Transcript e.4.1 state that some presynaptic neurons excite

OPTION E
E4
NEUROTRANSMITTERS AND SYNAPSES
E.4.1 STATE THAT SOME PRESYNAPTIC NEURONS EXCITE POST SYNAPTIC
TRANSMISSION WHILE OTHERS INHIBIT POST-SYNAPTIC TRANSMISSION.
Pre-synaptic neurons can either excite or inhibit post-synaptic
transmissions. (AP = “all-or-nothing”)
 This depends on which neurotransmitter (NT) is used and which
receptors they bind to.

http://www.youtube.com/watch?v=LT3VKAr4roo
http://learn.genetics.utah.edu/content/addiction/reward/neurontalk.html
E.4.1 STATE THAT SOME PRESYNAPTIC NEURONS EXCITE POST SYNAPTIC
TRANSMISSION WHILE OTHERS INHIBIT POST-SYNAPTIC TRANSMISSION.
Excitatory: NT stimulates an AP in the post-synaptic neuron
 NT binding to the receptors opens sodium gates, causing sodium
to flow in, depolarizing the neuron.
 Na+ in, neuron more positive, depolarization occurs.
 NT: e.g. glutamate, acetylcholine (Ach), norepinephrine (NE),
dopamine

E.4.1 STATE THAT SOME PRESYNAPTIC NEURONS EXCITE POST SYNAPTIC
TRANSMISSION WHILE OTHERS INHIBIT POST-SYNAPTIC TRANSMISSION.
Inhibitory: NT prevents an AP in the post-synaptic neuron
 NT binding to the receptors opens potassium gates, causing
chloride to flow in, hyperpolarizing the neuron.
 Cl- in, neuron more negative, more difficult to depolarize,
impulse inhibited.
 NT: e.g. GABA, dopamine

E.4.1 STATE THAT SOME PRESYNAPTIC NEURONS EXCITE POST SYNAPTIC
TRANSMISSION WHILE OTHERS INHIBIT POST-SYNAPTIC TRANSMISSION.
GABA = -Aminobutyric acid
 GABA is a NT that opens chloride (Cl-) ion channels on the
post-synaptic membrane. Cl- rushes in, hyperpolarizing the
post-synaptic neuron and reducing APs.
 GABA is important in regulating nervous processes – a “calming”
or depressive effect (reducing activity).
 It prevents neurons from overfiring,
and can be used as a drug to help
people with anxiety or stress-related
disorders.
 Alcohol mimics the effect of GABA,
further increasing hyperpolarization
and therefore greatly reducing
nerve activity.

E.4.2 Explain how decision-making in the CNS can result from the
interaction between the activities of excitatory and inhibitory
presynaptic neurons at synapses.

Important points to remember:
- axons of many neurons feed into the dendrite of the postsynaptic neuron
- each axon contributes to the membrane potential of the postsynaptic neuron
- effects of the each input
can be either excitatory
or inhibitory
- effect is summative and
is added up at the axon
hillock.
E.4.2 Explain how decision-making in the CNS can result from the
interaction between the activities of excitatory and inhibitory
presynaptic neurons at synapses.
 If the summative effect of the inputs reaches threshold, an AP
is propagated.

Spatial Summation:
multiple inputs

Temporal Summation:
multiple firing from one input
http://hsc.uwe.ac.uk/synapses_neuro/summation.htm
E.4.3 Explain how psychoactive drugs affect the brain and
personality by either increasing or decreasing postsynaptic
transmission.
Excitatory drugs
Inhibitory drugs
Mimic inhibitory NTs
-↑ hyperpolarization of
post-synaptic neuron
- fewer APs
- e.g. alcohol mimics GABA
effects, reducing APs
Blocks excitatory NTs
- prevents APs
- e.g. opiates (heroin)
block pain pathway by
competitive inhibition
Block re-uptake pumps
for NTs
- NT remains in synapse
-e.g. cocaine’s effect on
dopamine
Mimic excitatory NTs
- ↑ depolarization, more APs
-e.g. nicotine
Block inhibitory NTs
- prevent inhibition of APs
-e.g. caffeine competitively
inhibit adenosine
http://outreach.mcb.harvard.edu/animations/synapse.swf
E.4.4 List three examples of excitatory and three examples of
inhibitory psychoactive drugs.
Excitatory
- Nicotine: stimulate alertness and memory, nausea and vomiting
- Cocaine/crack: increases heart rate, respiration, alertness
- Amphetamines/ecstasy: causes anxiety and psychosis.
http://www.talktofrank.com/drugs-on-the-brain
http://www.jellinek.nl/brain/index.html
E.4.4 List three examples of excitatory and three examples of
inhibitory psychoactive drugs.
Inhibitory
- Benzodiazepines: muscle relaxant, reduces anxiety.
- Cannabis: slows and prevents movement, impairs reasoning skills.
- Alcohol: reduces heart rate, breathing rate, and blood pressure.
http://www.jellinek.nl/brain/index.html
E.4.5 Explain the effects of THC and cocaine in terms of their
action at synapses in the brain.
Excitatory drugs = Cocaine
Normal:
-Dopamine acts as an excitatory NT
-Dopamine is re-uptaken at the pre-synaptic neuron pumps
With Cocaine:
-Blocks receptors on reuptake pump
-Dopamine not re-uptaken; remains in synaptic cleft
-More dopamine is released
-Increased post-synaptic transmission
Effect on mood/behavior
-Enhanced feelings of pleasure (dopamine is a “pleasure” NT)
-Increased energy and alertness
-Highly addictive
-Associated with depression (body reduces its own dopamine)
http://thebrain.mcgill.ca/flash/i/i_03/i_03_m/i_03_m_par/i_03_m_par_cocaine.html#drogues
E.4.5 Explain the effects of THC and cocaine in terms of their
action at synapses in the brain.
Inhibitory drugs = THC (cannibis)
Normal:
-Two pathways to consider
1) pathway released dopamine, increasing feelings of pleasrue
2) GABA has an inhibitory effect on release of dopamine
With THC:
-Inhibits GABA release by binding to cannaboid receptors
-GABA cannot inhibit dopamine
-More dopamine is released
-Increased post-synaptic transmission
Effect on mood/behavior
-Enhanced feelings of pleasure (dopamine is a “pleasure” NT)
-Intoxication (drunk feeling), hunger, memory impairment
http://thebrain.mcgill.ca/flash/i/i_03/i_03_m/i_03_m_par/i_03_m_par_cannabis.html#drogues
E4.6 DISCUSS THE CAUSES OF ADDICTION, INCLUDING
GENETIC PREDISPOSITION, SOCIAL FACTORS, AND DOPAMINE
SECRETION.

Addiction
- a chronic neurological disorder with genetic,
psychosocial and environmental characteristics.
- is characterized by changes in the brain resulting in a
compulsive desire to use a drug.
- “Reward centers” in the brain play a key role in
reinforcing behavior that may lead to addiction.
E4.6 DISCUSS THE CAUSES OF ADDICTION, INCLUDING
GENETIC PREDISPOSITION, SOCIAL FACTORS, AND DOPAMINE
SECRETION.

Reward Pathway
- makes one feel good when he/she engages in behaviors
that are necessary for survival (e.g. eating, drinking)
• Dopamine is the NT most prevalent
in the reward pathway.
- generate a feeling of pleasure
- high levels of dopamine cause a
feeling of euphoria
- user may seek to repeat by using
the drug again (addictive)
- withdrawal of the drug leads to
anxiety, depression and craving
E4.6 DISCUSS THE CAUSES OF ADDICTION, INCLUDING
GENETIC PREDISPOSITION, SOCIAL FACTORS, AND DOPAMINE
SECRETION.



Some people are genetically more pre-disposed to
becoming addicted than others.
May be the result of genetically determined deficiency of
dopamine receptors.
The children of addicts are more likely to become addicts
themselves.
E4.6 DISCUSS THE CAUSES OF ADDICTION, INCLUDING
GENETIC PREDISPOSITION, SOCIAL FACTORS, AND DOPAMINE
SECRETION.
Psychosocial factors are a heavy influence in addiction:
 peer pressure
 availability
 legality or religion
 family
 cultural tradition
 timing (adolescents more susceptible)
 poverty/ social deprivation
 traumatic life experience
 mental health problem