Neuronal signalling Flashcards
describe the general structure of a neurone
cell body + dendrites
axon
terminal branches of axon
what are the 2 types of synapses?
synapses are between..?
electrical
chemical (more common + complex)
2 neurones
OR
a neurone + an effector
define synapse
the point where electrical conduction is converted to chemical conduction
what is all activity within a neurone based on?
what is does this generate?
changes in electric charge of the cytoplasm
- due to movement of + or - ions across the cell membrane
membrane potential
what type of potential occurs in the dendrite/cell body region?
what about in the axon?
graded potential
= changes in charge are variable in amount
action potential
= changes in charge are always identical
what are the types of electrical responses?
intrinsic:
- silent
- beating
- brusting
reposes to external:
- sustained response
- accommodation
- delay
how is neuronal activity measured?
what are the 2 methods?
treat membrane as part of a circuit
electrodes placed to make contact with nerves
impalement
= charge movement
patch clamping
= channel activity
describe the experimental set-up for measuring neuronal activity
e.g. giant squid axon
an electrical stimulator is connected to an electrode in sea water and an electrode in the axon
an oscilloscope is connected to the sea water and axons via electrodes
what are the 2 types of clamping?
why is it important?
if current clamping occurs
= change in pd
if voltage clamping occurs
= change in current
important to keep 1 variable constant so that another can be measured
what are the features of electrical synapses?
gap-junctions between cells
= continuity
ions can diffuse directly
no delay
ions can move bidirectionally
what are the features of chemical synapses?
no continuity
-> slight delay
associated with neurotransmitters released from vesicles
unidirectional propagation of signals
describe the process which occurs at a chemical synapse
- AP invades
- Ca2+ influx
- depolarisation -> release of NT via exocytosis
- NT diffusion
- ligand binding results in opening of ligand-gated ion channels
- depolarisation
- transmitter recycling
- vesicular membrane recycling
describe fast chemical transmission
NT is released directly into the cleft
ligand binding directly stimulates opening of Na+ channels
describe slow chemical transmission
large vesicles release NT
release may not be towards postsynaptic cell
ligand binding functions via GPCR
-> causes ion channels to open via intracellular signalling pathways
give an example of a fast chemical synapse
motor-end plate
neurones surrounded by Schwann cells, directly contact muscle
active zones of neurone are in close contact with junctional folds of muscle
- contain ACh receptors
ACh binds to receptors which are ionotropic
-> allows entry of Na+
-> current travels through muscle
what is the equation for pd?
how do changes in membrane potential (pd) occur?
V = current x resistance
due to the changes in resistance by the closing of channels
-> prevents ion movement (=current)
how are post-synaptic potentials generated?
quanta of NTs cross the synapse
NTs bind to receptors
-> opens channels
-> charge movement
= change in potential
what are the 2 types of postsynaptic potentials?
excitatory
- related to Na+
- makes membrane more +ve
inhibitory
- related to K+
- makes membrane more -ve
how do membranes enforce selective permeability?
neuronal membranes contain ion channels:
- some are non-gated
= stay open all the time - some are gated
= open when action potential is present
-> causes change in permeability of membrane
describe the features of ion channels and ion movement
facilitated diffusion (no ATP)
selective
- only 1 type of ion
dynamic
- can be open or closed (gated)
what are the 2 types of channels in a typical neurone?
voltage-gated
= if membrane potential changes -> channel opens
ligand-gated
= if NT binds to receptor -> channel opens
give 3 examples of voltage-gated ion channels are their effects
Na+
- depolarisation
= makes membrane potential more +ve
K+
- depolarisation
= makes membrane potential more -ve
Ca2+
- causes NT release
what does charge separation result from?
give an example
the different permeability of the membrane to +ve and -ve ions
K+ is free to move out of the cell but will eventually stop when -ve K+ charges outside the cell repel
(even if conc grad favours this movement)
= equilibrium potential
what is the Nernst potential?
what does it assume?
membrane potential at which there is no net flow of that ion from one side of the membrane to the other
- there’s a difference in conc of an ion across a membrane
- the membrane is selectively permeable to 1 type of ion only
what is the reversal potential?
what does this value give a clue to?
membrane potential at which there is no ionic current
the ion responsible for a current/ AP
- based on the varying [out]/[in] ratios of ions
determining is a postsynaptic current will be excitatory (more+) or inhibitory (more-)
what does the Goldmann equation calculate?
the membrane potential when considering the opening of the 3 main ion (Na+, K+ and Cl+) channels
what is the standard resting potential?
what must occur for an action potential to be generated?
-40 to -90 mV
potential must get more +ve
sum of excitatory inputs» inhibitory inputs
to exceed threshold
what does opening Na+ channels result in?
what about K+?
what about Cl-?
positive ions enter
= depolarisation
= excitatory PSPs
negative ions exit
= repolarisation
= inhibitory PSPs
negative ions enter
= hyperpolarisation
= IPSPs
what does opening of Ca2+ ligand-gated ion channels result in?
what type of PSP is this?
NT release
EPSP
Ca2+ is a positive ion
give 2 examples of receptors that lead to Na+ channel opening
ACh
glutamate
