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alevelsblr-blog · 6 years ago

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Getting On Your Nerves: Neurones and Drug Mode of Action

The people: Avengers is the most ambitious crossover event in history

Me: *makes a post that covers biology and psychology at the same time*

Today I’m covering my biological psychology module which includes learning about neurones and how drugs work. This isn’t on my biology specification but it might be on yours – so I’m tagging it biology AND psychology. Aren’t I just wild?

Biological psychology assumes that behaviour comes from our biology – that is, our genes, hormones, brain structure etc – and one of the behaviours that it explains is how the body can become addicted. To learn about this, though, you must first learn about the Central Nervous System (CNS).

There are two types of nervous system (clusters of nerves), the other being the Peripheral Nervous System. The CNS consists of the brain and the spinal cord and is pretty much where all communication and decisions occur since messages are sent around the body from the CNS.

Nerves are made up of bundles of specialised cells called neurones. A neuron is pictured below:

Dendrites are short branches at the “top” end of the nerve cell. They receive impulses from the neuron before in a process called neurotransmission. The cell body contains a nucleus, which has the information for the cell. The length of a neuron is called an axon, made up of insulating myelin sheath. Gaps within it are called nodes of Ranvier – electrical impulses jump along these. At the end of the neuron there are axon terminals where neurotransmission takes place over a synapse.

So now you know about the structure of a neuron, the next thing to learn is how messages are passed between them.

Imagine a nerve made up of two neurons. The pre-synaptic neuron is stimulated and action potential is reached. This is kind of like an electrical impulse that travels down the axon towards the terminals.

Between two neurons, there is a gap called the synapse. Neurotransmission is sometimes referred to as synaptic transmission, so it kind of makes sense why the first neuron is called the pre-synaptic neuron.

At one end of the presynaptic neuron, where the terminals are, there are neurotransmitters (chemical messages) in vesicles, which essentially just contain them. When the action potential stimulates the vesicles, they then fuse with the terminal button and release neurotransmitters into the synaptic gap.

On the post-synaptic neuron, there are specific receptor sites on the dendrites that the neurotransmitters are attracted to. The lock and key model is important here; a certain neurotransmitter can only bind to a complementary receptor site. Once the transmitters reach them, they stimulate action potential and the process starts again. Neurotransmitters then detach and either get eaten by enzymes in the synaptic gap or are reabsorbed through the reuptake pump.

There are different types of neurons – sensory neurons carry information from the sense organs (e.g. eyes) to the brain, motor neurons carry information from the CNS down their long axons to muscles and interneurons only communicate within their region.

Since there’s different types of neurons, there’s different types of neurotransmitters too. Excitatory neurotransmitters (also known as neuromodulators or monoamines) pass on electrical impulses and increase the likelihood that a post synaptic neuron will be activated and pass on the message. Examples of this include dopamine, adrenaline and serotonin. On the other hand, there are inhibitory neurotransmitters (endorphins) that block impulses between neurons and therefore decrease the likelihood that the post synaptic neuron will be activated to pass on the impulse.

Here are some examples of each kind of neurotransmitter:

Acetylcholine – excitatory, related to voluntary muscles, inhibition and memory

Dopamine – inhibitory and excitatory, related to voluntary muscles, emotional arousal.

Serotonin – inhibitory and excitatory, related to sleep and temperature regulation.

GABA is an inhibitory neurotransmitter that is closely involved with nearly 40% of synapses in the brain, so most neurones have GABA receptors.

Mode of action describes the action of neurotransmitters at the synapse. Drugs can act through mechanisms like neurotransmitters do. Some drugs can bind to receptors and have the same effect as a neurotransmitter. Some can block the receptor so neurotransmitters cannot fit into them.

In addition to these methods, drugs can work by influencing the making, movement, release or inhibition of neurotransmitters, such as preventing their recycling so they reattach to receptor sites.

Types of drugs that exist include agonists and antagonists. An agonist drug is a drug which mimics a neurotransmitter and increases post-synaptic activity by stimulating post synaptic receptors. An antagonist drug limits the effect of a neurotransmitter therefore reducing post-synaptic activity, perhaps through block post-synaptic receptors or preventing the release of neurotransmitters.

These drugs can further be categorised into psychoactives; depressants and stimulants. Psychoactive stimulants increase post-synaptic activity to cause motor arousal and alertness whereas depressants reduce it, slowing down brain activity and relax muscles.

Cocaine, for example, acts on dopamine. It blocks the dopamine uptake pump in the presynaptic terminal so the dopamine remains active in the synapse, continuing to bind to postsynaptic receptors and cause excitement.

Unfortunately, addiction comes at a cost. Withdrawal is a set of symptoms which occur when there is a sudden drop in blood levels of certain drugs, often the opposite to the initial effects of it. Withdrawal occurs when you are physically dependent on the drug.

However, if you continue to take the drug, you may develop a tolerance ( a decreased sensitivity due to exposure) so more drug is needed to produce the same effect. Tolerance to one drug may also cause tolerance to other drugs with similar mechanisms, and this is called cross tolerance.

Tolerance can essentially be metabolic or functional. Metabolic tolerance is when the amount of drug reaching the sits of action decreases and functional tolerance occurs when there is a reduction in the responsiveness of the receptors. Tolerance to psychoactive drugs is mainly functional. Two naturally occurring processes cause tolerance – down regulation and enzymes.

Down regulation is where the number of receptor sites or their sensitivity is reduced. Since there are less receptors, more drug is needed for the same effect.

Enzymes in the liver break down drugs, so increased exposure to drugs means more of these enzymes are produced, making the body more efficient at removing drug molecules so more drug is needed.

From these facts, you can easily see how addiction occurs. If the symptoms of withdrawal are too much, there is no other option than to continue using. In addition, what starts as a small problem can get quickly larger if the body develops tolerance to the drug.

SUMMARY

· Biological psychology assumes that behaviour comes from our biology – that is, our genes, hormones, brain structure etc.

· Central Nervous System (CNS) consists of the brain and the spinal cord and is pretty much where all communication and decisions occur.

· Nerves are made up of bundles of specialised cells called neurones.

· Dendrites are short branches at the “top” end of the nerve cell which receive impulses from the neuron before in a process called neurotransmission.

· The cell body contains a nucleus, which has the information for the cell.

· The length of a neuron is called an axon, made up of insulating myelin sheath.

· Gaps within it are called nodes of Ranvier – electrical impulses jump along these. At the end of the neuron there are axon terminals where neurotransmission takes place over a synapse.

· In neurotransmission, the pre-synaptic neuron is stimulated and action potential is reached. This is kind of like an electrical impulse that travels down the axon towards the terminals.

· Between two neurons, there is a gap called the synapse.

· At one end of the presynaptic neuron, where the terminals are, there are neurotransmitters (chemical messages) in vesicles. When the action potential stimulates the vesicles, they then fuse with the terminal button and release neurotransmitters into the synaptic gap.

· On the post-synaptic neuron, there are specific receptor sites on the dendrites that the neurotransmitters are attracted to - a certain neurotransmitter can only bind to a complementary receptor site.

· Once the transmitters reach them, they stimulate action potential and the process starts again. Neurotransmitters then detach and either get eaten by enzymes in the synaptic gap or are reabsorbed through the reuptake pump.

· Sensory neurons carry information from the sense organs (e.g. eyes) to the brain, motor neurons carry information from the CNS down their long axons to muscles and interneurons only communicate within their region.

· Excitatory neurotransmitters pass on electrical impulses and increase the likelihood that a post synaptic neuron will be activated and pass on the message e.g. dopamine, adrenaline and serotonin.

· On the other hand, there are inhibitory neurotransmitters that block impulses between neurons and therefore decrease the likelihood that the post synaptic neuron will be activated to pass on the impulse.

· GABA is an inhibitory neurotransmitter that is closely involved with nearly 40% of synapses in the brain, so most neurones have GABA receptors.

· Mode of action describes the action of neurotransmitters at the synapse.

· Some drugs can bind to receptors and have the same effect as a neurotransmitter. Some can block the receptor so neurotransmitters cannot fit into them.

· In addition to these methods, drugs can work by influencing the making, movement, release or inhibition of neurotransmitters, such as preventing their recycling so they reattach to receptor sites.

· An agonist drug is a drug which mimics a neurotransmitter and increases post-synaptic activity by stimulating post synaptic receptors. An antagonist drug limits the effect of a neurotransmitter therefore reducing post-synaptic activity, perhaps through block post-synaptic receptors.

· These drugs can further be categorised into psychoactives; depressants and stimulants. Psychoactive stimulants increase post-synaptic activity to cause motor arousal and alertness whereas depressants reduce it, slowing down brain activity and relax muscles.

· Withdrawal is a set of symptoms which occur when there is a sudden drop in blood levels of certain drugs, often the opposite to the initial effects of it. Withdrawal occurs when you are physically dependent on the drug.

· Drug users develop tolerances (decreased sensitivity due to exposure) so more drug is needed to produce the same effect. Tolerance to one drug may also cause tolerance to other drugs with similar mechanisms, and this is called cross tolerance.

· Tolerance can essentially be metabolic or functional. Metabolic tolerance is when the amount of drug reaching the sits of action decreases and functional tolerance occurs when there is a reduction in the responsiveness of the receptors

· Down regulation is where the number of receptor sites or their sensitivity is reduced. Since there are less receptors, more drug is needed for the same effect.

· Enzymes in the liver break down drugs, so increased exposure to drugs means more of these enzymes are produced, making the body more efficient at removing drug molecules so more drug is needed.

· Addiction occurs as a result of physical dependence, tolerance and the effects of withdrawal.

HAPPY STUDYING!

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alevelsblr-blog · 6 years ago

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January 12th,2019

Who needs a nervous system when you are a nervous system? Bad joke I kept cracking when I made these notes lol

(open for hq)

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alevelsblr-blog · 6 years ago

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What is Schizophrenia?

Schizophrenia is a long term mental illness that is characterised by a variety of symptoms that are high in severity such as hallucinations (seeing or hearing things that are not there), muddled thinking patterns (trouble with connecting thoughts or pausing whilst explaining something) and delusions (inaccurate beliefs that are deemed abnormal and are persistent), it can often result in frequent changes of moods - all of this has often led to a stigmatisation of the illness and a belief that those who suffer from it can potentially be dangerous or violent, but this is a mere stereotype and when violent behaviour is displayed by those with the illness, this is often caused by other external factors such as intoxication and will often be inflicted on the individual themselves.

There are two categories often used to describe the symptoms of schizophrenia: positive and negative. Now, in everyday life these terms are often used interchangeably with ‘good’ and ‘bad’ - but in psychology they are used to describe when something, like a behaviour is added (positive) and when something is taken away or reduced. So positive symptoms appear due to the schizophrenia and negative symptoms are behaviours/thoughts that are reduced due to the schizophrenia

Positive symptoms: having visual or auditory hallucinations, believing the government (or other) are after you, a distrust in others, irrational beliefs (thought disorders), long pauses

Negative symptoms: a lack of motivation, a lack of interest in activities and everyday life, a lessened experience of emotion, problems with memory, reduced movement

What causes schizophrenia?

As with all illnesses and disorders, it is impossible to come up with a definitive cause for schizophrenia and is likely a combination of multiple interacting factors. A few examples are:

Genes: There is a significant trend that shows how schizophrenia tends to run in families, the percentage of individuals who develop the illness increases from 1% in the general population too 10% if they have an intermediate relative with it. This in increases to roughly 40-65% in MZ (identical) twins whom share 100% of their DNA.

Biological: it may be that those with schizophrenia have an imbalance of brain chemicals (neurotransmitters) such as dopamine. Additionally, there may be a difference in brain structure, these ideas are still being researched.

Environment: Of course, the concordance rate for schizophrenia or any illness with never be 100% because there is no one cause, this leads scientists to believe that genetic or biological factors may interact with the environment to cause the illness. Environmental factors are anything that happens to us or that we experience externally, this could be things such as trauma, malnutrition as a child or birth complications as well as drug induced psychosis.

Treatments:

Community Health Teams: made up of professionals such as social workers, mental health nurses, psychiatrists, psychologists etc. that are tailored to the individual and will support them in living their everyday life independently.

Antipsychotics: they block the transmission of the neurotransmitter dopamine, reducing the levels of it within the brain as too high levels have been associated with the symptoms experienced by schizophrenics.

Therapy/psychological treatment: therapies such as cognitive behavioural therapy and art therapy are commonly used to help with the psychological, cognitive and emotional aspects of the illness.

The debate:

Psychologists are still debating today whether schizophrenia is one illness itself of a combination of symptoms caused by a range of illnesses, and whether it should be a diagnosis or whether the symptoms should be focused on individually. Regardless of this debate, individuals are still diagnosed with it and so it is important to raise awareness for those who have to live with the diagnosis.

I would absolutely love to go more in depth on the variations of schizophrenia and the research behind it in the future - expect more! But, for now this was just a broad summary of the illness and its symptoms, I hope the information is useful. If you believe you or someone you know may experience the symptoms described, I encourage you to seek professional support and to know that you are not alone, schizophrenia impacts over 21 million people globally.

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alevelsblr-blog · 6 years ago

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Back to the basics: Laboratory experiments

Laboratory experiments are based on the positivist approach to studying human behaviour - they involved highly controlled environments (so any variables that may interfere with the results are controlled and the independent variable is manipulated) and use a standardised procedure.

The good things about this (yay!):

The study can be replicated: as the procedure is standardised (there is a set list of instructions for carrying at the experiment, the same measures are taken each time) this means the experiment can be repeated to test for reliability (the consistency of results).

Highly controlled conditions: this means the results are more likely to be accurate and objective, which would be valued by a positivist psychologist.

Cause and effect: relationships can be established due to the highly controlled environment - as all external variables have been controlled or eradicated, we can be sure that it is the manipulation of the independent variable that is responsible for the outcome.

The bad things about this (oww!)

A lack of population validity: as lab experiments must be highly controlled (and so in a designated area with limited space) it is less likely that the researcher will be able to get a large number of participants as this would take a much longer time. Therefore, this limits the extent to which the outcome of the experiments can be generalised to wider society as the study population is not representative of society’s population.

Low ecological validity: as the environment of a study is highly artificial and controlled, it is unlikely that participants will behave the same as they would in their natural environment. Therefore, the results may not be a realistic representation of human behaviour.

Demand characteristics: as the experiment is not conducted in the participants natural environment they will be aware of the fact they are being studied which could lead them to behave in a certain way - maybe to please the researcher, or to spite them (the screw-you effect). This is also known as the Hawthorne Effect.

Researcher bias: as the researcher has a great deal of control and influence over the study, this could influence their recall of events and possibly the behaviour of participants.

Any requests? Let me know!

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alevelsblr-blog · 6 years ago

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DNA and the Genetic Code

After a short hiatus, I am back with a post on the nature of DNA, including a summary of what it is, what genes are, and what kinds of mutations occur. Next up is meiosis and I have plans for a post on protein synthesis (transcription, translation). Happy studying!

DNA is a polynucleotide made up of the monomer units of nucleotides. Nucleotides consist of an organic base, a pentose sugar and a phosphate group. In DNA, the bases can either be adenine, cytosine, guanine or thymine, and the pentose sugar is deoxyribose. Nucleotides are held together in complementary base pairing using hydrogen bonds – the bond between the sugar and the phosphate are called phosphodiester bonds. DNA exists in a double helix, containing two strands which run antiparallel to each other. Genetic information is stored in the base sequence of DNA.

Prokaryotes have no membrane-bound nucleus and their DNA is usually free-floating in the cytoplasm. Their DNA is arranged into a singular loop (circular) but some bacterium can also have extra circles of DNA called plasmids. Plasmids usually contain additional genes for survival such as antibiotic resistance. Eukaryotes, on the other hand, have linear chromosomes tightly coiled around proteins called histones in the nucleus. The existence of circular DNA in mitochondria or chloroplasts gives evidence that these organelles were derived from prokaryotic cells that had been engulfed.

Genetic information codes for the functions of cells by instructing what proteins the cells should make. There are 20 amino acids, which are the building blocks of polypeptides and therefore proteins. Because there are 20 amino acids, we know that it must be necessary to have three bases coding for each acid. A triplet codon essentially means the three bases which make up a code for a certain amino acid.

However, having three bases coding for each amino acid offers a total of 64 coding combinations means there are 44 which code for things other than amino acids. Some of these remaining codons code for existing amino acids, e.g. UUU and UUC both code for phenylalanine. Therefore, we can say that the genetic code is degenerate, since some of the codes are redundant. Other sequences may code for the start or stop of a polypeptide production.

The genetic code is said to be universal, since most triplets code for the same amino acids in different organisms. It is also said to be non-overlapping, because each base in the sequence is only read once. This means that the code UCCGAC can only be read as UCC GAC and not UCC CCG CGA GAC.

Genes are sections of DNA which code for polypeptides and functional RNA such as rRNA or tRNA. Polypeptides make up proteins so genes essentially code for proteins in an organisms. Genes are always located on a particular position on a section of DNA called a locus. The same genes are found at the same locus on every chromosome.

Chromosomes become visible at the start of mitosis (cell division). They are shown to be two ‘threads’ joined at the centre. Each thread is called a chromatid and is held together by histones. The centre of a chromosome is a centromere. Eukaryotes have varying numbers of chromosomes – humans have 23 from each parent (haploid) making the diploid number of 46 chromosomes in every cell. Each pair of chromosomes, derived from our mothers and fathers, are called homologous pairs because each one carries the same genes but not the same alleles.

An allele is an alternative form of a gene. For example, everyone has the code for eyes but you may inherit green eyes from your mother and blue eyes from your father. If the alleles are the same, it is likely you will present that characteristic. If they are different, the alleles will have different base sequences so code for a different polypeptide.

Changes in base sequences lead to mutations, meaning a change in the protein’s function. There many kinds of mutation. Imagine we start with the code BIG RED FOX.

Substitution mutations occur when nucleotides are replaced by a different nucleotide. As with any mutation, this could cause no effect (due to the code being degenerate – the replacement may code for the same amino acid as before). However, some substitutions can change a cell entirely. The polypeptide produced will differ by a single amino acid which could be crucial in functions such as forming the tertiary structure of a protein or preventing the contraction of sickle-cell anemia.

Our code may now read correctly but does not mean the same thing:

BUG RED FOX

Another kind of mutation is the deletion of bases, which could cause a frameshift. This occurs when a nucleotide is lost from the normal DNA sequence and usually means the code for the polypeptide completely changes. Since the code is non-overlapping and read in triplets, one deleted nucleotide causes the sequence to be read differently.

Our code would read:

BIR EDF OX (and would continue with the rest of the sequence – remember, everything is read in triplets!)

A sub-type of a frameshift mutation would be the insertion of a base. As you can see, it also throws the way the code is read:

BIG RED FLO X

Chromosome mutations are not uncommon. These are where whole chromosomes or parts of chromosomes change in structure. They can happen in two ways: the addition of entire chromosomes (e.g. having three or more sets of homologous chromosomes), often called polyploidy, or in a process called non-disjunction.

Non-disjunction is where pairs of chromosomes fail to separate in meiosis. This usually results in gametes with one more or one less chromosome. A typical example of non-disjunction in humans is Down’s syndrome, which is an additional chromosome 21.

SUMMARY

DNA is a polynucleotide made up of the monomer units of nucleotides. These consist of an organic base, a deoxyribose sugar and a phosphate group. The bases can either be adenine, cytosine, guanine or thymine and are held together in complementary base pairing using hydrogen bonds – the bond between the sugar and the phosphate are called phosphodiester bonds.

DNA exists in a double helix, containing two strands which run antiparallel to each other. Genetic information is stored in the base sequence of DNA.

Prokaryotes have DNA free-floating in the cytoplasm, arranged into a singular loop but some bacterium can also have extra circles of DNA called plasmids. Plasmids usually contain additional genes for survival.

Eukaryotes have linear chromosomes tightly coiled around proteins called histones in the nucleus. The existence of circular DNA in mitochondria or chloroplasts gives evidence that these organelles were derived from prokaryotic cells that had been engulfed.

There are 20 amino acids so we know that it must be necessary to have three bases coding for each acid. A triplet codon means the three bases which make up a code for a certain amino acid.

Having three bases coding for each amino acid offers a total of 64 coding combinations - therefore are 44 triplets which code for things other than amino acids. Some of these remaining codons code for existing amino acids, therefore the genetic code is degenerate, since some of the codes are redundant. Other sequences may code for the start or stop of a polypeptide production.

The genetic code is said to be universal, since most triplets code for the same amino acids in different organisms. It is also non-overlapping, because each base in the sequence is only read once.

Genes are sections of DNA which code for polypeptides and functional RNA. Genes are always located on a particular position on a section of DNA called a locus.

Chromosomes are made of to be two ‘threads’ joined at the centre. Each thread is called a chromatid,��held together by histones. The centre of a chromosome is a centromere. Each pair of chromosomes, derived from our mothers and fathers, are called homologous pairs because each one carries the same genes but not the same alleles.

An allele is an alternative form of a gene.

Changes in base sequences lead to mutations, meaning a change in the protein’s function.

The deletion of bases can cause a frameshift. This occurs when a nucleotide is lost from the normal DNA sequence and usually means the code for the polypeptide completely changes. Since the code is non-overlapping and read in triplets, one deleted nucleotide causes the sequence to be read differently.

A sub-type of a frameshift mutation would be the insertion of a base.

Chromosome mutations are where whole chromosomes or parts of chromosomes change in structure. They can happen in two ways: the addition of entire chromosomes (often called polyploidy) or in a process called non-disjunction.

Happy studying!

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