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Unit 5 > Myology > Flashcards

Myology Flashcards

1
Q

Give an overview of the function of muscle

A

Maintain posture
Enable movement
Vasoconstriction and vasodilation
Peristalsis
Cardiac motion
Heat generation 75% of ATP energy used in muscle contraction is released as heat
Stabilise joints

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2
Q

Give an overview of skeletal muscles

A

Voluntary control
Striated
Multiple peripheral nuclei
Is long and cyclindrical in appearance
Attaches to bone
Muscle fibres contract independently
Well developed sarcoplasmis reticulum and transverse tubules
Mainly fast twitch muscle fibres

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3
Q

Give an overview of cardiac muscle

A

Involuntary contraction
Stratified
Uninuclie located in the centre of the cell
Branches
Intercalated disks allows action potential to pass along fibres
Moderately developed sarcoplasmic reticulum and transverse tubules
Mainly slow twitch muscle fibres

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4
Q

Give an overview of smooth muscle

A

Not striated - more actin than myosin,
Involuntary control
Elliptical in shape
Uninucleus in the centre of the cell
Poorly developed sarcoplasmic reticulum and transverse tubules.
Gap junctions are generally present
Maintains rone without nervous stimulation, visceral smooth muscle does have pacemaker potential
Are mainly slow twitch muscle fibres

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5
Q

What is the epimysium?

A

The outer layer of connective tissue covering the whole muscle

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6
Q

What is a muscle fasicle?

A

A bundle of muscle fibres surround3 by perimysium

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7
Q

What is a muscle fibre?

A

An individual muscle cell or myocyte, surrounded by endomysium.
Contains myofibrils

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8
Q

What are myofibrils ?

A

Composed of actin and myosin make up a myofilament.

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9
Q

What is the hierarchy of muscle structure?

A

Muscle
Muscle fasicle
Muscle fibre or myocyte
Myofibrils
Myofilament

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10
Q

What is the locational relationship between transverse tubules and the sarcoplasmic reticulum?

A

A transverse tubule sits in between two sarcoplasmic reticulum’s. Together they are known as a triad
There is no physical connection between the two but the close proximity allows the t tubule to strand the action potential between sarcoplasmic reticulums.

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11
Q

What is meant by terminal Cristae?

A

The fusion of the sarcoplasmic reticulum near the t tubules

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12
Q

What is the importance of a z disk in muscle structure?

A

Z disks are filamentous proteins.
Marks the boundaries of a sarcomere

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13
Q

What are the different bands within a sarcomere?

A

H band is myosin only
A band is the dark band containing myosin and actin
I band is the light band containing actin only
The M line is the middle of the sarcomere

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14
Q

What is the role of titin?

A

A filamentous molecule that keeps actin and myosin in place
Attaches myosin to the z disks
Prevents from over contracting
Found in skeletal and cardiac muscle ??

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15
Q

Describe the structure of an actin filament?

A

G actin molecules clump together to form a F actin chain
This is a double stranded chain
There is one ADP molecule or active site per G actin
F actin inserts into the z disc

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16
Q

What is tropmyosin?

A

A protein component of actin.
Wraps around F actin chains like a spiral
Covers the active sites

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17
Q

What is troponin?

A

Part of the actin complex
Is a circular molecule with three compartments
C for calcium attachment
T for tropomyosin attachment
I for strong affinity to actin hence inhibiting the contraction

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18
Q

Describe the structure of myosin.

A

The tail of myosin is made up of two heavy chains wrapped around each other in an alpha helix shape.
Each heay chain then splits and folds to form a globular polypeptide head each
Each head is also associated wih two light chains (four light chains in total)
The heads control the function during muscle contraction

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19
Q

What is the significance of M proteins and myosmesin?

A

Bind to the mid point of the myosin molecules make up the M line

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20
Q

What other proteins are associated with actin?
Not troponin of tropomyosin

A

a-actinin dimers - anchor to actin polymers to form the Z line
Nebulin - anchored to actinin at the Z line, extends along each F actin molecule
Tropomoduline - capps the end of each actin, away from the Z line, caps the length of the actin molecule
Myotilin - helps anchor actin the the z disk
All help stabilise actin and control its length

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21
Q

What proteins are associated with mysoin?

A

Titin - acts like an elastic ban anchors the myomesin to the Z line, this recoils the sacromere back to its orignal shape during relaxtion and also prevents excessive stretching
Telethonin: found at the z disk, helps anchor titin

22
Q

What is the function of desmin molecules in the sarcolemma?

A

Form a network of molecules running between Z disks, helps to ensure the whole muscle shortens not just one sarcomere

23
Q

What is the function of filamen proteins?

A

Anchors actin and myotilin to the sarcolemma.

24
Q

What is the function of the dystrophin glycoprotein complex?

A

Anchors the sarcolemma to the endomysium.
Dystrophin links the actin to sarcolemma via desmin
Four transmembrane sarcoglycans anchor within the sarcolemma
The dystroglycans attach the comples to laminin which attaches to the endomysium.

25
Q

What is the importance of the epimysium in correlation to bones?

A

The bundles of fibres mainly type 1 collagen within the epimysium, collect togther to form tendons which connect to the periosteum or connective tissue surrounding the bones.

26
Q

What are some key features of a neuromuscular junction?

A

Axon of a terminal motor neuron
Synpatic cleft
Junction folds of sarcolemma
T tubules
Lots of mitochondria in both the axon and the muscles
Acetylcholine NT and nicotinic receptors.

27
Q

What are the different types of synapses?
How are they different?

A

The chemical synapse e.g synpatic cleft . impulse is passed on be neurotransmitters
The electrical synpase. impulse is passed by a connection of gap junctions allowing ion movement directly.

28
Q

Describe the events that occur from the arrival of an action potential to end of the signal at a neuromuscular junction.

A

Action potential arrives.
This causes voltage gated calcium ion channels to open and calcium ions to enter the presynaptic plate
This causes vesicles containing acetylcholine to move towards and fuse with the membrane.
Acetylcholine is released into the synaptic cleft and diffuses towards the muscles.
Ach binds to nicotinic receptors on the muscles, this causes ligand gated sodium ion channels to open causing an action potential to be generated at the sarcolemma
Voltage gated calcium ion channels in the sarcoplasmic reticulum open
Acetylcholine esterase breaks down acetylcholine to stop the action potential from being continually signalled.

29
Q

Describe the synthesis of acetylcholine.

A

Choline and Acetyl CoA produce acetylcholine
Aided by choline acetyltransferase enzyme

30
Q

Explain the degradation of acetylcholine.

A

Acetylcholine esterase breaks acetylcholine down into Choline and Acetate.
Choline is recycled back into the nerve terminal for future production of acetylcholine.

31
Q

What is the impact of botulinus toxin?

A

Blocks ACh release from presynaptic terminals by binding to high affinity receptor’s
Causes paralysis of muscles
Can lead to death is affects respiratory or cardiac muscles
Is produced by a pathogenic bacteria
Is also used in botox

32
Q

What is curare used for?

A

d-Tubocurarine is used in anaesthesia
Competes with ACh for nicotininc recepeotrs
Decreases the size of the end plate potential
In maximal doses can cause paralysis

33
Q

What is the used of neostigmine?

A

Used to treat myasthenia gravis.
Inhibits acetylcholine esterase, this prolongs and enhances the action of ACh at the motor end plate helping to reduce muscle weekness

34
Q

Explain the temporal relationship in excitation contraction coupling in skeletal muscle?

A

The action potential preceeds to calcium influx
The calcium ion influx proceeds the muscle contraction

35
Q

What happens in excitation contraction coupling?
Up until the cross bridge cycle

A

The transverse tubules spread the action potential deeper from the sarcolemma.
The depolarisation of the T tubules causes the L-type dihydropropyridine receptors to undergo a conformational change, this may causes some in movement of calcium ion from the ECF into the cell but this is not necessary for skeletal muscle
The conformational change also opens ryanodine receptors on the SR (t-type), this causes calcium ions to be released from the SR into the sarcoplasms
The intracellular concentration of caclium ions increases

36
Q

What occurs during the cross bridge cycle?

A

ATP binds to the myosin head and hydrolyses but the products ADP and Pi remain on the head. This moves the head so it is perpendicular but not bound to the actin.
Ca2+ binds to C troponin, this causes a series of conformational changes moving tropomyosin to expose myosin binding sites or active sites on actin.
Myosin head binds to actin forming a crossbridge, and the energy stored from the ATP causes the power stroke as phosphate released.
One head of the cross bridge tilts allowing the release of the stored ADP.
Another ATP molecule instantly binds causing the detachment of the head.
The ATP molecule is cleaved to recock the head, allows the cycle to start again.

37
Q

What happens to calcium after muscle contraction occurs?

A

Once the muscle contraction has finished the calcium ions reacculumate in the SR by activa transport via SR Ca2+ ATPase (SERCA) causinf muscle relaxation

38
Q

What other terms are used to describe slow muscle fibres?

A

Type 1 fibres or slow twitch muscle

39
Q

What other terms are used to describe fast muscle fibres?

A

Type 2 or white muscle fibres

40
Q

What are some key features of slow muscle fibres?

A

Smaller
Innervated by smaller nerve fibres
More extensive capillary supply, hence more oxygen supply
High levels of mitochondria for oxidative metabolism. Has very high levels of metabolic activity.
Contains large amount of myoglobin.
Not easily fatigued, weaker but longer lasting contraction

41
Q

What is myoglobin?

A

An iron containing protein similar to Hb in rbcs.
Very high affinity for oxygen, stores it until it needs to be released for the mitochondria.
It gives slow twitch muscle its reddish appearance.

42
Q

What are some features of fast muscle fibres?

A

Larger fibres for stronger contraction
Extensive SR for rapid release of Ca2+
Less extensive blood supply and less mitochondria as less metabolic activity.
Large amounts of glycolytic enzymes.
easily fatigued, stronger but shorter lasting contraction.

43
Q

What are the two different types of fast twitch muscle?
What properties make the different?

A

Fatigable = lots of ATPase for rapid release of energy from ATP but poor resynthesis of ATP as little SDH
Fatigue -resistance =Lots of ATPase so rapid release of energy, also have more SDH so faster synthesis of ATP.

44
Q

How does each type of muscle fibre slow/fast (fatigable and fatigue resistant) stain when testing for ATPase and SDH?
What does this mean?

A

Darker stains means more present:
ATPase: slow twitch is white, fatiguable is dark brown, fatigue resistant is light brown
SDH: slow twitch is dark brown, fatiguable is white, fatigue resistant in light brown.

45
Q

What is meant by a motor unit?

A

1 motor neuron and all of the muscle fibres it innervates
consists of only one type of muscle fibre e.g slow or fast.

46
Q

Describe the structure and features of motor neurons?

A

Cell bodies lie within the brainstem or spinal cord
Axons are myelinated and large in diameter
Propagate action potentials at high velocities

47
Q

How does the work vary between isometric and isotonic contraction?
What equation can be used to demonstrate this?

A

Work = load x distance
In isometric the distance stays the same so o, hence the work is smaller. This means muscle contraction will not shorten the length of the whole muscle.
In isotonic contraction this distance changes hence the work is larger.This means muscle contraction will be shortening the whole muscle length

48
Q

What happens in excitation-contraction coupling in smooth muscle?

A

Intracellular calcium ion concentration increases.
calcium ions bind to calmodulin
Calmodulin binds to and activates myosin light chain kinase, this causes the ATPase activity of myosin heads to increase.
Low concentrations of calcium ions causes calponin and caldesmon to bind to and inhibit actin, this inhibition is released at higher concentrations of calcium.
This allows cross bridge cycle to occur with the strength of contraction dependent on the level of intracellular calcium.

49
Q

What mechanisms can increase intracellular calcium ion in smooth muscle?

A

Depolarisation - note does not need a full action potential to open voltage gated calcium ion channels
Hormones and Neurotransmitters - to open ligan gated calcium ion channels
- cause IP3 gated calcium ion release from the SR.

50
Q

What cellular mechanisms can cause smooth muscle to relax?

A

Hyperpolarisation - causes voltage gated calcium ion channels to close
cAMP inhibits calcium ion channels
cGMP inhibits IP3 induced SR release
Increase activity of SR Ca2+ATPase.

51
Q

What type of skeletal muscle fibres is this?
how can you tell?

A

Slow twitch
Darker Z lines
Lots of mitochondria clustered under the sarcolemma and between layers of sarcomeres

52
Q

What type of skeletal muscle fibres are these?
How can you tell?

A

Fast twitch
Lighter z lines
Mitochondria are between longitudinal layers of sarcomeres.

Unit 5 (12 decks)

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