Muscle structure Flashcards by Zohaa Qaisar

What are the three types of muscle?

Smooth: involuntary control

Cardiac: autonomous control and influenced by chemicals

Skeletal: voluntary control

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What muscle types are the following:

In muscles around eye
walls of airway
biceps

skeletal
smooth
skeletal

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What types of arrangement can muscle fibres have?

(Parallel)
Fusiform
Triangular

(Pennate - fibres between tendons)
Unipennate
Bipennate
Multipennate

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Microstructure to macrostructure of muscles?

Myofilaments –>Myofibrils –> Myofibres –> Fascicles –> Muscle ( tendon then bone )

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What is the epimysium, perimysium and endomysium?

Around muscle
Around fascicles
Around muscle fibres

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What is the:
sarcolemma?

sarcoplasm?

sarcoplasmic reticulum?

Plasma membrane covering fascicles

cytoplasm with myoglobin and mitochondria

network of fluid filled tubules

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What is the t-tubule?

Tunnel into the centre of muscle fibres

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What two proteins are myofibrisl made of?

Actin and Myosin

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Describe the myofibre components?

A band in the middle = thick myosin
I band on either side - thin actin
( A band also shows myosin, actin overlap )

Z discs are dense proteins seperating sarcomeres
H zone is the centre with no overlap
M line is the centre line within H zone

draw diagram

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Describe the structure of myosin?

Two globular heads

Single tail formed by two alpha- helices

100 molecules = single myosin

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Describe the structure of actin?

Actin molecules twisted into a helix

Each molecule has a myosin binding site

Filaments also contain troponin and tropomyosin proteins

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Describe the sliding filament theory?

During contraction:

I - band became shorter

A - band remained the same

H - zone narrowed

Distance between Z disc got shorter

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Initiation of muscle contraction:

Action potential opens VG (a)

(a) enters (b)
(a) triggers exocytosis of (c)
(d) diffuses across cleft

Binds to (d) receptor inducing action potential in muscle

Currents flow from depolarised region to adjacent region and across muscle fibre membrane

(d) is broken down by (e), muscle fibre response ceases.

a - calcium ion

b - pre-synaptic cleft

c - vesicles

d - acetycholine

e - acetylcholine esterase

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Activation of muscle contraction:

Action potential enter (a)

(b) receptor in (a) senses change in voltage and changes shape of protein linked to (c)

Once (c) is opened calcium is released from (d) into space surrounding actin

Calcium binds to (e) which allowed (f) to move

Cross-bridges attach to actin

Calcium is actively transported into SR continuously while potential continue,

a - T tubules

b - Dihydropyridine ( DHP)

c- Ryanodine receptor

d - sarcoplasmic reticulum

e- troponin

f - tropomyosin

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How does Excitation contraction coupling happen?

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 the 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

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Which protein filament does the ‘pulling’ during contraction?

Myosin ( pulls actin across it )

Describe the neural control of muscle contraction

Upper motor neurones in brain and lower motor neurones in brainstem or spinal cord

What is a motor unit?

Single motor neurone together with all the muscle fibres that it innervates.

Each motor neurone supplies 600 muscle fibres so requires single stimulation of one motor unit.

What three types of motor units are there?

Slow twitch, low force, fatigue resistant (S , Type 1)
Fast twitch, moderate force , fatigue resistant ( FR, Type IIA )
Fast twitch, high force, highly fatiguable ( FF, Type IIB )

What are the characteristics of Slow motor units?

Smallest diameter cell bodies

Small dendritic trees

Thinnest axons

Slowest conduction velocity

What are the characteristics of Fast motor units?

Large diameter cell bodies

Larger dendritic trees

Thicker axons

Faster conduction velocity

same characteristics for Fast fatiguable and fast fatigue resistant.

Why is the innervation ratio relevant?

The innervation ratio defines the number of muscle fibres innervated by a single motor neurone.

Low ratio : e.g. 1:23 in eye muscles allows finer control

Large ratio: e.g. 1:1000 in calf allows more strength

Are there different types of muscle fibres?

There are, randomly distributed throughout the muscle.

Muscles have different proportions of slow and fast twitch muscles.

can stain with ATPase staining method

What are the Characteristics of slow muscle fibres?

High myoglobin content

Red colour

High Aerobic capacity

Low Anaerobic capacity

What are the Characteristics of fast, fatigue resistant muscle fibres?

High Myoglobin content Pink colour Moderate Aerobic capacity High Anaerobic capacity

What are the Characteristics of fast, fatiguable muscle fibres?

Low Myoglobin content White colour Low Aerobic capacity High Anaerobic capacity

Which of the following would have the greatest proportion of slow type muscle fibres? - Back muscles - Extra ocular - biceps brachii

( usually postural control ) Back muscles

How does the brain regulate the force a single muscle can produce?

Recruitment and Rate coding

How is recruitment used for muscle force regulation? * understand graph

Motor units are not randomly recruited, there is an order. Smaller units are recruited first - slow twitch units As more force is required, more units are recruited. This allows fine control (e.g. when writing), under which low force levels are required.

How is rate coding used for muscle force regulation? * understand graph

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

What are neurotrophic factors?

Growth factor which prevent neuronal death and promotes growth of neurones after injury

What happened in the experiment when the nerves supplying a slow and fast muscle fibres switched nerves supplying?

If a fast and slow twitch muscle are cross innervated, the slow one becomes fast and vice versa meaning: Motor unit and fibre characteristics are dependent on the nerve which innervates them So nerve has some effect on characteristics of the muscle fibre it innervates

What three types of muscle contractions are there?

Concentric - shorten muscle to produce movement Eccentric - lengthen muscle to produce force ( muscle fibres can be damaged with this quite often ) Isometric - produces force doesn't change length

If someone placed a book on your outstretched hand and it was slightly too heavy for you too hold, which contraction type would you be making?

Eccentric | book would move towards floor so muscle would start lengthening

What can cause changes in fibre types?

( between fast ) -Type IIB to IIA most common following training ( slow to fast ) - Type I to II possible in cases of severe deconditioning or spinal cord injury. -Microgravity during spaceflight results in shift from slow to fast muscle fibre types Ageing associated with loss of type I 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).