Download Chapter 3 Synapses

Chapter 3
Synapses
Synapses
Presynaptic Neuron
• Sends the signal
Postsynaptic Neuron
• Receives the signal
Postsynaptic
Potentials
Excitatory Postsynaptic
Potentials (EPSP)
• Neurotransmitters from a
neural message cause a
deplolarization in the next cell
-70 mV up to -67 mV
• Make it more likely the next
cell will fire
Postsynaptic
Potentials
Inhibitory Postsynaptic
Potentials (IPSP)
• Neurotransmitters cause a
hyperpolarization in the next
cell
-70 mV up to -72 mV
• Less likely the next cell will
fire
Postsynaptic
Potentials
Factors: Determining EPSP
and IPSP
• Type of neurotransmitter
• Type of receptor
Post Synaptic Potentials
Graded Responses
• EPSP and IPSP can vary in
strength
Video: Lecture 4 Neural
Communication_Excititory and
Inhibitory
Postsynaptic Potentials
“The postsynaptic potentials created at a single
synapse typically have little effect on the firing of
the postsynaptic neuron (Bruno & Sakmann,
2006). The receptive areas of most neurons are
covered with thousands of synapses, and whether
or not a neuron fires is determined by the net effect
of their activity.” –Pinel, p. 81
Postsynaptic Potentials
Integration
• EPSP and IPSP travel to the
base of the axon hillock where
they are summed
Postsynaptic Potential
Temporal Summation
• Two EPSPs in rapid
succession at one synapse are
additive
• Same for IPSPs
Spatial Summation
• Synaptic inputs from
separate locations combine
their effects on a neuron
Postsynaptic Potentials
“Each neuron continuously integrates signals over
both time and space as it is continually bombarded
with stimuli through the thousands of synapses
covering its dendrites and cell body. Remember
that, although schematic diagrams of neural
circuitry rarely show neurons with more than a few
representative synaptic contacts, most neurons
receive thousands of such contacts.”
-Pinel, p. 82
Post Synaptic Potentials
Reflexes
Sensory neuron, goes to spine (afferent signal)
Stimulates a motor neuron, which contracts the
muscle (efferent signal)
Temporal Summation
One light tap does not produce reflex
Two light taps in a row will
Spatial Summation
Two taps in slightly different locations will also
stimulate a reflex
Synapses
Structure of Synapses
• Synapses can occur between
axon and
* Dendrite (most common)
* Soma
* Axons
Neurotransmitter Molecules
Neurotransmitters
• Over 100 neurotransmitters
molecules
• Different categories based on
different chemical compounds
• Most neurons make and
release 1 or 2 types of
neurotransmitters
Neurotransmitter Molecules
Notable
Notable
• GABA
• Endorphines
• Glutamate
• Endocanabanoids
• Acetylcholine
• Serotonin
• Adenosine
• Dopamine
• Norepinephrine
• Epinephrine
• Neuropeptide Y
Release of Neurotransmitters Molecules
Exocytosis
• Release of neurotransmitter
molecules
• Action potential causes
positive calcium ions to enter
the terminal
*This depolarizes the
terminal
Exocytosis
• Vesicles to fuse to membrane
• Contents emptied into
synaptic cleft
Release of Neurotransmitter Molecules
Activation of Receptors
Receptor
• Protein that contains binding
sites for neurotransmitters
“Most neurotransmitters bind to
several different types of
receptors.” –p. 89
Reuptake and Degradation
Reuptake
• Almost immediately,
neurotransmitters that have
been released are drawn back
into the presynaptic neuron
• Recycling
Enzyme Degradation
• Enzymes break apart
neurotransmitters
Hormones
Hormones
• Chemicals secreted in most
cases by glands (or neurons),
carried by blood to other
organs, where they exert their
effects