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Muscle > Muscle > Flashcards

Muscle Flashcards

1
Q

Outline the different features of an actin and myosin

A

Actin filaments- helical array of G-actin proteins- tropomyosin molecule covering actin-myosin binding sites held in place by troponin complex
Myosin molecules- tails form filament by wrapping around each other and hinged head with a binding site for actin and ATP

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2
Q

What happens during a muscle contraction?

A

During a muscle contraction- Ca2+ ions are released from the sarcoplasmic reticulum. These will bind to troponin molecule causing it to change shape, this pulls on the tropomyosin moving it away from the actin-myosin binding sites
Head of myosin will form an actin-myosin cross bridge with actin filament and a power stroke will occur. Ca2+ also activates ATPase activity of myosin- after power stroke myosin binds to ATP- causes breaking of bridge and energy used to reset myosin molecule back to original position
High intracellular Ca (10^05mM) is temporary (millisecond) before being actively transported back into sarcoplasmic reticulum.

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3
Q

Explain what the sarcomere is and how this changes in a muscle contraction

A

End of the sarcomere is marked by the Z-lines. These hold the actin filaments. In the middle of sarcomere there is the M- line- discs made of cross connecting elements of cytoskeleton holding myosin filaments
I- band- actin only
A- band- whole of myosin filament
H- zone- myosin only
During contraction- I band, H-zone and sarcomere gets smaller. A band stays same.

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4
Q

Structure of skeletal muscle

A
  • Sarcomeres held in register by cross connections (intermediate filaments) between z- discs
  • Gives striated appearance
  • Linked to membrane and out to connective tissue
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5
Q

Relationship between myofibrils and fibres

A
  • Myofibrils= many sarcomeres joined together

- fibres contain many myofibrils

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6
Q

Why is the nuclei seen to be on the side of the muscle fibre

A

Good for repair of muscle

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7
Q

What is a syncytium and why is this useful- give an e.g. of one

A
  • Hundreds of muscle cells fuse to form syncytium- allows for multinucleated nature of skeletal muscle
  • e.g. placenta
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8
Q

How wide / long is a muscle fibre

A

20-100 micrometres wide 1mm-8cm length

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9
Q

What is the length tension relationship in skeletal muscle?

A
  • We see the most tension when there is some overlap between myosin and actin
  • Muscles adapted to be within this maximal range
  • Never no overlap and never full overlap (as lack of tension)
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10
Q

Explain membranes seen within skeletal muscle

A
  • endomysium (loose connective tissue) around each muscle fibre- connects to basement membrane
  • Perimysium- mixed connective tissue (dense and loose) forming fascicles
  • Epimysium- loose connective tissue between fascia and muscle body
  • Fascia- dense connective tissue covering muscle
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11
Q

Perimysium vs Perineurium

A
  • perineurium= layer of endothelial like cells VS

- perimysium= connective tissue

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12
Q

Structure cardiac muscle

A
  • NOT syncytial fibres
  • mono/ di-nucleated cells with limb- like extensions
  • Extensions connect to neighbouring cells via intercalated discs forming fibre- like 3D networks
  • Produce force in direction of cells axis
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13
Q

Difference between myocardium and cardiomyocytes

A 
Myocardium= cardiac muscle tissue 
Cardiomyocytes= individual muscle cells
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14
Q

What surround cardiomyocytes

A
  • layer of close connective tissue

- layer of squamous endothelium

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15
Q

Why are the cells not all in 1 direction in cardiac muscle

A
  • allow for wringing motion

- allows for effective emptying of blood from atria/ventricles

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16
Q

Which are bigger cardiomyocytes or skeletal muscle fibres

A
  • cardiomyocytes- single cells much smaller

- syncytia- bigger

17
Q

Difference between cardiac and skeletal muscle

A
  • cardiac: more mitochondria, nuclei in middle and each individual cell has basement membrane not sarcolemma
18
Q

Explain what mitochondria and intercalated discs look like on a SEM

A
  • Mitochondria- darker patches

- Intercalated discs- zig- zag black line-

19
Q

Features of the intercalated discs

A
  • Desmosomes- allow longitudinal force transfer due to strong adherence
  • low-resistance gap junctions- allow transfer of membrane depolarisations
20
Q

Structure of smooth muscle

A
  • Spindle arrangement
  • No intercalated discs
  • No sarcomeres- no striations
  • 3D Actin- myosin networks
  • Held together by intermediate filaments forming a tough scaffold- like structure
21
Q

Structure of myosin in smooth muscle

A
  • All heads on 1 side of myosin filament facing 1 way and on the other side facing the opposite direction
  • Thick myosin filaments are a bit shorter
22
Q

Which cells have most power / contraction amplitude

A

Skeletal muscle- syncytia most power (most myosin)
Cardiac- rhythmic wall contractions over long time period
Smooth- large contraction amplitude (as no z-lines) and versatility but lower power output

23
Q

How to muscles extend

A

External antagonistic force is necessary

24
Q

Outline different antagonistic forces for different types of muscle

A

Skeletal- antagonist muscles
Cardiac- blood pressure
Smooth muscle- tube pressure

25
Q

How does skeletal muscle control their contraction?

A
  • motor nerves of somatic nervous system
  • 1 synapse per nerve fibre (middle)
  • AP only generated by motor end plates
  • quick feedback via proprioception (spindle fibres- info about lengths of changes in muscle) and Golgi tendon organs (info about contraction strength)
  • precise control of movement
26
Q

What is a motor unit

A

Motor neuron + muscle fibres it innervates

27
Q

How does smooth muscle control contraction?

A
  • motor nerves of autonomic NS
  • varicosities- (1 per cell in multiunit muscles and fewer in single- unit muscles)
  • gap junction to help spread impulse
28
Q

Multiunit vs single unit smooth muscle

A
  • multiunit- each smooth muscle cell behaves independently

- single unit- each muscle cell is interconnected so many gap junction

29
Q

How does the heart control contraction?

A
  • SAN starts wave of excitation over atria
  • Bundles at AVN
  • Run down septum and over walls of heart via Purkinje fibres
  • all specialised heart cells not nerves
30
Q

explain Purkinje fibres in more detail

A
  • consist of purkinje cells
  • Heart cells
  • Filled with some contractile fibres but mainly glycogen granules (anaerobic respiration)
  • distribute AP down target areas in ventricle walls
  • individual myocytes are activated via gap junctions

Muscle (4 decks)

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