Muscular System Flashcards
What is myalgia?
Muscle pain
What is myasthenia?
Weakness of the muscles
What is the myocardium?
Muscular component of the heart
What is myopathy?
Any disease of the muscles
What is myoclonus?
A sudden spasm of the muscles
What is the sarcolemma?
Outer membrane of a muscle cell
What is the sarcoplasm?
Cytoplasm of a muscle cell
What is the sarcoplasmic reticulum
The smooth ER of a muscle cell
What are the three forms of muscle?
Cardiac, smooth and skeletal
Which forms of muscle are striated?
Skeletal and cardiac
Which forms of muscle are non-striated?
Smooth
What is the cell length of skeletal muscle?
1mm-20cm
What is the cell length of cardiac muscle?
50-100 micrometres
What is the cell length of smooth muscle?
20-200 micrometres (but up to 0.5mm in uterus)
What is the cell diameter of skeletal muscle?
10-100 micometres
What is the cell diameter of cardiac muscle?
10-20 micrometres
What is the cell diameter of smooth muscle?
5-10 micrometres
What is the cell morphology of skeletal muscle?
Long parallel cylinders
Multiple peripheral nuclei
Striations
What is the cell morphology of cardiac muscle?
Short branched cylinders
Single central nucleus
Striations
What is the cell morphology of smooth muscle?
Spindle shaped
Tapering ends
Single central nucleus
No striations
On the basis of certain stains, which three fibre types have been found in skeletal muscle?
Narrower red fibres
Intemediate pink fibres
Wider white fibres
Which muscle fibre type has numerous mitochondria and rich vascularisation?
Red
Which muscle fibre type is involved in faster, stronger contractions?
White
Which enzymes are red fibres rich in?
Oxidative enzymes. Poor in ATPase
Which muscle fibre type has more neuromuscular junctions?
White
Where are the typical locations of red fibres?
Limb muscles, postural muscles of back
Where are the typical locations of white fibres?
Extraocular muscles, muscles controlling fingers
What is myoglobin?
A red protein containing haem, functioning as an oxygen-storing molecule providing oxygen to the working muscles
Where is myoglobin present?
In skeletal and cardiac muscle but not smooth
When does haemoglobin often give up oxygen to myoglobin?
When pH is lowered - active muscles produce CO2/lactic acid which results in more acidic conditions that promotes this transfer
If there are many nuclei and they are peripheral, which type of muscle is it?
Skeletal
What is the perimysium?
Connective tissue carrying nerves and blood vessels that surrounds a fascicle (bundle of muscle fibres)
What are the dark longitudinal streaks in a histological slide of skeletal muscle fibres?
Mitochondria
What is a striated muscle cell called?
Muscle fibre
What is a myofibril?
Any of the elongated contractile threads found in striated muscle cells.
Which are the thin filaments in muscle fibres?
Actin, tropomyosin, troponin
Which is the thick filament in muscle fibres?
Myosin
What is the A band?
The comparatively dark area entirely within a sarcomere. This area is composed of thick filaments and thin filaments.
What is the I band?
The lighter areas alternating with A-Bands; these areas straddle the Z-line and are composed of thin filaments
What is the H zone?
A subdivision of the A-Band in the center of the sarcomere where only thick filaments are present
Where do thin filaments attach?
Z line
Where do thick filaments attach?
Span the A band
What is the Z line?
The partitions within a muscle fibre that section it into sarcomeres.
What is the sarcomere?
The portion of a muscle fibre between two successive Z-lines.
What happens when destruction of muscles > replacement?
Atrophy
What happens when replacement of muscles > destruction?
Hypertrophy
What does disuse atrophy involve?
Loss of protein, reduced fibre diameter, loss of power
When do muscles start to atrophy with age?
+30 years old
How much loss of muscle is there by 80 years old?
50%
What does hypertrophy involve?
More contractile proteins, increase in fibre diameter, more power
What happens to the I band during contraction?
Shrinks
What happens to the A band during contraction?
Does not shrink
What happens to the H zone during contraction?
Shrinks
How is muscle length adjusted?
Increases by frequent stretching (addition of sarcomeres)
What is thought to often feature in some cardiac pathologies eg enlarged ventricles?
Overstretching, such that the A and I filaments can no longer re-engage
What is used as a marker for cardiac ischaemia?
Troponin assays
How soon is troponin released from ischaemic cardiac muscle?
Within an hour
How soon must you measure troponin levels after cardiac ischaemia?
Within 20 hours
True or False:
Quantity of troponin is proportional to degree of damage
False
What is creatine kinase?
An important enzyme in metabolically active tissues like muscle
What can creatine kinase be used to diagnose?
Heart attacks (MIs)
True or False:
Creatine kinase increase is largely proportional to infarct size
True
What can a rise in plasma creatine kinase also result from?
Intramuscular injection, vigorous exercise, a fall (especially in the elderly), rhabdomyolysis, muscula dystrophy and acute kidney injury
What does each thick filament consist of?
Many myosin molecules, whose heads protrude at opposite ends of the filament
What does the actin filament fom?
A helix with tropomyosin molecules coiled around it
What is attached to each tropomyosin molecule?
Troponin complex
What happens when increased amounts of ionic calcium bind to TnC of troponin?
A conformational change that moves tropomyosin away from actin’s binding sites - allowing myosin heads to bind actin and contraction to begin
As the myosin head pivots and bends, pulling the actin filament, what is released?
ADP and Pi
When new ATP attaches to the myosin head, what happens?
The cross bridge detaches
As ATP is splt into ADP and Pi in the last step of muscle contraction, what happens?
Cocking of the myosin head occurs
What is the rigor configuration?
Myosin head tightly bound to actin molecule
What causes rigor mortis?
Lack of ATP that thus perpetuates the tight binding of the myosin head to actin
What are the stages of muscle contraction?
Myosin head attaches to actin;
ATP binds the myosin head causing it to uncouple from actin;
Hydrolysis of ATP causes the uncoupled myosin head to bend and advance a short distance (5nm);
The myosin heaed binds weakly to actin filament causing release of Pi which strengthens binding and causes the power stroke in which the myosin head returns to its former position
ATP binds to the myosin head causing detachment from actin, myosin head binds tightly again and cycle repeats
What is a t tubule?
A deep invagination of the sarcolemma
What are the events leading to contraction of skeletal muscle?
1) Nerve impulse along motor neuron axon arrives at neuromuscular junction
2) Prompts release of acetylcholine into synaptic cleft causing local depolarization of sarcolemma
3) Voltage-gated sodium channels open causing sodium ions to enter the cell
4) General depolarization spreads over sarcolemma and into T tubules
5) Voltage sensor poteins of T tubule membrane change their conformation
6) Gated calcium ion release channels are activated
7) Calcium ions are rapidly released into sarcoplasm
8) Calcium ions bind to the TnC subunit of troponin, thus initiating the contraction cycle
In cardiac muscle, distinct myofibrils are absent. What do the myofilaments form instead?
Actin and myosin form continuous masses in the cytoplasm
In contrast to skeletal musscle, where do the T tubules of cardiac muscle lie in register with?
The Z bands, not the A-I junction
What is hypertrophy of the cells?
Enlargement of individual cells
What is hyperplasia of the cells?
Multiplication of the cells
How do tissues increase in size?
Hypertrophy or hyperplasia
What is the release of natriuretic peptdes by the heart usually in response to?
Heart failure - stimulated by atrial and ventricular distension
What are the main physiological actions of natriuretic peptides?
Reduce arterial pressure by decreasing blood volume or vascular resistance
What is Atrial Natriuretic Peptide (ANP)?
28 amino acid peptide that is synthesized, stored and eleased by atrial myocytes in response to atrial distension.
In which states are elevated levels of ANP found in?
Hypervolemic states which occur in congestive heart failure
What is Brain-type Natriuretic Peptide (BNP)?
32 amino acid peptide that is synthesised by the ventricles and brain.
What does proteolysis of pro-BNP result in?
pro-BNP (108 amino acids) results in BNP (32 amino acids) and the N terminal piece of pro-BNP - NT-pro-BNP (76 amino acids)
What are both BNP and NT-pro-BNP diagnostic markers for?
Heart failure
What to natriuretic peptides serve as?
A counter-regulatory system for the renin-angiotensin-aldosterone system
What are Purkinje fibres?
Purkinje fibers are special fibers that are located in the atrioventricular, or AV, bundle of the heart. Their function is to send nerve impulses to the cells in the ventricles of the heart and cause them to contract and pump blood either to the lungs or the rest of the body.
What do Purkinje fibres consist of?
Large cells with abundant glycogen, sparse myofilaments and extensive gap junction sites
Does contraction still rely on actin-myosin interactions in smooth muscle?
Yes
What are myoepithelial cells?
Modified smooth muscle cells forming a basketwork around the secretory units of some exocrine glands
How does skeletal muscle tissue regenerate?
Mitotic activity of satellite cells so that hyperplasia follows muscle injury. Satellite cells can also fuse with existing muscle cells to increase mass
Is cardiac muscle capable of regeneration?
No, following damage, fibroblasts invade, divide and lay down scar tissue
Can smooth muscle cells divide?
Yes. Smooth muscle cells retain their mitotic activity and can form new smooth muscle cells
