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Physiology > Muscles > Flashcards

Muscles Flashcards

1
Q

What are the types of muscle

A

Skeletal

Cardiac

Smooth

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2
Q

How is muscle classified

A

Striated or not

Voluntary or not

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3
Q

Classify skeletal muscle

A

Multinucleated
Striated
Long stacked in parallel

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4
Q

Classify cardiac muscle

A

Uninucleated
Striated
Stacked end to end intercalated disk

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5
Q

Classify smooth muscle

A

Uninucleated
Not striated
Sheets or tubes

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6
Q

What does controlled muscle contraction allow?

A

Movement of joints limbs and whole body

Propulsion of contents through various hollow internal organs

Emptying of contents of certain organs to external environment

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7
Q

Describe skeletal muscle

A

Controlled by the CNS

Neurons with cell body in the motor cortex synapse on motor neurons in the SC

Motor neurons with cell body in spinal cord send axons to synapse on muscle cells

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8
Q

Nerve muscle synapses is called

A

Neuromuscular junctions

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9
Q

The group of muscles cells controlled by a motor neuron is called a

A

Motor unit

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10
Q

Explain the motor unit

A

Each muscle is composed of a large number of muscle cells. In mammals each muscle cell receives ONLY ONE synapse

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11
Q

The motor unit consists of

A

One motorneuron

And all the muscle cells it innervates

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12
Q

The NMJ is ___ compared to a central synapse

A

HUGE

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13
Q

How is the NMJ special

A

It’s huge

The postsynaptic membrane is folded and has a high density of nAChR

A single AP in a motor neuron will always cause an AP in the postsynaptic muscle cell

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14
Q

Explain how there is no summation of EPSP

A

So much ACh released so many receptors the EPSP brings muscle cell to threshold

High number of voltage gated Na+ channels at the synapse

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15
Q

What is a single skeletal muscle called

A

A muscle fibre

Fibres usually extend entire length of muscle

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16
Q

What is a muscle fascicle

A

Bundle of fibres

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17
Q

What are the structures of the myofibral

A

Actin myosin and Titin

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18
Q

What are thick filaments

A

Myosin

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19
Q

Describe thick filaments (myosin)

A

Protein molecule consisting of two identical subunits shaped like a golf club

Tail ends are intertwined with each other

Heads project out

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20
Q

What do myosin heads form

A

Cross bridges between thick and thin filaments

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21
Q

What are the two important sites of a myosin head

A

An actin binding site

A myosin ATPase

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22
Q

What are thin filaments

A 
Actin 
Titin
Tropomyosin
Troponin
Nebulin
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23
Q

Describe actin

A

Primary structural component of thin filaments

G-actin monomers are spherical but assemble into long chains

Each actin molecule has a special binding site for attachment with a myosin head

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24
Q

The binding of actin with a myosin head results in what

A

Contraction of a muscle fibre

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25
Q

Describe tryopomyosin and tropinin

A

Regulatory proteins

Tropomyosin are thread like molecules that lie alongside the grove of the actin spiral and covers myosin binding sites

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26
Q

Describe tropinin

A

Made of three polypeptide units

  • one binds with tropomyosin
  • one binds with actin
  • one can bind with Ca

When not bound to Ca tropinin stabilizes tropomyosin in blocking position over actins cross bridge binding sites

When Ca binds to tropinin tropomyosin moves away from the blocking position this allows actin to bind to myosin

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27
Q

Describe Titin

A

Giant elastic protein

Joins M lines to Z lines at opposite ends of sarcomere

Two important roles

  • helps stabilize position of thick filaments in relation to thin filaments
  • improves muscle elasticity
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28
Q

Describe nebulin

A

Aligns actin filaments

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29
Q

How does a muscle shorten

A

When actin and myosin fibres slide past each other

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30
Q

In general explain muscle contraction (4 steps)

A

Binding = myosin binds to actin

Power stroke = cross bridge bends pulling thin myofilaments in

Detachment = cross bridge detaches at end of power stroke and returns to original form

Binding = cross bridge binds to more distal actin and cycle repeats

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31
Q

Myosin is properly called a ____

A

Motor protein

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32
Q

Define a motor protein

A

A protein that hydrolyzes ATP to convert chemical energy to carry out mechanical work

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33
Q

Muscle cells have extensive network of endoplasmic reticulum called

A

Sarcoplasmic reticulum (SR)

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34
Q

Describe the SR

A

Has a very high Ca concentration

Has a powerful Ca ATPase transporter
- uses ATP to pump Ca from cytoplasm into SR

Also has a Ca binding protein called Calquestrin which helps maintain Ca concentration

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35
Q

Describe T-tubules

A

Run perpendicular from surface of muscle cell membrane into central portions of the muscle fibre

T-tubules aligned on the edges of the A band

Are continuous with surface membrane - action potential on surface membrane also invade T-tubules

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36
Q

The spread of action potential down a T tubule triggers release of _____ from ___ to ___

A

Ca
Sarcoplasmic reticulum
Cytosol

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37
Q

What is the A band made up of

A

Thick filaments

Myosin

38
Q

The voltage gated Ca channel has two purposes

A

1) to act as a voltage sensor that can open the Ryanodine receptor
2) lets in small amounts of Ca and contributes to the opening of RyR

39
Q

What is rigor mortis

A

3-4 hours after death (peak at 12 hours)

After death intracellular Ca rises and leaks out of SR

40
Q

Rigor mortis subsides when __

A

Enzymes start to break down myosin heads

41
Q

Ca allows myosin to bind to actin BUT when dead (rigor mortis) ..

A

ATP is needed to separate myosin from actin

Dead cells can’t produce more ATP

So once bound cross bridges can’t detach

42
Q

Describe the relaxation of muscles

A

Action potentials stop arriving at NMJ
ACh dissociates from AChR gets degraded
Ca dissociates from tropinin pumped back into SR
Tropomyosin moves back into position blocking cross bridge binding site
Muscle ceases to maintain tension
Actin and myosin slip past each other pulled by Titin and antagonistic muscles

43
Q

What is myasthenia Gravis

A

Common symptoms

  • drooping eyelid
  • blurred or double vision
  • slurred speech
  • difficulty chewing and swallowing
  • weakness in arms and legs
  • chronic muscle fatigue
  • difficulty breathing

Muscle Weakness

44
Q

Myasthenia Gravis treatment

A

Anticholinesterase treatment

  • drugs that inhibit ACh esterass within the NMJ
  • allow ACh to remain in the NMJ longer
45
Q

Contraction-relaxation steps requiring ATP

A

Splitting of ATP by myosin ATPase for power stroke

Active transport of Ca back into SR

Na/K ATPase

46
Q

Energy sources for contraction

A

1) creatine phosphate
- first energy storehouse tapped at onset of contractile activity

2) oxidative phosphorylation
- takes place within muscle mitochondria if sufficient O2 is present

3) glycolysis
- supports anaerobic or high intensity exercise

47
Q

Creatine phosphate is used when

A

During times of rest when ATP demand is low muscle stores energy in the form of creatine phosphate

First store of energy tapped to fuel muscle contraction

Provide 4-5 times the energy of stored ATP

Limited supply (only a few min)

48
Q

Oxidative phosphorylation is used when

A

The process that provides energy during light to moderate exercise

Uses stores of glycogen in muscle (30min)
Good yield of ATP
Aerobic exercise
Adequate supply of oxygen

49
Q

Oxidative phosphorylation maintains adequate oxygen by

A

Increase ventilation
Increase heart rate and force of contraction
Dilate skeletal blood vessels

50
Q

Anaerobic glycolysis is used when

A

Primary source of ATP when oxygen supply is limited
During intense exercise

Rapid supply of ATP only a few enzymes involved

Very low ATP yield

  • only two per glucose molecule
  • lactic acid acidifies muscle and contributes to fatigue
51
Q

What causes muscle fatigue

A

Central fatigue

  • CNS
  • psychological

Peripheral fatigue

  • decrease in ACh
  • receptor desensitization
  • changes in RMP
  • impaired Ca release
  • pH
  • lack of ATP is not thought to be a factor
52
Q

Explain generation of tension

A

Takes several AP to cause generation of maximal tension

Two therories:
-intracellular Ca reaches its Maximum after first AP

  • takes several AP to increase intracellular Ca enough to saturate actins myosin binding sites
53
Q

Summation and tetanus develop because ____ and allows greater exposure of actin binding sites and therefore maximizes interaction with myosin

A

Sustained elevation of increases Ca

54
Q

Types of motor units

A

Turkey= fibre types grouped together

Mammals= interspersed most have 3 types of Motor units

  • slow twitch
  • Fast twitch (x2)
55
Q

Slow twitch = __

Fast twitch = ___

A

Oxidative which is red muscle

Fast twitch oxidative-glycolytic which is red muscle

Fast twitch glycolytic which is white muscle

56
Q

Explain slow twitch oxidative

A

Slow fatigue resistant

Small amounts of tension for long periods of time without running down energy stores

Lots of mitochondria

Small fibres

Well vascularized myoglobin

57
Q

Explain fast twitch oxidative glycolytic

A

Fast fatigue resistant

Generate lots of tension moderately fast

Somewhat resistant to fatigue

Moderate # of mitochondria

Fibres are larger then slow twitch

58
Q

Explain fast twitch glycolytic

A

Fast fatiguable

White muscle

Generate most tension

Fatigue rapidly

Few mitochondria (anaerobic)

Fibres are larger then slow twitch

59
Q

First motor units recruited

Next recruited

Last recruited

A

Slow twitch fatigue resistant
Each MU has only a few fibres and small motorneuron

Motor units that include fast fatigue resistant fibres and these motor neurons are slightly larger

Fast fatigue and the largest MN including the most fibres

60
Q

Cardiac muscle cells are

A

Interconnected by intercalated discs and form functional syncytia

Within intercalated discs two kinds of membrane junctions

  • desmosomes
  • gap junctions
61
Q

What are the 3 types of cardiac muscle cells

A

Myocardial auto rhythmic cells

Myocardial contractile cells

Conducting cells

62
Q

Describe myocardial autorhythmic cells

A

Initiate and maintain electrical activity in the heart

Do not contract

63
Q

Describe myocardial contractile cells

A

Working cells

99% of cardiac muscle cells

Contractile muscle part of the heart does the mechanical work of pumping

Joined electrically by gap junctions

64
Q

Describe conducting cells

A

Carry electrical signals from the pacemakers to the contractile cells

65
Q

Where do cardiac impulses originate

A

At the SA node

66
Q

Where do AP spread in the heart

A

Throughout the right and left atria

67
Q

The impulse passes from where to where in the heart

A

From atria into ventricles through AV node

68
Q

What is the only point of electrical contact between chambers in the heart

A

AV node

69
Q

The action potential is briefly delayed at the AV node because

A

Ensures atrial contraction precedes ventricular contraction to allow complete ventricular filling

70
Q

After the AP is delayed at the AV node where does it travel

A

Rapidly down interventricular septum by means of bundle of His

71
Q

The impulse eventually rapidly disappears throughout the myocardium by means of what

A

Purkinje fibres

72
Q

Rest of ventricular cells activated by cell to cell spread of impulse through ___

A

Gap junctions

73
Q

Describe intrinsic conduction system

A

Autorhythmic cells initiate AP

No real resting membrane potential

IF : a Na current

ICaT : fast calcium current

ICaL : slow calcium current

Use calcium influx rather then VG sodium for rising phase of AP

74
Q

Pacemaker potential =

A

Membrane slowly depolarizers “drifts” to threshold, initiates AP and the membrane repolarizes to -60 mV

75
Q

Ap of contractile cells

A

Rapid depolarization

Rapid partial early repolarization, prolonged period of slow repolarization (plateau phase)

Rapid final (repolarization phase)

76
Q

Why is the AP of contractile cells so long?

A

Plateau primarily due to activation of slow L-type Ca channels

Ensures adequate ejection of blood

77
Q

How does the long AP contractile cells avoid tetanus

A

Long AP causes long refractory period and long contraction

78
Q

Excitation contraction coupling in cardiac contractile cells

A

Ca entry through ca channels in T tubules triggers massive release of Ca from SR RyR

Ca induced Ca release leads to cross bridge cycling and contraction

Key role for secondary active transport

79
Q

Describes smooth muscle

A

Highly variable
Must operate over a range of lengths
Layers may run in several directions
Small spindle shaped cells with one nucleus

Contracts and relaxes much more slowly
Uses less energy
Sustains contractions for extended periods

80
Q

Classify smooth muscle

A

Location
- vascular gastrointestinal, urinary, respiratory, reproductive, ocular

Contraction pattern
- phasic or tonic

Communication

  • single unit smooth muscle or visceral smooth muscle
  • multi unit smooth muscle
81
Q

What’s the difference between single unit smooth muscle cells and multi unit

A

Single
- are connected by gap junctions and the cells contract as a single unit

Multi
- are not electrically linked and each cell muscle must be stimulated independently

82
Q

Describe smooth muscle structure and function

A

Not arranged in sarcomeres

Contraction initiated by electrical or chemical signals or both

Controlled by the autonomic nervous system

Lacks specialized receptor regions

83
Q

Ca is from where in smooth muscle

A

From the extracellular fluid and sarcoplasmic reticulum

Ca initiates a cascade ending with phophorylation of myosin light chain and activation of myosin ATPase

84
Q

Describe the structure of the smooth muscle cytoskeleton

A

Intermediate filaments and protein dense bodies form a cytoskeleton

Actin attaches to the dense bodies

Each myosin molecule is surrounded by actin filaments

85
Q

Smooth muscle SR and t tubules

A

Amount of SR varies and is less organized

No t tubules but caveolae
- small invaginations in cell

86
Q

Describe the protein filaments of smooth muscle

A

Actin is more plentiful then in striated

Lack troponin

Less myosin, but are longer and the entire surface is covered in myosin heads

Additional cytoskeleton with intermediate filaments and dense bodies

87
Q

Smooth muscle myosin has ____ all along its length

A

Hinged heads

88
Q

Describe sarcoplasmic calcium release in smooth muscle

A

Ryanodine receptor (RyR) calcium release channel

Calcium induced calcium release (CICR)

IP3 receptor channel

Store operated Ca channels

89
Q

Describe smooth muscle cell membrane calcium entry

A

Voltage gated Ca channels

Ligand gated Ca channels or receptor operated calcium channels (ROCC)

Stretch-activated calcium channels

  • open when pressure or other force distorts cell membrane
  • known as myogenic contraction (arteries)
90
Q

describe smooth muscle regulation

A

Many controlled by both sympathetic and parasympathetic neurons

Hormones and paracrines also control smooth muscle contraction

  • histamine constricts smooth muscle of airways
  • nitric oxide relaxes smooth muscles of blood vessels (mall sex response)
91
Q

Describe smooth muscle contraction

A

Electromechanical coupling
-contraction caused by electrical signaling or mechanical signalling and contraction dependent on changes in membrane potential

Pharmacomechanical coupling
- contraction caused by chemical signalling , no changes in membrane potential required

Physiology (15 decks)

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