8/22 Neurotransmission - Glendinning Flashcards
steps in neuron activation
- receive stimuli
- sensory input: pseudouni- and bipolar
- synaptic input: bi- and multipolar
- integrate the input
- APs are activated at trigger zone (area with increased number of Na channels, can initate AP)
resting membrane potential
number
what generates it?
-65mV
- osmotic and electrical forces
- selective permeability
- energy dependent Na/K pump
Na, Cl, Ca (out > in)
K (in > out)
electrical inputs in a nerve cell
neuronal inputs as graded potentials
inputs stimulate or inhibit an action potential
- stimulate: depolarizing (positive, excitatory)
- inhibit: hyperpolarizing (negative, inhibitory)
neuronal inputs are graded potentials → show small changes in RMP in response to inputs
- size of change varies based on strength of input → leads to varied AP firing rate/nt release
EPSP vs IPSP
EPSP: excitatory postsynaptic potential
- depolarizing
- excitatory, graded : usually from opening of Na or Ca channeles
- < 1mV
IPSP: inhibitory postsynaptic potential
- hyperpolarizing
- inhibitory, graded : usually from opening of K or Cl channels
“impact factor”
graded membrane potentials attenuate (weaken) rapidly with distance from start point
“IMPACT FACTOR” depends on:
- location (impact could be greater if stim closer to trigger zone!)
- strength of synapse
4 neuron-to-neuron synapses
AD - axodendritic
AA - axoaxonal
AS - axosomatic
DD - dendrodendritic
summating effection on action potentials
spatial vs. temporal
spatial : number of inputs received summed
temporal : timing of inputs builds up to AP
what’s the point of inhibition/summation?
don’t always want the SAME level of response to an AP! sometimes, want a bigger response than other times
consider:
- postural demands
- environmental changes (ex. terrain)
- goal of movement
combo of excitatory and inhibitory inputs leads to summed state → differential firing rate and force of contraction for diff levels of response
presynaptic inhibition
postsynaptic inhibition
presynaptic inhib:
inhibitory inputs at AXON TERMINALS → selective blocking of synaptic output!
postsynaptic inhib:
inhibiory inputs on POSTSYN NEURON → can inhibit entire neuron
saltatory conduction
axon diameter implications
myelination produces segments of axon that are insulated - CANT trigger AP there
AP instead jumps to successive nodes of Ranvier
greater axon diameter leads to…
- increased conduction velocity!
- higher space constants : signal can move further before decaying
- larger internodal spaces
factors affective conduction velocity
- amt of myelin
- conduction velocity
chemical synaptic transmission
when AP makes it to the axon terminal…
- Ca channels open (Ca influx into terminal) → synaptic vesicles fuse with presynaptic terminal
- nt is released → binds to receptors on postsynaptic membrane
* leads to opening of ion channel!
* *fate of nt released via exocytosis?*
degradation by enzymes, removal by glial cells, reuptake by presyn cell, diffuse away,
two families of postsynaptic receptors
1. ligand gated ion channels
- ionotropic : receptor linked directly to ion channels
- FAST (<1 ms)
2. G protein coupled receptors
-
metabotropic : receptor does not have channel, affects G-protein activation instead
- G-protein dissociates and interacts directly or indirectly with ion channel
- bc of the Gprotein middleman → slower!
- responsible for neuromodulation
major neurotransmitters
excitatory vs inhibitory
PNS
- excitatory : Ach (nicotinic)
CNS
- excitatory : glutamate
- inhibitory : GABA or glycine (spinal cord)
glutamate
major excitatory nt in CNA
- contained in approx 50% of all neurons (virtually all excitatory neurons)
receptors:
ionotropic (excitatory)
ex. AMPA receptor (Na in, K out)
ex. NMDA receptor (Na/Ca in, K out)
ex. kainate
metabotropic (excitatory or inhibitory depending on state of neuron)
