nuchal ligament helps to raise the head in large animals such as cattle and horses.

44
Q

What is the relationship between muscle length and amount of shortening?

What is the relationship between muscle length and shortening velocity?

A
  • *Increased** muscle length increases muscle shortening (sarcomeres in series).
  • *Increased** muscle length increases shortening velocity.
45
Q

______ _______ = muscle force generated during cross-bridge activity (when a muscle is stimulated).

A

Muscle tension = muscle force generated during cross-bridge activity (when a muscle is stimulated).

46
Q

Maximum force increases with increased ____ _____ _______ of the muscle (more sarcomeres in parallel). So… ______ muscles can create more force

A

Maximum force increases with increased cross-sectional area of the muscle (more sarcomeres in parallel). So… bigger muscles can create more force

47
Q

During isometric contraction, how do muscles develop tension without changing length?

What are some examples of isometric contraction?

A

Sarcomeres shorten slightly and elastic components stretch.

e.g. maintaining body posture, gripping an object, carrying a heavy object.

48
Q

Name and describe the two types of isotonic (muscle length is altered) muscle contraction.

What happens to sarcomeres and elastic elements in each?

Give an example of each type.

A

Isotonic concentric contraction:

  • Muscle shortens while the load remains constant
  • Sarcomeres shorten significantly and elastic elements stretch
  • Length of whole muscle shortens and joint angle changes
  • e.g. biceps curls (upwards motion)

Isotonic eccentric contraction:

  • Load exceeds muscle tension
  • Load pulls muscle to a longer length
  • Sarcomeres are lengthening while generating force - exact mechanism still debated - elastic elements lengthen
  • e.g. When setting down a heavy object, biceps curl (down stroke)
49
Q

Complete the following on isometric recording:

  • muscle ______ but is not allowed to move a load; measures force generated, or _______.
  • i.e. load is much greater than the capacity to generate force
A

Complete the following on isometric recording:

  • muscle contracts but is not allowed to move a load; measures force generated, or tension.
  • i.e. load is much greater than the capacity to generate force
50
Q

Complete the following about studying muscles under isotonic conditions:

  • Muscle ______ and moves a load; measures __________ (change of length)
  • Contraction is _________ until force developed is sufficient to move the load.
A

Studying muscles under isotonic conditions:

  • Muscle contracts and moves a load; measures shortening (change of length)
  • Contraction is isometric until force developed is sufficient to move the load.
51
Q

What is a muscle twitch and what are its three phases?

A

A twitch is the mechanical response of a muscle to a single action potential.

3 phases:

  1. Latent period
  2. Contraction phase
  3. Relaxation phase

AP lasts approx 2ms – a small fraction of the duration of the twitch

52
Q

What causes the latent period of a muscle twitch?

A

Latent period is mainly due to the delay before Ca2+ concentration increases in cytosol.

53
Q

Why does a muscle twitch take so much longer to diminish after its peak than an action potential does?

A

Duration of twitch after peak reflects time taken to pump Ca2+ back into the sarcoplasmic reticulum.

54
Q

What property of action potentials determines the force developed by a muscle fibre?

A

The frequency of action potentials determines the force developed by a muscle fibre.

55
Q

What is the relationship between frequency of action potential stimulation of a muscle and force generated?

What happens when more stimuli are applied before a muscle has completely relaxed?

What is (physiological) tetanus?

Label the following diagram:

A
  • Low frequency stimulation allows muscle fibres to relax completely before the next contraction.
  • Increasing frequency: if further stimulus is applied before the muscle has completely relaxed, summation occurs: twitches overlap and greater force is produced.
  • High frequency stimulation produces a smooth fused contraction called tetanus. In mammals the force of tetanic contraction is 3-5x higher than that of a singe twitch
56
Q

Explain the relationship between force generated and fibre length in terms of sliding filament theory (think back to frog leg prac).

A

Force and fibre length

  • The amount of tension developed by a skeletal muscle fibre depends on the length of the muscle at the time it is stimulated.
  • Maximal tension is achieved when muscle is set at lengths near its normal relaxed length in the animal.
  • At shorter or greater lengths, development of tension is less.

Sliding filament theory (see diagram):

  • When muscle is shortened the thin filaments begin to overlap one another so that the amount of contact area between actin and myosin heads decreases
  • When muscle is over-lengthened (stretched), the thick and thin filaments decrease in the amount they overlap by pulling away from one another, which likewise decreases the amount of contact area between actin and myosin heads
  • At optimal force-generating length, thick and thin filaments in each sarcomere overlap one another optimally, maximising force generated by maximising contact area for myosin heads with actin binding sites
57
Q

Exlain the two ways that strength of a muscle contraction can be increased

A
  1. Increasing frequency of stimulation (only increases 3-5 x )
  2. Increasing numbers of motor units activated (= recruitment)
58
Q

What is a motor unit and how do different units vary?

A

Motor unit = single motor neuron + all innervated muscle fibres.

Vary in size – few muscle fibres to several 1000.

  • Small units responsible for fine motor control
  • Large units responsible for creating more force
  • Most muscles contain range of motor unit sizes
  • All fibres in a motor unit are of the same type.
  • All or nothing response to an action potential (AP).
59
Q

Explain the graded response of muscle force and the initiation of large rapid movements in terms of motor unit recruitment.

A
  • Smallest motor units are recruited first.
  • As more motor units are recruited this increases strength of contraction (= a graded response).
  • During rapid movements (eg. Jumping, throwing), large motor units can be activated without prior stimulation of smallest ones
  • During an isotonic contraction muscle will shorten as soon as contractile force exceeds the external load and movement is initiated.
    • Increasing recruitment of further motor units will increase the velocity of the movement.
60
Q

Explain the relationship between load and shortening speed during isotonic concentric contraction.

A

Load directly influences the velocity (speed) at which a muscle shortens.

Speed of shortening :

  • is highest when the load is zero
  • decreases with increasing load
  • falls to zero when load exceeds the maximal contractile force (= isometric contraction)
61
Q

Explain the relationship between muscle length, cross sectional area, force, load, and work.

A
  • Work = force (N) x distance (m) - length matters
  • Muscles do increasing amounts of work, up to about 40% of maximum load, then work decreases (see diagram)
  • the amount of work a muscle can do in general depends on its volume
  • force depends on cross-sectional area
  • Length of muscle does not contribute to force but is important in determining amount of work done
    • Longer muscles can shorten more ( due to increased number of sarcomeres in series)
    • Length also affects velocity of shortening (increased velocity with increased length).
62
Q

Explain the relationship between pennation and muscle force (ACSA vs PCSA)

A

Pennation enables the number of muscle fibres to be increased without enlarging volume

  • Physiological cross-sectional area (PCSA) may differ from the anatomic cross-sectional area (ACSA).
  • PCSA = total cross-sectional area of all fibres within a muscle.
  • Pennation enables muscle fibres to be aligned at an oblique angle compared with fusiform (spindle shaped) muscles and allows PCSA to be increased.
  • Pennation increases the PCSA by increasing the number of sarcomeres per anatomical cross-sectional muscle area and hence increases the maximal force that can be generated (see diagram)
  • Fusiform muscles eg. hamstrings have higher contractile velocity but lower force-output. Pennate muscles eg. quadriceps generate more force.
63
Q

What is the function of the epimysium, perimysium, and endomyseum?

A

Connective tissue links individual skeletal muscle cells in a bundle, which aids in transmitting force to the tendons. Another important function of various layers of connective tissue is that they provide a pathway for blood vessels, lymphatics, and nerve fibers.

They join to the tendon entotendineum and epitendineum (which join to bone) for connective strength.

VAP II (11 decks)

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