Muscle Structure and Contraction Flashcards
1
Q
How is muscle contraction regulated?
A
- SR of striated muscle specialised for sequestration of Ca ions released upon receiving signal relays by T-tubules from NMJ
2
Q
What is a T-tubule?
A
- Tubule that passes in a transverse manner from sarcolemma across a myofibril of striated
3
Q
What triggers contraction and regulation in skeletal and cardiac muscle?
A
- Triggered when AP in neuron reaches NMJ and ACh released
- Electrical signal propagated along sarcolemma into T-tubules
- AP passes through T tubules to SR, causing Ca release
- Ca ions diffuse through sarcoplasm and bound by Tn-C subunits of troponin complex on actin filaments
4
Q
What are ryanodine receptors?
A
- Calcium channels located on SR terminal cisternae
- Sensitive to depolarisation of T-tubule
5
Q
What diseases are associated with muscle structure and contraction?
A
- Duchenne and Becker muscular dystrophy
- Limb girdle muscular dystrophies
- Familial hypertrophic cardiomyopathy
- Malignant hyperthermia
6
Q
Describe Duchenne and Becker Muscular Dystrophy
A
- Only males
- Lack dystrophin protein
- Becker MD affects same protein- only partly functional-milder
- Duchenne is early onset and most common MD
- X-linked recessive inherited from mother 2/3 times
7
Q
What is dystrophin?
A
- Structural protein that acts as scaffolding for actin
8
Q
Describe limb girdle muscular dystrophies
A
- Heteregenous set of progressive genetic disorders characterised y atrophy of voluntary muscles of hip and shoulder areas
- Age, severity and progression is very variable
- Types 1A-G and 2A-W- many different types
- Characterised by different mutations across different gene coding proteins that function in sarcolemma
9
Q
Describe familial hypertrophic cardiomyopathy
A
- 1/500 worldwide
- Caused by usually dominant mutations in genes
- Exact mechanism unknown, can develop anytime
- Variable symptoms
- Increased risk of sudden death
10
Q
What genes are often mutated in familial hypertrophic cardiomyopathy?
A
- MYH7- cardiac β myosin heavy chain
- MYBPC3- cardiac myosin binding protein C- associated with myosin and provides structural supports, helps regulate muscular contractions
- TNNT2 and TNNI3 make cardiac troponin T and I
11
Q
What fuels muscle contraction?
A
- ATP immediate source of energy for contraction
- Although muscle fibres contain only enough ATP for a few twitches
- ATP store is replenished as needed
12
Q
What sources of high energy phosphate are there to keep ATP source filled?
A
- Phosphocreatine
- Muscle glycogen
- Cellular respiration
13
Q
What is phosphocreatine?
A
- Provides short bursts of energy used to regenerate ATP rapidly for first few mins prior to full activation of glycogenolysis
- Synthesised from Arg and Gly and phosphorylated by creatine kinase
14
Q
What are the three forms of creatine kinase?
A
- MM (muscle)
- BB (brain)
- MB (cardiac tissue)
15
Q
What is creatinine?
A
- Creatinine-P is unstable and undergoes slow, spontaneous degradation to P and creatinine- excreted by muscle into plasma and filtered by urine at contrast rate
- Normal plasma conc- 20-80 mmol/L
- Albumin to creatinine ratio in urine used to assess elevated protein in urinw and marker of kidney damage
