1. Neurobiology and Communication
The cells of the nervous system and neurotransmitters at synapses

2. Add notes here

4. Myelination and the glial cells

5. What are we learning today
Some of the details of how a synapse works.
How neurotransmitters work.
How neural pathways are constructed.
What plasticity of the brain is.

6. synaptic cleft

7. Neurotransmitters and synapses
Neurones transmit electrical impulses.
Synapses transmit chemical messages.
Synapses are the meeting of an axon terminal with a dendrite.
The narrow space between them is called a synaptic cleft.
The neuron before the cleft is called the presynaptic neuron, the one after is called the postsynaptic cleft.
Chemical messengers (neurotransmitters) pass messages across the cleft.
Neurons also connect to muscle fibres and endocrine gland cells with a synaptic cleft.

8. Neurotransmitters and synapses
At the axon terminal vesicles store neurotransmitters.
These are released ( by exocytosis) into the cleft when an impulse arrives.
They diffuse across the cleft and bind to receptors on the nerve endings on the dendrite.
This initiates an impulse.
Examples of neurotransmitters include
acetylcholine and norepinephrine (noradrenalin).

9. Synapses and an impulse
The neurotransmitters need to be removed from the cleft by either re-uptake or by enzyme degradation.
This prevents the continuous stimulation of the post synaptic neurone.
For example acetylcholine is broken down by acetylcholinesterase and noradrenaline is reabsorbed into the presynaptic neurone.
Post synaptic receptors determine whether the signal generated is excitatory or inhibitory.
Neurotransmitters only occur in vesicles on one side of the synapse ensuring the impulse can go only in one direction.

10. Synapses and an impulse
Receptors require a certain amount of neurotransmitter to create an impulse.
If a weak stimulus does not produce enough secretion of neurotransmitter then the signal is not passed on.
This is how weak stimuli or signals can be filtered out.
However a collection of weak stimuli can produce enough neurotransmitter to allow the firing threshold of the post synaptic neuron to be reached.
This is called summation.

11. Examples of neurotransmitters
Action of transmitter
acetylcholine
Excitatory at skeletal muscle varies at other sites
norepinephrine
Excitatory or inhibitory depending on receptor
serotonin
GABA
Inhibitory
dopamine
More later on the effect of these on behaviour and mood

12. Examples of chemicals effecting neuron impulse transmission
Curare – relaxes muscles by binding to acetylcholine receptors
Strychnine- a poison that inhibits motor neurones
Questions on page 256

13. Neural pathways Neural pathways can be very complex
Pathways can be converging, diverging or reverberating.
The brain develops or alters pathways depending on sensory input and this is called plasticity.

14. Converging pathways
Impulses from several sources meet at a common destination.
This can mean a series of weak impulses can produce a response.
This is how the rods in the retina work. Each rod will respond to dim light but on their own would not produce a response.
Several rod impulses converge to reach the threshold needed to transmit an impulse in the optic nerve.

15. Diverging pathways
An impulse from one place can be split and sent to a number of different destinations.
This can be seen in fine motor control in the hands, (cerebrum motor area to hand muscles).
In temperature control the hypothalamus sends information to sweat glans, skin arterioles and skeletal muscle simultaneously.

16. Reverberating pathways
These pathways have neurons which have a branch that form synapses with neurons earlier in the pathway sending impulses back through the circuit.
These type of pathways can be seen in the control of breathing (a rhythmical and continuous activity).
They are also involved in STM.

17. Plasticity of response
The brains ability to create new neural pathways or to bypass neural pathways is called plasticity.
This occurs at different times in a human life depending on development and circumstances i.e. some are major, others minor.
Early development of the brain
Learning new skills
Brain damage response
Suppressing reflexes
Ignoring sensory impulses
Questions page 264

18. Neurotransmitters, mood and behaviour
What are we learning?
What some of the different neurotransmitters are?
What effect they have on mood and behaviour?
How disorders of neurotransmitters can be treated?
What happens in drug tolerance and addiction?
NEUROTRANSMITTERS
The chemicals that allow communication between neurons
Two of these include endorphins and dopamine

19. Endorphins Endorphins are made in the hypothalamus.
They are like neurotransmitters that act as painkillers.
They bind to receptors at synapses blocking pain signal transmission.
Production of endorphins is increased by physical and emotional stress, severe injury, extended vigorous exercise and eating certain foods like chocolate.
Increased production can have an influence on feelings of euphoria, appetite regulation and the releases of sex hormones.

20. Dopamine
Produced in several areas of the brain including V and N centres in the limbic system
Dopamine induces feeling of pleasure.
It reinforces behaviour in the reward pathway in the brain
N and V centres

21. Dopamine Reward Pathway
V centre releases dopamine when hunger, thirst or sexual need is being satisfied.
Dopamine is carried to N centre where more dopamine is released.
This produces a feeling of pleasure.
This reinforces the effect of survival behaviours.
V and N are known as the pleasure centres of the brain.
The route between V and N is called the reward pathway.

22. Neurotransmitter related disorders and their treatment
Clinical use of chemicals that act as neurotransmitters or block the effect of neurotransmitters is becoming more common.
These chemicals are very similar to the bodies natural neurotransmitters.
They act as
Inhibitors
Agonists
Antagonists

23. Inhibitors
These act by preventing the degradation of neurotransmitters by enzymes (i.e. cholinesterase) or by preventing reabsorption of neurotransmitters by presynaptic neurons (i.e. norepinephrine).
Agonists
These bind to certain neurotransmitter receptors on the post synaptic neuron. They trigger normal cellular response.
Antagonists
These occupy certain receptors on the post synaptic neuron preventing the normal neurotransmitter from binding. They reduce or halt the normal signal response.

24. Research neurotransmitter related illnesses
i.e. Alzheimer’s, Parkinson’s, Schizophrenia, GAD, depression

25. What have you learned?

26. Mode of action of recreational drugs
Recreational drugs include cocaine, cannabis, ecstasy (MDMA), alcohol, nicotine, etc..
They can have their effect by:
stimulating the release of natural neurotransmitters
acting as agonists which imitate the effect of neurotransmitters
prevent enzyme degradation of neurotransmitters
inhibiting reabsorption of neurotransmitters.
Because of this they alter mood, behaviour, perception and cognition.
Many of these drugs effect neurotransmission in the reward pathway of the brain which is one reason they are addictive.
Research the effects of these drugs specifically on the
nervous system

27. Summary of effects of drugs
Effect on system
Effect on behaviour, mood, etc.
cocaine
blocks dopamine re-uptake channels
cannabis
binds to cannabinoid receptors
ecstasy (MDMA)
stimulates serotonin and inhibits its re-uptake
alcohol
binds to GABA receptors elevating dopamine levels
nicotine
activates nicotine receptors increases dopamine, serotonin and epinephrine

28. Drug addiction and tolerance
Drug addiction and tolerance are related to the action of the drug being taken.
Addiction is now classified as a disease which has come from a person’s brain over-riding self-control in their need for more of the drug.
Tolerance is when an addictive drug no longer has the same effect despite taking the same concentration of the drug. Only a higher dose will give the same original effect.

29. Sensitisation
Sensitisation comes about when the drug acts as an antagonist.
These drugs block neuroreceptors preventing the normal neurotransmitter acting on them.
More receptors develop to compensate and the receptors become sensitive to the antagonistic drug.
This leads to addiction to the drug.

30. Desensitisation
Desensitisation comes about when the drug acts as an agonist.
These drugs stimulate receptors repeatedly giving feelings of euphoria or well being (e.g. dopamine receptors).
The number of receptors decreases and those remaining become less sensitive to the drug.
This leads to drug tolerance as a larger dose is needed to produce the same effect from reduced receptors.
Questions on page 274

31. Consolidation Complete the summary
Complete matching and multiple choice questions ch. 19
Make notes from textbook
Review power points from blog
Make notes using Scholar