MD2002- Skeletal and Cardiac Muscle Flashcards

1
Q

What are the three classifications of muscle?

A

Skeletal, smooth and cardiac

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2
Q

What are the characteristics of skeletal muscle fibre?

A

Multinucleated

Contains mitochondria

Has transverse tubules

Has myofibrils and sarcomeres

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3
Q

In skeletal muscle fibres what do each of these three terms refer to;

Sarcolemma
Sarcoplasm
Sarcoplasmic Reticulum

A

Plasma Membrane
Cytoplasm
Smooth ER

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4
Q

Describe the structure of skeletal muscles

A

Voluntary, striated
Attached to bone
Interaction of the body with the external environment

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5
Q

What are myofibrils?

A

The structure that give skeletal and cardiac muscle their characteristic striated appearance

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6
Q

How are striations formed?

A

Results from the orderly arrangements of thick and thin filaments

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7
Q

What three things are cardiac muscles dependent on?

A

Intrinsic properties
Hormones
Autonomic nervous system

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8
Q

What are the characteristics of cardiac muscles?

A

Have one or two nuclei, located centrally

Striated

Are branching cells with intercalated discs with desmosomes and gap junctions

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9
Q

What is the function of nodal cells?

A

To stimulate their own action potentials

Called automaticity or auto-rhythmicity

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10
Q

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

A

250ms

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

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11
Q

What are intercalated discs?

A

A mechanical connection between adjacent cardiac muscle cells (structural)

Electrical connection between adjacent cardiac muscle cells (functional)

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12
Q

Describe the structure of gap junctions?

A

Constructed from a hexagonal array of protein subunits- connexins

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13
Q

What are gap junctions the site of?

A

Low electrical resistance

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14
Q

What is the function of gap junctions?

A

Act as a communicating channel- connexon

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15
Q

Where are skeletal muscles innervated from?

A

Primary motor complex in the brain synapse on the motor neuron (located in the grey matter of the ventral horn)

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16
Q

What is a motor unit?

A

Defined at the motor neuron and the skeletal muscle fibres it innervates

17
Q

What is the only way to stimulate a skeletal muscle?

A

By stimulating the nerve fibres which connect to it

18
Q

What are the axons which stimulate skeletal muscles called?

A

Motor or somatic efferent neurons

19
Q

Where are motor neurons located?

A

Either the brainstem or the spinal cord

20
Q

What characteristics of motor neurons allow minimal delay when stimulating skeletal muscle fibres?

A

They are myelinated

Largest diameter

Propagate action potentials at high velocities

21
Q

What enzymatically degrades ACh?

A

Acetylcholinesterase

22
Q

What is myasthenia gravis?

A

An auto-immune disease

Muscle weakness that increases during periods of activity and improves after periods of rest

Paralysis of respiratory muscle

Eye and eyelid movement, facial expression, mouth movements especially susceptible

23
Q

What causes myasthenia gravis?

A

Production of antibodies

Directed against the ACh receptor (nicotinic)

Some impair the ability of ACh to bind

Some lead to destruction of receptors

24
Q

Explain myositis

A

Inflammation

25
Q

Explain muscular dystrophy

A

Inherited disorders with progressive weakness

26
Q

Explain myasthaenia

A

Fatigueable weakness (worse on exercise)

27
Q

Explain myotonia

A

Sustained contraction/slow relaxation

28
Q

Explain channelopathy

A

Ion channel disorders

29
Q

Explain metabolic myopathies

A

Metabolic/enzyme defects