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MSK physiology Flashcards

1
Q

What are the 3 different types of muscle tissue in the body?

A

Skeletal, cardiac and smooth muscle.

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2
Q

Which muscle tissues are striated and unstriated ?

A

Striated - cardiac and skeletal

Unstriated - smooth muscle

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3
Q

Which muscle tissues are voluntary and involuntary?

A

Voluntary - Skeletal (innervated by the somatic nervous system)

Involuntary - Cardiac and smooth muscle (innervated by the autonomic nervous system)

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4
Q

What are the physiological functions of skeletal muscle?

A
  • Maintenance of posture
  • Purposeful movement in relation to external environment
  • Respiratory movements
  • Heat production
  • Contribution to whole body metabolism
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5
Q

Skeletal muscle fibres are organised into motor units - what is a motor unit ?

A

The motor unit is a single alpha motor neuron and all the skeletal muscle fibres it innervates.

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6
Q

T or F

Muscles which serve fine movements (e.g. external eye muscles, muscles of facial expression; and intrinsic hand muscles) have more fibres per motor unit

A

False - they have fewer.

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7
Q

Look at the table to note some of the differences between skeletal and cardiac muscle

A
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8
Q

what type of muscle tissue is this ?

A

skeletal muscle

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9
Q

what type of muscle tissue is this ?

A

cardiac muscle

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10
Q

what are the different levels of skeletal muscle organisation ?

A
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11
Q

What is excitation contraction coupling ?

A

The process whereby the surface action potential results in activation of the contractile mechanism of the muscle fibre.

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12
Q

How does the action potential transmitted in alpha motor neurons causes muscle contraction?

A

Ca2+ is released from the lateral sacs of the sarcoplasmic reticulum when - The surface actionPotential spreads down the transverse(T)-tubules.

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13
Q

What are T tubules?

A

Extensions of the surface membrane that dip into the muscle fibre

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14
Q

What is the transmitter at the neuromuscular junction in skeletal muscle ?

A

acetylcholine

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15
Q

What attaches muscle to bone?

A

tendons

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16
Q

What attaches bone to bone ?

A

ligaments

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17
Q

How far do skeletal muscle fibres usually extend?

A

the entire length of the muscle

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18
Q

Each muscle fibre contains many myofibrils - what are myofibrils ?

A

These are specialised contractile intracellular structures

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19
Q

The myofibrils have alternating segments of thick and thin protein filaments - what forms the thin and the thick filaments ?

A

Thin filament - Actin appears lighter

Thick filament - Myocyin appears darker

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20
Q

What are actin and myocyin arranged into?

A

Sarcomeres - the functional units of muscle (functional unit of any organ is: the smallest component capable of performing all the functions of that organ)

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21
Q

Appreciate the different zones of the sarcomere

A
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22
Q

Between what 2 lines is the sarcomere found ?

A

Z-lines

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23
Q

What is muscle tension produced by ?

A

Produced by sliding of actin filaments on myocin filaments

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24
Q

What does force generation in muscle contraction depend on ?

A

Depends upon ATP-dependent interaction between thick (myosin) and thin (actin) filaments.

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25
Q

How does Ca++ swtich on cross bridge formation ?

A

Ca2+ binds to troponin. This results in repositioning of troponin-tropomyocin complex to uncover the cross bridge binding sites on actin.

26
Q

where is Ca++ completely derived from in skeletal muscle ?

A

sarcoplasmic recticulum

27
Q

What is the link between excitation and contraction

A

Ca++

28
Q

What is Ca++ needed to do in muscle contraction ?

A

To switch on cross bridge formation.

29
Q

What is ATP required for during muscle contraction ?

A

To power cross bridges

30
Q

What is ATP required for during muscle relaxation?

A
  • Release cross bridges
  • To pump Ca2+ back into the sarcoplasmic reticulum
31
Q

What are the 2 main factors influencing the tension developed by a skeletal muscle ?

A

(1) The number of muscle fibres contracting
(2) The tension developed by each contracting muscle fibre

32
Q

In skeletal muscle:
the duration of action potential is much shorter than
the duration of resulting twitch. Therefore what is possible in-relation to muscle contraction?

A

It is therefore possible to summate twitches to bring about a stronger contraction through repetitive fast stimulation of skeletal muscle.

33
Q

Use the images following to show how increased frequency of AP can summate the twitches and also cause tenatus.

A
34
Q

Cardiac muscle cannot be tenatised - T/F?

A

True - this is due to the long refractory period.

35
Q

If skeletal muscle is stimulated once what is produced ?

A

A single muscle contraction called a twitch. (doesn’t bring about meaningful skeletal muscle activity)

36
Q

What does the tension developed by each of the contracting muscle fibres depend on ?

A
  • depends on frequency of stimulation and summation of contractions and
  • length of muscle fibre at the onset of contraction
  • thickness of muscle fibre
37
Q

Does skeletal muscle have an optimum length to produce maximum muscle tension?

A

Yes - maximum muscle tension develops at optimum muscle length.

38
Q

How is skeletal muscle tension transmitted to bone?

A

Via the stretching and tightening of muscle connective tissue and tendon.

39
Q

What are the two different types of skeletal muscle contractions called?

A

Isotonic and isometric contractions

40
Q

Define what isotonic muscle contractions are and what movements it is involved in ?

A

Used for:

  • (1) body movements and for
  • (2) moving objects.

Muscle tension remains constant as the muscle length changes.

41
Q

Define what isometric muscle contractions are and what movements they are involved in ?

A

Used for:

  • (1) supporting objects in fixed positions
  • (2) maintaining body posture.

Muscle tension develops at constant muscle length.

42
Q

As muscle load increases what happening to velocity of muscle shortening?

A

It decreases.

43
Q

Are skeletal muscle fibres all the same ?

A

No

44
Q

What are the main differences between skeletal muscle fibres?

A

The enzymatic pathways for ATP synthesis:

  • Some muscle fibres have a greater resistence to fatigue due to the fact that they have a greater capacity for ATP synthesis.
  • The activity of myosin ATPase - this determines the speed at which energy is made available for cross bridge cycling i.e. the speed of contraction
45
Q

What are the 3 main different metabolic pathways that supply ATP in skeletal muscles ? and explain briefly each.

A
  • Transfer of high energy phosphate from creatine Phosphate to ADP - immediate source for ATP
  • Oxidative phosphorylation: main source when O2 is present
  • Glycolysis: main source when O2 is not present
46
Q

What are the 3 different types of skeletal muscle fibres?

A
  1. Type I
  2. Type IIa
  3. Type IIx
47
Q

What activities are Type I skeletal muscle fibres usually involved in?

A

Slow oxidative type I fibres (also known as slow-twitch fibres) are used mainly for prolonged relatively low work aerobic activities e.g. maintenance of posture, walking.

48
Q

What activities are Type IIa skeletal muscle fibres usually involved in?

A

Fast oxidative (Type IIa) fibres (also known as intermediate-twitch fibres) use both aerobic and anaerobic metabolism and are useful in prolonged relatively moderate work activities e.g. jogging.

49
Q

What activities are Type IIx skeletal muscle fibres usually involved in ?

A

Fast glycolytic (Type IIx) fibres (also known as fast-twitch fibers) use anaerobic metabolism and are mainly used for short-term high intensity activities e.g. jumping.

50
Q

What is the activity of motor units influenced by ?

A

Influenced by inputs from the brain and from a variety of receptors - which can be excitory or inhibtory.

51
Q

What is a reflex action?

A

A stereotyped response to a specific stimulus. They are the simplest form of coordinated movement.

52
Q

Define what stretch reflex is

A

Serves as a negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle (resting muscle length is often the optimum length for muscle contraction).

Helps maintain posture e.g. while walking

53
Q

Explain what happens during a stretch reflex

A
  • The sensory receptor is the muscle spindle and is activated by muscle stretch
  • This increases firing in the afferent neurons
  • The afferent neurons synapse in the spinal cord with the alpha motor neurons (efferent limb of the stretch reflex) that innervate the stretched muscle.
  • Activation of the reflex results in contraction of stretched muscle
54
Q

What can stretch reflexes identify ?

A

They can localise lesions

55
Q

What are muscle spindles?

A
  • They are the sensory receptors for stretch reflex
  • Muscle spindles are collection of specialised muscle fibres
  • Muscle spindles are known as intrafusal fibres
56
Q

Where are muscle spindles found ?

A

Within muscle bellies and run parallel to muscle fibres

57
Q

What are skeletal muscles fibres also know as?

A

extrafusal fibres

58
Q

What are the sensory nerve endings in muscle spindles known as ?

A

Annulospiral fibres

59
Q

What happens at muscle spindles sensory endings when muscle is stretched?

A

Discharge from the muscle spindles sensory endings increases

60
Q

What are the efferent neurons that supply muscle spindles called, and how do they help maintain muscle spindle sensitivity ?

A

Gamma (g) motor neurons - they adjust the level of tension in the muscle spindle fibers to maintain their sensitivity.

61
Q

What are some different causes of impairment of skeletal muscle function?(4)

A
  • (1) intrinsic muscle disease
  • (2) neuromuscular junction disease
  • (3) pathology of lower motor neurons
  • (4) disruption of input to motor nerves
62
Q

What are the symptoms of muscle disease?

A
  • Muscle weakness / tiredness
  • Delayed relaxation after voluntary contraction (myotonia)
  • Muscle pain (myalgia)
  • Muscle stiffness

MSK (22 decks)

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