The Muscular System Flashcards
Functions of skeletal muscle
- Produce movement of body parts
- Support soft tissues
- Maintain body posture and body position
- Communication
- Control of openings and passage ways
- Maintain body temerature
Universal characteristics of muscles
- Reponsiveness
- Conductivity
- Contractility
- Extensibility
- Elasticity
What are myofibrils surrounded by?
Epimysium
How many heads does each myosin filament have?
About 300 heads
How many cycles does a head go through each second?
About 5
What does Cap Z do? Where is it present?
Caps actin polymerisation. Present on Z disc/line
What does nebulin do?
Binds to actin and acts as a molecular ruler to establish the length of the actin filament
What does tropomodulin do?
Caps depolymerisation on actin on minus end
Which end of actin is at the Z discs/lines?
Plus end
What does titin do?
Acts as a spring. Folds and unfolds for myosin
Sarcomere: Power stroke
- ATP binds to myosin head, causing dissociation of the actin-myosin complex
- ATP hydrolysed –> myosin head returns to resting conformation
- Cross-bridge forms and myosin head binds to new position on actin
- P is released. Myosin heads change conformation –> power stroke
- ADP is released
How is a contraction initiated?
- Nerve impulse reaches neuromuscular junction. Ca2+ channels open and influx of Ca2+ causes release of Each by exocytosis
- Binding of ACh to post-synaptic receptors causes Na+ channels to open and Na+ enters sarcoplasm which results in AP
- Ca2+ released by sarcoplasmic reticulum and binds to troponin –> conformational change which displaces tropomyosin thus unmasking myosin binding sites
- Myosin heads slide along actin filament - requires ATP
- Process terminates when nerve impulse stops. ACh then degraded by acetylcholinesterase. Ca2+ reabsorbed and detaches from troponin
What do calcium ions bind do in the sarcomere?
Troponin (C)
Give an example of a chemical that blocks Na+ channels
Tetrodotoxin
Give an example of a chemical that blocks Ca2+ channels
omega-Conotoxin
Give an example of a chemical that blocks K+ channels
Dendrotoxin
Give an example of a chemical that stops ACh release
Tetanus toxin
Botulinum toxin
Give an example of a chemical that blocks AChR channels
d-Tubocurarine
What does dendrotoxin act on?
K+ channels
What is botulinum toxin often found in?
Homemade preserves (jams)
What does botulinum toxin produce? What does the product do?
Endoproteinase - cleaves proteins required for ACh exocytosis
Clinical uses of botulinum toxin
- Treatment of strabismus - cross-eyed
- Bleapharospasm - uncontrolled eyelid muscles
- Botox
Which fibres are metabolically expensive: slow or fast ?
Fast
What colour muscle is slow oxidative muscle?
Red
Example of slow oxidative muscle
Soleus
What colour is fast glycolytic (IIb) muscle?
White
Slow oxidative or fast glycolytic: Which is fatigue resistant?
Slow oxidative
Slow oxidative or fast glycolytic: Which has a low glycogen content?
Slow oxidative
Slow oxidative or fast glycolytic: Which has few mitochondria?
Fast glycolytic
What are type IIb muscle fibres? Give an example
Fast oxidative. Gastrocnemius
Phosphocreatine reaction
Creatine Phosphocreatine
Requires creatine kinase
What is fatigue?
Weakening of a muscle
Shortage of glycogen
Increase in lactic acid levels
Failure of motor neurone to produce ACh
