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Normal Physiology > Smooth Muscle > Flashcards

Smooth Muscle Flashcards

1
Q

Gap junction is present in skeletal muscle. True or false?

A

False, gap junction is present only in visceral smooth muscle, and it allows the impulses to travel to next cell.
While in SKM there’s no gap between the fibers and impulses can’t travel to next fiber.

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2
Q

Why there’s no need for T-system in smooth muscle?

A

T- system is not present in smooth muscle and that’s because the cells are small in size, the surface is enough to excite all the cell (no need for membrane invagination)

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3
Q

What do T-system do in SKM?

A

It transmit impulses deeper to the SKM fibers

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4
Q

Sacroplasmaptic reticulum in SM?

A

It’s very poorly developed. Some vesicles remain store ca+ in a minor quantity, but ca+ comes mostly from the extracellular space rather than stored in the cell itself. And it’s used for SM cell contraction

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5
Q

Contractile filaments in both SKM and SM

A

In both SKM and SM, actin, myosin and tropomyosin are present.
But troponin is only present in SKM fibers to keep actin and tropomyosin hold together.
While in SM we have ca+ binding proteins (calmoduling) which do the same function as troponin in SKM fiber.

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6
Q

What trigger contraction in SM?

A 
Electrical stimuli
Mechanical stimuli (stretch the SM)
Chemical stimuli (NT, hormones)
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7
Q

Speed of contraction in both SKM fibers and SM?

A

In SKM we can find fast motor unites and slow motor units (takes 10s to 100s)
While in SM its slower than the slowest contraction in SKM fibers (it takes up to minutes)

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8
Q

Relaxation differences between SKM and SM?

A

Fast relaxation in SKM due to ca+ pump has great activity, it pumps ca+ out from the cytoplasm into SPR very fast.
While slow relaxation in SM due to low ca+ pump activity, it pumps ca+ very slow .

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9
Q

Automaticity?

A

It’s present only in visceral SM cells. These cells can generate impulses itself and respond to it without any external stimuli.

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10
Q

Do SKM fibers have automticity?

A

No! Because they need stimulation from nerve endings to the skeletal Neuromuscular fiber.

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11
Q

The innervation of SM

A

Autonomic nervous system. It regulate the strength of SM contraction.
Since some SM have automaticity, the ANS can tell if the cell need stronger contraction or more frequent

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12
Q

Smooth muscle types?

A

Two types unitary (visceral) and multi-unitary (non-visceral)

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13
Q

Differences between unitary and multi-unitary SM

A 
In unitary there’s gap junction between the cells but no gap junction can be found in multi-unitary, each cell is a single unite and are isolated.
Only visceral (unitary) have automaticity 
All the cells in multi-unitary are innervated, while not every cell in unitary are innervated since they have automaticity.
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14
Q

Eye papillary and ciliary muscle are found in?

A

Multi-unitary SM

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15
Q

Gastro intestinal system, bronchii and tracheal muscle are found in?

A

Unitary SM

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16
Q

What is varicosity?

A

Its enlargement in the nerve fiber, and it function as presynaptic terminal in the synapse. And it includes vesicles and mitochondria

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17
Q

Smooth muscle have no?

A

Have no neuromuscular synapse

No sacromeres

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18
Q

What is the function of mitochondria in SM?

A

Generate energy for NT synthesis
Reuptake of NT
Restoration of normal membrane potential and Ca+ ions concentration

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19
Q

The process of and effect in SM

A

First impulses travels to cell membrane, it stimulate NT releasing from varicosities out in the same patterns in neuromuscular synapse: Ca+ influx, Ca+ binds to calomdulin and stimulate vesicles fusion with the varicosity membrane
Then NT released yo interstitial space, they diffuse into many SM cells, and NT binds to the corresponding receptor causing an effect

20
Q

neurotransmitters in SM are?

A

parasympathetic NT: ACH that bind to its receptor Muscarinic receptor
Sympathetic NT: Norepinephrine NE ( alfa receptors) and small amount of Epinephrine E (beta receptors)

21
Q

On what the response depends in SM cells?

A

On the number of receptors, because NT can choose different receptors, if alfa receptors are more in case of NE the response is excitation, but if beta receptors are more then the response will be relaxation

22
Q

Principal of contraction on SM cells

A

The actin is attached to dens bodies and myosin in between, they stretch in different direction.
And they have a great intensity of shortness more than in SKM fibers

23
Q

Triggers on smooth muscle contraction

A
  1. Electromechanical coupling: it open Ca+ voltage gated channel (dihydropiridine receptors gate) Ca+ influx, bund to Rynodine receptors in smooth EPR, Ca{ released causing contraction
24
Q

Triggers of SM contraction

A
  1. Pharmacomechanical coupling:
    Substances (NT, Hormones) bind to the receptors and cause mechanical action (contraction).
    They bind to G-protein and opem Ca+ ligand gated channel, and activite alfa substances that generate second messengers
25
Q

Triggers of SM contraction

A

Myogenic coupling:
By deformation of cell (stretching the cell)
Opens Ca+ deformation gated channel, lead to Ca+ influx, then Ca+ concrete increases

26
Q

What is the enzyme Myosin Light Chain Kinase?

A

It phospholerate light chain in myosin head and increase ATPase activity

27
Q

What is caldesmon and calpomin?

A

Caldesmon: is a Ca+ sensitive protein in SM and it hold tropomyosin over the active site on the actin filament (it function like Troponin T part)
Calpomin: is a Ca+ binding protein located on actin. When calmodulin complex binds to it, it causes inhibition of calponin which decreases the myosin ATPase activity so the myosin head can bind to actin

28
Q

Mechanism of relaxation

A

Ca+ is removed from the cell to the outside or back to storage place by 2 ways, either by
Ca+ pump, it pumps Ca+ out of the cell back to the EPR
Or Ca+/Na+ exchange transport, where Na+/K+ pumps Na+ out against its gradient, causing lower Na+ concentration intracellularly , and transport Ca+ out of the cell where the ca+ contraction decreases and inactive Ca+ CAM complex

29
Q

When Ca+ calmodulin complex breaks down

A

It puts back caldesmon and calponin back to their initial places on actin

30
Q

The process of reflex

A

1 receptor: it convert the energy of the stimuli to AP
2 afferent neuron: conduct impulses from the receptors to CNS
3 integreting center: include all the synapses in the CNS
4 efferent neuron: carries information from the CNS to effector
5 effector: it releases response to the previously applied stimuli

31
Q

Classification of reflex

A
  1. Due to organization
  2. Due yo level of realization
  3. Due to number of synapse in the reflex arch
  4. Due to elicited response
32
Q

Describe corneal reflex.

A
  • It’s somatic nervous system
  • The level of realisation is mesencephalic reflex
  • polysynaptic reflex
  • motor elicited response.
33
Q

Reflex time is ..

A

The time from onset of stimulus until the reflex response

34
Q

Factors that affects reflex time

A
  1. Number of synapses
  2. Velocity of conducting in nerve fiber in the reflex arch
  3. Strength of the stimuli
  4. Facilitation
  5. Inhibition
  6. Fatigue
35
Q

What are proprioreceptors?

A

They are locomotor system receptors which sen signals to the brain about location of every part of the body and the changes on it’s location
There are two main proprioreceptors :
Muscle spindle and Golgi tendon

36
Q

Describe muscle spindle

A

It’s located in SKM belly and it sense muscle stretch and its changes
It consist of Intrafusal fibers, that have myosin and actin filaments on their distal part,
And it consist also of Extrafusal part, they’re innervatedby A alfa fibers and triggers contraction. They have actin and myosin filaments all along thr longitudinal axis

37
Q

Muscle spindle afferent fibers

A

Afferent fibers has:

  1. Primary nerve fibers Ia: it begins from central part of both intrafusal fibers, it’s sensitive to fast stretch and it’s monosynaptic
  2. Secondary nerve fibers II: it’s located in flower spread ending and begin from nuclear chain fiber. It’s sensitive to slow stretch and it’s polysynaptic
38
Q

Muscle spindle efferent fibers

A

It begins from AY- nerve fibers, from
Y-motor neurons in the CNS.
It’s sensitive to stretch so incase it’s activated it will cause stretch for the muscle and in case inactivated the muscle will become loose.

39
Q

Phasic stretch reflex

A 
It’s triggered by fast stretching 
Start from muscle spindle
Has Ia fibers (primary nerve fibers)
Monosynaptic reflex, it synapse in only one segment of the spinal cord
Has shorter reflex time
The effector is A alfa 
And it has strong stimuli
40
Q

Tonic stretch reflex

A 
Triggered by slow stretching
The receptor is muscle spindle
Has secondary nerve fibers (II)
Its polysynaptic reflex, it synapse in multiple segments of the spinal cord
The effector is A alfa
Has longer reflex time
Weak stimuli
41
Q

What is Golgi tendon?

A

It’s a proprioreceptor, located inside the muscle tendon and it senses tension of muscle and it’s changes.
- it’s made of Ib sensory fibers
It need high threshold to be activated.

42
Q

What is the neuronal pathway which decreases activity in muscle antagonists?

A

Inhibitory neurone to inhibit the antagonist muscle

43
Q

Example on innervation if antagonists

A

If we wish to extend the arm, the the flexor should be inhibited and extensor are activated

44
Q

Activation of MLCK lead to

A

Activation and not relaxation

45
Q

Regulatory proteins in SM

A

Calmodulin
Calponin
Caldesmon

Normal Physiology (2 decks)

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