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MD2002 > Cardiac and Skeletal Muscle > Flashcards

Cardiac and Skeletal Muscle Flashcards

1
Q

What are the main three types of muscle ?

A

Cardiac, smooth, skeletal

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2
Q

Is skeletal muscle voluntary/involuntary ? Striated/non-striated ?

A

Voluntary

Striated

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3
Q

What are the defining characteristics of skeletal muscle cell ?

A
  • Multinucleated
  • Striated
  • Many mitochondria
  • Transverse Tubules (T Tubules)
  • Myofibrils & sarcomeres
  • Intracellular structures: Sarcolemma (=plasma membrane), sarcoplasm (= cytoplasm), sarcoplasmic reticulum (= smooth ER)
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4
Q

Is skeletal muscle attached to bone ?

A

Yes

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5
Q

What structures give skeletal muscle its characteristic striated appearance ?

A

Myofibrils (due to the orderly arrangements of thick and thin filaments)

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6
Q

Which kind of muscle is cardiac muscle most similar to structurally ? Functionally ?

A

Skeletal

Smooth

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7
Q

What is the activity of cardiac muscle dependant upon ?

A
  • Intrinsic properties
  • Hormones
  • Autonomic nervous system
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8
Q

What are the defining characteristics of cardiac muscle cell ?

A
  • One to two nuclei, centrally located
  • Striated
  • branching cells with intercalated discs with desmosomes and gap junctions
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9
Q

Which kind of mechanism do cardiac muscle cells use to contract ?

A

Sliding filament mechanism

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10
Q

What are nodal cells ?

A

Cardiac muscle cells which have the ability to stimulate their own action potentials. Called automaticity or auto-rhythmicity.

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11
Q

What is the absolute refractory period of cardiac muscle cells ? Why is it necessary ?

A

About 250ms

Because it prevents tetanic contractions which would interfere with the heart’s ability to pump.

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12
Q

What are intercalated discs ?

A

Mechanical and electrical connection between adjacent cardiac muscle cells

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13
Q

What are the subunits of gap junctions ?

A

6 connexins acting as a channel called a connexon

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14
Q

What is the electrical significance of gap junctions ?

A

They are sites of low electrical resistance between cells

Critical to the heart’s ability to be electrically coupled.

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15
Q

Where do the neurons which synapse on the motor neuron, in the grey matter of the ventral horn, originate from ? Where does the motor neuron then project/what does it do ?

A

From the primary motor cortex in the brain

Projects to the periphery and activates skeletal muscle

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16
Q

What is a motor unit defined as ?

A

Motor neuron + the skeletal muscle fibers it innervates

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17
Q

Can a motor neuron innervate more than one muscle fibre ? Can a muscle fibre be innervated by more than one motor neuron ?

A

Yes

No

18
Q

Within one muscle, do you find one, a few, or many motor units ?

A

Many

19
Q

Give an example of an action using muscles relying on motor units with relatively few fibres, and an action using muscles relying on motor units with more fibres.

A

Typing (fine motor movement in general)

Actions using legs

20
Q

How many branches of motor neurons innervate a muscle fibre ?

A

Just one branch of motor neuron per muscle fibre

21
Q

What is the overall mechanism by which action potential is initiatied in skeletal muscle ?

A

Stimulation of the nerve fibres to a skeletal muscle

22
Q

What is the name of the nerve cells whose axons innervate skeletal muscle fibres ? Where are the cells of those nerve cells located ?

A

Motor neurons or somatic efferent neurons

In either the brainstem or spinal cord

23
Q

What is the myelination/diameter status of the axons of motor neurons ?
What is the effect of this on velocity of action potential propagation ?

A

Myelinated, and largest-diameter axons in the body

Propagate action potentials at high velocities

24
Q

Do the axon terminals of a motor neuron contain vesicles similar, or different, to the vesicles found at synaptic junctions between two neurons ?

A

Similar

25
Q

What neurotransmitter do the vesicles in the axon terminals of motor neurons contain ?

A

Acetylcholine

26
Q

What is the name of the region of the muscle fibre plasma membrane that lies directly under the terminal portion of the axon ?

A

Motor end plate

27
Q

What is the name of the junction of an axon terminal with the motor end plate ?

A

Neuromuscular junction

28
Q

What does the neuromuscular junction consist of ?

A

Axon terminals, motor end plates on the muscle membrane

29
Q

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

A

ACh is rapidly degraded enzyma,cally by the ac,on of acetylcholinesterase

30
Q

What kind of receptor binds ACh ?

A

Nicotinic cholinergic receptor (chemically gated ion channels)

31
Q

How many molecules of ACh does the nicotinic cholinergic receptor bind at once ?

A

Two

32
Q

What is the opening mechanism of nicotinic cholinergic receptor for ACh ?

A

Binds two ACh molecules, which opens a non-specific monovalent cation channel, which allows Na+ to get into end plate region and K+ to leave end plate region.

33
Q

What are all the events occurring at the motor end plate ?

A
  1. Action potentials arriving at the axon terminal open voltage gated Ca2+ channels
  2. Inward diffusion of Ca2+
  3. Fusion of acetylcholine-containing vesicles (ACh) with the pre-synaptic membrane
  4. ACh diffusion across the 20 nm synaptic cleft
  5. Nicotinic Ach receptors (nAChR) permit monovalent cations to flow through
  6. Net entry of Na+ into end plate region causes depolarisation - end plate potential (epp)
  7. Action potential triggered in muscle fibre membrane
  8. ACh degradation by acetylcholinesterase
34
Q

What is Myasthenia gravis ? What are its symptoms ?

A

An autoimmune disease

Symptoms:

  • muscle weakness that increases during periods of ac,vity and improves aher periods of rest
  • eye and eyelid movement, facial expression, chewing, talking, and swallowing are especially suscep,ble
  • paralysis of the respiratory muscles
35
Q

What is the cause of myasthenia gravis ?

A

Production of auto-antibodies
• most commonly directed against the acetylcholine receptor (nicotinic)
• some impair the ability of acetylcholine to bind to receptors whilst some lead to the destruction of receptors

36
Q

What is myostisis ?

A

Inflammation in muscle(s)

37
Q

What is muscular dystrophy ?

A

Inherited disorders with progressive weakness

38
Q

What is myasthenia ?

A

Fatigueable weakness (worse on exercise)

39
Q

What is myotonia ?

A

Sustained contraction/slow relaxation

40
Q

What is channelopathy ?

A

Ion channel disorders

41
Q

What is metabolic myopathies ?

A

Metabolic/enzyme defects causing muscle disorders

MD2002 (77 decks)

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