A5 Pharmacology Flashcards
Compare excitory and inhibitory neurotransmitters.
Excitatory neurotransmitters cause positively charged ions to enter the post-synaptic neuron and trigger depolarisation, increasing the likelihood of a response.
Inhibitory neurotransmitters cause negatively charged ions to enter the post-synaptic neuron and trigger hyperpolarisation, decreasing the likelihood of a response.
Describe fast-acting and slow-acting neurotransmitters.
Fast-acting neurotransmitters bind directly to ion channels to initiate a rapid response (<1 millisecond) while slow-acting neurotransmitters bind to G-protein coupled receptors to initiate a slower response (milliseconds – minute).
- Examples of fast-acting neurotransmitters include glutamate (excitatory) and GABA (inhibitory).
- Examples of slow-acting neurotransmitters include dopamine, serotonin and acetylcholine.
Describe in detail slow-acting neurotransmitters.
Slow-acting neurotransmitters are called neuromodulators because they can modulate the efficiency of synaptic transfer. They trigger second messenger pathways within the post-synaptic cell, which allows for a longer, more sustained duration of action (i.e. ion channels are open for longer to meditate greater depolarisation) and long term alterations to cellular activity to improve synaptic transfer (i.e. increased expression of ion channels).
Define a psychoactive drug.
A chemical substance that changes brain function and results in alterations in perception, mood or consciousness by either increasing postsynaptic transmission (stimulants) or decreasing postsynaptic transmission (sedatives).
What are stimulant drugs?
Drugs that increase postsynaptic transmission. They mimic the stimulation provided by the sympathetic nervous system (i.e. ‘fight or flight’ responses).
Examples of stimulants include caffeine, cocaine, amphetamines, ecstasy (MDMA) and nicotine.
What are depressant drugs?
Drugs that decrease postsynaptic transmission. They slow down brain activities and relax muscles by reducing stimulation of the central nervous system. They may induce sleep (sedatives).
Examples of sedatives include benzodiazepines, barbiturates, alcohol and tetrahydrocannabinol (THC = cannabis).
Describe the effects on the nervous system of two stimulants.
*Stimulants increase postsynaptic transmission and mimic the stimulation provided by the sympathetic nervous system.
1) Nicotine
Nicotine mimics the action of acetylcholine by binding to acetylcholine receptors. It is not broken down by the enzyme acetylcholinesterase, resulting in overstimulation of the receptors. Nicotine raises dopamine levels in the brain (leading to addiction) and activates parasympathetic pathways (calming effect).
2) MDMA
MDMA increases the secretion of dopamine and seratonine from the vesicles and binds to reuptake pumps, slowing their rate of uptake. This increases the levels of dopamine and seratonine in the synaptic cleft, prompting feelings of euphoria and heightened sensation.
Describe the effects on the nervous system of two sedatives.
*Sedatives decrease post-synaptic transmission and reduces stimulation of the central nervous system.
1) Benzodiazepines eg. rohypnol
Benzodiazepines bind to GABA receptors on the post-synaptic neuron and increase the efficiency of GABA action.
GABA triggers the opening of ion channels to cause hyperpolarisation – benzodiazepines enhance this effect. They promote sleep-inducing and muscle relaxing responses by the body.
2) Tetrahydrocannabinol (THC)
THC binds to cannabinoid receptors on presynaptic neurons. This blocks the release of inhibitory neurotransmitters that prevent dopamine secretion. By preventing the inhibition of dopamine secretion, THC causes a sense of euphoria and emotional well-being.
Define addiction.
A dependence on a substance or an activity which results in its repeated and compulsive use.
What are factors that can contribute to addiction?
- Genetic predisposition
Particular addictions can run in families, suggesting a genetic predisposition. Specific genes might influence the rate of drug metabolism or intensity of drug effect. - Social environment
Cultural traditions, peer pressure, mental health, poverty and being raised in an environment with prevalent drug use. - Dopamine secretion
Long-term substance abuse will lead to the down-regulation of dopamine receptors, requiring higher doses to achieve the original effect. Consequently, addicts must continue to take drugs in order to achieve a diminishing level of reward.
How do anaesthetics work?
Anaesthetics interfere with neural transmission and block sensation. This allows for surgical intervention. There are two types: local anaesthetics and general anaesthetics.
Describe the differences between local anaesthetics and general anaesthetics.
Local anaesthetics will not result in a loss of consciousness and only cause a reversible loss of sensation to the affected area.
General anaesthetics induce a temporary loss of consciousness as they interfere with neural transmissions in the brain.
What are endorphins?
Endorphins are neuropeptides produced by the pituitary gland that function as the body’s natural painkiller. They are typically released by the body during periods of stress, injury or physical exercise. They are inhibitory neurotransmitters and their effects have a slow onset but last a long time.
How do endorphins act as natural painkillers?
Pain is perceived when impulses are sent from pain receptors to sensory areas of the brain. Endorphins bind to receptors on pre-synaptic neurons to block the transmission of pain signals.
