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MSK > Skeletal muscle physiology 2 > Flashcards

Skeletal muscle physiology 2 Flashcards

1
Q

What two things is the tension developed by a skeletal muscle influences by?

A

The number of muscle fibres contracting

The tension developed by each contracting muscle fibres

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2
Q

What 4 things might cause impairment to the skeletal muscle?

A

1- intrinsic muscle disease
2-neuromuscular junction disease
3-pathology of lower motor neurones
4-disruption of input to motor nerves

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3
Q

What is motor unit recruitment?

A

A stronger contraction could be achieved by stimulation of more motor units

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4
Q

What does asynchronous motor units recruitment during sub maximal contraction help to prevent

A

muscle fatigue

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5
Q

What does the tension developed by each individual contracting muscle fibre depend on?

A
  • frequency of stimulation
  • summation of contraction
  • length of muscle fibre at onset of contraction
  • thickness of muscle fibre
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6
Q

In skeletal muscle the duration of AP is the same as the duration of resulting twitch T/F

A

False- the duration of AP is much shorter than the duration of resulting twitch.

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7
Q

Is it possible to summate twitches to bring about a stronger contraction through a repetitive fast stimulation of skeletal /cardiac muscle- if so what is it called

A

YESfor SKELETAL- muscle tetanus. When no opportunity to relax between stimuli
no for cardiac- cannot be tetanised

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8
Q

What is a twitch

A

a single contraction caused by the skeletal muscle being stimulated once . It produces little tension

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9
Q

Maximal titanic contraction can be achieved when the muscle is at its optimal length before the onset of contraction t/f

A

t

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10
Q

The resting length of a skeletal muscle is approx its optimal length T/F

A

T

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11
Q

Skeletal muscle tension-
As a result cross bridge cycling ( _____ ____)- is transmitted to bone via the stretching and tightening of muscle connective tissue and tendon (_____ _____)

A

contractile component

elastic component

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12
Q

What is isotonic contraction used for?

A

Body movements and moving objects.

muscle tension remains constant as the muscle length changes

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13
Q

What is isometric contraction used for?

A

Supporting objects in fixed positions or for mainining body posture. Muscle tension develops at constant muscle length

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14
Q

the maximum the load the lower the velocity of shortening. Why is this?

A

The velocity of muscle shortening decreases as the load increases

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15
Q

What are the main differences between different types of skeletal muscle fibres

A
  • enzymatic pathway for ATP synthesis
  • the resistance to fatigue-muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue
  • Activity of myosin ATPase- this determines the speed at which energy is made available for cross bridge cycling i.e. the speed of contraction
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16
Q

Each motor unit contains many types of motor fibres T/F

A

F- each motor unit usually contains one type of muscle fibres

17
Q

Metabolic pathways that supply ATP in muscle fibre inc

A
  • transfer of high energy phosphate from creatine to ADP
  • oxidative phosphorylation
  • glycolysis
18
Q

Describe type 1 skeletal fibres

A

Slow-twitch fibres- used for prolonged relatively low work aerobic activities

low myosin ATP activity- slow
Adundance of mitochondria so can do oxidative phosphorylation therefore resistance to fatigue
high myoglobin so can store oxygen
appear red in colour

e.g.walking

19
Q

Describe type 11b skeletal fibres

A

Fast twitch fibres - use anaerobic metabolism nd are mainly used for short-term high intensity actvivity e.g. jumping

high levels of myosin ATPase activity- fast
abundance of enzymes that do anaerobic glycolysis
appear whitish in colour

20
Q

Describe type 11a skeletal fibres

A

Fast oxidative fibres (intermediate-twitch fibres) use both aerobic and anaerobic metabolism. Useful in prolonged moderate work e.g. jogging

can be oxidative phosphorylation and glycolysis- mixture of the two

21
Q

What is a reflex action?

A

A stereotypical response to a specific stimulus

22
Q

The neural pathways for reflexes are important in ____ _____ in the motor system

A

localising lesions

23
Q

What is the simplest monosynaptic spinal reflex?

A

Stretch reflex- serves as a negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle

24
Q

What is the sensory receptor in the stretch reflex?

A

Muscle spindle- stretching this increases firing in the affront neurons

25
Q

Stretch reflex - where so the affront neurones synapse and what with?

A

spinal cord with the alpha motor neurones ( efferent limb of the stretch reflex) that innervate the stretched muscle

26
Q

How can the stretch reflex be elicited?

A

Tapping the muscle tendons with a rubber hammer

27
Q

What muscle is stretching in the knee jerk

A

quadriceps femoris

28
Q

What fibres are muscle spindles known as

A

intrafusal

n.b. ordinary muscle fibres referred to as extrafusal vibres

29
Q

What are muscle spindles

A

a collection of specialised muscle fibres. fOUND WITHIN BELLY OF MUSCLES AND RUN PARALLEL TO ORDINARY MUSCLE FIBRES

30
Q

What are the sensory nerve endings on muscle spindles called

A

annulospiral fibres

31
Q

Muscle spindles have their own efferent nerve supply T/F

A

T-Called gamma motor neurones. They adjust the level tension in the spindles to maintain their sensitivity when muscle shortens during contraction.

32
Q

T/F

The discharge from he muscle spindles sensory endings decreases as the muscle is stretched

A

F the discharge from the muscle spindles sensory endings increases as the muscle ( and hence spindles) is stretched

33
Q

The contraction of intrafusal fibres does not contribute to the overall strength of muscle contraction. T/F

A

T

34
Q

What are some genetically determined myopathies that can cause intrinsic muscle disease?

A

Congenital myopathies
Chronic degeneration- e.g.muscular dystrophy
Abnormalities in muscle membrane ion channels e.g. myotonia

35
Q

What are the 4 acquired myopathies that cause intrinsic muscle disease

A

Inflammatory e.g. polymyosititis, inclusion body myosititis
Non-inflamamtory e.g. fibromyalgia
Endocrine e.g. Cushing syndrome, thyroid disease
Toxic myopathies e.g. alcohol, statins

36
Q

What are symptoms of muscle disease

A

muscle weakness/tiredness
delayed relaxation after contraction ( myotonia)
Muscle pain (myalgia)
muscle stiffness

37
Q

What 5 investigations may be useful in neuromuscular disease

A

1 EMG

  1. Nerve conduction studies
  2. Muscle enzymes
  3. Infalmamtory markers
  4. Muscle biopsy
38
Q

What are EMG helpful to differentiate

A

primary muscle disease from the muscle weakness caused by neurological disorders

39
Q

What should be done at the same time as the EMG

A

Nerve conduction studies

MSK (11 decks)

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