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Semester 2 Molecular Medicine > Skeletal and cardiac muscle > Flashcards

Skeletal and cardiac muscle Flashcards

1
Q

What are the characteristics of skeletal muscle?

A
  • Multinucleated
  • Striated - sarcomeres
  • Voluntary control
  • Attached to bone
  • Many mitochondria
  • T tubules
  • Specific terms: Sarcolemma (membrane), Sarcoplasm (cytoplasm), sarcoplasmic reticulum
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2
Q

What makes up a sarcomere?

A

From Z line to Z line

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3
Q

What is a myofibril?

A

Lots of sarcomeres

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4
Q

What is the activity of cardiac muscle dependent on?

A
  • Autonomic nervous system
  • Hormones
  • Intrinsic properties
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5
Q

What are the characteristics of cardiac muscle?

A
  • One to two nuclei per cell
  • Striated appearance
  • Intercalated discs with gap junctions and desmosomes
  • Nodal cells
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6
Q

What is the absolute refractory period of cardiac muscle and what is the significance of this?

A

250ms

• Prevents tetanic contractions which would interfere with the heart’s ability to pump

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7
Q

What is the structural function of intercalated discs?

A

To provide a mechanical connection between adjacent cells

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8
Q

What is the functional use of intercalated discs?

A

To allow electrical connection between adjacent cardiac muscle cells

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9
Q

Describe the structure of a gap junction

A
  • Formed from an array of 6 hexagonal protein subunits called connexins
  • Connexon formed which can act as a communicating channel
  • Central pore approx 1.5nm in diameter
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10
Q

Describe the characteristics of a gap junction

A
  • Communicating channel
  • Allows small molecules of less than 500MW to pass through
  • Site of low electrical resistance
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11
Q

What is a motor unit?

A

The motor neurone and the muscle fibre it innervates

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12
Q

What determines the number of muscle fibres innervated?

A
  • The muscle and its movements/actions

* e.g. fine motor control requires less motor units with relatively few fibres in comparison to the leg muscle

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13
Q

Which type of neurone innervate skeletal muscles? Describe their properties

A

Somatic efferent neurones
• Cell bodies in the spinal cord or in the brain stem
• Myelinated axons with the largest diameter axons in the body
• Propagate action potentials at high velocities

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14
Q

What is the motor end plate?

A

The plasma membrane of the muscle fibre directly under the terminal portion of the axon

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15
Q

What neurotransmitter is used in the neuromuscular junction?

A

Acetylcholine

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16
Q

What is acetylcholine degraded by?

A

Acetylcholinesterase

17
Q

Describe and name the receptor on the motor end plate

A
  • Nicotinic acetylcholine receptor
  • 2 binding sites for ACh
  • Monovalent non specific cation channel
  • Allows Na+ and K+ to pass
18
Q

Give a summary of the events at the motor end plate

A
  1. Action potential arrives at the terminal end of the axons, causing voltage gated calcium channels to open
  2. Influx of Ca2+ into the axon terminal
  3. ACh containing vesicles move and fuse to the pre-synaptic membrane
  4. ACh diffuses across the 20nm synaptic cleft
  5. 2 ACh bind to the nicotinic acetylcholine receptors
  6. Net entry of Na+ into the end plate causing depolarisation: end plate potential
  7. Action potential is triggered in the muscle fibre membrane.
19
Q

What is myasthenia Gravis?

A

An autoimmune disease causing muscle weakness that increases in times of activity and improves over periods of rest

20
Q

What are the causes of myasthenia gravis

A

• Production of autoimmune bodies against the acetylcholine receptor, either:

  • impair the ability of the acetylcholine to bind to the receptor
  • Leads to the destruction of the receptor
21
Q

What is a muscle myopathy?

A

Neuromuscular disorders in which the primary symptom is muscle weakness due to the dysfunction of the muscle fibre

22
Q

Give 6 muscle myopathies

A
  1. Myositis
  2. Muscular dystrophy
  3. Myasthaenia
  4. Myotonia
  5. Channelopathy
  6. Metabolic myopathy
23
Q

Myositis

A

Inflammation

24
Q

Muscular dystrophy

A

Inherited disorders with progressive weakness

25
Q

Myasthaenia

A

Fatigueable weakness (worse on exercise)

26
Q

Myotonia

A

Sustained contraction/ Slow relaxation

27
Q

Channelopathy

A

Ion channel disorder

28
Q

Metabolic myopathy

A

Metabolic/ enzyme defects

Semester 2 Molecular Medicine (27 decks)

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