neurotransmission Flashcards
what structures compose the central nervous system?
- Brain
- Spinal cord
what structures make up the peripheral nervous system?
sensory neurons - afferent nerves
motor neurons - efferent nerves
what is the difference between the somatosensory system and the autonomic system?
somatosensory = neurons that recieve sensory information and control movement of skeletal muscle
autonomic system = neurons that receive sensory information and regulate movement of smooth muscle and cardiac muscle as well as glandular secretion - sympathetic and parasympathetic
what do the terms afferent and effferent mean?
afferent = transmit information towards the CNS
efferent = transmit information away from the CNS
what are the two kinds of postsynaptic potentials?
- excitatory post-synaptic potential - small depolarizaiton
- inhibitory post-synaptic potential -hyperpolarization (holding of resting membrane potential) by opening of K+ channel and the neurotransmitter binding opening Cl- channels
what is the “threshold voltage”?
-55 mV = when a certain spot on the neuron reaches this value, an action potential is generated
describe the process of an action potential
- depolarization pushes membrane potential across the action potential threshold
- reduced voltage opens several voltage-gated Na+ channels in that portion of the plasma membrane - Na+ influx leads to further depolarization
- voltage gated K+ channels open (and Na+ channels close)- K+ efflux repolarises plasma membrane
- voltage- gated K+ channels close (leaving plasma membrane hyperpolarized)
- resting membrane potential restored by Na+/K+ pump
describe the ‘action potential graph’ from the perspective of the voltage gated sodium channels/potassium channels
what is the refractory period?
period when a further stimulus applied to a neuron or muscle fiber will not trigger another action potential - membrane is depolarized and the neuron is refractory -
can you get smaller / larger aciton potentials?
no they are all or none
- strong stimuli produce action potentials of the same amplitude as weak stimuli - the strength of the stimulus is encoded in the frequency of the action potentials that it generates
describe the steps of synaptic transmision
- action potential reaches and depolarizes axon terminal
- depolarisation actiates voltage-gated presynaptic Ca2+ channels (Ntype, Ptype)
- localised Ca2+ entry triggers exocytosis of neurotransmitters (NTs) from synaptic vesicles into the synaptic cleft, through the activation of Ca2+ sensitive fusion proteins
- NTs diffuse into the synaptic cleft
- NTs bind and activate receptors on the post-synaptic membrane
- inactivation of neurotransmitters
how does an electrical synapse travel between two cells?
two cells are connected by gap junctions - formation of channels between the cytosolic compartments of the two cells - permit communication between cells by the direct propagation of ionic current from one cell to the other
what sort of transmission is between neural cells?
chemical transmission - unlike the electrical transmission in muscle cells
the change in voltage cuases the calcium channels to open- this calcium causes the vesicle terminals to bind to the cleft - they release the neurotransmitters
what types of neurotransmitters are inhibitory?
GABA and glycine
what kind of neurotransmitters are excitatory?
acetylcholine and glutamate
what neurotransmitters can be both excitatory and inhibitory?
serotonin, dopamine, noradrenaline
what occurs at an excitatory synapse?
the NT at an excitatory synapse depolarises the post-synaptic membrane potential - they continue the depolarization across the post-synaptic cleft so it excites the next channel
what occurs at the inhibitory synapse?
the NT an inhibitory synpase hyperpolarizes the post-synaptic membrane potential
ex) the binding of GABA A to GABA A receptors on the post-synaptic membrane activates ligand-gated chloride channels - the Cl- influx hyperpolarizes the post-synaptic membrane potential
what are ionotropic receptors?
they are ligand gated ion channels - NT binding increases permeability to ions
Fast synaptic transmission
what are metabotropic receptors?
- G protein couple receptors
- slower synaptic transmission
- NT binding triggers activation of G protien that either directly modifies function of ion channels or triggers the production of a chemical second messenger that modifies ion channels
- mediates short term as well as long term effects (gene expression)
local anaesthetics like lidocaine work how?
by blocking the voltage gated Na+ channels
where are neurotransmitters synthesized?
they are synthesized locally within the axon terminal
how are neurotransmitters inactivated?
- inactivated/degraded by enzymes in the synaptic cleft or
- taken up by presynaptic neuron via transporter protein -repackaged and recycled s
how do Selective serotonin reuptake inhibitors work?
they give serotonin a longer time to sit in the synaptic cleft - allowing more time to be taken up by the receptors
