Chapter 2 - Synapses & Module 14.1 - Substance Use & Addiction Flashcards
How did Sherrington discover synapses?
Through studying reflexes of dogs and their automatic muscular responses to stimuli. A sensory neuron excites a second neuron which excites a motorneuron which excites a muscle. This is called a reflex arc. When Sherrington pinched the dogs foot, the dog flexed that leg after a short delay. Speed of conduction was slower than that of an action potential. He inferred delay was due to axons communicating.
What is a reflex arc?
A circuit from sensory neuron to muscle response
What is temporal summation?
Repeated stimuli in a short time have a cumulative effect
What is a presynaptic neuron?
The neuron that delivers transmission.
What is a postsynaptic neuron?
The neuron that receives transmission.
What is a graded potential?
May be either depolarisations (excitatory) or hyperpolarisations (inhibitory).
What is EPSP?
Excitatory postsynaptic potential.
A graded depolarisation. Allows more sodium ions to enter the cell.
What is spatial summation?
Summation over space. Synaptic inputs from separate locations combine their effects on a neuron.
What does an inhibitory synapses do?
Prevents the probability of an action potential occurring. At inhibitory synapses, input from an axon hyper polarises the postsynaptic cell. This increase in positive charge in the cell moves it further from the threshold and decreases an action potential.
What is IPSP?
Inhibitory postsynaptic potential
Temporary hyperpolarisation. It selectively opens the gates for potassium ions to leave the cell (carrying a positive charge) or for chloride ions to enter (carrying a negative charge).
What did Loewi do and discover?
Loewi stimulated the vagus nerve to slow a frogs heart rate down and then collected fluid from the heart and transferred it to a second frogs heart. The second frogs heart rate slowed down. Loewi concluded that messages are communicated by chemicals.
What are the major events at the synapses?
1) Neurons synthesise chemicals that serve as neurotransmitter.
2) Action potentials travel down the axon. At the presynaptic terminal, an action potential enables calcium to enter the cell. Calcium releases neurotransmitters from the terminals and into the synaptic cleft (space between the presynaptic and postsynaptic terminals).
3) The released molecules diffuse across the cleft, attach to receptors, and alter the activity of the postsynaptic neuron.
4) The neurotransmitter molecules separate from their receptors.
5) The neurotransmitter molecules may be taken back into their presynaptic neuron for recycling or they may diffuse away.
6) Some postsynaptic cells send reverse messages to control the further release of neurotransmitters by presynaptic cells.
Name types of neurotransmitters
Amino acids - acids containing an amine group (NH2)
Monoamines - chemicals formed by a change in certain amino acids
Acetylcholine - a chemical similar to an amino acid, except that it contains an N(CH3)3 group instead of NH2.
Neuropeptides - chains of amino acids
Purines - A category of chemicals including adenosine and its derivatives
Gases - nitric oxide
What does nitric acid do?
Increases blood flow to highly active areas of the brain by dilating nearby blood vessels
How does the body synthesise neurotransmitters?
It makes them from amino acids, which it gain from proteins in the diet.
What are catecholamines?
Epinephrine, norepinephrine, dopamine. They contain a catechol group
How is acetylocholine made?
Acetyl coenzyme A (from metabolism)
+
Choline (from metabolism or diet)
How is dopamine and norepinephrine and Epinephrine made?
Phenylaline (from diet) --> Tyrosine --> Dopa --> Dopamine --> norepinephrine --> epinephrine
How is serotonin made?
Tryptophan (from diet) --> 5-hydroxytryptophan --> serotonin (5-hydroxytryptamine)
What is choline present in?
Eggs, milk and peanuts
What is phenylketonuria?
Lack of the enzymes to convert phenylaline to tyrosine. They need to minimise phenylaline in their diet.
What does tryptophane do?
Tryptophane is the precursor to serotonin. It crosses the blood-brain barrier by a transport system. Trypotophane in the diet controls the amount of serotonin in the brain. Serotonin levels rise after eating foods rich in tryptophane, such as soy, and fall after eating foods low in it, such as maize. You can increase tryptophane entry into the brain by consuming less phenyl aline and more carbs. Carbs release insulin which takes competing amino acids out of the blood stream.
What does the presynaptic neuron store neurotransmitters in?
It stores high concentrations of neurotransmitters in vesicles (tiny nearly spherical packets). Nitric acid is released as soon as it is formed.
What is MAO?
Monoamine oxidase - an enzyme located in the presynaptic terminal that breaks serotonin, dopamine and norepinephrine that breaks these transmitters into inactive chemicals.
What is exocytosis?
When depolarisation opens voltage-dependent calcium gates in the presynaptic terminal and it causes bursts of releases of neurotransmitters.
What is ionotropic effects?
Neurotransmitters exert it and it corresponds to the brief on/off effects. When neurotransmitters binds to an ionotropic receptor, it opens the central channel enough to let a particular type of ion pass through (transmitter-gated or ligand-gated channels). Effect begins quickly and has a half-life of about 5ms. It is well suited to convey visual and auditory information.
What is glutamate?
Glutamate is a neurotransmitter that often excites ionotropic synapses. Most inhibitory inotropic receptors use the neurotransmitter GABA (gamma-amino butyric acid).
What is GABA?
Gamma-amino butyric acid. It opens chloride gates enabling chloride ions with a negative charge to cross the membrane rapidly.
What is glycine?
An inhibitory transmitter mostly found in the spinal cord
What is acetylcholine?
An excitatory transmitter
What is a metabotropic effect?
Neurotransmitters exert effects by initiating a sequence of metabolic reactions that are slower and longer lasting than ionotropic effects. They use many neurotransmitters.
How does a neurotransmitter cause a metabotropic effect?
When the neurotransmitter attaches to a metabotropic receptor, it bends the receptor protein that goes through the membrane of the cell. On the other side of the receptor is a G protein (a protein coupled to GTP - guanosine triphosphate - an energy storing molecule). The concentration of a second messenger (i.e. cyclic adenosine monophosphate (cyclic AMP)). The second messenger opens or closes ion channels or activates a portion of a chromosome. Metabotropic effect influences activity in much of the cell over a long time.
What are neuropeptides?
They are neuromodulators. They are synthesised in the soma and slowly transported to other parts of the cell. Neuropeptide release requires repeated stimulation. After a dendrite releases neuropeptides, nearby neutrons release them too. They are important for hunger, thirst and other long-term changes in behaviour.
What role do receptors play?
The brain has a variety of receptors. Receptors differ in chemical properties, roles in behaviour and responses to drugs. It is possible to devise drugs with specialised effect on behaviour. A drug that chemically represents a neurotransmitter is able to bind to its receptor.
What are hallucinogenic drugs?
Drugs that distort perception (i.e. LSD). They chemically resemble serotonin and attaches to serotonin type 2A receptors and causes stimulation at inappropriate times or for longer than usual durations.
What does nicotine do?
Nicotine stimulates acetylcholine receptors (called nicotonic receptors) on neutrons that release dopamine so nicotine increases dopamine release there.
What do antipsychotic drugs do?
They block dopamine receptors. It results in decreased pleasure and motivation.
What are opiate drugs and what do they do?
Morphine, heroin and methadone
They attach to receptors that release endorphins. Opiates relieve pain by attaching to receptors in the brain.
What happens after acetylcholine activates a receptor?
It is broken down by acetylcholinesterase into acetate and choline
What happens to serotonin and the catecholamines after activating a receptor?
They do not break down into inactive fragments at the postsynaptic neuron. They detach from the receptor. The presynaptic neuron reuptakes most molecules intact and reuses them. This occurs through special membrane proteins called transporters.
What happens to transmitter molecules not taken up by transporters?
They are broken down by an enzyme, COMT
What do stimulant drugs do?
Amphetamine and cocaine
They inhibit the transporters for dopamine, thus decreasing repute and prolonging dopamine’s effect. Amphetamine also blocks the serotonin and norepinephrine transporters. Methamphetamine acts like amphetamine but stronger. A while after taking the stimulant, the user has a dopamine deficit and feels reduced energy, reduced motivation and depression.
What do anti-depressants do?
They block the dopamine transporter but more weakly than amphetamine and cocaine.
How does methylphenidate work?
Methylphenidate (Ritalin) acts like cocaine and blocks the reuptake of dopamine. Differences are due to dose and time course. Cocaine is typically sniffed or injected to produce a rush. Methylphenidate increases dopamine levels over a slow time frame.
What are auto receptors?
Receptors that respond to the released transmitter by inhibiting further synthesis and release. The postsynaptic terminal can release further chemicals (nitric acid, anandamide and 2-AG) that inhibit further release.
What do cannabinoids do?
They bind to anandamide and 2-AG receptors on presynaptic terminals or GABA. The cannabinoids indicate to the receptor that the message was received and stops both excitatory and inhibitory messages from many neurons.
When are electrical synapses important?
They are involved where exact synchrony of two cells is important (i.e. rhythmic breathing).
How do electrical synapses work?
The membrane of one neuron comes into direct contact with the membrane of another. This is called a gap junction. Fairly large pores of the membrane of one neuron line up precisely with similar pores in the membrane of the other cell. These pores are large enough for sodium and other ions to pass through and the pores remain open constantly. When the neuron depolarises, the sodium passes into the other cell quickly. This quickly depolarises it and the cells essential act as one neuron.
What is a hormone?
A chemical secreted by cells in one part of the body and carried by the blood to influence other cells. Hormones coordinate long lasting changes in multiple parts of the body. There are two types of hormones - protein hormones (larger chains of amino acids) and peptide hormones (shorter chains of amino acids). Hormones attach to a receptor where they activate a secondary messenger (similar to metabotropic synapses).
What does the pituitary gland do? What are its parts and what do they do?
The pituitary gland is made up of 2 parts. The posterior pituitary (made up of neural tissue) is attached to the hypothalamus. The hypothalamus synthesises oxytocin and vasopressin, which move down the axons to the posterior pituitary where they are released. The posterior pituitary is similar to the hypothalamus.
The anterior pituitary (made up of glandular tissue) responds to the secretion of hormones by the hypothalamus that tell it to release other hormones. The hypothalamus maintains consistent levels of hormones throughout the body by a negative feedback system.
What is an antagonist drug?
When it blows neurotransmitters
What is an agonist drug?
When it mimics or increases the effects of the neurotransmitter.
What is affinity?
When a drug binds to a receptor
What is efficacy?
Its tendency to activate the receptor
What role does the nucleus accumbens play in addiction?
It is central to reinforcing experiences. Addictive drugs strongly activate it by releasing dopamine and norepinephrine there.
How do stimulant drugs work?
Stimulant drugs block the reuptake of dopamine or reverse dopamine transporter so it releases dopamine instead of producing reuptake.
What do opiates do?
Opiates inhibit neurons that release GABA that inhibits the firing of dopamine neutrons.
What is a craving?
An insistent search for an activity
How does drug abuse impact on impulsivity?
Addictive drugs disrupt activity in the prefrontal cortex and other areas for restraining impulse. The prefrontal cortex fails to overrule reward seeking behaviour, even if there is a cost to it.
What is tolerance?
As an addiction develops, many effects, especially the enjoyable effect, decreases.
What is withdrawal?
The body comes to expect the drug under certain circumstances, it reacts strongly when the drug is absent.
How does predisposition to drug addiction work?
Can be genetic or environmental
- A mother who drinks alcohol during pregnancy increases the probability that the child will develop alcoholism later.
- Childhood environment - a gene controls GABA receptors. Those with a less sensitive form of the receptor tend to have difficulty inhibiting their impulses, including those leading to alcohol abuse and antisocial behaviour. Those who grew up with close parental supervision were much less likely to develop impulse problems.
What is type II (B) alcoholism?
Rapid onset before age 25. Mostly men with a family history of alcoholism.
What is type I (A) alcoholism?
Develops gradually after 25. Usually due to stressful life and less on genetics. More effective treatment.
What characteristics result in more likely chance of alcoholism?
Those who were impulsive, risk taking, easily bored, sensation seeking and outgoing.
When a vigorous pinch excited a dog’s flexor muscle, it decreased excitation of the extensor muscle of the same leg. Sherrington cited this observation as evidence for what?
Inhibitory synapses
During an EPSP, the gates in the membrane open. During and IPSP, the gates open.
sodium…….potassium or chloride
Although one pinch did not cause a dog to flex its leg, a rapid sequence of pinches did. Sherrington cited this observation as evidence for what?
Temporal summation
Although one pinch did not cause a dog to flex its leg, several simultaneous pinches did. Sherrington cited this as evidence for what?
Spatial summation
In what way were Sherrington’s conclusions important for psychology as well as neuroscience?
He demonstrated the importance of inhibition
What evidence led Sherrington to conclude that transmission at a synapse is different from transmission along an axon?
The velocity of a reflex is slower than the velocity of an action potential
What evidence led Sherrington to conclude that transmission at a synapse is different from transmission along an axon?
Sherrington found that the velocity of conduction through a reflex arc was slower than the velocity of an action potential along an axon. Therefore, some delay must occur at the junction between one neurone and the next.
What is the difference between temporal summation and spatial summation?
Temporal summation is the combined effect of quickly repeated stimulation at a single synapse. Spatial summation is the combined effect of several nearly simultaneous stimulations at several synapses into one neuron.
What was Sherrington’s evidence for inhibition in the nervous system?
Sherrington found that a reflex that stimulates a flexor muscle prevents contraction of the extensor muscles of the same limb. He therefore inferred that an inter-neuron that excited motor neurons connected to the flexor muscle also inhibited the input to the extensor muscle.
What ion gates in the membrane open during EPSP? What gates open during an IPSP?
During an EPSP, sodium gates open. During an IPSP, potassium or chloride gates open.
Can an inhibitory message flow along an axon?
No. Only action potentials propagate along an axon. Inhibitory messages IPSPs decay over time and distance.
In which of these ways does a metabotropic synapse differ from an ionotropic synapse?
a. Its effects are faster to start and briefer in duration
b. Its effects are fast to start and last longer
c. Its effects are slower to start and briefer in duration
d. Its effects are slower to start and last longer
d. Its effects are slower to start and last longer
The amino acid tryptophan is a precursor to which neurotransmitter?
Serotonin
A drug would prevent an action potential if it:
blocks the movement of sodium across the membrane.
Which type of glia remove waste material in the nervous system?
Astrocytes
When a membrane is at rest, what attracts potassium ions to the inside of the cell?
the electrical gradient
An axon has many branches, each of which swells at its tip. These are known as:
presynaptic terminals
The brain’s most abundant excitatory neurotransmitter is , and its most abundant inhibitory neurotransmitter is .
Glutamate… GABA
Which function is NOT performed by glia? Select one: a. transmitting information b. guiding the growth of axons and dendrites c. removing waste materials d. building myelin sheaths
a. transmitting information
One disadvantage of the blood-brain barrier is that it keeps out most forms of nutrition. T or F
True
The primary source of energy used by the brain is fat. T or F
False
An efferent axon carries information away from a structure. T or F
True
An afferent axon brings information into a structure. T or F
True
What was Loewi’s evidence that neurotransmission depends on the release of chemicals?
He stimulated one frog’s heart, collected fluid around it, transferred it to another frog’s heart, and saw changes in its heart rate.
Suppose you want to cause the presynaptic terminal of an axon to release its transmitters. How could you do so without an action potential?
Inject calcium into the presynaptic terminal
Which of the following is NOT one of the brain’s neurotransmitters?
a. Glucose
b. Glutamate
c. Serotonin
d. GABA
a. Glucose
What are the nodes of Ranvier?
gaps in the myelin sheath
An axon releases chemicals:
into the junction between neurons.
Of the following, the most important consideration in developing a drug that will act in the brain is:
Select one:
a. how long the drug will act.
b. if the drug can be inexpensively manufactured.
c. if the drug will cross the blood-brain barrier.
d. the number of people who will use the drug.
c. if the drug will cross the blood-brain barrier.
Which of the following describes selective permeability?
Select one:
a. Only certain molecules are allowed to cross the membrane freely.
b. Only certain types of stimulation will result in an action potential.
c. Ions can only travel in certain directions across the membrane.
d. All molecules must pass through designated channels.
a. Only certain molecules are allowed to cross the membrane freely.
One of the most distinctive features of neurons compared to other types of cells is their:
a. lack of a cell membrane.
b. size. Incorrect
c. number of mitochondria.
d. shape.
If a drug was given that temporarily inactivated the sodium-potassium pumps, action potentials would cease immediately. T or F
False
What is the point from which an axon releases chemicals into the synapse?
The presynaptic terminal
A small gap is usually present between neurons. T or F
True
The blood-brain barrier is made up of closely packed glial cells. T or F
False
The all-or-none law applies to:
axons
What is a second messenger?
A chemical released inside a cell after stimulation a metabotropic synapse
Which of the following is true of neuropeptides?
a) They are released close to their receptors.
b) A neuron releases them at a steady rate almost constantly.
c) They produce rapid, brief effects.
d) They are released either in large quantities or not at all.
d) They are released either in large quantities or not at all.
Which of these drugs exerts its behavioural effects by binding to the same receptor as a neurotransmitter?
a) amphetamine
b) cocaine
c) Nicotine
d) marijuana
c) Nicotine
Which neurotransmitter is broken into two pieces to inactivate it, after it excites the postsynaptic neuron?
acetylcholine
What does a transporter protein do at a synapse?
It pumps used neurotransmitter molecules back into the presynaptic neuron.
Except for the magnitude and speed of effects, methylphenidate (Ritalin) affects synapses the same way as which other drug?
Cocaine.
Which of these drugs acts by inhibiting release of neurotransmitters from the presynaptic neuron?
a) opiates
b) cannabinoids
c) nicotine
d) amphetamine and cocaine
b) cannabinoids
In contrast to the posterior pituitary, the anterior pituitary
is glandular tissue that produces hormones that control other endocrine organs.
One of the most distinctive features of neurons compared to other types of cells is their:
Shape
What does a highly active brain area do to increase its blood supply?
In a highly active brain area, many stimulated neurons release nitric oxide, which dilates the blood vessels in the area and thereby increases blood flow to the area.
Name the three catecholamine neurotransmitters.
Norepinephrine, dopamine and epinephrine.
When the action potential reaches the presynaptic terminal, which ion must enter the presynaptic terminal to evoke the release of the neurotransmitter.
Calcium
What are second messengers, and which type of synapse relies on them?
At metabotropic synapses, the neurotransmitter attaches to its receptor and thereby releases a chemical (the second messenger) within the postsynaptic cell, which alters metabolism or gene expression of the postsynaptic cell.
How are neuropeptides special compared to other transmitters?
Neuropeptides are released only after prolonged stimulation, but when they are released, they are released in large amounts by all parts of the neuron, not just the axon terminal. Neuropeptides diffuse widely, producing long-lasting effects on many neurons.
How do LSD, nicotine, and opiate drugs influence behaviour?
LSD binds to one type of serotonin receptor. Nicotine binds to one type of acetylcholine receptor. Opiates bind to endorphin receptors.
What happens to acetylcholine molecules after they stimulate a postsynaptic receptor?
The enzyme acetylcholinesterase breaks acetylcholine molecules, acetate and choline, which are then reabsorbed by the presynaptic terminal.
What happens to serotonin and catecholamine molecules after they stimulate a presynaptic receptor?
Most serotonin and catecholamine molecules are reabsorbed by the presynaptic terminal. Some of the molecules are broken down into inactive chemicals, which then diffuse away.
How do amphetamine and cocaine influence the dopamine system?
They interfere with the reuptake of dopamine.
Why is methylphenidate generally less disruptive to behaviour than cocaine is despite the drugs’ similar mechanisms?
The effects of a methylphenidate pill develop and decline in the brain much more slowly than do those of cocaine.
How do cannabinoids affect neurons?
Cannabinoids released by the postsynaptic neuron attach to receptors on presynaptic neurons, where they inhibit further release of both glutamate and GABA.
To say that a drug has an affinity for a particular type of receptor is to imply that the drug ____.
Binds to that receptor.
As an addiction develops, many of its effects, especially the enjoyable effects, decrease, a phenomenon known as____.
Tolerance
Which neurotransmitter has been repeatedly connected with addictive drugs?
Dopamine
A drug that mimics or increases the effects of a neurotransmitter is called a(n) ____.
Agonist
A drug that blocks the effects of a neurotransmitter is called a(n) ____.
Antagonist
The brain area most often linked to drug addiction is the ____.
Nucleus accumbens
Symptoms of marijuana withdrawal include anxiety, sweating, vomiting, and diarrhea. T or F
False
With respect to drug effects, “efficacy” means the tendency of a drug to ____.
Activate a receptor
Addictive drugs strongly activate the nucleus accumbens by releasing dopamine or norepinephrine there. T or F
True
Studies of the genetics of addiction have implicated the gene that controls COMT, an enzyme that breaks down norepinephrine. T or F
False
After a long period of abstinence, exposure to cues associated with the substance are very unlikely to trigger a renewed craving. T or F
False
Is a drug with a high affinity and low efficacy an agonist or an antagonist?
An antagonist because by occupying the receptor it blocks out the neurotransmitter.
How do opiates influence dopamine synapses?
Opiates stimulate endorphin synapses, which inhibit neurons that inhibit release of dopamine. By inhibiting an inhibitor, opiates increase the release of dopamine.
