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CJ: UoL Medicine Semester Two (ESA2) > MSK 4 - Skeletal Muscle > Flashcards

MSK 4 - Skeletal Muscle Flashcards

1
Q

What are the three types of muscle?

A
  • skeletal (striated)
  • cardiac (striated)
  • smooth (non-striated)
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2
Q

Give some characteristics of skeletal muscle?

A
  • multinucleated
  • fused cells
  • attached to skeleton
  • voluntary
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3
Q

Give some characteristics of cardiac muscle

A
  • branched uninucleated
  • heart only
  • intercalated discs
  • involuntary
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4
Q

Give some characteristics of smooth muscle

A
  • distance cells
  • spindle shaped
  • wall of internal organs
  • involuntary
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5
Q

What are the functions of skeletal muscle?

A
  • movement
  • posture
  • joint stability
  • heat generation
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6
Q

What is fasciculation?

A

Small, local, involuntary muscle contractions and relaxation. May be visible under skin.

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7
Q

What attaches a muscle to a bone?

A

Tendon

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8
Q

What is the function of circular muscles?

A

They act as sphincters to adjust opening.

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9
Q

How are circular muscles arranged?

A

They have concentric fibres, and attach to skin, ligaments and fascia rather than bone. Eg. orbicularis oris, which is around the mouth

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10
Q

What are the three main categories of parallel muscles?

A
  • Strap (fibres run longitudinally to contraction direction) eg. Sartorius
  • Fusiform (wider and cylindrical shaped at centre) eg. Biceps brachii
  • Fan-shaped (fibres converge at one end and spread over) eg. Pectoralis major
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11
Q

What is a pennate muscle?

A

One or more aponeuroses run through the muscle body from the tendon

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12
Q

Give an example of a multipennate muscle

A

Deltoid (this has central tendon branches)

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13
Q

What is the origin of a muscle?

A

A point on bone, typically proximal, which has greater mass and is more stable during contraction than the muscle’s insertion

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14
Q

What is a muscle’s insertion?

A

This is the structure (bone, tendon or connective tissue) that the muscle attaches to. Usually distal and moved by contraction.

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15
Q

What are compartments in limbs?

A

Limbs are divided into compartments by fascia - eg. The lower leg has four compartments

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16
Q

What is compartment syndrome?

A

When trauma in one compartment causes internal bleeding which exerts pressure on blood vessels and nerves.

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17
Q

What are the symptoms of compartment syndrome?

A
  • deep constant, poorly localised pain
  • aggravated by passive stretch of muscle group
  • paresthesia (pins and needles)
  • compartment feels tense/firm
  • swollen shiny skin with bruising
  • prolonged capillary refill time
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18
Q

How is compartment syndrome treated?

A

Fasciotomy, which can be covered by a skin graft

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19
Q

What are agonist muscles?

A

‘Prime movers’ - the main muscles responsible for a particular movement

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20
Q

What are antagonist muscles?

A

These oppose prime movers

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21
Q

What is the role of synergist muscles?

A

They assist prime movers. They cannot perform the movement alone, but their angle of pull assists

22
Q

What is the role of neutraliser muscles?

A

They prevent the unwanted actions of a joint that would otherwise occur with an agonist

23
Q

What is the role of fixators?

A

These act to hold a body part immobile whilst another body part is moving

24
Q

What is the difference between isotonic and isometric contraction?

A

Isotonic - constant tension, variable muscle length

Isometric - constant length, variable tension, eg. hand grip

25
Q

What is the difference between concentric and eccentric isotonic contraction?

A

Concentric - muscle shortens

Eccentric - muscle exerts a force while being extended eg. walking downhill

26
Q

What are the three types of levers in the human body?

A
  • first class lever “see-saw” (effort at one end, load at the other, fulcrum in the middle) eg. head
  • second class lever “wheelbarrow” (effort at one end, fulcrum at other, load in middle) eg. standing on tip toes
  • third class lever “fishing rod” (effort in middle, load at one end, fulcrum at other) eg. biceps in elbow flexion
27
Q

What is the name given to what happens when ATP is depleted after death, causing myosin heads to be unable to detach?

A

Rigor mortis

28
Q

What is a motor unit?

A

An alpha-motor neurone and the muscle fibres it innervates

29
Q

True or false - muscle with less fibres are usually better at fine control, while muscles with more fibres are usually more powerful?

A

True

30
Q

What are the three main muscle fibre types?

A
  • slow type I
  • fast type IIA
  • fast type IIX

There are also several intermediates. Classification is based on myosin heavy chain expression.

31
Q

Give some characteristics of Type I muscle fibres.

A
  • slow oxidative
  • aerobic, many mitochondria
  • red colour
  • high myoglobin levels
  • fatigue resistant
  • rich capillary supply
  • first type to be recruited: standing, walking
32
Q

Give some characteristics of type IIA muscle fibres

A
  • aerobic, many mitochondria
  • high myoglobin levels
  • red-pink colour
  • rich capillary supply
  • moderate fatigue resistance
  • second type to be recruited: walking, running
33
Q

Give some characteristics of type IIX muscle fibres

A
  • anaerobic glycolysis, few mitochondria
  • low myoglobin levels
  • white/pale colour
  • poor capillary supply
  • rapidly fatigable
  • last type to be recruited: sprinting, jumping
34
Q

What do intrafusal muscle fibres do?

A

They facilitate proprioception, allowing us to touch things accurately without watching our limbs

35
Q

How are intrafusal muscle fibres innervated?

A

Two sensory neurones (type 1a and type 2), and gamma motor neurones

36
Q

What does large-fibre sensory neuropathy cause?

A

Patients are unable to perform accurate movements without watching the affected limb

37
Q

What is the size principle of muscle contraction?

A

Small motor neurones are recruited before large, so motor units mostly have fibres types:
Slow type I -> fast IIa -> fast IIx

38
Q

What is it called when muscles cannot contact any further/faster?

A

Fused tetanus

39
Q

Why are healthy muscle never fully relaxed (except in REM sleep)?

A

Baseline tone due to motor neuron activity and muscle elasticity

40
Q

What is hypotonia?

A

A lack of skeletal muscle tone - this is a symptom rather than a condition. Most common in babies after birth, known as ‘floppy baby syndrome’

41
Q

Give some examples of conditions that can cause hypotonia

A
  • muscular dystrophies
  • spinal muscular atrophy
  • Charcot-Marie-Tooth disease
42
Q

Outline how the neuromuscular junction functions

A
  • action potential opens voltage gated Ca2+ channels and triggers vesicle fusion and ACh release
  • nACh channels open, Na+ flows into cell
  • ACh rapidly broken down in synaptic cleft by AChE
  • depolarisation opens voltage-gated Na+ channels in muscle cell
  • action potential occurs
43
Q

How is Ca2+ released into the muscle?

A
  • voltage gated Ca2+ channels (DHP receptors) in the T-tubules release some calcium
  • ryanodine receptors in SR are triggered by DHP receptors to allow rapid Ca2+ release
44
Q

What does Ca2+ do once it is released into the muscles?

A
  • Ca2+ binds to troponin, tropomyosin reveals actin binding sites for myosin heads
  • relaxation is facilitated by Ca2+ being pumped back into the SR via Ca2+ pumps
45
Q

Why is the resting membrane potential lower for skeletal muscle than other tissues?

A

Skeletal muscle has a high concentration of Cl- leak channels, so it is close to Nernst potential for Cl-

46
Q

Give a disease caused by a channelopathy of the Cl- channel in skeletal muscle

A

Myotonia congenita

47
Q

Give a disease caused by a channelopathy of the Na+ channel (alpha subunit) in skeletal muscle

A

Potassium aggravated myotonia, paramyotonia congenita, hyperkalemic periodic paralysis

48
Q

Give a disease caused by a channelopathy of the Ca2+ channel (alpha 1s subunit) in skeletal muscle

A

Hypokalaemic periodic paralysis

49
Q

What is myotonia congenita?

A

Inherited muscle stiffness which particularly occurs in the leg muscles. May be made worse by cold and inactivity.

50
Q

What causes myotonia congenita?

A

Normally in skeletal muscle, Cl- ions help to bring the membrane potential back to baseline. In myotonia congenita this can’t happen, so the muscles go into myotonia

51
Q

What are the short term sources of ATP in muscle?

A
  • stores of ATP in muscle fibre (very short term)
  • creatine phosphate
  • glycolysis
  • oxidative phosphorylation

CJ: UoL Medicine Semester Two (ESA2) (87 decks)

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