Electrical signals
• Sodium ions
• Potassium ions
• Generate an action
potential at the axon
hillock
• Travels down the axon to
the terminal –
regenerating the action
potential in each portion
of the membrane
synapse
neurotransmitters
• Chemical signals released by presynaptic
neurons
• Bind to receptors on postsynaptic neuron or
effector cells
• Stimulate or inhibit them
• 50+ different molecules have been identified
• Classified chemically and functionally
Other examples
•
•
•
•
•
Histamine
GABA
Glutamate
Glycine
Endorphins
Postsynaptic membrane receptor
• Receive
neurotransmitter
• Specialized to
open/close ion channels
• Produces graded local
change to membrane
potential/voltage
according to amount of
NTM released and time
it sticks around
Types of synapses
• Where the axon
synapses with the
postsynaptic cell
• Graded potentials
dissipate in strength as
spread – most effective
type of synapse?
Effects
Excitatory Synapses
• Depolarization (more +) of
postsynaptic membrane
• Channels allow Na+ and K+
ions to diffuse
simultaneously
• Local graded depolarization
= EXCITATORY
POSTSYNAPTIC POTENTIAL
(EPSP)
• Helps trigger an action
potential
Inhibitory Synapses
• Induce hyperpolarization
(more -) of postsynaptic
membrane
• More permeable to K+, Clor both
• Less likely to “fire” an action
potential, or requires a
larger depolarizing current
• INHIBITORY POSTSYNAPTIC
POTENTIAL (IPSP)
Neural integration
• Reflects sum of all incoming neural
information received
• Both stimulatory and inhibitory inputs
• Axon hillock keeps a running account of all the
signals it receives
modeling
• Seekers: must find the right message
• Neuron chain, standing hand to hand – once
stimulated, must pass the message from one
person to the next until reaches axon hillock.
• Axon hillock: keeps a running total of the
charge
Problem solve: how do you get your
message to “win”?
• Must adhere to the same rules…but can alter
everything else
Summation: add together to influence
activity of post-synaptic neuron
temporal
• 1 or more presynaptic
neurons transmit impulses
in rapid-fire order
• Quick succession, before
signal dissipates
spatial
• Postsynaptic neuron
stimulated by a large
number of terminals from
same or different neurons
at the same time
• Large number of receptors
bind neurotransmitters