overview of neural f..

Overview of Neural Anatomy, Function and
Neurotransmitters
by Dave Harper
Recap of neural structure.
Principles of neurotransmission.
- communication within neurons
- communication between neurons
Neurotransmitters.
Short - versus long - lasting changes.
for animations used see:
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter45/animations.html#
http://www.blackwellpublishing.com/matthews/animate.html
Neurons look different but share basic structures ...
soma
dendrites
axon
neuron fig
terminal
buttons
synapse
COMMUNICATION WITHIN NEURONS
Achieved by the passage of an electrical
pulse from one end of the neuron to other
along the axon.
Axons are electrically charged due to the
imbalance of electrically charged ions.
outside (+)
inside (-)
-70 millivolts
few
many
K+
Na+
(potassium) (sodium)
many
Cl(chloride)
many
few
K+
Na+
(potassium) (sodium)
few
Cl (chloride)
many
A(proteins)
ACTION POTENTIAL
A brief change in the electrical charge of the
axon brought about by Na+ and K+ flowing into
and out of the cell respectively.
K+ leaves
Na+ enters
Na+ stops entering
K+ stops leaving
animation
1&2
The sodium-potassium pump is an active
process that returns & maintains levels of
Na+ and K+
sodium-potassium
pump fig
NOTES:
1) extremely quick (100s of metres per
second) - and it needs to be!
2) stimulus intensity coded by the rate of
firing.
3) all or none affairs - an action potential
either happens the same way each time - or
it does not happen at all.
COMMUNICATION BETWEEN NEURONS
Whereas communication along axon involves
action potential, communication between
neurons involves neurotransmitters.
The neurotransmission cycle ...
synapse fig
animation
1&2
When a neurotransmitter and receptor
combine together two possibilities:
1. The resting potential may become less
negative (an excitatory post-synaptic potential
- E.P.S.P).
Effect of E.P.S.P is to INCREASE probability
that the receiving neuron will 'fire' (i.e.
produce an action potential).
OR
2. The resting potential may become more
negative (inhibitory post-synaptic potential
- I.P.S.P).
Effect of I.P.S.P is to DECREASE probability
that the receiving neuron will fire.
ipsp / epsp combos
NEUROTRANSMITTERS
Many n.t.s and for each n.t. there are a number
of specific receptor types.
---> ‘lock & key’ analogy
Neurotransmitters viewed as chemicals that:
- are located in specific regions of neurons;
- are released under specific stimulation;
- act on a specific set of receptors;
- and induce changes in membrane potentials.
Some common neurotransmitters ...
Family
Transmitter
Receptors
Amino acids
Glutamate
GABA
NMDA, AMDA
GABAa, GABAb
Quaternary amine
Acetylcholine
muscarinic, nicotinic
Monoamines
Dopamine
Norepinephrine
Serotonin (5-HT)
D1, D2 ...
α-1, α-2, β-1, β-2
5-HT1, 5-HT2 ...
Neuropeptides
Beta-endorphin
Leu-enkephalin
opiate receptors
(e.g. ε, δ)
Neurotransmitters can have immediate
effects on postsynaptic potential or quite
long-lasting effects which may involve
metabolic or structural changes.
FAST (direct)
ion-channel receptor
opens ion channel
if Na+ channel
if K+ channel
if Cl- channel
Na+ in to cell
K+ out of cell
Cl- in to cell
EPSP
IPSP
IPSP
animation
1&2
SLOW (indirect )
G-protein linked receptor
G-protein opens
ion channel
EPSP or IPSP
triggers 2nd
messenger
opens
ion
channel
influences
cell
metabolism
alters
cell
DNA
animation
1&2
The discovery of long term changes in synaptic
efficacy was important in terms of identifying
possible mechanisms that underlie learning and
memory (i.e. long term changes in behaviour must
surely be reflected in long term neural changes).
Perhaps the most important process in this
regard is LONG TERM POTENTIATION (LTP).
Bliss & Lomo (1973).
LTP - experimental setup
(illustrated for hippocampal brain slice)
LTP setup fig
change in potentiation
measured using
population EPSP (an
extra-cellular measure
of excitation across a
group of cells)
LTP - graphical illustration of change in postsynaptic potential
Why might LTP be important?
• long lasting therefore a mechanism underlying
memory & learning.
• prominent in many brain structures implicated in
learning and memory.
• elicited by relatively low levels of stimulation
• conditioning produces LTP-like changes in brain.
• drugs that block LTP block learning.