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B > Muscle Microstructure > Flashcards

Muscle Microstructure Flashcards

1
Q

Three types of muscle

A

Smooth muscle
Cardiac muscle
Skeletal muscle

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2
Q

Smooth muscle function

A

Smooth muscle is under involuntary control, from the autonomic nervous system

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3
Q

Cardiac muscle

A

Contract autonomously , under the influence of the autonomic nervous system and circulating chemicals

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4
Q

Skeletal muscles

A

Voluntary control , usually attached to bones and contract to bring about movement

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5
Q

Skeletal muscle function

A

Skeletal muscles are under voluntary control from the somatic nervous system
They are usually attached to the bones
They contract to bring about movement

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6
Q

Arrange,ent of muscle fibres

A

Parallel
Fusiform
Triangular

Pennate - unipennate, Bipennate and multipennate

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7
Q

What is a fascicles

A

Bundles of muscle fibres ( myofibres

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8
Q

Sarcolemma and T tubules

A

Covered by plasma membrane - sarcolemma

T tubule tunnels into centre and this has many ion channels and so the whole area of the muscle can be excited

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9
Q

Sarcoplasm

A

Myoglobin and mitochondria present

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10
Q

Sarcoplasmic reticulum

A

Network of fluid filled tubules

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11
Q

Structure of myofibrils

A

1-2 um in diameter
Extend along the entire length of the myofibres
Composed of two main types of protein - actin and myosin

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12
Q

What gives muscles the striated appearance

A

Light and dark bands
However the actin and myosin do not extend along length of myofibres
They overlap and are arranged in compartments called sarcolemma

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13
Q

Dark bands

A

A band and are composed of myosin

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14
Q

Light bands

A

I band and are composed of actin ( thin)

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15
Q

What separates the sarcomeres

A

Z discs

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16
Q

What moves to cause the muscle contraction

A

The binding of myosin filaments to the actin heads causes the muscle contraction and force generation

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17
Q

Structure of myosin

A

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

18
Q

Structure of actin

A

Actin molecules twist into helix
Each molecule has a myosin binding site
Filaments also contain troponin and tropomyosin

19
Q

Sliding filament theory of muscle contraction

A

During contraction the I band becomes shorter
A band remains the same length
H zone narrows or disappears

20
Q

Myasthenia Graves

A

Where the antibodies attack the ACh receptor , this residual ACh can be prolonged and so remains at the receptor

21
Q

Initiation of muscle contraction

A

Action potential along surface membrane and T tubule

Dihydropridine ( DHP) receptor in T tubule membrane senses change in voltage and changes shape of the protein linked to the ryanodine receptor

This opens ryanodine receptor calcium channel into sarcoplasmic reticulum

Calcium released from ST into space around filaments

22
Q

What happens in the initiation of muscle contraction after the calcium ions have been released from the SR into the space around the filaments

A

Calcium binds to troponin and tropomyosin moves which allows cross ridges to attach to actin

Calcium ions are actively transported into the SR continuously while AP continue .

ATP driven pump and so uptake rate =/< release rate

23
Q

Excitation contraction coupling

A

In the presence of calcium ions movement of troponin from tropomyosin chain
Movement exposes myosin binding site on the surface of the actin chain
Charged myosin heads bind to exposed site on actin filament
This binding and discharge of ADP causes myosin head to pivot ( the power stroke) - pulls actin filament towards the centre of the sarcomeres
ATP binding - releases myosin head from actin chain
ATP hydrolysis - provides energy to recharge myosin head

24
Q

What is a motor unit

A

Name given to a single motor neuron together with all the muscle fibres that it innervates . Stimulation of one motor unit causes contraction of all muscle fibres in that unit

25
Q

How can fine control be maintained in terms of motor units

A

Having only one nerve innervate has

26
Q

Three types of motor units

A 
Slow, ( S type 1) 
Fast fatigue resistant( FR, type IIA) 
Fast fatiguable ( FF , type II B)
27
Q

Which muscle contains the greates proportion of slow twitch type muscle fibres

A

Muscles with postural muscle control tend to have a greater proportion of slow twitch muscle fibres

28
Q

What are motor unit types classified by

A

Amount of tension generates
Speed of contraction
Fatiguability of the motor unit

29
Q

Type IIB

A

Fast twitch
High force
High fatigue

30
Q

Type IIa

A

Fast twitch
Moderate force
Fatigue resistant

31
Q

Type I

A

Slow twitch
Low force
Fatigue resistant

32
Q

Regulation of muscle force

A

Recruitment - there is an order in which muscle fibres are recruited . ‘ size principle’ . As more force is required , more units are recruited. This allows fine control ( e.g. when writing ) where low force levels are required

Rate coding - a motor unit can fire at a range of frequencies , slow units fire at a lower frequency. As the firing rate increases, the force produced by the unit increased.

33
Q

What are neurotrophic factors

A

Are types of growth factors
Prevent neuronal death
Promote growth of neurones after injury

34
Q

Effect of neurotrophic factors

A

Motor units and fibre characteristics are dependent on the nerve which innervates them
If a fast and slow twitch muscle are cross innervates , the slow one becomes fast and vice versa
The motor neurone has some effect on the properties of the muscle fibres it innervates

35
Q

Three types of muscle contraction

A

Isometric
Concentric
Eccentric

36
Q

Isometric

A

Produces force but doesn’t change length

37
Q

Concentric

A

Shortens muscle to produce movement

38
Q

Eccentric

A

Contraction in which muscle is producing fforce but muscle is getting longer - dumbbell which is heavier than the person can handle and so the muscle is still contracting but overall the movement is outwards.

This is when MUSCLE DAMAGE can occur and the muscle can get torn as it’s too heavy

39
Q

What is the most common change in fibre type following training

A

Change from type IIB ( fatiguable) to IIA ( less fatiguable)

So from fast fatiguable to fatigue resistant

40
Q

Microgravity and changing of muscle fibre types

A

Type 1 to II possible in cases of severe de conditioning or spinal cord injury. Microgravity during space flight results in shift from slow to fast muscle fibre types

41
Q

Ageing and change in muscle fibre types

A

Ageing associated with loss of type 1 and II fibres but also preferential loss of type II fibres. This results in a larger proportion of type I fibres in aged muscle ( evidence from slower contraction times )

B (24 decks)

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