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IMS > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

1
Q

What are the 3 Major types of Muscle?

A

Smooth
Cardiac
Skeletal

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2
Q

Describe Smooth muscle?

A
  • Lines tubular and hollow structures in the body
  • Smooth muscle cells and gap junction
  • Spindle shape with central nucleus
  • Contractile cytoskeleton arranged diagonally
  • Actin anchored to dense bodies arranged within intermediate fibres
  • Myosin scattered throughout cell
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3
Q

Describe Cardiac Muscle?

A
  • Striated with single branched cell
  • Central nucleus and lots of mitochondria
  • Specialised thickenings of sarcolemma (intercalated discs with desmosomes)
  • Gap junctions for electrical signals
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4
Q

Describe Skeletal Muscle?

A
  • Major muscle type 40% body weight
  • Movement of bones
  • Surrounded by connective tissue (epimysium) beneath muscle fasicle surrounded by perimysium
  • Muscle fascicles composed of multinucleate fibres and myoblasts
  • Satellite cells along muscle fibres
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5
Q

Describe Muscle Fibre?

A
  • Consists of Myofibrils
  • Myofibrils extend the length of the cell
  • 2 forms; thin actin, thick myosin
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6
Q

Describe Excitable cells in muscle function?

A
  • Membrane potential dependent on permeability of sodium
  • RMP -95mv
  • Depolarisation associated with opening ligand and voltage gated channels
  • Depolarisation promotes release of calcium from SR
  • Re-polarisation changes in potassium permeability
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7
Q

Describe coordination of Excitation?

A

Muscle fibres all have to contract simultaneously, achieved because signal to contract is distributed evenly to T-tubules

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8
Q

What are T-tubules?

A

Narrow tubes that extend from the sarcolemma into the sarcoplasm of the muscle fibre then around myofibrilshow Excitable cells Coordinate

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9
Q

What is the Mechanism of Excitable cells Coordinating?

A

T-tubules fill with extracellular fluid and allow a rapid conduction of potential changes throughout muscle, tightly bound to membrane of the SR

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10
Q

Describe the Sarcoplasmic Reticulum?

A

Forms tubular network around each myofibril either side of each T-tubule, the SR enlarges and fuse forming large chambers the terminal cisternae

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11
Q

What is a Triad?

A

Association between encircling T-tubule and a pair of terminal Cisternae

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12
Q

Where is Calcium stored?

A

Sarcoplasmic Reticulum

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13
Q

How is Calcium released from the SR?

A

When a muscle fires a AP that potential change is conducted along T-tubule allowing release of Calcium from SR into Sarcoplasm

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14
Q

What is the Sliding Filament model?

A

The contractile filaments actin and myosin are arranged into myofibrils, when they slide across each other when a muscle contracts

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15
Q

What are Sarcomeres?

A

Myofibril’s contractile units

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16
Q

What are each Sarcomere seperated by?

A

Thin line known as Z disc

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17
Q

What Thin Actin Sarcomere filament attached to?

A

I band

18
Q

What band can be found between the I bands?

A

A band - Darker

19
Q

What happens when Muscles contracts with the bands?

A

Actin filaments of the I band slide over myosin filaments of A band so Z discs move closer together

20
Q

Describe Myosin?

A
  • Protein with 2 identical heavy chains bound to a pair of light chains
  • Amino terminal of heavy chain forms motor head domain, carboxyl end of heavy chain forms a helix tail, second heavy chain forms dimer
  • Dimers polymerise into stable bipolar filaments with free head groups at either end
21
Q

Describe Actin?

A

Consists of chain of globular actin molecule, each has a binding site for myosin head
- Actin helix coupled at every 7th molecule to 2 proteins tropomyosin and troponin

22
Q

Describe Tropomyosin?

A

Rod shaped molecule that binds via troponin molecule to groove of actin helix where masks myosin binding site

23
Q

Describe Troponin?

A

Bind the 4 Calcium ions, troponin goes through conformational change moving tropomyosin from myosin binding site

24
Q

Describe 3 types of Troponin?

A

Troponin I - Actin
Troponin T - Tropomyosin
Troponin C - Calcium

25
Q

Describe Muscle Contraction?

A

Contraction is a result of muscle cell excitation

  • Stored Ca released from SR
  • Ca binds to TC which creates conformational change in troponin complex
  • Tropomyosin molecule moves away from actin binding sites which allows myosin head to bind
  • Driven by conversion of ATP to ADP
26
Q

Describe control of Skeletal muscle?

A

A single axon will branch within the perimysium and expand at ends to form synaptic terminals form apposing muscle fibre

27
Q

Describe mechanism behind control of Skeletal muscle?

A

Synaptic terminal and cleft and sarcolemma (NMJunction) occur halfway down muscle fibre

  • When depolarised ACh travels across synaptic cleft and binds to ACh receptors in sarcolemma triggers opening of sodium to AP
  • Motor end plate rich in ACh of sarcolemma, folded to increase surface area and no of ACh receptors
28
Q

Describe Length-Tension relationship?

A

Tension generated is dependant on number of cross bridges formed between actin and myosin - stretching muscle can modify this by overlap of filaments

  • Relationship between degree of stretch and tension is positive and linear
  • Cross bridges between filaments decrease the relationship becomes negative
29
Q

Describe a Muscle Twitch?

A

Single stimulation of a muscle induces a single contraction

30
Q

What are the 3 Main phases of a Twitch?

A

Latent period - 2ms
Contraction Phase - 15ms
Relaxation - 25ms

31
Q

Describe Stimulus Frequency?

A

When a second stimulation arrive immediately after end of relaxation phase next contraction will be bigger, will happen for first 30-50 stimulation, because of increasing calcium

32
Q

Describe Incomplete Tetanus?

A

Summation of contraction when second stimulus arrives after relaxation phase, subsequent stimulations at the same frequency will induce tension to rise until it reaches a max value

33
Q

Describe Complete Tetanus?

A

Increasing stimulating frequency, eliminating relaxation phase muscle will contract smoothly upto max tension

34
Q

Describe Motor units?

A

Muscle fibres are innervated by motor neurons - innervating 100’s of fibres by a single neuron called a motor unit

35
Q

What is muscle tone?

A

Resting tension when muscle fibres/cells are always in a state of contraction even though muscle is at rest

36
Q

What does Muscle tone enable?

A

Maintenance of posture

Diameter of tubular structures so resistance to flow

37
Q

Describe Isotonic Contractions?

A

Equal tension when tension rises and muscles lengthen

38
Q

What are the 2 types of Isotonic contractions?

A

Concentric

Eccentric

39
Q

Describe Concentric Contractions?

A

Tension weight will move but tension in the muscle will remain

40
Q

Describe Eccentric Contractions?

A

Weight cannot be moved but muscle lengthens

41
Q

Describe Isometric Contractions?

A

Tension generated in muscle does not exceed the resistance to force - muscles maintain posture

IMS (53 decks)

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