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
