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Y2 - MSK > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

1
Q

What are the functions of skeletal muscles?

A 
Maintaining posture
Purposeful movement
Respiratory movement
Heat production
Contribution to metabolism
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2
Q

What causes the dark and light bands that make up striations?

A

Dark - myosin

Light - actin

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3
Q

What initiates skeletal muscle contraction, and what is this called?

A

Motor neuron stimulation

Neurogenic

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4
Q

In excitation contraction coupling, where is the calcium released from?

A

All from the sarcoplasmic reticulum

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5
Q

Is there continuity of cytoplasm between nerve and skeletal muscle cells?

A

No

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6
Q

What is the neurotransmitter at the neuromuscular junction?

A

Acetylcholine

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7
Q

What is a motor unit?

A

A single alpha motor neuron and all the skeletal muscle fibres (cells) it innervates

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8
Q

Where precision is more important than power, will there be few or many muscle fibres per motor unit?

A

Few

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9
Q

Where power is more important than precision, will there be few or many muscle fibres per motor unit?

A

Many

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10
Q

What are the cytoskeletal elements of muscle cells?

A

Actin and myosin

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11
Q

What does skeletal muscle consist of?

A

Parallel muscle fibres bundled by connective tissue

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12
Q

What do muscle fibres consist of?

A

Myofibrils (made up of sarcomeres end to end)
Sarcolemma
Mitochondria

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13
Q

What is the functional unit of skeletal muscle?

A

Sarcomere

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14
Q

What is a functional unit?

A

The smallest component capable of performing all the functions of that organ

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15
Q

What is a sarcomere found between?

A

Two Z-lines

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16
Q

What is the A-band?

A

The area covered by myosin, including where actin overlaps

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17
Q

What is the H-zone?

A

Area of myosin that doesn’t overlap with actin

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18
Q

What is the M-line?

A

Extends vertically down the middle of the A band within the centre of the H-zone

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19
Q

What is the I-band?

A

The area of actin that doesn’t overlap with myosin

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20
Q

How is muscle tension produced?

A

The sliding of actin filaments on myosin filaments

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21
Q

What is excitation contraction coupling?

A

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

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22
Q

What are T-tubules?

A

Extensions of the surface membrane that dip into the muscle fibre

23
Q

What is the process of excitation contraction coupling in skeletal muscle?

A
  1. The spread of action potential down the T-tubules triggering the release of calcium from the SR
  2. Calcium binds to troponin, causing tropomyosin to move out of the way to allow cross bridge formation
  3. Myosin head binds to actin to form a cross bridge
  4. ATP is hydrolysed to ADP and Pi, triggering power stroke that pulls the thin actin filament inwards, causing contraction
24
Q

What two factors does graduation of skeletal muscle tension depend on?

A

Number of muscle fibres contraction within a muscle

The tension developed by each contracting muscle fibre

25
How does increased number of muscle fibres affect muscle tension?
Increased muscle tension
26
What is the purpose of asynchronous motor unit recruitment?
Helps prevent muscle fatigue
27
What does the tension developed by each contracting muscle fibre depend on?
Frequency of stimulation Summation of contractions Length of muscle fibre at the onset of contraction Thickness of muscle fibre
28
Which is longer, the duration an action potential or the duration of the resulting muscle twitch?
The duration of the resulting muscle twitch is much longer
29
What is the result of repetitive fast stimulation of skeletal muscle?
Summation of twitches, bringing about a stronger contraction
30
What is tetanus?
Sustained muscle stimulation without rest leading to maximal sustained contraction
31
Why can cardiac muscle not be tetanised?
It has a refractory period, which skeletal does not
32
What is a single twitch, and what is its result?
If muscle is stimulated once a twitch is produced which produces little tension and is not useful for activity
33
What is twitch summation, and what is its result?
When a skeletal muscle receives a second stimulation before it completely relaxes This adds to the first and greater muscle tension is developed
34
When can maximal titanic contraction be achieved?
When the muscle is at its optimal length before the onset of contraction, usually approximately resting muscle length
35
How is muscle tension transmitted to bone?
Via the stretching and tightening of muscle connective tissue and tendons
36
What is isotonic contraction?
Muscle tension remains constant as the muscle length changes
37
What is isometric contraction?
Muscle length remains constant as muscle tension changes
38
What are some differences in skeletal muscle fibres?
Enzymatic pathways for ATP synthesis Resistance to fatigue The activity of myosin ATPase
39
What are the metabolic pathways for ATP production in skeletal muscle?
Transfer of high energy phosphate from creatine phosphate to ADP Oxidative phosphorylation Glycolysis
40
Which pathways for ATP production are used when oxygen is present and not present?
Oxygen present -oxidative phosphorylation | Oxygen not present - glycolysis
41
What are the main three types of skeletal muscle fibres?
``` Slow oxidative (type I/slow twitch) Fast oxidative (type IIa/intermediate twitch) Fast glycolytic (type IIx/fast twitch) ```
42
What are the features of slow oxidative fibres?
Aerobic metabolism Used in long lasting, low effort activities E.g. maintenance of posture, walking
43
What are the features of fast oxidative fibres?
Aerobic and anaerobic metabolism Long lasting, moderate effort activities E.g. jogging
44
What are the features of fast glycolytic fibres?
Anaerobic metabolism Short term, high effort activities E.g. jumping
45
What is a reflex?
A stereotyped response to a specific stimulus
46
What is the stretch reflex?
A negative feedback mechanism that resists passive change in muscle length to maintain optimal resting length of muscle
47
What is the process of the stretch reflex?
1. The sensory receptor (the muscle spindle) is activated by muscle stretc 2. This increases firing in the afferent neurones 3. Afferent neurones synapse in the spinal cord with the alpha motor neurones that innervate the stretched muscle 4. Motor neurones cause action in the muscle
48
What can test the stretch reflex?
Tapping the muscle tendon with a rubber hammer stretches the muscle, resulting in its contraction
49
What are muscle spindles, and how do they work?
Specialised muscle fibres that run parallel to ordinary muscle fibres They have sensory nerve endings that activate as the muscle is stretched Motor neurones that supply them are called gamma motor neurones The motor neurones adjust the level of tension to maintain their sensitivity when they shorten during contraction
50
What can impair skeletal muscle function?
Intrinsic disease of muscle Disease of NMJ Disease of lower motor neurones which supply the muscle Disease of input to motor nerves
51
What are conditions that can cause muscle disease?
Congenital abnormalities Muscular dystrophy (degeneration of contractile elements) Myotonia (abnormalities in membrane ion channels) Inflammatory myopathies (e.g. polymyositis) Non-inflammatory (e.g. fibromyalgia) Endocrine (Cushing, thyroid) Toxic myopathies (alcohol, statins)
52
What are symptoms of muscle disease?
Muscle weakness/tiredness Delayed reaction after voluntary contraction (myotonia) Muscle pain (myalgia) Muscle stiffness
53
What are investigations for muscle disease?
``` Electromyography (EMG) Nerve conduction studies Muscle enzymes (e.g. creatine kinase) Inflammatory markers Muscle biopsy ```
54
What can EMGs show?
Frequency and amplitude of muscle fibres action potentials Will not provide definitive diagnosis Help differentiate primary muscle disease from muscle weakness caused by neurological disease

Y2 - MSK (9 decks)

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