1. Where nerve impulses convert to neurotransmitters
THE SYNAPSE
Where nerve impulses convert to neurotransmitters
© 2016 Paul Billiet ODWS

2. The synapse A gap (about 20nm)
Where the nerve impulse passes from one cell to the next
The electrical signal (the action potential)  a chemical signal to cross the gap between the cells
Neurotransmitter
The neurotransmitter crosses by diffusion
This creates a small delay.
© 2016 Paul Billiet ODWS

3. Designer signals
Neurotransmitters give the nerve signal more specificity
Neurotransmitters also control the operation of the nervous system by inhibition or excitation
Many drugs that try to cure problems in the nervous system operate at synapses.
© 2016 Paul Billiet ODWS

4. Neurotransmitters and hormones
Neurotransmitters are hormones working over a very short distance
Some of them work both at synapses and in the circulatory system
E.g. Adrenalin (epinephrin).
© 2016 Paul Billiet ODWS

5. 1. Action potential arrives at terminal button
Vesicle storing neurotransmitter
Ca2+ channel
Membrane receptor for neurotransmitter
© 2016 Paul Billiet ODWS

6. starklab.slu.edu/neuro/synapse.jpg
© 2016 Paul Billiet ODWS

7. 3. Ca2+ stimulates vesicles to fuse with membrane
2. Depolarisation opens Ca2+ channels
Ca2+ enters terminal button
Ca2+
4. Exocytosis of neurotransmitter
It diffuses 20nm across the synaptic cleft
© 2016 Paul Billiet ODWS

8. The passage across the synapse
An action potential travels down an axon to the terminal buttons
The membrane of a terminal button depolarises
Voltage-gated Ca2+ channels to open
Ca2+ ions flood into the terminal button
This stimulates hundreds of synaptic vesicles, packed with neurotransmitter, to fuse with the membrane of the terminal button
Exocytosis
The Ca2+ ions are then pumped out again.
© 2016 Paul Billiet ODWS

9. They open when the neurotransmitter binds
5. Neurotransmitter receptor sites on the postsynaptic membrane are ion channels.
They open when the neurotransmitter binds
6. Localised depolarisation as ions leak in or out of membrane.
© 2016 Paul Billiet ODWS

10. The passage across the synapse
Neurotransmitter diffuses across cleft to postsynaptic membrane
Neurotransmitter molecules bind with specific receptor sites on postsynaptic membrane
The receptor sites are ligand-gated ion channels
These channels let Na+ ions in or K+ ions out causing localised depolarisation of the membrane.
© 2016 Paul Billiet ODWS

11. 8. Neurotransmitter destroyed by enzymes in the cleft
8. Neurotransmitter destroyed by enzymes in the cleft. Stops signal being perpetuated.
7. Action potential generated which travels down the postsynaptic cell.
© 2016 Paul Billiet ODWS

12. A new action potential
If the localised depolarisations build up to the nerve cell threshold, a full action potential will be produced
This will travel away, down the postsynaptic neuron
The action of the neurotransmitters stops: (i) as they dilute by diffusion in the synaptic cleft (ii) by hydrolysis through the action of enzymes there
Important: The signal must not be perpetuated indefinitely
© 2016 Paul Billiet ODWS

13. The neuromuscular junction is a synapse
The motor end plate is the terminal button of a motor neuron that makes contact with a muscle cell
The motor end plate releases the neurotransmitter acetylcholine that ultimately causes the muscle cell to contract
© 2016 Paul Billiet ODWS

14. biology.clc.uc.edu/fankhauser/Labs/Anatomy_...
© 2016 Paul Billiet ODWS

15. education.vetmed.vt.edu/Curriculum/VM8054/Lab...
© 2016 Paul Billiet ODWS

16. Blocking synapses Poisons Psychotic drugs Medication Botox
Neonicotinoid pesticides
© 2016 Paul Billiet ODWS

17. Nip & tuck
Botox = a neurotoxin produced by a bacterium Chlostridium botuninum
It causes food poisoning (botulism)
The toxin blocks the release of acetyl choline neurotransmitter to muscles
Causes muscle paralysis
Cosmetically used to smooth lines and creases
Medically used to relax muscles that causing illnesses such as spasms and strabismus (cross-eyed).
© 2016 Paul Billiet ODWS

18. Neuro-active pesticides
Neonicotinoids mimic the neurotransmitter acetylcholine
Nicotinoids cannot be broken by the enzyme in the synapse
So the signal continues
Causing paralysis
These pesticides have been associated with honey bee deaths in many countries.
© 2016 Paul Billiet ODWS