Chapter 3: Neurobiology & Psychopharmacology

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Welcome to the Deep Dive.

We're here to give you that essential knowledge fast.

And today, we're tackling a big one.

The neurobiology and pharmacotherapy you absolutely need for psychiatric nursing foundations.

We're sticking strictly to our source material here.

Right.

So if you need a solid, quick grasp on why psychiatric meds work and how they work, well, we're going to break down brain structure, those chemical imbalances, and really the mechanisms of the major drug classes.

Okay, let's start by framing this.

It's complex, right?

Mental disorders are fundamentally physiological.

We're talking physical changes in the brain.

And these come from a mix of

So psychotropic medications, the term actually means to turn the mind.

They aim to bring things back into balance by targeting these physical changes.

Yeah.

And what's really interesting, I think, is that we've had these drugs for, what, over 50 years.

But for some of them, we still don't know the exact mechanism, not fully.

That's true.

And those early ideas, like, you know, schizophrenia is just too much dopamine or depression is just low serotonin.

Yeah.

Single bullet theories.

Exactly.

We now know it's way more complicated.

It's like a huge interconnected chemical orchestra in there.

Oversimplifying doesn't really help.

All right, let's start with the brain's most basic job.

Maintaining homeostasis.

Think of it as the body's continuous surveillance system.

It's always monitoring inside and out, making sure everything stays stable and responds appropriately.

And that constant monitoring.

That's why our emotions and our physical body are just completely linked, isn't it?

Absolutely.

Like when anxiety hits, the brain kicks sympathetic nervous system into gear, that's your fight or flight.

And that's why you actually feel your heart pounding.

You breathe faster, maybe get those sweaty palms.

It's a direct physical thing.

Right.

And that connection, emotion to physical response, it runs straight through our main stress regulator.

That's the hypothalamic -pituitary -adrenal axis.

You'll hear it called the HPA axis.

It's literally a chain reaction.

Hypothalamus releases CRH.

That tells the pituitary to release agrinocorticotropin, and that tells the adrenal glands,

okay, pump out cortisol, the stress hormone.

And when that axis gets disturbed, it's a real sign of illness.

The material points out that people with major depressive disorder often have elevated cortisol,

which unfortunately also suppresses their immune system.

Yeah, that's a key point.

And conversely, it notes that patients with severe PTSD symptoms, they often show lower levels of circulating cortisol.

It's quite distinct.

Interesting difference.

We also have to think about the brain's role in our basic drives, sex, hunger, thirst, and also setting our internal clock.

This clock runs on circadian rhythms, those 24 -hour cycles in our physiology.

And the source mentions evidence that the way these rhythms regulate neurotransmitters, like norepinephrine and serotonin, seem to be altered in mood disorders.

So the timing mechanism itself might be off.

Okay.

So if the brain structure is the hardware, let's quickly map out the key parts before we get into the wiring.

You've got the brainstem first.

That's the really primitive core, right?

Controls basic survival, heart rate, breathing.

Crucial.

And importantly, it contains those ascending pathways, the mesolimbic and mesocortical, that send signals upward.

Signals going where?

Up to the limbic system.

This is really the hub for emotional status and psychological function.

And it heavily uses dopamine, norepinephrine, and serotonin.

That mesolimbic pathway in particular is highlighted for its role in psychological reward.

So that links into substance use disorders.

Correctly.

Then tucked away underneath and behind is the cerebellum.

Right, our coordination center.

Manages voluntary movement balance.

And that's why some psych meds, especially older antipsychotics, can cause those movement side effects, like tremors or stiffness, because they affect the cerebellum.

That's a big part of it, yes.

It disrupts that fine motor regulation.

Got it.

And then the big one, the cerebrum, the cortex.

Yes, the wrinkly bits on top.

That's where all the conscious mental activity happens.

Memory, language,

our sense of who we are.

And remember, it has specialized lobes.

Frontal for thought and movement, temporal for sound and emotion processing,

occipital for vision,

and parietal for managing sensation.

Okay, let's zoom right in now, down to the cellular level.

The brain's got what, something like 100 billion neurons?

Roughly, yeah.

A staggering number.

And they carry electrical impulses.

It's basically about moving positive ions, sodium rushes in, potassium flows out, that creates the action potential of the signal.

But that electrical signal can't just jump the gap between neurons, right?

No, exactly.

When the impulse gets to the end of one neuron, it triggers the release of neurotransmitters.

These are the chemical messengers.

They float across the gap, the synapse, and then they bind to a receptor on the next cell, the receiving neuron.

And that interaction, the neurotransmitter hitting its specific receptor, that's basically the target for almost every single psychotropic drug we use.

Okay, so the message gets delivered.

What happens then?

How does the brain clean up?

Good question.

There are two main ways.

First, some neurotransmitters get destroyed right there in the synapse by an enzyme,

like cholinesterase breaks down acetylcholine almost immediately.

Okay.

But the second way, and this is really common, is reuptake.

The releasing cell basically vacuums the neurotransmitter back up.

Like recycling?

Sort of.

It takes it back inside where it can either be repackaged for reuse or destroyed by enzymes inside the cell, like MAO, which breaks down monomines, norepinephrine, dopamine, serotonin.

And that reuptake, that's what most modern antidepressants mess with, isn't it?

They block that vacuuming process.

Precisely.

They block the reuptake pump, leaving more neurotransmitters hanging around in the synapse to keep stimulating the next cell.

Got it.

Okay, so let's quickly connect the main neurotransmitters to the disorders, like the table in the source material shows.

Right, the highlights.

So dopamine, DA,

too little is linked to Parkinson's and depression,

too much.

Schizophrenia and mania, norepinephrine and E and serotonin, 5 -HT.

A decrease in either is connected to depression.

An increase in any, though, could be linked to mania, anxiety, even schizophrenia.

Okay.

What about GABA?

GABA is our main inhibitory neurotransmitter, calms things down.

So a decrease is linked to anxiety, schizophrenia, mania.

Increasing GABA logically reduces anxiety.

Makes sense.

And glutamate?

Glutamate is the opposite.

It's the main excitatory one.

A decrease in its NMDA receptor activity seems linked to psychosis.

But too much glutamate activity can actually be toxic to neurons that's implicated in neurodegeneration, like an Alzheimer's disease.

Hashtag visualization dysfunction at the latency period.

Wow.

Okay.

We just blitzed through a ton of brain anatomy and chemistry.

Let's maybe pause for a sec.

It's incredibly complex, isn't it?

It really is.

And it's important to remember, like you said, we're still diagnosing based on signs and symptoms, right?

We don't have a blood test that says low serotonin.

Exactly.

Which is why these neurotransmitter hypotheses are so important.

They're our best models right now.

Take depression.

The hypothesis suggests a deficiency in

norepinephrine, serotonin, maybe dopamine.

But here's the crucial part.

That long -term deficiency makes the receiving receptors upregulate.

Meaning they get more sensitive.

More sensitive.

And there might even be more of them.

They're basically straining to catch any little bit of neurotransmitter they can find.

Okay.

So then you start an antidepressant.

It immediately blocks reuptake.

So there's more neurotransmitters in the synapse.

Right.

Immediately.

But the brain is still in that upregulated, overly sensitive state.

Ah.

So it takes time for the receptors to calm down.

Exactly.

It takes time, usually about four to eight weeks, for those receptors to finally downregulate, to desensitize back towards a normal level.

And that's the delay.

That explains why patients don't feel better right away.

Precisely.

And knowing that, explaining that mechanism to a patient, that's maybe one of the most important things a nurse can do.

It helps manage expectations, reduces frustration during that waiting period, and really promotes sticking with the medication.

It turns waiting into, well, informed hope.

That's a great way to put it.

Okay, and for schizophrenia, the model is basically the reverse.

Largely, yes.

It's associated with too much dopamine transmission.

Either the brain is releasing too much, or the receptors are just overly responsive to it.

So how do we actually see these biological differences?

That's where brain imaging comes in.

The source mentions two types.

Structural imaging, like CT scans or MRIs, they show the physical anatomy.

So you might see things like enlarged ventricles, which are sometimes found in individuals with schizophrenia.

And the other type.

Functional imaging.

PT scans, fMRI, specity.

These show the brain in action.

They measure things like glucose metabolism or blood flow, indicating which areas are more or less active.

And the evidence there is pretty compelling, isn't it?

Oh, absolutely.

The text mentions PT scans clearly showing decreased glucose use in the frontal lobes of unmedicated patients with schizophrenia.

And similarly, decreased activity in the prefrontal cortex and depression.

Seeing these images really drives home the point that these are biological illnesses.

Hashtag have pharmacological principles and genetic risk.

Okay.

So moving toward the drugs themselves, two key concepts we need.

First, pharmacodynamics.

That's what the drug does to the body, right?

It's action and the response.

Exactly.

Mechanism of action effects.

And second, pharmacokinetics, often remembered by the acronym ADME.

Absorption, distribution,

metabolism, excretion.

Right.

That's about the drug's movement through the body.

How it gets in, where it goes, how it's broken down, and how it gets out.

Okay.

And in pharmacodynamics, the basic actions are pretty straightforward.

Fundamentally, yes.

Drugs act as either agonists or antagonists.

Agonists mimic the natural neurotransmitter.

They bind to the receptor and stimulate it, causing the same effect or sometimes even a stronger one.

And antagonists?

Antagonists just block the receptor.

They sit there, occupy the space, and prevent the natural neurotransmitter from binding and doing its job.

They obstruct the action.

Simple enough.

But then there's the patient variability.

Ah yes, pharmacogenetics.

This is huge.

It's how an individual's specific genetic makeup influences how they metabolize drugs.

This mostly happens through a set of liver enzymes called the cytochrome P450 system, or CYP enzymes.

Think of it like the body's main drug processing factory.

And genetic variations mean some people's factories run slow, while others run fast.

If you're a poor metabolizer, your factory is slow.

The drug builds up in your system, leading to higher blood levels, potentially more side effects, even toxicity.

And if you're a rapid metabolizer?

Your factory is super efficient, maybe too efficient.

You break down and clear the drug really quickly.

So you might get less therapeutic effect at standard doses, because it doesn't stay around long enough.

Which leads us to a really critical nursing point, a major safety issue highlighted in the text.

Yes, the HLA -B1502 allele.

Right.

It mentions that individuals of Asian ancestry with this specific gene variant have a much, much higher risk of developing Stevens -Johnson syndrome, a potentially fatal scare reaction if they take the mood stabilizer carbamazepine.

It's a significant risk, and it means that ideally these patients should be tested for this allele before even starting the medication.

Right.

It's a prime example of pharmacogenetics impacting safety.

Hashtag major medication classes and actionable cautions.

Okay, let's connect all this back to the actual medication classes.

How do these drugs target the imbalances we've discussed, and what are the key things nurses need to watch out for?

Let's start with anti -anxiety drugs and hypnotics.

The classic ones are benzodiazepines, like lorazepam, Ativan.

They work by binding to the GABA receptor complex.

This makes GABA, our main inhibitory neurotransmitter, work better.

Essentially, they help open up chloride channels on the neuron, letting negative ions in, which makes the cell less likely to fire.

Result?

A calming effect.

But they come with significant cautions.

Oh, absolutely.

Sedation is a big one, also ataxia, like problems with coordination.

And there's a real potential for misuse and dependence.

Plus, a huge safety warning.

Mixing benzos with other CNS suppressants, especially alcohol or opioids, can be fatal due to respiratory depression.

Okay, so they provide quick relief, but that dependence risk is serious.

What's the number one thing a nurse should track if someone's newly started on a benzo to watch for potential misuse?

You really need to monitor how often they're requesting it and how much.

Are they running out early?

Are they reporting escalating anxiety right when the dose wears off?

Those are definite red flags for developing dependence or misuse.

Makes sense.

What about other options?

Busperone.

Right.

Busperone is different.

It's used for generalized anxiety, but it's a partial serotonin agonist, specifically at the 5 -HT1A receptor, not gaybaragic.

Key differences.

Yeah.

It takes weeks to work so it's not for panic attacks or acute anxiety.

And importantly, it's not a controlled substance.

Less risk of dependence.

Good distinction.

All right, moving on to antidepressants.

The big players now are the SSRIs, Selective Serotonin Reuptake Inhibitors, like Flocoxine Prozac.

So they block that serotonin vacuum cleaner we talked about.

Exactly.

Leaving more serotonin available in the synapse.

But they have well -known side effects, like sexual dysfunction, GI issues.

Why is that?

Because that extra serotonin doesn't just hit the good receptors involved in mood, it also stimulates other serotonin receptor subtypes, like hitting 5 -HT2A and 2C receptors is linked to sexual side effects.

Hitting 5 -HT3 and 4 often causes nausea or diarrhea.

It's about lack of perfect selectivity.

Also, Floxetine specifically has a really long half -life, which impacts switching meds.

Okay.

Then there are the SNRIs Iserotonin Norepinephrine Reuptake Inhibitors, Venlafaxine Deloxine.

Right.

These block reuptake of both serotonin and norepinephrine.

So what's the key implication of adding norepinephrine back into the mix?

Well, that norepinephrine boost can affect blood pressure and heart rate.

It's often dose -dependent higher doses mean a greater risk.

So monitoring vital signs is important.

A potential advantage, though, is that SNRIs can be quite effective for treating neuropathic pain, likely due to that NE component.

Okay.

Let's touch on the older classes because they teach us a lot about side effects.

TCAs, tricyclic antidepressants like amitriptyline.

Yeah.

These were workhorses, but they're not first line anymore.

Why?

Side effects and lethality and overdose.

Lethality due to heart problems.

Yes.

Specifically cardiac conduction disturbances and overdose can be fatal.

And their side effects really illustrate receptor blockade issues.

Like a shotgun approach.

Kind of.

They block NE and serotonin reuptake, which is what you want, but they also hit other receptors unintentionally.

They block histamine H1 receptors, muscarinic M1 cholinergic receptors, and alpha -1 adrenergic receptors.

And each of those blockades causes predictable problems.

Exactly.

H1 block that leads to sedation and weight gain.

M1 block that gives you anti -cholinergic effects.

Dry mouth, blurred vision, constipation, urinary retention.

Alpha -1 block.

That causes orthostatic hypotension feeling dizzy when you stand up.

It's a direct link.

Which is why newer agents are preferred, if possible.

What about MAOIs?

Monoamine oxidase inhibitors like phenylzine.

These are even older and more complex.

They work by inhibiting the MAO enzyme inside the neuron, preventing it from breaking down norepinephrine, serotonin, and dopamine.

But they come with major cautions.

You need a washout period.

Usually about two weeks before switching from an MAOI to another antidepressant like an SSRI or vice versa to avoid dangerous interactions like serotonin syndrome.

And the diet restrictions.

Oh yeah, the big one.

Patients must avoid foods high in tiramine.

Things like aged cheeses, cured meats, red wine, soy sauce.

Why?

What happens?

If they eat tiramine while on an MAOI, it can trigger a hypertensive crisis.

A sudden dangerous spike in blood pressure that can lead to stroke or even death.

Requires absolute dietary adherence.

Wow, that's intense.

It really shows how far we've come.

Any novel treatments mentioned?

Yes.

The source briefly touches on esketamine, which is related to ketamine.

It's an NMDA antagonist used for treatment -resistant depression, but it's given under supervision due to risks like dissociation.

And also brexanolone, the first drug specifically approved for postpartum depression.

It interacts with GABA receptors and requires a continuous 60 -hour 5E infusion in a healthcare setting.

Okay, next up, mood stabilizers.

Lithium is the classic, the gold standard for bipolar disorder.

Its mechanism isn't perfectly understood, but it seems to affect electrical conductivity in neurons, maybe substituting for sodium or potassium ions in some processes.

And the critical nursing point for lithium.

It has a very narrow therapeutic index.

The dose that works is incredibly close to the dose that causes toxicity.

So regular blood tests are non -negotiable.

Absolutely essential.

Monitoring lithium levels is paramount to ensure safety and efficacy.

What else is used for mood stabilization?

Anticonvulsants are widely used now.

Drugs like Valprote, Depakote, carbamazepine, Tegretol, Lamotrigine, Lamictal.

They seem to work by stabilizing neuronal membranes, making them less excitable.

Cautions with these.

Yes.

Valprote needs liver function tests, LFTs, and complete blood count CBCs monitored.

And it carries a high risk of birth defects, so it's generally avoided in pregnancy.

Lamotrigine requires a very slow gradual dose increased titration to minimize the risk of Stevens -Johnson syndrome.

And didn't you mention carbamazepine earlier with the genetic risk?

Yes, that's the HLAB 1502 risk.

Plus, there's a key interaction.

Valprote can dramatically increase Lamotrigine levels.

So if a patient is on both, the Lamotrigine dose usually needs to be cut significantly.

Good to know.

Okay, antipsychotics.

Big category.

FGA versus SGA.

Right.

First generation antipsychotics, FGAs.

Also called Typicals.

Think Haloperidol.

They primarily work by blocking dopamine D2 receptors.

They're generally effective for the positive symptoms of schizophrenia, hallucinations, delusions.

But their big drawback is side effects related to blocking dopamine elsewhere.

Blocking dopamine in the nigrostriatal pathway causes extrapyramidal symptoms.

EPS.

Things like acute dystonia, muscle spasms, akathisia, restlessness, Parkinsonism, tremor, rigidity.

And the really worrying one, tardive dyskinesia.

Yes, tardive dyskinesia, TD.

Those involuntary, often writhing movements, especially of the face and tongue.

It can be permanent even after stopping the drug.

So monitoring is key.

The AIMS scale.

The abnormal involuntary movement scale.

AIMS.

Regular AIMS testing is a fundamental nursing responsibility for anyone on an FGA to detect TD early.

FGAs also block dopamine in the tuberoinfundibular pathway, which can lead to hyperprolactinemia, increased prolactin levels, causing things like breast enlargement or lactation, even in men, and menstrual irregularities in women.

Okay, so then came the second generation antipsychotics, SGA's, or A -typicals.

Like risperidone, olanzapine, clozapine.

How are they different?

They block dopamine D2 receptors too, but generally less tightly than FGAs.

And crucially, they also block serotonin 5 -HT2A receptors.

This dual action is thought to be why they often cause less EPS than FGAs, and why they seem better at treating the negative symptoms of schizophrenia like apathy, lack of motivation, as well as the positive one.

But they have their own major issue.

Yes.

The big caution with many SGA's is the significantly increased risk for metabolic syndrome.

Meaning weight gain.

Significant weight gain, yes.

Plus increased blood sugar, potentially leading to type 2 diabetes, and adverse changes in cholesterol levels.

It's a major health concern requiring regular monitoring of weight, BMI, glucose, and lipids.

And clozapine is singled out?

Clozapine is often considered the most effective antipsychotic, especially for treatment -resistant schizophrenia.

But it has the highest risk for metabolic side effects, and carries a risk for a granulocytosis, a dangerous drop in white blood cells.

Neutropenia.

Which means?

Strict monitoring.

Patients on clozapine need regular absolute neutrophil count, ANC blood tests, initially weekly, to catch this early.

It's a very rigorous process.

Just a quick mention for the last couple categories.

For ADHD, the main treatments are psychostimulants, like methylphenidate and phetamines.

They work by blocking the reuptake of norepinephrine and dopamine.

They are controlled substances due to potential for misuse.

Common side effects include insomnia, decreased appetite, potential for increased heart rate and blood pressure, and maybe some growth suppression in kids.

And finally, Alzheimer's disease.

What are the targets there?

Two main neurotransmitter systems.

First, acetylcholine.

We see a loss of cholinergic neurons in Alzheimer's.

So we use cholinesterase inhibitors, like Dunpezol, Aricept.

Exactly.

They inhibit the enzyme that breaks down acetylcholine, thereby increasing the amount available.

This primarily helps with memory and cognitive symptoms.

And the other target?

Glutamate.

Remember we said excess glutamate can be neurotoxic?

In Alzheimer's, there might be excessive stimulation of NMDA receptors by glutamate.

So Mementine, Namenda is used.

It's an NMDA receptor antagonist.

It sort of shields the receptors from this overstimulation, hopefully slowing down neurodegeneration.

That was a really comprehensive run through of a foundational chapter.

If we had to boil it down, what are the absolute key takeaways?

I'd say three things.

First, and maybe most important, mental disorders are physiological.

They involve real, measurable changes in brain structure and function.

They are not character flaws.

Absolutely.

Critical point.

Second.

Second, almost all psychotropic drugs work by influencing neurotransmitters.

Primarily, they manipulate one or more of the big five.

Dopamine, norepinephrine, serotonin, GABA, or acetylcholine.

Usually by affecting release, reuptake, or receptor binding.

And third.

Third, side effects are often predictable.

If you know which other receptors a drug might accidentally block, like H1 for histamine and one for muscarinic, alpha 1 for idrenergic, you can anticipate common side effects like sedation, dry mouth, or dizziness.

Right.

Understanding the off -target effects turns rote memorization into actual clinical reasoning.

That's powerful.

So we've talked a lot about how drugs work, how genetics influence metabolism, and even specific genetic risks like HLA -B1502 with carbamazepine.

It makes you wonder, doesn't it?

Here's something to think about.

How different would psychiatric care look in the future if, say, genetic testing became standard practice before anyone started any psychotropic medication?

Could we shift from managing symptoms after they appear towards a more personalized, maybe even preventative, biological approach based on individual genetic profiles?

Just something to mull over.

Thank you so much for joining us on this deep dive into psych nursing foundations, the neurobiology, and pharmacotherapy.

We hope this helps solidify that core knowledge.

We'll see you next time.