Muscle Tissue Flashcards
What is myalgia?
Muscle pain
What is Myasthenia?
Weakness of the muscle
What is 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?
The outer membrane of a muscle cell
What is the sarcoplasm?
The cytoplasm of the muscle cell
What is a sarcosome?
The mitachondria
What is the sarcomere?
The contraction unit in striated muscle
What is the sarcoplasmic reticulum?
The smooth endoplasmic reticulum of a muscle cell
What is the epimysium?
The dense connective tissue that surrounds the entire muscle tissue
What is the perimysium?
Connective tissue that surrounds a muscle fasicle
What is the endomysium
Connective tissue that surrounds individual muscle fibres
What is a muscle fibre?
A striated muscle cell, each cell contains numerous myofibrils
In myofibrils what are the thick and thin filaments?
Thin filaments = actin
Thick filaments = myosin
What is the structure of skeletal muscle fibres
- Have peripheral nuclei
- Bordered by endomysium that contain cappillaries and venules
- Striations of alternating dark A bands and light I bands with a thin Z band in the middle of each I band
What are t-tubules?
At each AI junction one transverse tubule extends down from sarcolemma
What is the sliding filament theory?
1) Myosin cross bridge attaches to the actin myofilament
2) Working stroke- the mysoin head pivots and bends as it pulls on the actin filament, sliding towards the M line. ADP and inorganic phosphate are released
3) As new ATP attaches to the myosin headgroup the cross bridge detatches (myosin head group in low energy configuration)
4) As ATP is split into ADP and Pi cocking of the myosin head occurs
What is the structure of myosin?
- An individual myosin molecule has a rod like structure from which it has two heads
- Each thick filament consists of many myosin molecules whose heads protrude ay opposite ends of the filaments
What two components make up an actin molecule?
Two protein components:
- F-actin fibres
- G-actin globules
What three components make up the thin filaments?
- Actin
- Tropomyosin
- Troponin
What is the M line?
Where the myosin molecules lack myosin heads
What is the role of calcium ions in the contraction mechanism?
- As calcium binds to TnC of troponin a conformational chage moves tropomyosin away from actin’s binding sites
- This allows myosin heads to bind actin, and contraction can begin
- The tropomyosin sits in the cleft of the G-actin ‘spheres’
What are the names and functions of the troponins involved?
TnT = binds to troponin TnC = binds to calcium TnI = Inhibitor
In 7 stages, explain innervation/contraction coupling
1) ACh released by motor neurone binds to receptors on motor end plate
2) Action potential generated in response to binding of ACh and subsequent end plate potential is propagated across the surface membrane and down t-tubules
3) Action potential triggers calcium release from sarcoplasmic reticulum
4) Calcium binds to TnC on actin filaments; conformational change leads to actin binding to myosin head groups
5) Powered by ATP, cross bridge cycling occurs
6) Calcium ions actively taken up by sarcoplasmic reticulum when there is no longer local action potential
7) With calcium no longer bound tropomyosin blocks actin binding sites
What is Duchene muscular dystrophy?
- Most common muscular dystrophy
- Inherited through X-linked recessive pattern
- Mutations of the dystrophin gene
- Absence of dystrophin allows:
- Excess calcium to enter the muscle cell
- Calcium taken up by the mitachondria
- Water taken with it
- Mitachondria burst
- Muscle cells burst (rhabdomyolysis)
- Creatine kinase and myoglobin levels high in the blood
What are the signs and symptoms of duchene muscular dystrophy?
- Sway back
- Poor balance
What markers are used for cardiac ischaemia?
Troponin I and T
What is botox and how is it used?
- Botulism toxin produced by Clostridium botulinum
- Blocks neurotransmitter release at the motor end plate
- Causes non-contractile state of skeletal muscle (flacid paralysis)
- Clinically used to treat muscle spasms (eg. cervical dystonia)
- Used cosmetically to treat wrinkles
What is organophosphate poisoning?
- Organophosphates are used as pesticides
- Inhibits normal functioning of ACh esterases so ACh activity is potentiated at the neuromuscular junction
What are the signs and symptoms of organophosphate poisoning?
Muscarinic Symptoms (SLUDGE) S = salivation L = Lacrimation U = urination D = defecation G = GI cramping E = Emesis
Nicotinic Symptoms (MTWTF) M = muscle cramps T = tacchycardia W = weakness T = Twitching F = Fasciculations
What is malignant hypothermia?
- Severe reaction to anaesthetics (succinylcholine)
- Autosomal recessive inheritance pattern- RyR1 gene
- Affects males more than females
- Causes massive contractile fasciculation
- -> muscle rigidity caused by increased calcium release leading to excessive heat and metabolic acidosis
- Leads to increased muscle breakdown and hyperkaleamia
