1.5: electrical signaling by neurons

humans are a

• biological/physiological system, not an electrical system

  • we rely on our brain to process and convey information quickly and effectively

how do brains process and convey info quickly and effectively

• by way of neurons and their axons and synapses

• neurons send information via electrical signaling

dendrites

receive information

soma (cell body)

proceses information

axon hillock

most proximal part of axon (where an AP can start)

myelin sheath

• insulation for the axon

node of ranvier

space between each myelin

• holds voltage gated channels

presynaptic terminal

the end of a neuron’s axon that can release neurotransmitters to communicate with other cells

synapse

the junction that separates 2 neurons

neurons are bounded by a

• semi-permeable membrane that is electrically polarized

  • important for how the neurons send signals

semi-permeable

things selectively allowed in and out of cell

extracellular fluid

0mV

intracellular fluid

~-65 mV (-70mV)

resting membrane potential

the electrical charge difference across a cell's plasma membrane when it is inactive.

• -70mV

• means the inside of the cell is more negative than the outside

inside of cell is more __ than the outside

negative

the membrane is made up of

• lipid (fat), but has different proteins and channels embedded into it

  • these serve as passages into and outside of the cell

• without protein channels, no ions could flow in/out of the cell

  • different types of ion channels exist!

ion channels

• allows ions whose size and charge “fit” to diffuse through

• made up of subunits that surround a central aqueous pore

• channels are placed where they make sense

ion channel characteristics

• multiple states

• gating

• selectivity

multiple states of ion channels

• open vs closed

  • open: ions can flow

  • closed: ions cannot flow

gating of ion channels

• voltage-gated and ligand-gated (and others)

selectivity of ion channels

• they are picky

• pores of channels aren’t wide enough to let any ion through

• size of the pore and nature of amino acids that line it allow some ions in to diffuse more easily than others

• some channels aren’t selective at all, while others are very picky

membrane changes

• changes in relative permeability of the membrane ions (K+ and Na+) are the basis for electrical signaling by the neurons

depolarization

• inside of the cell becomes more positive)

• more likely to create an action potential (long distance signal)

• excitatory

hyperpolarization

• inside of the cell becomes more negative

• less likely to create an action potential

• inhibitory

local potenial (vs AP)

• graded: can be hyper or depolarizing

• occur at the dendrites or soma of the neuron

• occur in response to a stimulus

• vary in strength and decrease with distance

  • involved in synaptic transmission

action potential (vs local potential)

• all or nothing electrical impulses

• originate at the axon hillock

• generated when the local potential reaches a certain threshold

• self-propagating and maintain strength over a distance

• responsible for long distance signaling in neurons

local potential

• like opening a small gate

• summation of local potentials can elicit a response

  • temporal summation

  • spatial summation

temporal summation

• type of local potential

• repeated stimuli at the same spot

spatial summation

• type of local potential

• multiple stimuli arriving at different spots on the membrane

action potential

• opening up the BIG gate

• LARGE change in polarity (all or none)

• ONLY depolarizing

  • takes place at voltage-gated channels

    • trigger zone

    • axon hillock

trigger zone

distal sensory neuron (where AP generates)

axon hillock

• most proximal part of axon where AP can be started in a neuron that is not sensory

• (where AP generates)

unmyelinated

• doesn’t mean NO myelin, but does not have a good coating