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MSK > 2. Skeletal muscle > Flashcards

2. Skeletal muscle Flashcards

1
Q

What is the structure of skeletal muscle?

A 
Striated
Multi-nucleated
fused cells
voluntary
myoglobin present
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2
Q

What is fasciculation?

A

Small , local involuntary contraction of muscle

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3
Q

What is fibrillation?

A

Involuntary contraction of individual muscle fibres

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4
Q

What are the 3 categories of parallel muscles?

A

Strap
Fusiform
Fan-shaped

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5
Q

What is an example of a strap muscle?

A

Sartorius

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6
Q

What is an example of a fusiform muscle?

A

Biceps brachii

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7
Q

What is an example of a fan-shaped muscle?

A

Pectoralis major

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8
Q

What are the 3 types of pennate muscles?

A

Unipennate
Bipennate
Multipennate

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9
Q

What is an example of a unipennate muscle?

A

Extensor digitorum longus

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10
Q

What is an example of a bipennate muscle?

A

Rectus femoris

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11
Q

What is an example of a multipennate muscle?

A

Deltoid

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12
Q

What is compartment syndrome?

A

Limbs are divided into compartments by fascia. Trauma in one compartment could cause internal bleeding or swelling which increases pressure on blood vessels and nerves.

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13
Q

How is compartment syndrome treated?

A

Fasciotomy - cutting fascia to relieve pressure

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14
Q

What is a motor unit?

A

An alpha-motor neurone and the muscle fibres it innervates.

Each fibre is innervated by one neurone, but one neurone can innervate many fibres.

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15
Q

What is isometric contraction?

A

A muscular contraction in which the length of the muscle does not change despite being under tension.

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16
Q

What is isotonic contraction?

A

A muscular contraction in which the length of the muscle changes.

17
Q

How is isotonic contraction categorised?

A

Concentric - muscle shortens e.g bicep in flexion

Eccentric - muscle lengthens e.g bicep in extension

18
Q

What is an example of a first class lever?

A

Very few in body

Flexion and extension of the head at the neck

19
Q

What is an example of second class lever?

A

Plantar flexion of foot

20
Q

What is an example of a third class lever?

A

Biceps brachii

Most common in the body

21
Q

What determines the power of a muscle?

A

Higher number of fibres per motor unit

22
Q

What determines the fine control of a muscle?

A

Lower number of fibrils per motor unit

23
Q

What are the 3 main types of muscle fibre, what is this based on?

A 
Slow type 1
Fast type 2a
Fast type 2x
based on myosin heavy chain expression
Each muscle has a different proportion of fibres depending on function.
24
Q

What are the properties of type 1 muscle fibres?

A
  • Slow oxidative
  • aerobic
  • high myoglobin
  • many mitochondria
  • rich capillary supply
  • fatigue resistant
25
Q

Which muscle fibres are the first to be recruited?

A

Type 1

26
Q

What movements/actions utilise type 1 muscle fibres?

A

Standing

Walking

27
Q

What are the properties of type 2a muscle fibres?

A
  • fast oxidative
  • aerobic
  • high myoglobin
  • many mitochondria
  • moderate fatigue
28
Q

What muscle fibres are the second to be recruited?

A

Type 2a

29
Q

What actions utilise type 2a fibres?

A

Walking, running

30
Q

What are the properties of type 2x muscle fibres?

A
  • fast glycolytic
  • anaerobic
  • low myoglobin
  • few mitochondria
  • rapidly fatigue
31
Q

What muscle fibres are the last to be recruited? During what type of exercise?

A

Type 2x

Running, sprinting, jumping

32
Q

What are intrafusal muscle fibres?

A

Muscle spindles within the muscle belly that act as proprioceptors and sense stretch.
Separated form rest of muscle by collagen sheath.

33
Q

Explain the innervation if intrafusal fibres.

A

Innervated by 2 sensory and 1 motor neurone:

  • Gamma motor neurone keeps fibres taught
  • Type 1a sensory neurones relay rate of change in muscle length to CNS
  • Type 2 sensory neurones provide position sense.
34
Q

What will patients with large fibre sensory neuropathy be unable to do?

A

Impeded output from muscle spindles, unable to perform accurate movement without visual input (e.g eyes closed)

35
Q

What are the 2 main ways to control muscle force?

A
  1. Size principle

2. Rate code

36
Q

Explain the size principle.

A 
Small motor neurones are recruited before large motor neurones.Motor units with most fibre types:
Slow type 1 (smallest) first
Fast 2a
Fast 2x (largest) last.
37
Q

Explain the rate code.

A

More action potentials increase the force produced.

Subsequent AP produce summation up to a limit.

38
Q

What is hypotonia?

A

Symptom of lack of normal basal skeletal muscle tone.

Most common in babies after birth (floppy baby syndrome)

39
Q

Why is the resting membane potential of skeletal muscle more negative than other cells?

A

Also have a high concentration of Cl- leak channels (Cl- has negative equilibrium potential).

MSK (16 decks)

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