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MD2002 > Skeletal and Cardiac Muscle > Flashcards

Skeletal and Cardiac Muscle Flashcards

1
Q

What are the 3 muscle tissue types?

A

+ Skeletal
+ Smooth
+ Cardiac

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2
Q

What is skeletal muscle also known as?

A

Voluntary muscle; striated muscle

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3
Q

What are the 5 characteristics of skeletal muscle cells/fibres?

A
  1. Multinucleated
  2. Contains many mitochondria
  3. Transverse (T) tubules
  4. Myofibrils and sarcomeres
  5. Specific names for some of the intracellular structures
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4
Q

In a skeletal muscle cell/fibre, what is the sarcolemma?

A

Plasma membrane

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5
Q

In a skeletal muscle cell/fibre, what is the sarcoplasm?

A

Cytoplasm

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6
Q

In a skeletal muscle cell/fibre, what is the sarcoplasmic reticulum?

A

Smooth ER

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7
Q

What are features of skeletal muscle?

A

+ Voluntary, striated
+ Attached to bone
+ Under voluntary control
+ Involved in interaction of the body with external environment

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8
Q

What are myofibrils?

A

The structures that give skeletal (and cardiac muscle) their characteristic striated appearance

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9
Q

What are striations a result of?

A

The orderly arrangements of thick and thin filaments

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10
Q

What are the structural features of cardiac muscle?

A

+ Striations
+ Muscle fibres
+ Intercalated discs
+ Nucleus

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11
Q

What are features of cardiac muscle?

A

+ Structurally like skeletal muscle

+ Functionally like smooth muscle

+ Activity dependent upon:

  • intrinsic properties
  • hormones
  • ANS
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12
Q

How many nuclei do cardiac muscle cells have?

A

One to two nuclei, centrally located

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13
Q

What mechanism does cardiac muscle use to contract?

A

The sliding filament mechanism, as it is striated

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14
Q

Cardiac muscle is made up of branching cells with what other structures?

A

INTERCALATED DISCS with desmosomes and GAP JUNCTIONS

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15
Q

What are gap junctions critical to in cardiac muscle?

A

The heart’s ability to be electrically coupled

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16
Q

What ability do nodal cells have?

A

The ability to stimulate their own actions potentials - called automaticity or auto-rhythmicity

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17
Q

What is the absolute refractory period of cardiac muscle (cells)?

A

250ms

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18
Q

What is the purpose of a refractory period?

A

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

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19
Q

What is the structural relevance of intercalated discs in cardiac muscle?

A

Provides a mechanical connection between adjacent cardiac muscle cells

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20
Q

What is the functional relevance of intercalated discs in cardiac muscle?

A

Provides an electrical connection between adjacent cardiac muscle cells

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21
Q

What are features of gap junctions?

A

+ Constructed from a hexagonal array of protein subunits - connexins

+ Sites of low electrical resistance between cells

+ Act as communicating channels - connexon

22
Q

What is the diameter of the central pore in a gap junction?

A

1.5 nm

23
Q

What size of molecules can pass through the central pore in a gap junction?

A

Small molecules (<500 MW) pass through

24
Q

How does skeletal muscle become activated?

A

Neurons from the primary motor cortex in the brain synapse on the motor neuron, which projects to the periphery and activates the skeletal muscle

25
Q

Where is the motor neuron located?

A

In the grey matter of the ventral horn

26
Q

What makes up a motor unit?

A

Axon and muscle fibres

27
Q

What is a motor unit defined as?

A

The motor neuron and the skeletal muscle fibres it innervates

28
Q

What is the link between motor neurons and muscle fibres?

A

One motor neuron innervates many muscle fibres, but one muscle fibre is innervated by only one motor neuron

29
Q

What is the only mechanism by which action potentials are initiated in skeletal muscle?

A

By stimulation of the nerve fibres to a skeletal muscle

30
Q

What are motor neurons also known as?

A

Somatic efferent neurons

31
Q

What are some physical features of axons of motor neurons?

A

+ Myelinated

+ Largest-diameter axons in the body

32
Q

Axons of motor neurons propagate action potentials at high velocities - what does this then allow?

A

Signals from the CNS to travel to skeletal muscle fibres with minimal delay

33
Q

What do axon terminals of a motor neuron contain?

A

Vesicles similar to the vesicles found at synaptic junctions between two neurons

34
Q

What do the vesicles found at the axon terminals contain?

A

Neurotransmitter - acetylcholine (ACh)

35
Q

What region is known as the motor end plate?

A

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

36
Q

What is the neuromuscular junction?

A

The junction of an axon terminal with the motor end plate

37
Q

Once ACh is released into the synaptic cleft, where does it go?

A

Ach is rapidly degraded enzymatically by the action of acetylcholinesterase

38
Q

What is the role of the nicotinic cholinergic receptor?

A

It binds (to) two ACh molecules, opening a nonspecific monovalent cation channel

39
Q

What does the open nonspecific monovalent cation channel allow to pass?

A

Na+ and K+

40
Q

What happens to acetylcholine (ACh)?

A
  1. Combines with nicotinic receptors

OR

  1. Metabolised by acetylcholinesterase (AChE)
41
Q

What do action potentials arriving at the axon terminal do?

A

Open gated Ca2+ channels

42
Q

What is myasthenia gravis?

A

An autoimmune disease that causes muscle weakness that increases during periods of activity and improves after periods of rest

43
Q

What actions are especially susceptible in myasthenia gravis?

A 
\+ Eye and eyelid movement
\+ Facial expression
\+ Chewing
\+ Talking
\+ Swallowing
\+ respiration
44
Q

How can myasthenia gravis affect the respiratory muscles?

A

Can cause paralysis of them

45
Q

What is the result of the production of auto-antibodies?

A

+ Most commonly directed against NACh receptors
+ Some impair the ability of ACh to bind to receptors
+ Some lead to the destruction of receptors

46
Q

What are some different types of muscle myopathies?

A 
\+ Myositis
\+ Muscular dystrophy
\+ Myasthenia
\+ Myotonia
\+ Channelopathy
\+ Metabolic myopathies
47
Q

What is myositis?

A

Inflammation

48
Q

What is muscular dystrophy?

A

Inherited disorders with progressive weakness

49
Q

What is myasthenia?

A

Fatiguable weakness (worse on exercise)

50
Q

What is myotonia?

A

Sustained contraction/slow relaxation

51
Q

What is channelopathy?

A

Ion channel disorders

52
Q

What are metabolic myopathies?

A

Metabolic/enzyme defects

MD2002 (85 decks)

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