Electrical Signals Flashcards
AP generation
originated via receptor potentials or CNS postsynaptic potentials
Generator/receptor potentials vs. action potential
Change in membrane potential depends on stimulus magnitude
Response to stimulus graded
No refractory period and potential local spread passively
Possible TTX insensitive
Generator potential
Localized graded potential in sensory nerve terminal
Signal adaptation
Sensitive to rate of change of stimulus- event detection
Sensitive to duration- magnitude detection (rate of change or absolute change)
Slowly adapting is tonic and rapidly adapting is plastic receptors which can turn off
Chemical synaptic transmission
Stimulus to nerve or receptor to axon to post synaptic membrane via dendrites across synaptic cleft
Electrical signal
Less common than chemical ions flow through gap junctions
Chemical synapse
More common
Synaptic vesicles fuse with membrane and release to synaptic cleft and flow through postsynaptic channels
Pre synaptic terminal
Prepackaged vesicle of neurotransmitter
1 quantum is thousands of neurotransmitters
Pre synaptic depolarization from incoming AP
Pre synaptic depolarization
AP from excitation secretion coupling or Ca dependent process
Synaptic cleft
20-50 micrometers
Transmission by diffusion
Can contain neurotransmitter breakdown and recycling
Post synaptic response
Receptor subtype dependent (excitatory or inhibitory) and fast or slow
Ionotropic transmission
Small synaptic vesicles
Ligand gated ion channel on post synaptic ion channel to allow Na in
Fast transmission
With ACh membrane depolarization leading to muscle contraction
Metabotropic transmission
Slow chemical transmission
Large synaptic vesicles release out side of pre synaptic terminal
Bind receptor and activate G protein which has activated subunit open Na ion channel
Membrane hyperpolarization to decrease Heart rate (ACh)
Excitatory post synaptic potential
Becomes positive while inhibitory becomes more negative than resting potential
Post synaptic potential transmission
Goverened by physical properties of pre/post synaptic interaction
Dendrite size and axon hillock is important
Effects are receptor dependent
Excitatory postsynaptic potentials- Glutamate EPSP
Goes to glial cells and not post synaptic membrane, bind their receptors to allow Na flow into post synaptic membrane
GABA
Released to glial cell for glutamine production
GABA binds receptor and does not allow for activation of ion transport, IPSP in post synaptic membrane
Pre vs. post synaptic inhibition
Pre synaptic- modulatory neuron synapses on one collateral of the presynaptic neuron and selectively inhibits one target
Post synaptic inhibition all targets inhibited signal is below threshold so no AP and no response
Post synaptic potential is graded
Dependent on amount of neurotransmitter release
Dependent on number receptors available post synaptically
Summation can lead to compound EPSP
Summation
Occurs at the axon hillock
Potentials as PSP rises above threshold to get action potential
Neuronal integration
Signal transmission usually wide spread because of axonal divergence
Signal integration from multiple sources via synaptic convergence
Strychnine poisoning
Binds glycine inhibitory post synaptic receptors in spinal cord and medulla
Death from anorexia and exhaustion
Saxitoxin
Loss of excitatory neurotransmission (Na channel blocker AP)
Dendrotoxin
Prolonged presynaptic depolarization
Neuronal coding
Adaptation or rate
Rate: as intensity of stimulus increases frequency or rate of action potentials will increase
Adaptation: as intensity of stimulus increases or decreases can generate potential or not
