4. Muscle contraction Flashcards

1
Q

What are the three types of muscle?

A

Skeletal
Smooth
Cardiac

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2
Q

What is meant by the term contraction?

A

The ability of a muscle to actively shorten and develop tension

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3
Q

What are the structures that make up the muscle?

A
Muscle 
Fasciculus
Fibre/cell 
Myofibril 
Sarcomere 
Filaments
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4
Q

Describe the actin filaments in the relaxed state?

A

The ends of actin filaments from Z discs barely overlap

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5
Q

Describe the actin filaments in the contracted state?

A

Actin filaments pulled inward, overlap to maximum extent

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6
Q

What are the features of the actin filaments?

A

Double stranded F-actin molecules comprising of polymerised G-actin molecules
2 strands of tropomyosin molecules
Troponin complex on each tropomyosin for contraction (binds to Ca2+)

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7
Q

How many myosin and actin filaments on each myofibril?

A

1500 myosin

3000 actin

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8
Q

Describe the first three steps of the sliding-filament mechanism

A
  1. Low Ca2+ conditions, tropomyosin blocks access to the myosin binding site of the actin
  2. In high Ca2+ conditions, Ca2+ binds to troponin
  3. The positions of troponin and topomyosin are altered on actin + myosin can now access its binding site on actin

complete the full theory

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9
Q

Describe what happens when the sarcomere length decreases

A

Unstretched muscle

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10
Q

Describe what happens when the sarcomere is at optimal resting length

A

Muscle can develop maximal tension

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11
Q

Describe what happens to increased sarcomere length?

A

Actin is pulled to end of myosin with no overlap. No tension

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12
Q

Describe excitation-contraction coupling in skeletal muscles

A

Action potential travels along a motor nerve to the neuromuscular junction

Nerve secretes small amount of acetylcholine

ACh opens channels on muscle membrane

Na+ flows into the cell – initiates an action potential

AP travels along muscle fibre membrane

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13
Q

Describe the T-tubule endoplasmic reticulum system?

A

Muscle membrane depolarized, AP flows rapidly through centre of fibre via the T-tubules. Sarcoplasmic Reticulum releases Ca2+

Rise in intracellular Ca2+ enables Ca2+-binding to troponin, tropomyosin moves and cross-bridge cycling occurs

Ca2+ actively pumped back into SR store. Relaxation

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14
Q

What causes the release of Calcium ions?

A

Action potential from Sarcoplasmic reticulum

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15
Q

What causes re-uptake of calcium ions?

A

Calcium pump

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16
Q

What is the force of muscle contraction regulated by?

A

Increasing the number of motor units contracting simultaneously

Increasing the stimulation frequency

17
Q

What is meant by tetany?

A

A continuous contraction occurring at high stimulation frequency

18
Q

Describe concentric contraction

A

Isotonic- constant tension- change in length

Concentric - Muscle shortens

19
Q

Describe eccentric contraction

A

Isotonic and eccentric (muscle lengthens)

20
Q

Describe isometric contraction

A

Isometric- constant length, produces tension

Muscle length stays constant

21
Q

What are the two classifications of skeletal muscle fibres?

A

Slow twitch type I and fast twitch type II

22
Q

Give an example of slow twitch type I

A

Postural muscles of the back

23
Q

What are the features of the slow twitch type I?

A
Slow, sustained contractions 
Oxidative metabolism 
Many mitochondria 
Red-myoglobin 
Resist fatigue
24
Q

What are the two fast twitch, type II?

A

Type IIA and Type IIB

25
Q

Give an example of Type IIA

A

Soleus in calf

26
Q

Give an example of type IIB

A

Extraocular muscle

27
Q

Describe the features of Type IIA fast twitch

A
Fast contractions 
Oxidative metabolism 
Many mitochondria 
Red-pink myoglobin 
Intermediate fatigue resistance
28
Q

Describe type IIB fast twitch features

A
Rapid contractions
Anaerobic glycolysis 
Few mitochondria 
White - little myoglobin 
High glycogen content
29
Q

Where is smooth muscle found?

A

Found in the gastrointestinal tract, uninary tract and walls of blood vessels

30
Q

What are the features of smooth muscle?

A

Single nuclei

No striations

31
Q

Describe the structure of smooth muscle

A

Actin filaments radiating from dense bodies

32
Q

What innervates smooth muscle?

A

Automatic nerve fibres

33
Q

Describe smooth muscle excitation

A

Typical smooth muscle action potential elicited by an external stimulus

34
Q

Describe smooth muscle spontaneous activity

A

Repetitive spike potentials, occur spontaneously in the smooth muscle of the wall

35
Q

Describe the smooth muscle excitation- contraction coupling

A

Has spontaneous electrical and mechanical activity
Activity can be phasic or tonic
Activity is modified by circulating hormones and neurotransmitters
Contraction velocity is less than skeletal muscle
Smooth muscle can maintain prolonged contractions at less energy cost of the other muscle types

36
Q

What are the features of skeletal muscles?

A

Striations
Troponin
Cross-bridge cycling
Neurogenic stimulation only excites in skeletal muscle
E-C coupling- depolarisation Ca2+ release from SR

37
Q

What are features cardiac muscle?

A
Striations 
troponin 
Cross-bridge cycling 
Spontaneous activity 
Neurogenic stimulation- modultaes cardiac muscle contraction 
E-C coupling- depolarisation Ca2+
38
Q

What are the features of smooth muscle?

A

Calmodulin
Spontaneous activity
Neurogenic stimulation- modulates smooth muscle contraction
E-C coupling - smooth muscle -depolarisation -Ca2+ - influx and CICR second messenger system