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Neuro > Histology of nerve and muscle > Flashcards

Histology of nerve and muscle Flashcards

1
Q

What are the three types of muscle

A
  1. ) Skeletal
  2. ) Smooth
  3. ) Cardiac
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2
Q

Skeletal muscle

A
  • Myofibres are arranged in fascicles
  • Connective tissue made up of:
    1. ) Epimysium
    2. ) Perimysium
    3. ) Endomysium
  • Rich vascular supply
  • Innervation: efferents and afferents
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3
Q

Skeletal muscle: innervation

A
  • Wach fibre is innervated by one nerve with cell bodies in the anterior horn of spinal cord/brainstem
  • One neuron innverates multiple muscle fibres: motor unit
  • Neuromuscular junction: synapse and acetyl choline
  • Proprioception: length/tension/rates of contraction fo muscle
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4
Q

Muscle fibre types

A
  1. ) Slow twitch (red fibres)

2. ) Fast twitch

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5
Q

Details of slow twitch fibres

A
  • Type 1
  • Oxidative
  • Fatigue resistant
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6
Q

Details of fast twitch fibres

A
  • Fatigue rapidly
  • Generate a large peak of muscle tension
  • 2A: glycolytic + oxidative
  • 2B: glycolytic (white)
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7
Q

Skeletal muscle histology

A
  • Can be studied by muscle biopsy
  • Requires use of frozen sections and good orientation
  • EM
  • Molecular tests
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8
Q

Enzyme histochemistry

A
  • method to look at activity of an enzyme in a tissue

- Will develop a colour substrate from the reaction that takes place

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9
Q

Motor units

A
  • lower motor neurons and the fibres it innervates
  • neurone + its fibres of same type
  • fibre type dependent on neuron
  • size varies: smaller muscles for hands need finer coordination so needs a smaller motor unit
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10
Q

How are motor units altered in denervating diseases

A
  1. ) Loss of innervation causes fibre atrophy
  2. ) Collateral sprouting from adjacent motor units allows reinnervation
  3. ) Larger motor units result: can be detected electro physiologically
  4. ) Conversion of fibres in fibre type grouping
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11
Q

Organisation of myofibrils

A

There are repeating assemblies of thick and thin filaments

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12
Q

What are the types of thick and thin filaments?

A

Thin filaments

  1. ) Actin
  2. ) Troponin
  3. ) Tropomyosin

Thick filaments:
1.) Myosin

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13
Q

What are the requirements for energy?

A
  • High energy requirement from ATP
  • Creatine phosphate: a short term energy store
  • CP replenished by creatine kinase
  • CK is released on muscle fibre damage
  • Measurement of serum CK: clinically useful
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14
Q

What are mitochondrial cytopathies

A
  • Disorders due to mutations of mitochondrial genes
  • Mitochondrial mutations: maternal inheritance
  • Brain is often affected
  • E.g. MERRF/MELAS/CPE
  • Heteroplasmy
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15
Q

How can mitochondrial diseases be diagnosed?

A

By muscle biopsy

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16
Q

How can mitochondrial diseases be diagnosed?

A
  • By muscle biopsy
  • Ragged red fibres
  • Electron transport chain defects: cytochrome oxidase negative fibres
  • Abnormal mitochondrial morphology
17
Q

Membrane structure

A
  • Has dystroglycans in the extracellular space

- In the intracellular space: sarcoglycans/dystrophin/actin

18
Q

Dystrophies + defects of sarcolemmal related proteins

A
  • They are genetically determines
  • Destructive + progressive disorders
  • Affect muscle
  • Defects of proteins that confer stability to the sarcolemma are one group of causes
19
Q

Dystrophin

A
  • A large protein encoded by a 2.4 million bp on Xp21
  • Confers stability to the muscle cell membrane
  • Deletion resulting in disruption of the reading frame
20
Q

Neuromuscular transmission features

A
  • Nerve impulse results in the release of ACh from synaptic vesicles
  • ACh binds to receptor
  • Cation entry results in depolarisation (end-plate potential)
  • An action potential travels across the muscle cell membrane + into the T-tubule system
  • Calcium is released from the sarcoplasmic reticulum (leading to contravtion)
  • Dissociated ACh is hydrolysed by acetyl cholinesterase in the NMJ
21
Q

What are disorders of neuromuscular transmission

A
  1. ) Myasthenia gravis
  2. ) Autoimmune disease
  3. ) Anti-AChR antibodies (reduction in ACh receptors)
  4. ) Acetyl cholinesterase inhibitors can improve muscle function
22
Q

Basic histology of peripheral nerves

A
  • Have perineurium

- Have epineurium

23
Q

Myelinated fibres

A
  • PNS: schwann cell is responsible for the myelin sheath
  • They are neural crest derived cells
  • Schwann cell: one is responsible for one segment of myelin
  • Nodes of Ranvier: where depolarisation of the membrane occurs. The nodes lie between adjacent myelin segments
  • ## Myelination allows saltatory conduction
24
Q

What are peripheral neuropathies?

A
  • Damage to motor/sensory neurons (neuronopathies)
  • Damage to axons (axonopathies)
  • Selective damage to myelin sheaths (demyelination)
25
Q

Axonial degeneration

A
  • Injury to axon: distal fragmentation
  • Globules of myelin + axon are taken up by the schwann cells
    Reinnervation is attempted: axonal sprouts form from proximal part of damaged axon
  • Regenerated axons can remyelinate
26
Q

What is demyelination

A
  • Injuries primarily to schwann cell

Neuro (33 decks)

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