Topic 1-neurons

Cards (40)

  • Neuron: A nerve cell that carries electrical impulses around the body.
  • Structure of a neuron:
    1. Dendrite (input)
    2. Axon hillock (integrate)
    3. Cell body
    4. Axon (output)
    5. Synapse
  • Synapse: the gap between neurones that allows the transmission of nerve impulses
  • Membrane potential: The difference in electrical potential between the inside and outside of a cell.
  • Ion channel: passive transport, selective permeability
    Ion pumps: active transport, require energy (ATP)
  • Nernst equation: equilibrium potential for ion
    R = universal gas constant
    F = Faraday constant
    T = temperature
    z = valence
    ionO = outside concentration of ion
    ionI = inside concentration of ion
  • Sodium/potassium pump:
    • for 1 molecule of ATP, 2 K+ in, 3 Na+ out
    • results in a concentration gradient of greater Na+ outside and K+ inside
    • higher electrical potential outside
  • Neuronal signaling steps:
    1. Initiation of action potential (axon hillock)
    2. Propagation of action potential (axon)
    3. Synaptic transmission (synapse)
    4. Synaptic integration (axon hillock)
  • Hyperpolarization: the resting membrane potential of a neuron is more negative than the threshold potential
  • Inhibitory postsynaptic potentials: increase membrane potential
  • Depolarization: The process of the membrane becoming more positive, causing the sodium channels to open and the potassium channels to close
  • Excitatory postsynaptic potentials: A type of postsynaptic potential that is generated by the action potentials of an excitatory neuron
  • Action potential: rapid depolarization and repolarization of cell
    • occurs at threshold potential
    • all or none action
    • refractory period
  • Voltage-gated ion channels: open and close in response to transmembrane voltage changes
  • Action potential events:
    1. at the threshold, voltage-gated Na+ channels open and sodium ions flow into the cell
    2. the opening of Na+ channels increases depolarization
    3. voltage-gated K+ channels open and potassium ions flow out of the cell
    4. Na+ channels close while K+ channels are still open during hyperpolarization
    5. K+ channels close when the membrane is hyperpolarized and the membrane potential returns to a steady state
  • Absolute refractory period: The time interval between the initiation of an action potential and the next action potential.
  • Relative refractory period: The time taken for the membrane potential to recover after a stimulus
  • Hodgkin-Huxley model: A model of the action potential that shows the relationship between the voltage across the membrane and the rate of ion flow across the membrane
  • Electrotonic conduction: the passive flow of a change in electric potential along a nerve or muscle membrane
    • passive, relatively fast, exponentially attenuating
  • Self-regenerating propagation: active propagation of an action potential, travels long distances, relatively slow
  • Nodes of Ranvier: Gaps between myelinated axons in the CNS; helps to propagate an action potential down an axon
  • Myelin: A fatty substance that insulates axons and speeds up the transmission of nerve impulses
  • Speed of propagation depends on:
    • axon diameter
    • myelination
    • temperatue
  • Synaptic transmission: passing the signal from one cell to the next
    • neurotransmitter released from presynaptic cell
    • received by receptors on postsynaptic cell
    • ion channels open on postsynaptic cell
  • Postsynaptic potentials: the electrical signal that is generated at the end of a neuron after a synaptic connection has been made
    • depends on neurotransmitters from presynaptic cell
    • receptors of the postsynaptic cell
    • EPSP or IPSP
    • Fast or slow
  • Inhibitory postsynaptic potential: A type of EPSP that is caused by a decrease in the probability of firing
  • Neurotransmitters: chemicals that are released from neurons and diffuse across the synapse
    • major CNS neurotransmitters:
    • Glutamate (primary excitatory)
    • GABA (primary inhibitory)
  • Neurotransmitter characteristics:
    • synthesized by and localized within presynaptic neurons, stored in terminal bouton
    • released by presynaptic neurons when action potentials occur
    • postsynaptic neurons contain receptors specific to it
    • a mechanism exists to remove it after release
  • Neurotransmitter reuptake: The process by which neurotransmitters are removed from the synaptic cleft. Can be:
    • active reuptake
    • enzymatic breakdown
    • diffusion
  • Ionotropic receptors: Receptors that respond to changes in the ionic composition of the extracellular fluid (fast EPSP)
  • Metabotropic receptors: embedded in cell membrane; when neurotransmitter is detected, initiates an extended cascade of molecular processes that eventually leads to ion channels opening
  • Nicotinic acetylcholine receptor-channel: unlocked by two ACh molecules, can also be unlocked by nicotine
  • Electrical transmission: not always chemical synapses
    • Gap junction:
    • cell membrane of presynaptic neuron and postsynaptic neuron are flush against each other
    • open ion channels form a tunnel
    • change in membrane potential conducts straight through open channels into postsynaptic cell
  • Strength of PSP at the trigger zone at a certain time depends on:
    1. strength of the PSP
    2. timecourse of PSP
    3. distance from the synapse
    4. time since action potential
  • Summation of PSPs:
    • trigger zone starts at the resting membrane potential
    • EPSPs add to membrane potential
    • IPSPs subtract from membrane potential
    • an action potential fires if the sum exceeds the threshold potential
  • Types of PSP summation:
    1. Spatial summation (different locations)
    2. Temporal summation (different times)
  • Artificial neural network: A network of interconnected nodes that mimics the structure of the brain.
    • Applications:
    • understanding mind and brain function
    • artificial intelligence
  • Brainbow: A technique that uses fluorescent dyes to label different parts of the brain.
  • Green fluorescent protein:
    • originally isolated from a jellyfish
    • gene for GFP inserted into DNA near the gene for a target protein
    • when the target protein is expressed, so is GFP
  • Brainbow basics:
    • a single brainbow transgene expresses red, cyan, or yellow
    • with multiple brainbow transgenes more colours can be expressed