Muscles Flashcards by Scarlett Enright

Functions of skeletal musckes

Produce movement of body parts
Support soft tissues
Maintain posture and body position
Communication
Maintain body temperature
Control of openings and passageways

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Universal characteristics of muscles

Responsiveness (excitability)
Conductivity
Contractility
Extensibility
Elasticity

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Responsiveness - excitability

Capable of response to chemical signals, stretch or other signals and responding with electrical changes across plasma membrane

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Extensibility

Capable of being stretched

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Contractility

Shortens when stimulated

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Elasticity

Returns to its original length after being stretched

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Average length of myofibre

5cm

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Average diameter of myofibre

100um

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Number of sarcomeres per myofibril

10000

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T-tubules

Sarcolemma invaginations that help propagate action potentials

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3 layers of connective tissue that surround myofibres

Endomysium
Perimysium
Epimysium

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Nuclei of skeletal muscle

Multinucleated
Nuclei at periphery of cell

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Parts of sarcomere

Z line
I band
A band
H zone
M line

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H zone

Only myosin

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H zone

Both myosin and actin

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I band

Only actin

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Motor units

The neuron and its associated muscle fibres that it innervates

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Small motor units

More precise movements

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Large motor units

Less precise movements

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What anchors the actin filament to the Z disc

Alpha-actinin
CapZ

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What maintains the certain length of the actin filament

Tropomodulin

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Nebulin

Consists of 35alphaA actin binding motifs
Acts as a molecular ruker

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Titin

Maintains myosin filament
Acts as a molecular spring

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What protein maintains the myosin filament in its position in the sarcomere

Titin

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Calcium removal/ muscle relaxation

SERCA on SR Ca2+ ATPase on membrane Na+/Ca2+ exchanger on membrane

Number of myosin heads in each myosin filament

300

Control of ACh levels

Acetylcholinesterase removes ACh and stops contraction Lack of depolarisation from neuron Botulism toxin prevents release Ca2+ channel blockers

How does botulism toxin prevent ACh release

SNAP protein inhibited

Contraction of muscles filament

ATP binds to myosin head, causing dissociation of actin-myosin complex ATP is hydrolysed causing myosin head to return to resting conformation A cross-bridge forms and myosin head binds to a new position on actin Pi is released- myosin head changes conformation, resulting in power stroke. Filaments slide past each other ADP is released

Neuromuscular junction

Action potential propagates down neurone to neuromuscular junction Depolarisation = Ca2+ influx signalling vesicle release SNARE (on vesicle) binds to SNAP and synaptobrevin (on nerve wall) and ACh is released by exocytosis ACh receptors present on sarcolemma Influx of Na+ causes depolarisation which is propagated down t-tubules Ca2+ enters the myocyte through L-type Ca2+ channels (dihydropyridine reticulum) Calcium-induced calcium-release through ryanodine receptors on sarcoplasmic reticulum Ca2+ binds to troponin C causing a conformational change and exposing the myosin binding site in actin

What does Ca2+ bind to on actin filament to expose myosin heads

Troponin C

Which receptors are found in the sarcoplasmic reticulum

Ryanodine receptors

Type of receptors on t-tubules

L-type Ca2+ channels - dihydropyridine receptors

Parts of Troponin

C T I

Troponin I

Inhibitory subunit

Troponin T

Binds to tropomyosin

Troponin C

Ca2+ binds

Cell characteristics of skeletal muscles

Long Cylindrical Striated

Tropomyosin

Covers myosin-binding sites on actin

Skeletal muscle neurotransmitter

ACh

Smooth muscle neurotransmitter

ACh Noradrenaline

Cardiac muscle neurotransmitter

Ach

Cell characteristics of smooth muscle

Spindle shaped

Cell characteristics of cardiac muscle

Cylindrical Striated Branched

Cell-cell characteristics of smooth muscle

Gap junctions in some visceral cells

Cell-cell characteristics of cardiac muscle

Intercalated discs Desmosomes Gap junctions

Nuclei of smooth muscle

One Central

Nuclei of cardiac muscle

One Central

Slow oxidative muscle fibres

Type 1

Oxidative muscle fibres

Type IIa

Glycolytic muscle fibres

Type IIb

Type 1 muscle fibres

Aerobic respiration for glucose metabolism Smaller Highly vascularised- provide O2 High myoglobin contents Very high mitochondrial density Low capacity for glycogen storage Activity for a long period of time

Type IIa muscle fibres

Aerobic respiration- metabolising glucose Larger fibres High number of blood vessels High levels of myoglobin High mitochondrial density High glycogen storage capacity Fatigue quickly

What gives muscle fibres a bright red colour

Myoglobin stores

Type IIb muscle fibres

Anaerobic respiration fibres Metabolise glucose Largest fibres Low vascularisation Low myoglobin levels Low mitochondrial density Very high glycogen storage capacity Fatigue fastest

Which muscle fibres are the largest

Type IIb

How is ACh released from the vesicle in synapse

SNARE (on vesicle) binds to SNAO and synaptobrevin (on nerve wall)

Which muscle fibre has greatest force of contraction

Type IIb

2 forms of creatine in muscles

Creatine - 40% Phosphocreatine - 60%

What enzyme catalyses the synthesis and degradation of phosphocreatine

Creatine kinase

Creatine at rest

Recycled into phosphocreatine in mitochondria

Muscle fatigue

Progressive weakness of muscle contraction until no response

What causes muscle fatigue

Decrease in ATP synthesis Lactic acid levels rise and lower pH of sarcoplasm Failure of motor neurons to produce ACh due to reduced availability of Ca2+

ATP production in fast fibres

Hydrolysis of phosphocreatine Glycolysis - 2 ATP produced (not 38)

Which of these is not a contractile cell? Fibroblast Myoblast Myoepithelial cell Myofibroblast Pericyte

Fibroblast

In the sarcomere the dark band A band corresponds to which protein?

Myosin

Skeletal muscle is striated because…

Myofibrils are in register

Excitation of the T tubular membrane system causes the concentration of what to rise in the sarcoplasm?

Calcium ions

The fibro-collagenous connective tissue that binds muscle fibres together to form fascicles is called:

Perimysium

Which statement concerning muscle fibre types is true? All muscles contain the same proportion of type 1 and 2 fibres Exercise increases the proportion of type 2 fibres in a muscle Postural muscles have a high proportion of type 2 fibres The proportion of type 1 and 2 fibres in a specific muscle varies between individuals Type 1 and 2 fibres can be distinguished on H+E

The proportion of type 1 and 2 fibres in a specific muscle varies between individuals

Skeletal muscles… Contain a stem cell population Contain pain receptors Contract when stimulated by dopamine Develop from embryonic endoderm Have a poor blood supply

Contain a stem cell population

Sharpey’s fibres: Are made of type 1 collagen Are specialised muscle fibres Connect endomysium to bone Connect bone to bone Do not penetrate bone

Made of type 1 collagen

Tendons… Are richly vascular Comprise loose fibrous connective tissue Connect bones to bones Heal rapidly if injured May lie in fibrocollagenous sheaths

May lie in fibrocollagenous sheaths

What might you look for to determine that a structure is a ligament rather than a tendon? Collagen fibres Elastin fibres Fibroblasts Myocytes Tendinocytes

Elastin fibres

Tendiocytes

Fibroblasts