2. Preview of today’s lecture
Electrochemical Communications
communication between neurons
Neurotransmitters
movie
3. Structure of a synapse
presynaptic membrane
postsynaptic membrane
synaptic cleft
4. Structure of a synapse
synaptic vesicles are produced by Golgi apparatus in the soma
OR
by recycled matter in the cisternae of the terminal button: Pinocytosis
5. Neurons – from electrical to chemical
• vesicles release neurotransmitters across
the synaptic cleft
• the released neurotransmitter leads to post-
synaptic potentials (hyperpolarization or
depolarization) that alter the firing rate of the
receiving neuron (decrease or increase)
• axon terminal contains synaptic vesicles
6. Structure of the synapse
• as viewed under an electron microscope
7. Structure of the synapse
• synaptic vesicles fusing with the presynaptic membrane
8. Structure of the synapse
• synaptic vesicles fusing with the presynaptic membrane
9. Neurochemicals
• Neurotransmitters - chemical substance released from the end of a
neuron during the propagation of a nerve impulse; it relays
information from one neuron to another.
• Neuromodulators – secreted in larger amounts and diffuse further
(composed of peptides)
• Hormones – produced in endocrine glands – released into
extracellular fluid to be taken up by specific target cells
10. Binding
• only specific neurotransmitters will bind with specific receptor sites –
like a key in a lock
• chemical that attaches to a binding site is a ligand
• neurotransmitters are naturally produced ligands
• neurotoxins are also ligands and various drugs have their effect in the
same manner – artificially produced ligands (e.g., LSD)
11. Neurons – from electrical to chemical
Only specific neurotransmitters will bind
with the post-synaptic membrane.
12. Binding sites
Axodendritic – synapse on the dendrite of the neuron
Axosomatic – synapse on the soma
Axoaxonic – synapse on the axon
Axodendritic Axosomatic Axoaxonic
13. Receptors
• neurotransmitter specific postsynaptic receptors
• open to allow ions to flow into the postsynaptic neuron
• two main types
• ionotropic
• metabotropic
15. Metabotropic receptors
• indirect method
• located nearby G-proteins
• G-proteins in turn activate
an ion channel
• slower to begin and longer
lasting
17. Excitatory or inhibitory post-synaptic potentials.
• once neurotransmitters are bound to the post synaptic membrane the
electrical charge is now altered in the receiving neuron
• the change in the
electric charge can be
more positive than
the resting potential
(excitatory) or more
Inhibitory
negative than the
resting potential
(inhibitory)
19. Post-synaptic potentials
• determined by the ion channel opened by the neurotransmitter and
not the transmitter itself
• graded – the potential dissipates with distance traveled
• smaller in magnitude than action potentials
• action potentials are always excitatory – post-synaptic potentials can
be either excitatory or inhibitory
20. Post-synaptic potentials
• excitatory PSP – typically related to sodium ion channels (rush of
Na+ into the cell makes it more positively charged)
• inhibitory PSP typically related to potassium ion channels (extra K+
maintained inside cell by sodium-potassium pump leaks out making
the cell more negatively charged)
• action of Cl– channels depends on the state of the receiving neuron
– if depolarised Cl– will bring the cell back to a resting state
21. Terminating the PSP
• reuptake – rapid removal of
neurotransmitter from the synaptic
cleft
• SSRIs (selective seratonin reuptake
inhibitors – e.g, Prozac) prolong the
PSP by inhibiting reuptake
22. Summation of post-synaptic potentials.
• whether the PSP leads to the excitation or inhibition of the neuron
depends on the combined effects of many PSPs
25. Autoreceptors
• autoreceptors respond to neurotransmitters they produce
• regulate synthesis and release of other transmitters
• metabotropic
• usually inhibitory – may control amount of neurotransmitter released
26. Other types of synapses
• axoaxonic – modulate the neurotransmitters in the presynaptic
neuron
• gap junctions – electrical synapses – the synaptic cleft is much smaller
– ions pass directly from one neuron to another
27. Why do you need to know all this?
• different disease processes involve different aspects of the basic
electrochemical transmission of neural information
• Parkinson’s Disease – dopamine deficiency
• Multiple Sclerosis – affects the myelin sheath of white matter
• Epilepsy – abnormal electrical stimulation
• Alzheimer’s Disease – neurofibrillary tangles may affect the
transport of neurotransmitters
28. Review Questions
1 ) Neuromodulators
A) are rarely of a peptide form.
B) are secreted from a neuron and only effect an adjacent neuron.
C) are inevitably inhibitory.
D) are secreted from neurons, but dispersed widely in the brain.
E) are typically secreted in very small amounts compared to neurotransmitters.
2 ) Most ________ are secreted into the extracellular fluid from endocrine glands or tissues.
A) neurotransmitters
B) neuropeptides
C) modulators
D) hormones
E) Pheromones
3 ) Large synaptic vesicles are produced in the
A) soma.
B) dendrites.
C) terminal buttons.
D) dendritic spines.
E) neuroglia.
29. Review Questions
4 ) Which of the following is true of neurotransmitter function?
A) Neurotransmitters diffuse widely in the brain to exert changes in metabolism.
B) Neurotransmitters directly alter ion channels using a second-messenger chemical.
C) Neurotransmitters are released into the synapse from the cistaerna.
D) Neurotransmitters open ion channels in the postsynaptic membrane.
E) Neurotransmitters alter ion channel activity for minutes.
5 ) Which of the following will produce an EPSP?
A) opening a sodium channel
B) closing a sodium channel
C) opening a potassium channel
D) opening a manganese channel
E) closing a calcium channel
Nice review animation
30. For Next Time
Start reading Chapter 3
Structure of the Nervous System
