Flashcards in Muscle Deck (165):
What is myalgia?
What is myasthenia?
What is myopathy?
Any disease of the muscle
What is the sarcolemma?
The outer membrane of muscle cells
What is the sarcoplasm?
The cytoplasm of a muscle cell
What are the 3 major muscle types?
Is skeletal muscle striated?
How big are skeletal muscle fibres?
- 1mm-20cm long
- 10-100µm in diameter
What shape are skeletal muscle fibres?
Long parallel cylinders
Describe the nuclei of skeletal muscle cells
Multiple peripheral nuclei
How are skeletal muscles connected?
Fascicle bundles and tendons
What controls skeletal muscle?
Are skeletal muscles under voluntary or involuntary control?
Describe the action of skeletal muscles?
Rapid and forceful
Is cardiac muscle striated?
How big are cardiac muscle fibres?
- 50-100µm long
- 10-20µm in diameter
Describe the shape of cardiac muscle?
Short, branched cylinders
Describe the nuclei of cardiac muscle fibres?
Single, central nucleus
How is cardiac muscle contraction controlled?
Intrinsic rhythm, under autonomic modulation
Is cardiac muscle contraction voluntary or involuntary?
Describe the nature of cardiac muscle rhythm?
Is smooth muscle striated?
How big are smooth muscle fibres?
- 20-200µm long
- 5-10µm in diameter
What shape are smooth muscle fibres?
Spindle shaped, tapering ends
Describe the nuclei of smooth muscle cells?
Single central nucleus
How is smooth muscle joined?
By connective tissue, gap and desmosome-type junctions
How is smooth muscle controlled?
Autonomic, intrinsic activity, caused by local stimuli
Is smooth muscle contraction voluntary or involuntary?
Describe the nature of smooth muscle contraction
Slow, sustained or rhythmic
How is skeletal muscle developed?
What does the myotube have?
A chain of multiple central nuclei
What happens to the chain of nuclei in myotubes?
They are gradually displaced to the cell periphery by newly synthesised actin and myosin filaments
What happens to myoblasts producing cardiac and smooth muscle?
They do not fuse, but develop gap junctions at a very early stage
How do skeletal muscle fibres differ from each other?
In their diameter and their natural colour in vivo
What stains corroborate the natural colour of skeletal muscle fibres?
Strain showing reaction to NADH in mitochondria
What are the 3 types of skeletal muscle fibre?
Which muscles are red, white and intermediate skeletal fibres present in?
What does the red:white:intermediate proportion depend on?
The functional role of the muscle
Comparatively, what is the diameter of red skeletal muscle fibres?
What are red skeletal muscle fibres rich in?
- Oxidative enzymes
Of what do red skeletal muscle fibres have few?
What kind of contraction does red skeletal muscle fibres induce?
Slow, repetitive, weaker
How quickly does red skeletal muscle fatigue?
Where are red skeletal muscle fibres found?
- Limb muscles of animals
- Postural muscles of back
- Breast muscle of migrating birds
Comparatively, how big are white skeletal muscle fibres?
What do white skeletal muscle fibres have lots of?
Of what do white skeletal muscle fibres have few?
- Oxidative enzymes
What kind of contraction do white skeletal muscle fibres induce?
Where are white skeletal muscle fibres typically found?
- Extra-ocular muscles
- Muscles controlling fingers
What links muscle to bone?
What is the epimysium?
Protective sheath over muscle
Where does the perimysium exist?
Between bundles of muscle fibres
Where are the blood vessels found with respect to the perimysium?
Outside of it
What are fasicles?
Bundles of muscle fibres wrapped by perimysium
Where is endomysium found?
Between muscle fibres
What are possible arrangements for muscle fibres?
Where do skeletal muscle fibres interdigitate?
At myotendinous junctions
How do skeletal muscle fibres interdigitate?
With tendon collagen bundles
Where does the sarcolemma lie?
Between the collagen bundles and muscle fibres myofilaments
What do the extrinsic muscles of the tongue do?
Protrude to tongue, retract it and move it from side to side
Where does the extrinsic muscles of the tongue have insertions?
Are the intrinsic muscles of the tongue attached to bone?
What is the result of the intrinsic muscles of the tongue not being attached to bone?
It allows the tongue to change shape, but not position
How to the skeletal muscles of the tongue often terminate?
With interdigitation with the collagen and extracellular matrix of surrounding connective tissues
What accounts for the mobility of the tongue?
The plascity and strength of connective tissues, and multidirectional orientation of the muscle fibres
What is a striated muscle cell called?
A muscle fibre
What is the plasmalemma of a muscle cell sometimes called?
What is the sarcomere?
The unit of striated muscle- the distance between two Z lines
Which band appears dark?
Which band appears light?
What happens to the sarcomeres in the sliding filament mechanism?
They get shorter-
- I band and H zone shorten
- A band remains the same
What are skeletal muscles composed of?
What are fasicles composed of?
Muscle fibres (cells)
What are muscle fibres composed of?
What are the myofibrils?
What forms the thin filaments of skeletal and cardiac muscle?
A complex of actin, tropomyosin and troponin
How can troponin assays be used as a diagnostic tool?
Can be used as a marker for cardiac ischaemia
What types of troponin especially are used as a marker for cardiac ischaemia?
I and T forms
How can troponin assays be used a marker for cardiac ischaemia?
It’s released from ischaemic cardiac muscle within an hour, so the smallest changes in troponin levels are indicative or cardiac muscle damage
Is the quantity of troponin found proportional to degree of muscle damage?
Describe the structure of an individual myosin molecule
Has a rod-like structure from which two ‘heads’ protrude
What does each thick filament consist of?
Many myosin molecules
How do the heads of the myosin in the thick filament protrude?
At opposite ends of the filament
What do actin filaments form?
What happens to the actin helix?
Tropomyosin molecules coil around it
What is the effect of the tropomyosin molecules coiling around the actin helix?
It reinforces it
What is attached to each tropomyosin molecule?
A troponin complex
What is true of the thick filaments in the centre of the sarcomere?
Thet are devoid of myosin heads
What happens to the myosin head in areas of potential overlap?
They extend towards the actin filaments
What is the role of ionic calcium in the contraction metabolism?
- When increased amount of ionic calcium bind to TnC of troponin, a conformational change moves tropomyosin way from actin’s binding sites
- This displacement allows myosin heads to bind to actin, and contraction begins
What conformational change is made on binding of calcium?
The troponin has moved down, taking tropomyosin with it
What is the result of the action of calcium in muscle contraction?
Muscle contraction only occurs in the presence of calcium ions
What is the sliding filament theory of muscle contraction?
- Myosin cross bridge attaches to the actin myofilament
- ADP+Pi released, producing the working stroke- the myosin head pivots and bends as it pulls on the actin filament, sliding towards the M line
- New ATP attaches to the myosin head, and the cross bridges detaches
- As ATP is hydrolysed into ADP+Pi, cocking of the myosin head occurs
What state is myosin in at the point of forming cross bridges?
High energy conformation
What is meant by the high energy conformation of myosin?
It has ADP+Pi attached
When is myosin in the low energy conformation?
When it has ATP attached to the head
What is the purpose of the cocking of the myosin head?
Means myosin is ready to bind to a new actin filament
What causes movement of skeletal muscle?
Individual myosin heads attaching and flexing at different times
What is the rigor configuration?
When the myosin head is bound tightly to actin molecule
What causes rigor mortis?
In death, lack of ATP perpetuates the rigor configuration
What is at the end of the axons?
Small terminal swellings
What do the small terminal swellings of the axon contain?
What causes the release of acetylcholine?
A nerve impulse
What happens to released acetylcholine?
It binds to receptors on the sarcolemma
What is the result of acetylcholine binding to receptors?
Initiates an action potential propagated along the muscle
Where do nerves come from?
The motor neurone cell body of the spinal cord
What is each nerve coming from the spinal cord known as?
A motor neurone
What happens to the motor neurone axon?
It branches, and joins to muscle fibres
What initiates the contraction of skeletal muscle?
A nerve impulse along the motor neurone arriving at the neuromuscular junction
What does the nerve impulse arriving at the neuromuscular junction prompt?
The release of acetylcholine (ACh) into the synaptic cleft
What does the release of ACh cause?
Local depolarisation of the sarcolemma
What happens as a result of the depolarisation of the sarcolemma?
Voltage-gated Na + channels open, and so it enters the cell
What does the influx of Na + to the sarcolemma cause?
General depolarisation, that spreads into the sarcolemma and into T tubules
What happens to T tubules once they’ve been depolarised?
Voltage sensor proteins of the T tubules change their confirmation
What is activated due to the change in T tubule conformation?
Gated Ca 2+ -release channel of adjacent terminal cisternae
What happens once the Gated Ca 2+ -release channels are activated?
Ca 2+ is released rapidly from terminal cisternae into sarcoplasm
What happens when Ca 2+ is released into the sarcoplasm?
It binds to the TnC subunit of troponin, activating the contraction cycle
What happens to Ca 2+ in the sarcoplasm once it has performed it’s function?
It is returned to the terminal cisternae of the sarcoplasmic reticulum
What features do cardiac muscle fibres have?
- Centrally positioned nuclei
- Intercalated disks
How many nuclei do cardiac muscle fibres have per cell?
1 or 2
What is the purpose of intercalated discs?
For electrical and mechanical coupling with adjacent cells
How does cardiac muscle differ from skeletal muscle?
Distinct myofibrils are absent
What is present instead of distinct myofibrils in cardiac muscle?
Myofilaments of actin and myosin form continuous masses in the cytoplasm
What arrangement do intercalated disks have?
What do intercalated discs act as substitutes for?
Z bands where cells meet end to end
What junctions to intercalated discs have?
What is the purpose of gap junctions in intercalated disks?
What is the purpose of adherens-type junctions?
To anchor cells and provide anchorage for actin filaments
How to the T tubules of cardiac muscle differ from those in skeletal muscle?
They lie in register with the Z bands, and not the A-I junction
What does the close association of the sarcoplasmic reticulum and T tubules at diads permit?
The release of ionic calcium into the sarcoplasm and subsequent muscle contraction
What do all cardiac muscle cells exhibit?
Spontaneous rhythmic contraction
Where is the spontaneous rhythmic contraction of cardiac muscle cells evident?
In embryonic cardiac muscle and in isolated mature muscle cells in tissue culture
How are action potentials generated in the heart?
In the sinoatrial node
What happens once an action potential has been generated in the sinoatrial node?
It passes to the atrioventricular node, and from there to the ventricles
How are nerve impulses carried in the heart?
By specialised myocardial cells called Purkinje fibres
What cells make up the Purkinje fibres?
Distal conducting cells
What do tracts of Purkinje fibres do?
Transmit action potentials from ventricles from the AV node
In what cells are Purkinje fibres large?
- Abundant glycogen
- Spare myofilaments
- Extensive gap junction sites
Do Purkinje fibres conduct impulses faster or slower than cardiac muscle fibres?
What does the rapid conduction of Purkinje fibres enable?
Ventricles to contract in a synchronised manner
What shape are smooth muscle cells?
What features do smooth muscle cells not have?
- T tubules
What does contraction of smooth muscle rely on?
Describe the contraction of smooth muscle compared to skeletal and cardiac?
Slower, more sustained, requires less ATP
What is the cause of the differences in contraction of smooth muscle?
Due to latch system
How long can smooth muscles remain contracted for?
Hours or days
Can smooth muscles be stretched?
What stimuli do smooth muscles respond to?
- Nerve signals
- Local concentration of blood gases
What structures do smooth muscles form?
What walls do smooth muscles often form?
Contractile walls of passageways or cavities
What do contractile walls have the ability to do?
Where are contractile walls found?
- Vascular systems
- Respiratory tract
- Genitourinary system
Where can smooth muscle be of clinical significance?
- High blood pressure
- Abnormal gut mobility
How can modified smooth muscle cells occur?
- Singly as myoepithelial cells
- As myofibrast cells
What are myoepithelial cells?
Stellate cells forming a basketwork around the secretory units of some exocrine glands
Give 4 examples of where myoepithelial cells are found
- Sweat glands
- Salivary glands
- Mammary glands
- Ocular lens
What does contraction of myoepithelial cells around glands do?
Assists secretion of sweat, saliva or milk into secretory ducts
What is the purpose of myoepithelial cell contraction in the ocular lens?
Dilates the pupil
What do myofibroblasts do?
Produce collagenous matrix at sites of wound healing, and also contract
What are most smooth muscle cells innervated by?
Autonomic nervous system fibres
What do the autonomic nervous system fibres that innervate smooth muscle cells do?
Release their neurotransmitters from varicosities into a wide synaptic cleft
How are smooth muscles thick and thin filaments arranged?
Diagonally within cells, spiralling down the long axis
What is the result of the arrangement of the filaments in smooth muscle?
It contracts in a twisting way
What do intermediate filaments in smooth muscle attach to?