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Nerve & Muscle > Cardiac & Smooth Muscle Pt. 2 > Flashcards

Cardiac & Smooth Muscle Pt. 2 Flashcards

1
Q

What causes the rising phase of the action potential during SA node depolarisation?

A

Calcium influx opposed to sodium

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2
Q

How does the resting membrane potential of the SA node differ?

A

It does not have a stable resting membrane potential

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3
Q

How is the pacemaker potential of the SA node shown?

A

The pacemaker potential is a slow depolarisation

There is a gradual depolarisation from -60 mV

This is due to the slow influx of calcium and reduced K+ permeability

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4
Q

When does an action potential occur?

A

At the threshold value of -40 mV

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5
Q

During SA node depolarisation, when and why does the depolarising phase occur?

A

It occurs from -40 - 0 mV

This is due to the opening of Ca2+ channels and rapid calcium influx

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6
Q

During SA node depolarisation, when and why does the repolarising phase occur?

A

This occurs when the Ca2+ channels close and the K+ channels open

K+ leaves the cell

The channels close at -60mV allowing the pacemaker potential to start over again

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7
Q

Why is the resting membrane potential of the SA node not stable?

A

This is due to the slow influx of calcium

At the threshold, Ca2+ channels will open and rapid depolarisation will occur leading to a cardiac action potential

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8
Q

What is the Frank-Starling law of the heart?

A

The resting length of cardiac muscle is set below its optimal level

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9
Q

Why is having sub-optimal overlap in cardiac muscle beneficial?

A

It gives cardiac muscle the ability to adjust the force of contraction

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10
Q

What happens to the myosin-actin overlap when cardiac muscle cells are stretched?

A

It increases the degree of overlap

This increases the force generated when the cells contract

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11
Q

Where is smooth muscle found?

A

It lines the walls of most hollow organs

This includes vascular, gastrointestinal, respiratory, urinary and reproductive systems

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12
Q

Why is smooth muscle an important therapeutic target?

A

It regulates variables such as blood flow, gastrointestinal motility and ventilation of the lungs

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13
Q

What happens to smooth muscle during septic shock?

A

Inadequate tone

Infection releases inflammatory mediators that cause dilation of systemic blood vessels

This leads to severe hypotension

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14
Q

How does the structure of smooth muscle allow for peristalsis?

A

It has an inner circular layer and outer longitudinal layer

Alternating contraction and relaxation of the 2 layers mixes substances in the lumen of hollow organs

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15
Q

What is the diameter and length of a smooth muscle cell?

A

2 - 10 micrometers diameter

40-600 micrometers length

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16
Q

Why is smooth muscle not striated?

A

Cells have more actin than myosin

The thick and thin filaments are not well organised

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17
Q

Do smooth muscle cells have T-tubules?

A

No but they have caveolae

Small indentations in the sarcolemma that may act like t-tubules

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18
Q

What does a smooth muscle cell look like?

A

It is not branched

It is an individual spindle-shaped cell with a central nucleus

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19
Q

Why does smooth muscle rely on external sources of calcium?

A

The sarcoplasmic reticulum is poorly developed

They have a poor internal calcium store

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20
Q

What two components of skeletal muscle does smooth muscle lack?

A

troponin and sarcomeres

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21
Q

In smooth muscle, where is actin and myosin anchored?

What is the motion of contraction and why?

A

Anchored to dense bodies

Actin and myosin filaments appear to spiral down the long axis of the cell

The cell contracts in a corkscrew like way

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22
Q

Is smooth muscle autorhythmic?

A

Some of it but not all of it

23
Q

What does smooth muscle contraction depend on and how is it regulated?

A

It depends on an increase in cytosolic Ca2+

It is regulated by myosin molecules of the thick filament, rather than the thin filament

24
Q

What happens in smooth muscle contraction after an increase in cytosolic Ca2+?

A

Ca2+ binds to calmodulin

Calmodulin interacts with myosin kinase to phosphorylate myosin

25
Q

Why must myosin be phosphorylated in smooth muscle contraction?

A

Once it is phosphorylated, the myosin can attach to the actin filament and form a cross-bridge

It can generate tension in a similar way to skeletal muscle

26
Q

What happens in smooth muscle contraction when cytoplasmic Ca2+ falls?

A

Ca2+-calmodulin complex dissociates

This inactivates myosin kinase

27
Q

How are the cross-bridges dephosphorylated?

A

After cytosolic Ca2+ falls, myosin phosphatase will dephosphorylate the cross-bridges

28
Q

How can smooth muscle maintain force over long periods of time?

What is the benefit to this method?

A

Cross-bridge cycling occurs more slowly in smooth muscle

Contraction occurs more slowly

The duration of contraction in response to a stimulus is long

Reduced ATP consumption

29
Q

Why is cross-bridge cycling much slower in smooth muscle?

A
  1. Smooth muscle myosin has a slow ATPase rate

It takes a long time for each cross-bridge to detach from the actin filament

  1. rate of Ca2+ removal from the cytoplasm is slow

this prolongs the duration of contraction

30
Q

How does nervous input differ in skeletal and smooth muscle?

A

Skeletal muscle cells receive input from only one nerve

Smooth muscle cells may receive inputs from more than one nerve

31
Q

What is meant by single-unit smooth muscle?

A

It contains gap junctions allowing it to act as a single unit

32
Q

Where is single-unit smooth muscle found?

A

Gastrointestinal, respiratory, urinary and reproductive tracts

In the walls of small arteries

33
Q

How is single-unit smooth muscle regulated?

How does electrical activity arise?

A

It is regulated by the autonomic nervous system

Electrical activity may arise spontaneously due to the presence of pacemaker cells

34
Q

What is meant by the myogenic response in single-unit smooth muscle?

A

It will contract in response to a stretch

35
Q

What is meant by multi-unit smooth muscle?

A

It lacks gap junctions so each cell is innervated individually

It allows for fine control

36
Q

Where is multi-unit smooth muscle found?

A

It allows for fine control so is found in ciliary muscle of the eye which controls pupil size

Piloerector muscles of hair follicles

37
Q

How is multi-unit smooth muscle innervated?

How is it different from single-unit?

A

It is innervated by the autonomic nervous system

There is no inherent response to stretch

It is not spontaneously active

38
Q

What are varicosities?

A

Autonomic nerves make multiple contacts with the cell

Each contact is a varicosity

39
Q

Why do autonomic nerves have no specialised post-junctional membrane?

A

Receptors are spread across the membrane

40
Q

What is dilated cardiomyopathy?

A

The heart enlarges as the ventricles become dilated

Function is impaired due to the enlarged ventricle

41
Q

How does dilated cardiomyopathy affect the lungs?

A

Muscles become weak and inefficient leading to a build up of fluid in the lungs

This is caused by left heart failure

Causes breathlessness

42
Q

What does right heart failure lead to?

A

Fluid build up in tissues and organs

43
Q

What is the prognosis for dilated cardiomyopathy?

A

Poor

50-60% of patients will survive more than 2 years

44
Q

What are the symptoms of dilated cardiomyopathy?

A

Shortness of breath, swelling of the ankles, tiredness, palpitations and chest pain

45
Q

what can cause dilated cardiomyopathy?

A

viral infection, autoimmune disease, excessive alcohol consumption or exposure to toxic compounds, pregnancy or familial disease

46
Q

What is hypertrophic cardiomyopathy?

A

A disease of the myocardium where a portion of the myocardium thickens with no obvious cause

47
Q

What are the symptoms of hypertrophic cardiomyopathy?

Which age group does it usually affect?

A

Usually asymptomatic

Symptoms can include shortness of breath, chest pain, palpitation, light-headedness and blackouts

Usually affects young people who are physically active

48
Q

What causes thickening of the tissue in hypertrophic cardiomyopathy?

A

Myocardial disarray

The normal alignment of muscle cells is absent

49
Q

What causes hypertrophic cardiomyopathy?

A

genetic mutation of important proteins needed for contraction of the heart

50
Q

What is leiomyoma (fibroids)?

A

benign growth of the female reproductive tract

it is a smooth muscle disorder

51
Q

How do fibroids usually present themselves?

A

Usually multiple growths with a diameter of 5mm or greater

52
Q

When are fibroids more prevalent and what are the symptoms?

A

More prevalent when the female is approaching the menopause

Cause heavy uterine bleeding and/or pain

53
Q

What is the cause of leiomyoma?

How many women experience symptoms?

A

Cause is unknown but is more common in the Afro-Caribbean race

20-50% of women are symptomatic

Nerve & Muscle (5 decks)

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