Somatic Nervous System And Muscle Contraction Flashcards
What are the three types of muscle?
β Skeletal
β Smooth
β Cardiac
How many muscle fibres are there in bundles and what are they called?
β fasciculi
What is the muscle fibre membrane called?
β Sarcolemma
What is a muscle fibre made from?
β 100s-1000s of myofibrils
What does the sarcoplasm contain?
β glycogen
β fat
β mitochondria
β enzymes
What does the sarcoplasmic reticulum do?
β Release Ca2+
What is a sarcomere?
β a contractile unit
What is the anisotropic band?
β high density band
What is the isotropic band?
β actin filaments
β titin
Describe how the actin myosin binding sites are exposed
β Troponin forms a complex with tropomyosin
β When Ca2+ binds to troponin it causes a conformational change to the troponin
β This causes the tropomyosin to move
β It exposes the actin-myosin binding sites
β Allows the myosin head to bind to the actin
Describe the sliding filament theory?
β Motor neuron stimulates a muscle to contract
β Release of Ca2+ into the muscle cell
β myosin has a globular head that ATP binds to
β ATP is hydrolysed
β Phosphate bond breaking provides energy for the power stroke
β releases ADP and an inorganic phosphate
βmyosin head is cocked
What does the somatic nervous system do?
β Provides voluntary control over skeletal muscle
What are motor neurons?
β Efferent neurons that innervate muscle
What does one motor unit include?
β A single motor neuron and all the muscle fibres it controls
How do motor units regulate the strength of contraction?
β Varying how many activated motor units are recruited
Describe what happens at a neuromuscular junction when a stimulus is applied?
β A stimulus from the brain causes an action potential
β ACh is released
β ACh binds to receptors and causes depolarisation of the membrane
β depolarisation moves along the membrane and through T tubules
β T tubules enter the muscle and cause depolarisation of the SR
β SR releases Ca2+
βIt is released into the cytosol and causes contraction of muscle fibres
What are the 2 types of cholinergic receptor?
β Muscarinic
β Nicotinic
How many molecules of ACh bind to a nicotinic receptor?
β 2
What does a single action potential produce?
β a single twitch
How do you get greater tension within a muscle?
β if an additional action potential arrives before the muscle relaxes from the first action potential
β There is summation of the two and greater contraction
What is tetanus?
β When the rate of action potentials is so high that the muscle doesnβt relax between stimuli
What is the mutated gene in DMD? (duchenne muscular dystrophy)
β dystrophin
What is the function of dystrophin?
β Connects the sarcomere to the plasma membrane
What happens to people with DMD?
β unable to walk by 10-12 years
β death by early to mid 20s
What are the effects of a lack of dystrophin?
β Dysfunction of the sarcolemma stretch
β ion pores open and there is increased intracellular Ca2+
β membrane gets torn
What is an indication of muscle damage in DMD?
β CK (creatine kinase) is lost from the cell and goes into the blood
β degradation of structural proteins
what is creatine kinase needed for?
β recycling of ATP
What enables patients with DMD to walk for longer?
β corticosteroids like prednisone
What is the definition of motor neuron disease?
β A group of disorders that selectively affect motor neurons
How do people with ALS die?
β Ventilatory failure
What is myasthenia gravis?
βchronic autoimmune motor neuron disease
β Body makes antibodies against AChRs at neuromuscular junctions
How do you treat myasthesia gravis?
β ACh inhibitors
