e4: neurotransmitters & synapses
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E4: Neurotransmitters & Synapses. Pp 481 - 488. Assessment Statements. E.4.1 State that some presynaptic neurons excite postsynaptic transmission and others inhibit postsynaptic transmission. - PowerPoint PPT PresentationTRANSCRIPT
E4: Neurotransmitters & Synapses
Pp 481 - 488
Assessment StatementsE.4.1 State that some presynaptic neurons excite
postsynaptic transmission and others inhibit postsynaptic transmission.
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.
E.4.3 Explain how psychoactive drugs affect the brain and personality by either increasing or decreasing postsynaptic transmission.
E.4.4 List three examples of excitatory and three examples of inhibitory psychoactive drugs.
E.4.5 Explain the effects of THC and cocaine in terms of their action at synapses in the brain.
E.4.6 Discuss the causes of addiction, including genetic predisposition, social factors and dopamine secretion.
Synaptic transmissionSome Pre-synaptic
neurons excite postsynaptic transmission
They are called excitatory pre-synaptic neurons
Some Pre-synaptic neurons inhibit postsynaptic transmission
They are called inhibitory pre-synaptic neurons
Excitatory and Inhibitory synapses
Excitatory Pre-synaptic neurons
Inhibitory Pre-synaptic neurons
Depolarises the postsynaptic membrane
Influx of Na+ ions
Possibly reaching threshold
Generation of new action potential
E.g. Acetylcholine
Hyperpolarises the postsynaptic membrane
Influx of Cl- or loss of K+ ions
Makes it more difficult to reach threshold
Lowers the resting potential
E.g. Gama-aminobutryic
acid (GABA)
An action potential in post-synaptic neurone will only occur if the potential difference at the axon hillock (specialized part of the cell body of a neuron that connects to the axon)rises above the threshold value
Decision-making in the CNS can result from the interaction between the activities of excitatory and inhibitory pre-synaptic neurons at synapses.Neurones form
synaptic junctions with the cell body of other neurones
A post synaptic neurone can have many pre-synaptic neurones forming synaptic junctions with it.
Pre synaptic neurones depolarise (excitatory) or hyperpolarise (inhibitory) the post synaptic membrane locally.
The sum of their effects takes place at the axon hillock
SynapsePre-
Pre-
Pre-
Post-
Post-Synaptic Potentials (PSPs) can be:Excitatory (EPSP)(+);or Inhibitory (IPSP) (-).
Post-synaptic
Pre-synaptic
Pre-synapticP
re-synapticP
re-synaptic
+
+-
-Synapse
The EPSP must build up in the postsynaptic neuron tothe threshold level to allow the formation of an actionpotential.
Synapse+
+
+-
E.g. this Neuron needs a 2 more “+” than “-” before it can generate an action potential.
Neurons can integrate signals from other neurons: 1) through spatial summation (different pre-
synaptic neurones ‘add together’ their local depolarisation's to reach threshold at the axon hillock)
Synapse+
+
+-
Summation of the depolarising effects of three different excitatory pre-synaptic neurones i.e. a+b+c
Having reached the threshold (T), a new action potential is generated in the post synaptic neurone
If the summation of the 3 is below threshold there would be no action potential or response from the central nervous system
+ Synapse++
+++
2) through temporal summation where a number of waves neurotransmitter from the same pre-synaptic neurone depolarises the post synaptic membrane (i.e. waves of depolarisation are added together to reach threshold).
The same pre-synaptic neurone(a)has a high frequency of action potentials arriving at the synapse. This sends a number of waves of neurotransmitter to depolarise the post synaptic membrane.
Waves of depolarisation (from one neurone) are added together to reach threshold
Pre-synaptic neurones depolarises the post synaptic membrane with a number of rapid stimulations.
Decision-making in the CNSsynapses are the sites of decision-making in the
braina post-synaptic neuron's membrane potential is
the summation of input from pre-synaptic neurons EPSPs depolarize post-synaptic neurons whileIPSPs hyper-polarize post-synaptic neurons
if the post-synaptic neuron reaches threshold potential at its axon hillock, it will produce an action potential
pre-synaptic neurons can vary in the frequency, but not intensity of their input, since action potentials are "all-or-none“ rule
Psychoactive drug:A Psychoactive drug is
chemical substancesthat acts upon the CNSaltering the state ofmind by changing(stopping or enhancing)the activity at the postsynaptic neuron. It result in changesin perception, mood,consciousness,cognition, andbehaviour.
Alcohol
Amphetamine
Marijuana
How psychoactive drugs affect the brain and personality:Psychoactive drugs affect the brain and personality by
either increasing or decreasing post-synaptic transmission.
The post-synaptic membrane contains receptors for the normal neurotransmitters. Normally when the neurotransmitter attaches to these receptors it either:Depolarise the post synaptic neuron resulting in an action
potentialHyperpolarise the post synaptic neuron resulting in no
action potentialA drug can therefore change post synaptic output by:
Blocking or enhancing the depolarising neurotransmitter Blocking or enhancing the hyperpolarise neurotransmitter
Major Neurotransmitters in the BodyNeurotransmitter Role in the BodyAcetylcholine (excitatory)
Dopamine (inhibitory)
Gamma-amino butyric acid
(GABA) (inhibitory)
used by the spinal cord neurons to control muscles and by many neurons in the brain to regulate memory.
produces feelings of pleasure when released by the brain, it has multiple functions depending on where in the brain it acts.
The most common inhibitory neurotransmitter in the brain.
Examples of excitatory & inhibitory psychoactive drugs:Excitatory psychoactive drugs;
Inhibitory psychoactive drugs;
nicotine,cocaine ,amphetamines.
benzodiazepines, alcohol ,tetrahydrocannabi
nol (THC).
Tetrahydrocannabinol (THC):Marijuana/ganja is the buds and leaves of the Cannabis sativa plant.
Marijuana contains more than 400 chemicals, including tetrahydrocannabinol (THC), the plant's main psychoactive chemical.
Cannabinoid receptors are activated by a neurotransmitter called anandamide.
Anandamide belongs to a group of chemicals called cannabinoids.
THC is also a cannabinoid chemical.
THC mimics the actions of anandamide, meaning that THC binds with cannabinoid receptors and activates neurons, which causes adverse effects on the mind and body.
Effects of Tetrahydrocannabinol (THC)THC affects brain’s short-term memoryTHC affects motor coordination & appetite THC increases heart rate and raises levels of
anxietyTHC contains cancer-causing chemicals similar to
those in tobacco THC affects higher order thinking THC users report feeling mellow and calmTHC mimics the neuro-receptor anandamideTHC binds to the post synaptic membrane receptor
s for anandamide called Cannabinoid ReceptorTHC effect is to hyperpolarise the post synaptic
neuron inhibiting generation of an action potential
Cocaine:Cocaine:- a powdered drug
that is made from the leaves of the coca plant grown primarily in South America.
Cocaine has been in use for centuries, many generations of South American Indians have chewed its leaves to give them strength and energy.
The drug is nowadays taken in by either snorting, injecting or smoking.
Dopamine is released by cells of the nervous system during pleasurable activities such as eating or having sex.
Once released, dopamine travels across a synapse, and binds to a receptor on a post-synaptic neuron.
This sends a signal to that nerve cell, which produces a good feeling.
Under normal conditions, once the dopamine sends that signal it is reabsorbed by the neuron that released it
Cocaine interferes with a chemical messenger in the brain called dopamine, which is involved in the body's pleasure response.
Effects of Cocaine:cocaine is an excitatory psychoactive drugs
that increases synaptic transmissionon post synaptic membrane receptor, it
prevents the removal of acetylcholineon pre-synaptic membrane, it prevents the
recycling of acetylcholineboth effects maintain the stimulation of the
post synaptic membrane cocaine also blocks the recycling of Dopamine
at the Pre-synaptic membrane, making dopamine to remain active in the synapse
dopamine is associated with a feeling of pleasure , thus cocaine creates a mood of euphoria
Drug addiction:Psychoactive drugs often cause
addictive behaviour i.e. an individual persists in use of drugs despite problems related to their use
habitual behaviour associated with addiction includes: craving for the use of the drug; lack of self control in limiting the
taking of the drug;increasing quantities must be taken
to achieve the same mental conditions;
development of withdrawal behaviour if unable to satisfy the craving for the drug.
Causes of addiction:(i) Genetic
predisposition;
Some people are more vulnerable to drug addiction than others,
studies indicates that genetic factors have some influence on addiction,
alcoholism, especially, tends to run in certain families
(ii) Social factors; various social factors correlate positively with addiction, including:cultural traditions; peer pressure; Poverty; social deprivation; traumatic life experiences;
mental health problems; etc
(iii) Dopamine secretion;
many addictive drugs are excitatory at dopaminergic synapses “reward pathway” giving a feel good effect/pleasure
addiction results from dopaminergic synapses responding to regular drug use
tolerance to a drug , leads to increased dosage to produce the desired effect
withdrawal is caused by normal levels of dopamine failing to produce pleasure hence craving for drugs
STOP DRUG ADDICTION!
Any Questions on Drugs?
Thank You!
A Drug-Free World: We Can Do It!
Self Assessment Questions (SAQs)Distinguish between
presynaptic excitatory & inhibitory neurons. [2]
Explain the process of decision-making in the CNS. [3]
Explain how psychoactive drugs affect the brain and personality of an individual. [3]
List 3 examples of excitatory & 3 examples of inhibitory psychoactive drugs. [2]
Explain the effects of THC and cocaine on the brain. [4]
Explain the effects of cocaine and cocaine on the brain. [4]
Discuss the causes of addiction. [6]
Sources: http://www.mun.ca/biology/desmid/brian/
BIOL2060/BIOL2060-13/1322.jpghttp://health.howstuffworks.com/marijuana.htmhttp://health.howstuffworks.com/crack3.htmhttp://intranet.canacad.ac.jp:3445/
BiologyIBHL2/5044http://click4biology.info/c4b/E/E4.htmhttp://en.wikipedia.org/wiki/Substance_dependencehttp://www.google.co.in/imageshttp://www.google.co.in/images?
hl=en&gbv=2&q=stohttp://www.daretoact.net/