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:
at the threshold, voltage-gated Na+ channels open and sodium ions flow into the cell
the opening of Na+ channels increases depolarization
voltage-gated K+ channels open and potassium ions flow out of the cell
Na+ channels close while K+ channels are still open during hyperpolarization
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
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:
strength of the PSP
timecourse of PSP
distance from the synapse
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:
Spatial summation (different locations)
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