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nuero > Muscle microstructure and contraction > Flashcards

Muscle microstructure and contraction Flashcards

1
Q

what are Muscle types

A

Smooth
Cardiac
Skeletal

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2
Q

what is smooth muscle controlled by

A

is under involuntary control from the autonomic nervous system

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3
Q

control of cardiac

A

muscle can contract autonomously, but is under the influence of the autonomic nervous system and circulating chemicals

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4
Q

control of skeletal

A

Skeletal muscles are under voluntary control, usually attached to bones and contract to bring about movement

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5
Q

what is a fusiform

A

larger in the middle and tapered at the end

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6
Q

what are pennate muscles

A

where muscle fibres are placed at angles to the tendon

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7
Q

unipennate

A

same direction from the tendon

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8
Q

bipennate

A

2 direction from the tendons

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9
Q

multipennate

A

multiple tendons and multiple fibres

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10
Q

what is a Fascicles

A

– bundles of muscle fibres

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11
Q

what is a fascicle made up of

A

myofibre –> myofibril –> myofilament

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12
Q

how many connective tissues are muscles made up of

A

3

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13
Q

what does the epimysium made up of

A

muscle fibre

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14
Q

what are muscle fascicle bounded by

A

perimysium

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15
Q

what do endomysium sorround

A

muscle fibre

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16
Q

what is a sacrolemma

A

the plasma membrane covering myofibres

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17
Q

what is the cytoplasm in the muscle fibre

A

sacroplasm

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18
Q

what does the sacroplasm contain

A

myoglobin and mitochondria

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19
Q

sarcoplasmic reticulum

A

Network of fluid filled tubules

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20
Q

what makes up a myofibre

A

myofibrils

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21
Q

what is a sacomere

A

a repeating unit

a z disk to another

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22
Q

what gives striated (striped) appearance

A

Light and dark bands

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23
Q

what is the thin filament/light band

A

actin

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24
Q

thick filament

A

myosin

25
Q

what separates sacromeres

A

Z-discs separate sarcomeres

26
Q

how are dark bands represented

A

A band (thick - myosin)

27
Q

and light

A

Light bands – I band (thin - actin)

28
Q

what causes muscle contraction

A

movement of actin over myosin

29
Q

strcuture of myosin

A

Two globular heads
Single tail formed by two α-helices
Tails of several hundred molecules form one filament

30
Q

Structure of skeletal muscles - actin

A

Actin molecules twisted into helix

31
Q

iniation of muscle contraction

A
  1. Action potential opens voltage gated Ca2+ channels
  2. Ca2+ enters pre-synaptic terminal
  3. Ca2+ triggers exocytosis of vesicles
  4. Acetylcholine diffuses across cleft
  5. Binds to acetylcholine receptors and induces action potentials (AP) in muscle
  6. Local currents flow from depolarized region and adjacent region
    AP spreads along surface of muscle fibre membrane
  7. Acetylcholine broken down by acetylcholine esterase. Muscle fibre response to that molecule of acetylcholine ceases.
32
Q

what happens in the muscle

A
  1. Action potential propagates along surface membrane and into T-tubules
  2. Dihydropyridine (DHP) receptor in T-tubule membrane: senses V & changes shape of the protein linked to ryanodine receptor,
    opens the ryanodine receptor Ca2+ channel in the sarcoplasmic reticulum (SR)
    Ca2+ released from SR into space around the filaments
  3. Ca2+ binds to troponin & tropomyosin moves allowing..
  4. Crossbridges to attach to actin
  5. Ca2+ is actively transported into the SR continuously while action potentials continue. ATP- driven pump (uptake rate < or = release rate).
33
Q

Excitation contraction coupling

A

In the presence of Ca2+ movement of troponin from tropomyosin chain
Movement exposes myosin binding site on surface of actin chain
‘Charged’ myosin heads bind to exposed site on actin filament
This binding & discharge of ADP causes myosin head to pivot (the ‘power stroke’)  pulling actin filament towards centre of sarcomere
ATP binding  releases myosin head from actin chain
ATP hydrolysis  provides energy to ‘recharge’ the myosin head

34
Q

where do upper motor nuerons have their cell bodies

A

motor cortex

35
Q

The motor unit

A

Name given to a single motor neuron together with all the muscle fibres that it innervates.
non of those muscle fibres is also innervated by another any other branches of another motor unit

36
Q

muscles which have fine control have many or few muscles fibres innervated by a motor neurone

A

few

37
Q

large muscles which are needed for large force have how many many or few muscle fibres innerveated by a single nuerone

A

many

38
Q

what are the types of motor units

A 
Slow
(S, type I)
Fast, fatigue resistant (mantain contractions for long periods of time)
(FR, type IIA)
Fast, fatiguable
(FF, type  IIB)
39
Q

what are the charatistcis of slow/type 1

A

smallest diameter cell bodies
small dendritic trees
thinnest axons
slowest conduction velocity

40
Q

fast, fatigue resistant

A

larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity

41
Q

fast gatiguable

A

larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity

42
Q

how are muscle fibres distributed throughout the muscle.

A

Randomly

Muscles have different proportions of slow and fast twitch muscles

43
Q 
Myoglobin content
Colour
Aerobic capacity
Anaerobic capacity
of slow
A 
Myoglobin content
High
Colour
Red
Aerobic capacity
High
Anaerobic capacity
Low
44
Q 
Fast, fatigue resistant (FR, type IIA)
Myoglobin content
Colour
Aerobic capacity
Anaerobic capacity
A

Myoglobin content High
Colour Pink
Aerobic capacity Moderate
Anaerobic capacity High

45
Q 
Fast, fatiguable (FF, type  IIB)
Myoglobin content
Colour
Aerobic capacity
Anaerobic capacity
A 
Myoglobin content Low
Colour White
Aerobic capacity 
Low
Anaerobic capacity High
46
Q

muscles involved in postural control have a greater proportion of slow or fast twitch fibres

A

greater proportion of slow twitch

47
Q

how much force and how fast would typw 1 produce

A

low force

long time

48
Q

type iia

A

moderate force

in moderate time

49
Q

type iib

A

high force

quickly

50
Q

what muscle fibres are high fatigue

A

type iib

51
Q

fatigue resistant

A

iia i

52
Q

what are the two mechanisms by which the brain regulates the force that a single muscle can produce.

A

Recruitment

Rate coding

53
Q

recruitement

A

how many motor nuerones are being bought in or involved to fire in order to produce a contraction
more morot unit recruited = more force produced

54
Q

Motor units are not randomly recruited, there is an order.

A

Motor units are not randomly recruited, there is an order.

55
Q

what is the order

A

Governed by the “size principle”. Smaller units are recruited first (these are generally the slow twitch units).
more force is required, more units are recruited.
This allows fine control (e.g. when writing), under which low force levels are required.

56
Q

Rate coding

A

what frequency are action potentials are sent down the nuerone
A motor unit can fire at a range of frequencies. Slow units fire at a lower frequency.

57
Q

As the firing rate increases

A

the force produced by the unit increases.

58
Q

when does summation take place

A

when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.

nuero (36 decks)

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