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Flashcards

Action potentials and muscles

Adrianna Bialecka Pharmacology University English 64 cards

Action potentials and muscles

Cards in this deck (64)

  1. 1What does the nervous system do?Regulates the major organs
    e.g. heart, lungs, vasculature, skeleted muscle
    -Pharmacological interference with this mode of regulation can be medically useful
  2. 2What are the classifications of the nervous system?What are the classifications of the nervous system?
  3. 3What is the resting membrane potential?-all living cells exhibit a RMP
    -The RMP is established by ion channels and ion pumps
    -its at -70mV    What is the resting membrane potential?
  4. 4What happens when excitable cells such as neurons and muscle/glands can alter the ion permeability of their membranes?can result in action potentials that travel along the neuron and transmit a signal
    -the propagation of action potentials is how the nervous system signals over long distances
  5. 5What are action potentials?it is the change in electrical potential that occurs across a cell membrane during the passage of a nerve signal
    -a localised and transient switch in electrical potential across the plasma membrane [approx. -60mV or -70mV to +45mV]
  6. 6What happens during an action potential?A cycle of membrane depolarisation, repolarisation, hyperpolarisation and return to the resting value
    -lasts 1-2ms
    -can be generated hundreds of times per second    What happens during an action potential?
  7. 7What causes an action potential?Electrical changes are due to voltage-gated Na+ and K+ channels that open and shut in response to changes in the membrane potential
    -Once a threshold potential is attained the cell responds with an all-or-nothing depolarisation
    -The cell responds in its own characteristic manner, irrespective of the magnitude of the stimulus
    -Once it is initiated it will spread along the axon and will NOT decreases in amplitude
  8. 8What are the five steps involved in action potential formation?1. Resting membrane potential
    2. Depolarisation
    3. Repolarisation
    4. Hyperpolarisation
    5. Return to resting membrane potential    What are the five steps involved in action potential formation?
  9. 9What causes resting membrane potential?-All voltage-gated Na+ channels are closed
    -All voltage K+ channels are open
    -All voltage-gated K+ channels are closed    What causes resting membrane potential?
  10. 10What causes Depolarisation?-A stimulus increases the membrane potential to a less negative value
    -At a critical threshold potential, Depolarisation activates voltage-gated Na+ channels
    -Changes in the conformation of these voltage-gated channels allow fast influx of Na+ into the cells    What causes Depolarisation?
  11. 11What are the two driving forces (acting in the same direction) that cause depolarisation?1. Na+ concentration gradient (low Na+ in IC)
    2. Resting membrane potential (negative IC)
  12. 12What happens during depolarisation?The permeability of the stimulated membrane region becomes vastly greater for Na+ than for K+
    -Thus the negative state inside the cell is reversed and the membrane potential reaches positive values    What happens during depolarisation?
  13. 13What causes repolarisation?-Na+ channels become inactivated, so further net inward movement of Na+ ceases
    -Delayed, voltage-gated K+ channels open, which repolarises the membrane (positive charge moves out)    What causes repolarisation?
  14. 14What causes Hyperpolarisation?-Before the efflux of K+ returns to resting level due to the inactivation of the voltage-gated K+ channels, a hyperpolarisation is observedWhat causes Hyperpolarisation?
  15. 15What causes the return to resting potential?-The number of ions that move to cause the large changes in action potentials is small (1 in 100,000)
    -Thus only small changes in total intracellular concentrations are produced
    -Ionic concentration gradients are re-established by Na+-K+ ATPase    What causes the return to resting potential?
  16. 16Summary of the components of action potentialsSummary of the components of action potentials
  17. 17What are action potential thresholds?-Not all stimuli cause sufficient depolarisation to generate an action potential
    -threshold is typically a stimulus of +15mV
    -Stimuli above threshold result in sufficient opening of Na+ channels so that the movement of Na+ IC exceeds movement of K+ EC
    -Above threshold stimuli initiate a positive feedback cycle
    -The amplitude of the action potential is all or nothing
    -dependent on initiating the positive feedback cycle not the stimulus strength
    -Subthreshold stimuli fail to activate the positive feedback cycle    What are action potential thresholds?
  18. 18How are action potential thresholds all or nothing?How are action potential thresholds all or nothing?
  19. 19Where do refractory states develop?At a membrane site which has just fired an action potentialWhere do refractory states develop?
  20. 20What is the absolute refractory period?Nerve or muscle membrane can not be excited even by the strongest stimulus
  21. 21What is the relative refractory period?Nerve or muscle membrane can be excited only by a stimulus greater than the initial threshold stimulus
  22. 22What effect does refractory period have on AP direction?can only travel in the direction away from the neuronal cell bodyWhat effect does refractory period have on AP direction?
  23. 23What causes the refractory periods?What causes the refractory periods?
  24. 24What are the two major ion channels in action potential formation?1. Voltage-gated e.g. voltage gated Na+ and K+ channels (AP) (open upon voltage change)
    2. Ligand-gated e.g. nicotinic Ach receptor, glutamate receptors (open upon ligand-binding; ionotropic receptors)
  25. 25How do the ion channels work in action potential formation?-Ion channels regulate the flux of ions across membranes by gating (open/closed) the channel pore
    -Ion channels influence the rate, not the direction, of ion flow across membrane
    -The rate and direction of ion flow, depend on both the concentration and electrical gradients across the membrane
    -Pore size and charge interactions determine the ion selectivity of channels
  26. 26What pharmacological agents act on ion channels?a) As drugs
    e.g. Na+ channel blockers as local anesthetics
    b) As research tools
    -neurotoxins to characterise the pharmacological, electrophysiological and biochemical properties of ion channels
    e.g. TTX (tetrodotoxin) to abolish Na+ current    What pharmacological agents act on ion channels?
  27. 27What are the sites of drug action at voltage-gated Na+ channels?What are the sites of drug action at voltage-gated Na+ channels?
  28. 28How is an action potential signal transmitted?1) from neuron to neuron (synapse)
    2) from neuron to muscle/gland
  29. 29What are the two types of synaptic transmission?1. Electrical (minority)
    2. Chemical (majority)
  30. 30What can information be transmitted from to?1. Neuron to Neuron
    2. Neuron to Muscle
  31. 31How does neurotransmission work in the neuron?How does neurotransmission work in the neuron?
  32. 32What are electrical synapse?-Direct flow of current from the presynaptic to the postsynaptic neuron through gap junctions
    -Allows for rapid and synchronous firing of interconnected cells
  33. 33What are chemical synapse?-Release of transmitter from presynaptic membrane, diffusion across synaptic cleft and bind to postsynaptic receptors
    -Allows for amplification of the synaptic response, i.e. a single AP releases thousands of neurotransmitter molecules
  34. 34Electrical synapse vs Chemical synapseElectrical synapse vs Chemical synapse
  35. 35What happens at chemical transmission?-At chemical synapses the pre- and postsynaptic elements are separated by a synaptic cleft
    -Chemical synaptic transmission involves a delay between action potentials in the pre- and post synaptic cells    What happens at chemical transmission?
  36. 36What are the two processes of chemical transmission?1) The presynaptic transmitting process
    2) The postsynaptic receptive process
  37. 37What happens during the presynaptic transmitting process?What happens during the presynaptic transmitting process?
  38. 38What happens during the postsynaptic receptive process?What happens during the postsynaptic receptive process?
  39. 39What is the summary of chemical transmissions?What is the summary of chemical transmissions?
  40. 40What small molecules can serve as transmitters?-Ach (acetylcholine)
    -GABA (y-aminobutyric acid)
    -Glycine
    -Glutamate
    -Serotonin
    -Dopamine
    -Noradrenaline (norepinephrine)    What small molecules can serve as transmitters?
  41. 41What does the action of a specific NT depend on?the properties of the receptors with which it binds e.g. ACh excites certain postsynaptic cells, while inhibiting others
    -ACh produces synaptic excitation at nicotinic ACh receptors at the neuromuscular junction
    -ACh slows heart at inhibitory muscarinic ACh receptors
  42. 42What are the two possibilities when neurotransmitters bind with postsynaptic receptors?i) opens postsynaptic ion channels (Na+, K+) resulting in depolarisation
    -excitatory postsynaptic potential (EPSP) (not an action potential)
    ii) opens postsynaptic ion channels (K+, Cl-) resulting in hyperpolarisation
    -inhibitory postsynaptic potential (IPSP)    What are the two possibilities when neurotransmitters bind with postsynaptic receptors?
  43. 43What do EPSP do in synaptic transmission?What do EPSP do in synaptic transmission?
  44. 44What do IPSP do in synaptic transmission?What do IPSP do in synaptic transmission?
  45. 45How do Chemical/Neurotransmitter receptors work?-Neurotransmitter receptors are membrane-spanning proteins
    -The receptor region exposed to the external environment of the cell recognizes and binds the neurotransmitter released from the presynaptic cell    How do Chemical/Neurotransmitter receptors work?
  46. 46What is the pharmacology at chemical synapses?What is the pharmacology at chemical synapses?
  47. 47What is Muscle?Muscle is an important regulator of many physiological systems
    e.g. skeletal, heart, vasculature, respiratory tracts
    -Thus it is a major target of drug action
  48. 48What are the three types of muscles?1. Skeletal (supports and moves skeleton)
    2. Cardiac (muscle of heart)
    3. Smooth (surrounds intestinal, respiratory, blood vessel tracts, etc)
  49. 49What is the structure of skeletal muscle?-The largest mass of somatic musculature
    -Most attached to bone (by tendons)
    -Responsible for movement and skeletal support
    -Contraction is usually voluntary
    -Muscle fibre (myocyte)- cylindrical, multinucleated muscle cell (80micrometers diameter, 20cm length
    -Composed individual mononuclear cells (myoblasts) fuse together
    -Arranged in parallel between tendons
    -Surrounded by a cell membrane (sarcolemma)
    -Muscle fibres bundle together to produce a muscle fascicle
    -A group of fascicles form a muscle    What is the structure of skeletal muscle?
  50. 50How is skeletal muscle excited?-The skeletal neuromuscular junction (NMJ)
    -Junction between somatic neuron and skeletal muscle (motor end plate)
    -Specialised sunapse
    -Usually located in middle of muscle fibre    How is skeletal muscle excited?
  51. 51How does the skeletal NMJ work?How does the skeletal NMJ work?
  52. 52How does skeletal muscle organised?-Skeletal muscle fibres are straited
    -Bundles of filaments called myofibrils run along axis of the cell
    -A serries of perpendicular light and dark bands
    -Due to an arrangement of thick and thin filaments in the cytoplasm
    -Repeated to form the basic contractile unit (sarcomere).    How does skeletal muscle organised?
  53. 53What does skeletal muscle look like (histology)?-Thick filaments: composed of the contractile protein myosin
    -Thin filaments: contain proteins actin, troponin and tropomyosin    What does skeletal muscle look like (histology)?
  54. 54How does skeletal muscle contract?-AP opens Na+ channels, propagates rapidly
    -T-tubules connect plasma membrane and sarcoplasmic (SR)
    -T-tubule contains dihydropyridine receptor (DHPR) (L-type Ca2+ channel)
    -upon depolarisation DHPR activates Ryanodine Receptor (RyR) in SR
    -release of Ca 2+ from SR into cytoplasm
    -troponin/tropomyosin blocks actin-myosin interaction
    -Ca 2+ binding to troponin release this block
    -Actin-myosin bind ->contraction    How does skeletal muscle contract?
  55. 55What is the diagram showing NMJ and muscle contraction fully?What is the diagram showing NMJ and muscle contraction fully?
  56. 56What is the sliding filament theory?-the way in which skeletal muscle contraction occurs upon binding of Ca2+ to troponin
  57. 57What is the structure of Cardiac muscle?-The walls of the heart (myocardium) are composed of cardiac muscle cells
    -The cells (cardiomyocytes) are tightly-bound and arranged in layers surrounding the heart chambers
    -Contraction enables blood to pump
    -Cardiac muscle are striated
    -Sarcomeres contains thick myosin and thin actin filaments
    -Short (2 micrometers) cells with branching processes
    -Separated from neighbouring cells by intercalated discs    What is the structure of Cardiac muscle?
  58. 58How does excitation of cardiac muscle work of a single unit?-A stimulus applied to any one part of the myocardium induces a wave of depolarisation, causing the entire myocardium to contract
    -Gap junctions present in the intercalated discs allow this spread of excitation between adjacent cells    How does excitation of cardiac muscle work of a single unit?
  59. 59How does cardiac tissue display automaticity?-displays automaticity (ability to initiate its own beat) and rhythmicity (regularity of activity)- does not require innervation
    -Initial Spontaneous depolarisation occurs in specialised cardiac nodes (sinoatrial node) which act as the pacemaker= generates pacemaker potential due to spontaneous reduction in K+ permeability
    -Action potential spreads through myocardial cells via gap junctions
    -Pacemaker potential can be modulated by sympathetic and parasympathetic (autonomic) stimulation
  60. 60How does the cardiac muscle contract?-AP dependent on voltage-gated Na+ and Ca 2+ channels
    -No direct coupling between plasma membrane and SR
    -Voltage-gated Ca2+ channels in plasma membrane open during repolarisation plataeu
    -Ca2+ entry activates Ryanodine Receptors (RyR) in SR
    -Release of Ca 2+ from SR into cytoplasm (positive feedback)
    -Ca2+ binding to troponin releases block
    -Actin-myosin bind ->contraction    How does the cardiac muscle contract?
  61. 61What is the structure of smooth muscle?-Major component of the airways, vasculature, digestive tract, urogenital tract,..
    -Mononuclear, spindle-shaped cells (1-2 micrometers diameter)
    -Smooth muscle cells are non-striated
    -Actin and myosin are present, but not arranged in regular arrays (sarcomeres)
    -Actin-containing filaments anchored to the cell membrane or dense bodies within the cytoplasm    What is the structure of smooth muscle?
  62. 62What controls smooth muscle contractions?-Innervated by sympathetic and parasympathetic (autonomic) stimulation
    -Involuntary
    -Do not have specialised motor end-plate region
    -Autonomic neurons divide into varicosities filled with neurotransmitters
    -Can act as a multi unit (multiple varicosities) or act as a single unit (one line of varicosities and gap junctions)    What controls smooth muscle contractions?
  63. 63What do neurotransmitters do?-can be excitatory (contract) or inhibitory (relax)
    -Some smooth muscles have spontaneous pacemaker potentials- enable normal contraction without innervation    What do neurotransmitters do?
  64. 64How does smooth muscle contract?-AP not required (those present depend on voltage-gated Ca 2+ channels
    -No direct coupling between plasma membrane and SR
    -Ca 2+ enters by
    >voltage-gated channels (AP)
    >ligand-gated cation channels (transmitters e.g. P2XR and ATP)
    >G-protein activation of IP3, activating IP3 receptors/channels on ER
    -Elevated [Ca2+] binds calmodulin (CaM)
    -Ca2+-CaM activates myosin light chain kinase (MLCK)
    -MLCK phosphorylates myosin
    -Actin-Myosin bind ->contraction    How does smooth muscle contract?

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University Pharmacology Flashcards on Action potentials and muscles, created by Adrianna Bialecka on 19/02/2025.
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