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Block 4 > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

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0
Q

What are the 3 types of multicellular muscle?

A

Skeletal
Cardiac
Smooth

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1
Q

Where can you find single cell units of muscle?

A

Myoepithelial cells - around acini of exocrine glands
Pericytes - surround blood vessels
Myofibroblasts - secrete collagen, contraction, key for wound healing

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2
Q

What are the 3 layers of supporting tissue in muscles?

A

Endomysium: surrounds individual muscle fibres
Perimysium: surrounds fascicles
Epimysium: surrounds the muscle as a whole

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3
Q

How is force generated in muscle cells transmitted to the surrounding tissue?

A

Muscle cells surrounded by an external lamina
Internal contractile proteins transmit force to link proteins including dystrophin
Link proteins span plasma membrane, transmit force to external lamina
External lamina of muscle cells binds myocytes into a functional unit

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4
Q

What are 3 disease types that affect muscles?

A

Neurogenic
Myopathies
Disorders of neuromuscular transmission

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5
Q

Describe the structure of skeletal muscle cells

A

Range of cell lengths
Long parallel cylinders, multiple peripheral nuclei, striated
Fascicle bundle, tendon attachments
Rapid forceful contractions

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6
Q

Describe the structure of cardiac muscle cells

A

Short cell lengths
Branched cylinders, single central nucleus, striated
Junctions join cells end to end
Lifelong variable rhythm

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7
Q

Describe the structure of smooth muscle cells

A

Spindle shaped, tapering ends, single central nucleus
Connective tissue, gap and desmosome junctions
Involuntary slow, sustained or rhythmic

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8
Q

What is a motor unit?

A

Individual motor nerves supplying a group of myocytes

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9
Q

Which cells in muscle can undergo mitosis?

A

Satellite cells (stem cells) can undergo mitosis after myocyte damage

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10
Q

How many capillaries are associated with each muscle fibre?

A

1-3 which reflects high energy requirements of the tissue

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11
Q

What are the 3 types of muscle fibres?

A

Type 1/slow twitch/red- aerobic metabolism e.g. posture
Abundant mitochondria and myoglobin, small size, fatigue resistant, recruited early, low SERCA activity, fine movement
Type 2/ fast twitch/white- anaerobic metabolism e.g. eye muscle, triceps, biceps
Few mitochondria, sparse myoglobin, abundant glycogen and glycolytic enzymes, large size, easily fatigued, recruited late, high SERCA activity, large force
Intermediate fibres
Most muscles contain a mixture of all three types (a checkerboard)

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12
Q

What does the supporting tissue of muscle carry and what are its components?

A

Carry: neurovascular bundles
Components: mainly fibroblasts and fibres (collagen and elastin)

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13
Q

How do muscle fascicle sizes vary?

A

Fine, highly controlled movements require small fasciculi
Gross movements can be achieved with large fasciculi
Size reflects function of the muscle

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14
Q

Why is skeletal muscle striated?

A

Myofibrils are arranged in register with each other

Held in place by z discs for actin and M lines for myosin

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15
Q

What is a sarcomere?

A

Contractile unit of the muscle

Z line to Z line

16
Q

What are the 2 muscle filaments?

A

Thin: Actin
Thick: Myosin

17
Q

Describe the bands of the muscle sarcomere

A 
I- broad light bands 
A- dark bands, myosin
H- between actin 
Z disc to embed actin
M Disc to embed Myosin
18
Q

What are t tubules and where are they found on myocytes?

A

Sarcolemma extends into the myocytes
Surrounds myofibril at junction I and A bands
Allows for synchronous myofibril contraction
At points at which actin and myosin overlap

19
Q

How are disorders of the neuromuscular junction grouped?

A

Pre-synaptic e.g. Botulism

Post-synaptic e.g. Myasthenia Gravis

20
Q

What are Terminal Cisternae?

A

Flattened sacs from sarcoplasmic reticulum on either side of T tubules
Calcium ions are concentrated here
Release of calcium enables cross bridge formation of actin and myosin

21
Q

Describe the process of the conducting system for contractile stimuli in
skeletal muscle

A

Release of Ach at neuromuscular junction
Depolarisation of motor end plate
Spread via T Tubules, voltage sensor induces change in SR calcium release channel
Sarcoplasmic reticulum releases calcium, 10 fold increase
Activation of sliding filament mechanism
SERCA pump restores calcium

22
Q

Describe the sliding filament theory of muscle contraction

A

Myosin has side projections/heads with ATP (hydrolysis releases
energy necessary for cross bridging)
Side projections can bind to actin when activated
High intracellular Ca2+ binds troponin, exposing myosin binding site on actin by change in conformation of tropomyosin
Myosin binds actin and pulls towards the centre of the sarcomere
Need plentiful ATP or rigor sets in

23
Q

How can the force of muscle contraction be increased at a cellular level?

A

Recruitment of more motor units

Increasing frequency of action potentials

24
Q

What are sources of energy in skeletal muscle?

A

Small pools of ATP and generate more from Creatine phosphate pool (ADP to ATP), Glycogenolysis, Glucose from blood, Fatty acids: from blood or muscle (Beta Oxidation)
If energy demands outstrip oxidative phosphorylation then an OXYGEN DEBT is established in the muscle

25
Q

What are neurogenic muscle disorders?

A

Damage to muscle innervation leading to atrophy of the muscle
Main groups: Motor Neurone Disease, Spinal Muscular Atrophy, Peripheral Neuropathies, Miscellaneous

26
Q

Describe ALS

A

Amylotrophic Lateral Sclerosis
Various genetic abnormalities: SOD1
Reduced capacity to detoxify cells or misfolded proteins cause ER stress, which causes cell injury

27
Q

What happens when muscle fibres are re-innervated?

A

Loss of normal mosaic pattern and clumping of fibres types instead

28
Q

What are myopathies?

A 
Disease affecting muscle physiology, structure or biochemistry 
Muscular dystrophy
Inflammatory myopathy e.g. polymyositis
Congenital myopathy
Metabolic myopathy
Toxic myopathy
29
Q

What are muscular dystrophies?

A 
Progressive destruction of muscle fibres
Inefficient linkage proteins 
Abnormal muscle function 
Strain on plasma membrane  
Progressive damage 
Cell necrosis 
Duchenne: 1:3000-5000 male births, Abnormal dystrophin
30
Q

What can cause inflammatory myopathies?

A

Infection
Autoimmune e.g. Polymyositis (T cell mediated muscle cell injury, Symmetrical proximal weakness swelling) and Dermatomyositis

31
Q

What are metabolic myopathies?

A

Endocrine: Thyroid abnormalities, Cushings, Iatrogenic corticosteroid myopathy

32
Q

What can cause toxic myopathies?

A

Ethanol

Chloroquine

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