Somatic Nervous System And Muscle Contraction Flashcards
What are the three types of muscle?
→ Skeletal
→ Smooth
→ Cardiac
How many muscle fibres are there in bundles and what are they called?
→ fasciculi
What is the muscle fibre membrane called?
→ Sarcolemma
What is a muscle fibre made from?
→ 100s-1000s of myofibrils
What does the sarcoplasm contain?
→ glycogen
→ fat
→ mitochondria
→ enzymes
What does the sarcoplasmic reticulum do?
→ Release Ca2+
What is a sarcomere?
→ a contractile unit
What is the anisotropic band?
→ high density band
What is the isotropic band?
→ actin filaments
→ titin
Describe how the actin myosin binding sites are exposed
→ Troponin forms a complex with tropomyosin
→ When Ca2+ binds to troponin it causes a conformational change to the troponin
→ This causes the tropomyosin to move
→ It exposes the actin-myosin binding sites
→ Allows the myosin head to bind to the actin
Describe the sliding filament theory?
→ Motor neuron stimulates a muscle to contract
→ Release of Ca2+ into the muscle cell
→ myosin has a globular head that ATP binds to
→ ATP is hydrolysed
→ Phosphate bond breaking provides energy for the power stroke
→ releases ADP and an inorganic phosphate
→myosin head is cocked
What does the somatic nervous system do?
→ Provides voluntary control over skeletal muscle
What are motor neurons?
→ Efferent neurons that innervate muscle
What does one motor unit include?
→ A single motor neuron and all the muscle fibres it controls
How do motor units regulate the strength of contraction?
→ Varying how many activated motor units are recruited
Describe what happens at a neuromuscular junction when a stimulus is applied?
→ A stimulus from the brain causes an action potential
→ ACh is released
→ ACh binds to receptors and causes depolarisation of the membrane
→ depolarisation moves along the membrane and through T tubules
→ T tubules enter the muscle and cause depolarisation of the SR
→ SR releases Ca2+
→It is released into the cytosol and causes contraction of muscle fibres
What are the 2 types of cholinergic receptor?
→ Muscarinic
→ Nicotinic
How many molecules of ACh bind to a nicotinic receptor?
→ 2
What does a single action potential produce?
→ a single twitch
How do you get greater tension within a muscle?
→ if an additional action potential arrives before the muscle relaxes from the first action potential
→ There is summation of the two and greater contraction
What is tetanus?
→ When the rate of action potentials is so high that the muscle doesn’t relax between stimuli
What is the mutated gene in DMD? (duchenne muscular dystrophy)
→ dystrophin
What is the function of dystrophin?
→ Connects the sarcomere to the plasma membrane
What happens to people with DMD?
→ unable to walk by 10-12 years
→ death by early to mid 20s
What are the effects of a lack of dystrophin?
→ Dysfunction of the sarcolemma stretch
→ ion pores open and there is increased intracellular Ca2+
→ membrane gets torn
What is an indication of muscle damage in DMD?
→ CK (creatine kinase) is lost from the cell and goes into the blood
→ degradation of structural proteins
what is creatine kinase needed for?
→ recycling of ATP
What enables patients with DMD to walk for longer?
→ corticosteroids like prednisone
What is the definition of motor neuron disease?
→ A group of disorders that selectively affect motor neurons
How do people with ALS die?
→ Ventilatory failure
What is myasthenia gravis?
→chronic autoimmune motor neuron disease
→ Body makes antibodies against AChRs at neuromuscular junctions
How do you treat myasthesia gravis?
→ ACh inhibitors
