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Hi Roz,

just starting the screen cast for unit. seems that the powerpoint doesnt match your powerpoint in the screen cast.

It has been updated now - thank you

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Hi Rosalyn, hope you had a lovely bank holiday :)

Can I just clarify that answer to the above question is technically 2 separate answers? I thought the sensory innervation to the larynx was by CNX and sensory innervation to the posterior 1/3 of the tongue was by CNIX.

I think there is another similar question in the practice MCQ where the answer is meant to be just one cranial nerve... 'The cranial nerve responsible for controlling movements of the pharynx and larynx, as well as taste sensation from the posterior third of the tongue, is the:' when I think again it is 2 separate ones, CNX and CNIX.

Thanks and hope that makes sense :D

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Hello, thank you - I hope you had a nice weekend too :)

Thank you for checking this. For the first question, indeed this could be two separate cranial nerves - I believe the wording should actualy be pharynx instead of larynx - that way the function is just CNIX, Glossopharyngeal, which innervates the posterior tongue and the pharynx for sensation.

For the second one you mention, again thatnks for spotting this - it should indeed be two separate cranial nerves, CNX for motor larynx/pharynx and CNIX for taste posterior 1/3.

Apologies if this has caused confusion and thank you again. I have now edited the questions on BB.

Best wishes

Rosalyn

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Apologies - here is the screenshot!

No worries - this one is in the 'Motor Tracts' quiz and again the right answer has not been selected on Blackboard - only the corticobulbar tract from this list contains UMNs. Thanks again for spotting this and I have updated the quiz just now. Apologies and Thanks again, Rosalyn.

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Hi Rosalyn,

Thank you very much for the MCQs you have added to blackboard - they have been very useful!

I just had a couple of Qs.. One question asked to select all of the structures found in the midbrain, and indicated that the lateral ventricles located in the midbrain? I didn't know if we were supposed to know this?

Secondly, there was another question asking which of the following contained upper motor neurons. I selected the corticobulbar tract, but the answer was the facial nerve, so I was a bit confused as to why.

These questions were both from the Nervous System MCQs I believe.

I have attached some screenshots of the questions so I hope that makes sense! Thank you!

-------------------

Hi there - thank you for this and spotting these answers didn't match up! I have removed the 'lateral ventricles' from the correct answers (it should not have been selected - only the cerebral aqueduct).

Thanks again and apologies for any confusion.

Rosalyn

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Hi Ros,

Thank you for all the resources you have provided, they have been very helpful!

I'm not sure if you're able to tell us this, but will the questions be structured by topics? For example, a section with a few questions on the nervous system before moving to a new topic or will all topics be mixed, like one question on nervous system, then the larynx, then embryology?

Hope this makes sense. Thank you :)

Hi there - thanks for this. You are really welcome for the resources - I am glad they are helpful!

For the exam - the questions are set up in the exam to appear in random order, which is recommended by the exams team so that everyone is in theory doing different questions at different times on their screens. I hope this is helpful in that at least you know what to expect.

Best wishes

Rosalyn

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Hello,

on the pharynx and tonsils practice quiz. The question:

Loss of the gag reflex indicates dysfunction of which cranial nerve? The answer stated it was vagus nerve but we were taught in both the cranial nerves lecture and pharynx lecture that this was the glossopharyngeal nerve, and when I have checked the cranial nerves worksheet, it also states it is the glossopharyngeal nerve. However, I have looked online and it says that the Vagus nerve can also have an impact but not as much as CN9 so can you confirm which is correct as it is conflicting when both answers could be.

Thanks

Helllo - thank you for this. It ws a Blackboard problem, which is now sorted and you are absolutely right - the correct answer here is the glosopharyngeal nerve CN9. Apologies about that and thanks for spotting it,

Rosalyn

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Hi Rosalyn,

For MND, on the lecture slides it says that

"Motor speech difficulties

amyotrophic lateral sclerosis (ALS) and Progressive bulbar palsy (PBP): mixed spastic and flaccid dysarthria as both upper and lower motor neurons are affected"

However, progressive bulbar palsy only affects lower motor neurons that affects swallowing and speaking - so how can it be both spastic and flaccid?

Thank you :)

--------------

Hi thanks for this. I read that clinically there can be areas of overlap between the ALS and PBP, and it's possible slide 26 refers to when both conditions occur together (which can happen).

But I see your point and I think that you should stick with the information strictly about PBP which is on slide 24 i.e:

Progressive bulbar palsy (PBP)

•This type of MND affects the lower motor neurons in the brainstem, which control the muscles involved in swallowing and speaking.

Hope this helps,

Rosalyn

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Hi Ros!

In question 14 of the full moc exam on blackboard (the intrinsic muscles of the larynx are derived from which PA?) it says the correct answer is PA4. In the revision session worksheet it says its PA6.

Would you be able to clarify which one is correct please :D

Hi there, thanks for spotting this!

Actually it's a bit of both - the 4th pharyngeal arch does develop into one of the intrinsic muscles of the larynx (the crycothyroid). The 6th arch develops into all of the other intrinsic muscles of the larynx. I have updated the worksheet to say that 6th arch develops into all of the intrinsic muscles of the larynx except the crycothyroid. Hope this makes it clearer and apologies that was missing from the worksheet.

Rosalyn

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Hi Rosalyn

First I’d just like to thank you for uploading practice questions and worksheets for us to revise. We honestly appreciate so much.

I was wondering if there will be practice questions/worksheet for the pharynx and larynx

Thank you :)

Hi there! thank you so much for the message - I really appreciate it and you are very welcome!

I've been thinking I may be able to provide some myself for S2 Weeks 5-7 based on the lectures. I will aim to upload a few early next week, hope this will be fine.

Best wishes

Rosalyn

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Hi, after doing some of the questions where you’re required to give multiple answers is there partial credit in the exam if you don’t get all the answers right ?

Hi there,

All of the questions in the actual exam only have one correct answer so partial credit won't be an issue. Hope this helps. I will add a note on Blackboard so this is clear to everyone - thank you.

Best wishes

Rosalyn

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Hi Rosalyn,

I was just wondering if in the exam there will be diagrams or any questions where we will have to identify the labelled parts on the diagram like in some of the practice questions.

Thanks

Hi, thanks for this. Not in the MCQ questions but it's possible in the structured answer questions (only the MMed Students will have these). Hope this helps, Rosalyn

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Hi Rosalyn,

I’m slightly confused about whether the cranial nerves innervations are ipsilateral or contralateral. Google seems to say that all of them are ipsilateral, except for trochlear which is contralateral. Therefore, would damage to the right corticobulbar tract result in damage to the right side of the face? And this would result in weakness of right upper facial muscles (as innervation is bilateral) and paralysis of lower upper facial muscles (as innervation is unilateral)?

Thank you!

--------------------------

Hello! Thanks for this.

What Google says above is just part of the explanation!

Firstly, regarding contralateral cranial nerves: There are three strictly contralateral cranial nerves for motor function (not just CNIV Trochlear). These are:

1. CNIV: Trochlear Nerve - contralateral

2. CNXII Hypoglossal Nerve - contralateral

3. CNVII Facial Nerve Branch to the Lower Face - contralateral

Second, all of the rest of the Cranial nerves (with the exception of CNI and CNII) are ipsilateral in that they innervate muscles on the same side, but they are also bilateral, so they do give innervation to the opposite side as well.

In your example: a right corticobulbar tract lesion involves the right upper motor neurons (UMN) for the upper and lower face so the following will happen:

1. For the upper facial muscles:

The lesion will damage the ipsilateral innervation to the right side of the upper face, but also the contralateral innervation to the left side of the upper face, as we would expect, because it gives bilateral innervation.

However, at the same time, the left corticobulbar tract not only innervates the upper left side of the face ipsilaterally but also the upper right side of the facial muscles contralaterally. So thanks to the bilateral innervation from the left side, the person will still be able to move the muscles of the right upper face (sometimes the innervation is not as powerful, and you may see general upper facial weakness on both sides, but the person can still move all the muscles of the upper face OK).

2. For the lower facial muscles:

The lesion on the right corticobulbar tract will damage the contralateral innervation to the lower face on the left side. Unfortunately the left corticobulbar tract cannot compensate for this, because it only innervates contralaterally to the right side of the lower face.

So overall, a right corticobulbar tract lesion affecting the UMNs for the CNVII facial nerve will result in normal expression of facial muscles in both sides of the upper face (although they may be slightly weak) but paralysis of the left lower facial muscles. In this case, you would only see facial droop on the lower left of the face.

Also if the damage instead affected the lower motor neurons on the right side of the face, then this would result in paralysis of the muscles of both the upper and lower right face, because the upper facial nerve will be damaged, and the facial nerve for the lower right of the face has already crossed over from the left and is now running down the right hand side of the face. Think about a situation where you might have a laceration to the right temporal region of the face. The laceration will cut the right upper facial nerve and also the lower facial nerve which crossed over from the left to innervate the right lower facial muscles. In the case of Bells Palsy (we didn't cover this in the module!) it damages all the LMNs of CNVII unilaterally, so we see upper and lower facial droop on the same side as the damage.

I hope this makes sense - it is also explained in your cranial handbook for Week 11 Semester 1. I think this diagram above may also explain it for the facial nerve.

I also just wrote this document which I hope will help:

https://docs.google.com/document/d/18WZ_9nLvCPTewMHaqvPKgAXj6ufaD7eq56VVVIVJWfE/edit

So please remeber for your exam that the lower face pathway for CNVII and the Hypoglossal (CNXII) motor pathway for muscles of the tongue are contralateral.

Many thanks

Rosalyn

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On the cell biology questions on the Google site - the question about Osmosis says that the correct answer is 'Water moves from a region of lower solute concentration to a region of higher solute concentration' but I thought (and have checked) that it is 'Water moves from a region of higher solute concentration to a region of lower solute concentration.' Can you clarify. Thanks

Hello, thanks for this. To clarify, the answer on the Google site is correct. We are looking at osmosis here, which states that water moves from where it (the water) is in higher concentration, to where it is in lower concentration.

So if we imagine placing a red blood cell into pure water, for example, which way will water move?

It will move from the water into the cell, because the concentration of water is higher outside the cell (pure water) than it is inside the cell. The cell contains molecules like ions and glucose which we call solutes, whereas the pure water has no solutes. The cell therefore has a higher solute concentration than the water.

Here you have to apply that knowledge to the quiz. If a solution has low solute concentration, then that means it is similar to pure water (not much solute dissolved in it), so water will flow from the area of lower solute concentration to the area of higher solute concentration (so, in the red blood cell example above, from the water into the cell).

What is important is the relative difference between the two solute concentrations. If we took the red blood cell and dropped it into an extremely high solute concentration, such as 90% glucose, then which way would water move?

It would now move from the red blood cell (where there is a lower solute concentration) to the 90% glucose solution, where there is a higher solute concentration.

This link gives 2 clear definitions:

Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration.

or

Osmosis is the net movement of water molecules across a partially permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

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Hi Rosalyn,

I hope you are well! I was wondering if we need to be able to name and state the function of the different white blood cells, or if this is just extra information for context? (The neutrophils, eosinophils, monocytes, basophils, lymphocytes and natural killer - Slide 8 of Sem 1 Week 4).

Thank you!

Hi there!

Thank you for this. Unfortunately I'm really sorry I can't really say what will not be in the exam from specific slides - so having an idea of the general components of blood - and then some of the different white blood cells/functions in brief would be fine - remember you wouldn't ever have to write these from memory, but just recognise them correctly in an MCQ where you have all the info there.

Hope this helps..

Best wishes

Rosalyn

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Head & Neck - external and internal jugular veins 

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Head & Neck - external and internal jugular veins 

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Hi Rosalyn,

Just wondering if we need to know if the facial, superficial temporal, retromandibular, maxillary and pterygoid venus plexus branch off from the internal or external jugular veins? (From Week 4)

From the diagram on the slides I wasn't quite sure. I know that you asked in the practice questions what artery the lingual artery branched off, so I was just wondering if we need to know the same for the veins.

Thanks!

Hi! Thanks for this. I see what you mean. No, you woud not need to differentiate which veins are feeding in to either the external or internal jugular specifically. But you might need to recognise the names of the main veins that drain blood from the external head and face from a list - for example, a question asking you to pick out which one of these blood vessels in the list is a blood vessel that carries blood away from the head.

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Hi Rosalyn,

I hope you are well. Would it be possible to release the answers to the revision worksheets from the Semester 1 and Semester 2 revision sessions?

Thank you very much!

Hi! Of course, sorry for the wait - I have now released the Semester 2 revision session answers - they are in the S2 W10 folder now (from Monday 29th April).

The semester 1 revision sheet answers were released previously after the session in Semester 2 Week 7 - please could you check the worksheet in the week 7 folder? Some of the answers on the tracts look blank on that worksheet but - you will find the answers in the Week 11 folder (and also the Week 9 folder) from Semester 1 when I first released that tracts worksheet.

Hope this helps, let me know if not!

Rosalyn

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Hi,

On the slides for motor function, it says that the lateral reticulospinal tract arises from the pons (reticular info), and the medial retriculospinal tract arises from the medulla (reticular info), however other sources say that it is the other way round ? Just wondering which way round is correct, and if it is important information to know ?

Thanks :)

Hello - thanks for this. I am not quite sure which slide you are referring to where it says this? The slide on reticulospinal tracts in Week 9 on Blackboard (slide 15) states the medial tract is the pontine tract (arising from pons) and the lateral tract is the medullary tract, arising from the medulla (in blue). Please do check this and let me know if there is some other info you are referring to where you have seen this the other way round? Many thanks, Rosalyn

Hi - this is the slide that I am referring to , I downloaded it from Blackboard yesterday but maybe I have a different version for some reason? Many thanks :)

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I've looked into this and that slide was from the slightly older version of the slides. The online source is actually incorrect for that diagram and I changed it for the updated version that I used for the screencast - that is the version you should use. I have changed it on the older version now though. Thanks for letting me know and apologies for any confusion.

Rosalyn

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Hi Rosalyn

I was wondering if you could re-release the mock exam for us to do again as a revision. It’ll be helpful for us to see if we improved.

Yes that's fine - that is done now for both MMed and BMed.

Rosalyn

Thank you

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WK11 sensory and motor tracts worksheet 

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WK11 sensory and motor tracts worksheet 

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Hi Rosalyn hope you've had a lovely easter break :)

I was going over the worksheets for the sensory and motor tracts from wk11 and in the answers sheet it states that the first synapse occurs in the medulla for the sensory spinothalamic tract. On the drawing on the same worksheet you have shown that the first synapse occurs in the dorsal horn. I hope i'm right in thinking that the first synapse of the spinothalamic tract occurs in the dorsal horn but i just wanted to double check as the worksheet gives 2 different answers... or i'm reading it wrong haha!

Thanks :D

Thank you! I hope you did too. Yes you are right - the spinothalamic tract does first synapse in the dorsal horn, so the table isn't correct - apologies - I have now amended it to state dorsal horn. Thank you so much for letting me know. Rosalyn

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Hi Rosalyn

Will we be marked less if we make spelling mistakes during the short answer question.

For example in week 4 worksheet, question

What is the name of the condition that occurs when the event at C does not occur?

I answered macrosomia instead of macrostomia.

Thank you

Hi there,

Thanks for this.

It does depend slightly on the context of the question and answer. Marks could still be awarded. In some cases it may be partial credit. It really depends on how crucial that word was to showing your knowledge and understanding of the particular situation, which is primarily what we are looking for.

I hope this helps, though I know it's not quite definitive.

Rosalyn

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Atkinson and McHanwell self-assessment q's  

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Atkinson and McHanwell self-assessment q's  

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On chapter 1 page 8, question 1.2 asks 'the position of the heart in relation to the ribs is...' with the option to select A. superficial, B. deep, C. superior and D. inferior. I had thought it would have been B, but the accompanying answer booklet says that the answer was C. Is this correct, and if so, why?

I hope this is clear :)

Hi there,

It seems to me the answer should also be B. This is also backed up on the 4th line of the text in this website where it says: (for the heart) '...its anterior surits anterior surface sits deep to the sternum and costal cartilages.'

I hope this helps and thank you for pointing it out.

Best wishes

Rosalyn

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Hi Rosalyn

In week 3 slides 11, it says “other clefts grow over” could you clarify what that means please.

Thank :)

Hello, thank you for this. Clefts 2,3 and 4 are pushed towards each other as the pharyngeal arches grow. Initially there is one large space underneath them as they merge. This is called the cervical sinus (a space).

This can be seen in the diagram above - follow the blue line and will see how clefts 2, 3 and 4 are pushed toward each other and 'grow over' to form the cervical sinus.

However, the space forming the cervical cinus normally is gradually enveloped on all sides and is 'obliterated', as the pharyngeal arches continue to grow and develop into structures of the face (and others).

The cervical sinus usally disappears completly around week 7 of foetal development.

Occasionally the cervical sinus persists - in children or adults this can fill with fluid and is known as a branchial cyst.

Hope this helps,

Rosalyn

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Hi Rosalyn

In our earlier PowerPoints (Respiratory Tract) the lining of the larynx is noted as being ciliated pseudostratified columnar epithelium, whilst in our PowerPoint for the Larynx, it is marked as being "respiratory epithelium."

Is there a specific term you would prefer us to use/know or are both terms acceptable?

Hello, thanks for this - both terms are acceptable. However, while you can use either, it may be easier when discussing about these cells in a clinical contect to refer to them as respiratory epithelium - for example... a client may show signs of damage or loss of their 'respiratory epithelium'. Because they are present in most of the conducting portion of the respiratory tract (not on the vocal folds), we can just talk about them generally as respiratory epithelium and assume that their features (pseudostratified columnar ciliated) are understood and don't need to be restated every time.

Hope this helps,

Rosalyn

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Hi Rosalyn,

A review of motor and sensory pathways will be helpful - I think it was Part 3 of the nervous system where I found it quite dense.

Thank you :)

Great - we'll go over those sensory and motor pathways. Thank you,

Rosalyn

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Hi Rosalyn

I was wondering if we can review the nervous system and practice short answer questions.

Thank you :)

Hi - thank you for this - yes of course :)

Is there anything specifically in the nervous system? Or just a review of everything - brain features/lobes, brain internal anatomy (brainstem), action potentials & synapses, spinal cord, sensory pathways and motor pathways, ANS.

The cranial nerves will be covered too.

Many thanks

Rosalyn

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Will the exam questions just be based on the info from the slides or will it be questions around when you have gone into further detail about things in the lectures and info from the reading? I felt like the mock exam covered more than just the slides content so wanted to clarify for revision

Thanks

Hi there, thank you for this - yes the exams are based on what is on the slides and the recommended reading is there to help consolidate this. Sometimes the exam questions require you to apply your knowledge from the slides to an unfamiliar situation or in a slightly different way, but essentially you should have everything you need to answer the questions from the slides. I hope this helps, Rosalyn

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Hi,

In the week 7 lecture on nervous system, the slide states that 2 CN emerge from the cerebrum and 10 emerge from the brainstem, however in the week 10 slides on cranial nerves, it says the accessory nerve stems from C1-4 and travels into the brainstem. Would it be that only 9 CN emerge from the brainstem?

Hello! thank you for this question about CNXI. Yes the lecture slides for week 10 are much more specific than Week 7 and the information in Week 10 is correct - CNXI emerges from the upper cervical spinal cord. However, it does first travel up and enter the skull through the foramen magnum and then exits the cranium again to travel back downwards in the neck and innervate the SCM and the trapezius. This reference agrees with this - stating that motor neurons at C1–2 innervate the sternocleidomastoid, while neurons at C3–4 innervate the trapezius (ref). The worksheet we did in week 11 also states that CNXI emerges from the upper cervical spinal cord.

However, I've looked into the Week 7 info again. It wasn't mentioned in the Week 10 slides (or my Week 10 worksheet), but the CNXI does also have a minor component which emerges from the medulla, and when it exits the cranium it runs alongside CNX (vagus) and also innervates (motor aspect) some of the pharyngeal constrictors, larynx, and muscles of the soft palate.

It appears that there is some ongoing controversy around CNXI as to whether it is therefore a true cranial nerve or not. You may find this article useful:

https://www.kenhub.com/en/library/anatomy/the-accessory-nerve.

Thank you so much for raising this as it will be important to highlight this in the Week 10 lecture slides in future.

So in summary, the major part of CNXI originates in the cervical region, but then enters the cranium and then leaves again near to the other cranial nerves. For this module and exam, please just focus on the main function of CNXI to be the innervation of the SCM and the trapezius.

I hope this helps,

Best wishes

Rosalyn

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Hello Rosalyn

When discussing the locations and orientations of the cranial nerves, do the nerves originate in the brain or do they originate at the structures they innervate?

Thanks

Hi - Thanks for this -

From an anatomical point of view, yes - all of the cranial nerves 'emerge' or 'originate' from the brain or brainstem at different points.

But it's important to note that the electrical impulse may originate in the tissue itself. For example, with sensory cranial nerves (or parts of cranial nerves), the nervous impulse originates in the sensory organ that it innervates and travels along that cranial nerve toward the brain.

I have therefore seen some sources saying ..'The optic nerve originates in the optic disc of the eye' for example, so I think you may come across sources saying the nerve is 'originating' in the tissue it innervates as well.

Meanwhile, motor impulses are initiated in the cortex and travel down to the brainstem to meet the cranial nerve that will transmit them out to the particular muscle or tissue of the face/head.

Hope this is what you meant and it helps,

Rosalyn

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It did help thank you! : )

Just to clarify, in the exam, if we were asked to state where a cranial nerve originates, we would have to give the area of the brain, unless it was specifying where the impulse was coming from?

Thanks again

Hi - that's great - and yes exactly, it would be specified in the question exactly what information you needed to state.

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In the Autonomic Nervous System powerpoint you stated that the hippocampus is involved in short-term memory, however in a previous powerpoint, according to my notes, it says that it is involved in long-term memory.

My notes could be wrong so I just want to double check.

Hello, thank you for pointing this out. The answer is both - the hippocampus is responsible for processing short-term memories and is also responsible for turning them into long term memories by sending them to other areas of the cortex for storage. Damage to the hippocampus can therefore affects both new memories and long term memories. The hippocampus is also needed for spatial navigation. This article may be useful:

https://www.webmd.com/brain/hippocampus-what-to-know

But I appreciate my slides are not consistent so I will amend this, thanks again for letting me know, Rosalyn

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Hello Rosalyn, one quick question.

I just wanted to clarify your use of the phrase 'flight and fright' in today's lecture. On the slide discussing the signs of nervousness in a client. Did you mean 'fright' or was this a typo for fight?

Kind Regards

Hello, thank you for pointing this out. To avoid any confusion we'll stick to 'fight or flight' throughout as the sympathetic response - and this is what is used in the course textbook as well. I have changed the wording on the client nervousness slide so it is all aligned as 'fight or flight' now. Hope this helps, best wishes, Rosalyn

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Afternoon!

Can we use these two terms interchangeably? So saying sensory cortex would be just as acceptable as somatosensory cortex?

Hi and thank you for this!

The somatosensory cortex is one specific type of sensory cortex. There is also the visual sensory cortex, the auditory sensory cortex, the gustatory sensory cortex and the olfactory sensory cortex. So no, it's not quite interchangeable - and to be specific it would be best to describe the area that we have been talking about in week 9 (Sensory function) as the Somatosensory Cortex, as it receives only somatosensory information. Referring to it as the sensory cortex is rather informal (and I think I have referred to it sometimes in the lectures as the sensory cortex) but if you are referring specifically to the somatosensory cortex then it would be better to refer to it as exactly that so there is no confusion with other sensory areas of the cortex. Hope this helps,

Rosalyn

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Hello

I would just like to check whether we do or do not need to know about the spinocerebellar tracts of the spinal column.

This was discussed in a video that I was watching, but as this wasn't in the PowerPoint, I'm assuming that we don't, but wanted to confirm anyway.

Hello, thank you for this.

No, you don't need to know about the spinocerebellar tracts as part of the Sensory Tracts at the moment - just the Dorsal Column (also known as the Dorsal Column Medial Lemniscus) and the Spinothalamic and Spinoreticular tracts.

Best wishes,

Rosalyn

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Hello!

In the nervous system part 2 quiz on the google site, there are a few questions asking about inhibitory and excitatory neurotransmitters.

I've read that both serotonin and adenosine are inhibitory however the quiz says that they are excitatory. Can you confirm which is correct? Thank you!

Hi there - thanks for this!

Serotonin is a bit more complex than the quiz allows for - so thank you for asking this. You are right in that several websites do say serotonin is inhibitory; however, it is also exitatory as well. There are many different serotonin receptor types in the same family, and it depends which one is stimulated, as to whether it will be excitatory or inhibitory. The serotonin receptors are called 5-HT receptors. As well as being ligand-gated ion channels, some of the 5-HT receptors are called G-coupled protein receptors (which we haven't covered in class). The Stat Pearls article above gives a good summary - have a look in the section called 'Cellular Level' and also 'Function'. This article also talks about the effect of serotonin being receptor dependent: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3318857/pdf/jocmr-01-72.pdf.

I will update the quiz to reflect that serotonin can be both excitatory and inhibitory and thanks for pointing this out!

Regarding adenosine - you are right - it is generally an inhibitory neurotransmitter so the quiz is not quite correct as it does not allow you to select adenosine as well as GABA as an inhibitory neurotransmitter, so I will update this. Thanks again :)

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Introduction

Serotonin is a monoamine neurotransmitter that plays a role in several complex biological functions.[1][2] Its common abbreviation is 5-HT because of its chemical name: 5-hydroxytryptamine. The attribution for the discovery of serotonin is that it occurred serendipitously by Vittorio Erspmarer during his attempt to purify extract from enterochromaffin cells in 1935.[3]

Serotonin forms from the hydroxylation (i.e., the addition of -OH group) and decarboxylation of the tryptophan amino acid. The highest concentration of serotonin is in the enterochromaffin cells of the gastrointestinal tract, with small amounts in the central nervous system and platelets. Serotonin induces changes in the cell by its action on the serotonergic receptors, which are coupled to different G proteins mediating intracellular changes.[2]

The biological function of serotonin plays several roles in the human body, such as influencing learning, memory, happiness, and reward, as well as physiological processes such as regulation of sleep, behavior, and appetite.[4] Serotonin plays a significant role in the pharmacodynamic activities of antidepressants, such as SSRIs and SNRIS. This compound is not only found in mammals but is also present in insects, plants, and fungi. Therefore, the consumption of these organisms can affect serotonin levels in humans, occasionally leading to adverse effects.[1]

Fundamentals

Serotonin is a compound that functions in both the central nervous system and the peripheral nervous system. It acts in the form of the hormone, neurotransmitter, and mitogen in our body.[2] The compound was first discovered in the year 1935 by a Roman scientist name Vittorio Erspamer. The isolation of serotonin came as a result of researchers looking for a substance that platelets released, leading to vasoconstriction. It was also initially called enteramine following discovery due to its function of smooth muscle contraction in the gastrointestinal tract after its release from the enterochromaffin cells.[4]

Later, researchers identified that serotonin is also released as a neurotransmitter in the human brain. These excretory clusters of neurons became known as the serotonergic system. The various functions of serotonin in the CNS are comprehensive and relate to the action of the serotonergic system on the forebrain, brainstem, and cerebellum.[2] Projections from the rostral nuclei of this system help regulate temperature, appetite, sleep cycles, emesis, and sexual behavior. The most clinically relevant function of serotonin is in psychiatric disorders; most commonly, its absence appears to be related to depression, anxiety, and mania.[5][4]

At the most simple level, serotonin functions by meditating an animal's perception of its own bodily resources. When the levels of basic resources such as food, water, and sleep are sufficient, the animal shows higher levels of serotonin, correlating to an increased perception of happiness.[5] However, when these physiological needs are lacking, an adverse effect occurs.[2]

Cellular Level

There are seven subtypes of serotonin receptors present in the body.[2] Most subtypes exhibit heterogeneity and further subdivide into 5-HT1A, 5-HT2B, 5-HT3, etc. Six of these subtypes involve G-protein-coupled receptors.

The 5-HT receptor is unique in that it involves a ligand-gated Na/K ion channel similar to gamma-aminobutyric acid (GABA) and N-methyl-d-aspartic acid.[5]

5-HT1 and 5-HT5 receptors negatively couple with adenylyl cyclase; the activation of these receptors downregulates cyclic AMP. 5-HT receptor upregulates the inositol triphosphate and diacylglycerol pathways, resulting in intracellular Ca release. A combination of 5-HT4, 5-HT6, and 5-HT7 receptors activate adenylyl cyclase, increasing cAMP activity.[4]

The Na/K cation channel associates with 5-HT results in plasma membrane depolarization. The termination of serotonergic activity is facilitated by the reuptake of 5-HT from the cellular synapse.

Molecular Level

Serotonin is a biogenic monoamine; its production occurs in two steps. The essential amino acid tryptophan is hydroxylated to 5-hydroxytryptophan (5-HTP) by tryptophan hydroxylase. In a second step, 5-HTP undergoes decarboxylation to form 5-HT. Early studies have shown that hydroxylation and decarboxylation occur almost instantaneously in the presence of tryptophan.[2][4]

Serotonin is synthesized and stored within the central nervous system (CNS) in the presynaptic neurons (serotonergic neurons, pineal gland, and catecholaminergic neurons). Serotonin is present in nine groups of cell bodies isolated to the pons and midbrain. The raphe nuclei are the major nuclei, possessing both ascending serotonergic fibers that project to the forebrain as well as descending fibers extending to the medulla and spinal cord. A small number of serotonergic nuclei also reside in reticular formation with fibers that remain within the medulla.[6]

In the CNS, serotonin processing occurs in several ways. Upon neuronal depolarization, there is a release of serotonin into the synaptic cleft. It can bind to either postsynaptic serotonin receptors (5-HT receptors) or presynaptic serotonin autoreceptors.[1]

Serotonin binding to the autoreceptor acts as negative feedback against the further release of serotonin into the synaptic cleft. The highly selective serotonin transporter (SERT), which is located on the presynaptic membrane, functions to remove serotonin from the synaptic cleft.[7] Once transported into the presynaptic neuron, serotonin is recycled back into presynaptic vesicles, where it is protected from metabolism. Metabolism by monoamine oxidase (MAO) occurs within the cytosol of the neuron. An alternate pathway for serotonin exists in the pineal gland; it converts to melatonin.[2]

Serotonin originating from enterochromaffin cells is released into the portal circulation and undergoes rapid elimination from the plasma by way of uptake into platelets and liver metabolism. Serotonin transporters on the platelet membrane, and enterochromaffin cells function to uptake serotonin into those cells. Serotonin escapes uptake, and liver metabolism reaches the lung, where it then undergoes metabolism.[7]

Function

Serotonin is a direct-acting neurotransmitter that is commonly stored in presynaptic vesicles. Upon activation of the nerve by adjacent nerve impulses, serotonin is released into the synaptic cleft, where it can bind to postsynaptic receptors.[1] These postsynaptic serotonin receptors, also known as 5-hydroxytryptamine receptors, either act as G-couple protein receptors or ligand-gated ion channels. This activation ultimately allows activation of a second intracellular messenger cascade producing either an excitatory or inhibitory response.[2]

An estimated 90% of the serotonin in the human body is stored in enterochromaffin cells located in the gastrointestinal tract. Upon luminal and basolateral secretion, the compound is absorbed by circulating platelets. Once activated, serotonin functions to mobilize intestinal contraction and direction via the stimulation of myenteric neurons.[2][4] Although only 10% of serotonin is produced by neurons located in the central nervous system, it is for its function in the brain for which it is better known. The various functions of serotonin in the central nervous system include sleep, hunger, mood, memory, and learning management.

When excessive serotonin is released from the enterochromaffin cell, it frequently is introduced to the bloodstream, where it interacts with blood platelets. The platelets absorb the serotonin and store it until clot forms. However, once a clot forms, the serotonin is re-released in the blood, where it can regulate hemostasis and blood clotting.[8] At elevated levels, serotonin functions by contracting vascular smooth muscle cells leading to vasoconstriction. However, at lower levels, serotonin facilitates endothelial class to release nitric oxide leading to vasodilation.[8]

Testing

The liver metabolizes excess serotonin into a compound known as 5-HIAA. This process of metabolism begins with the oxidation of the compound to an aldehyde by a monoamine oxidase. The aldehyde is then further oxidation by aldehyde dehydrogenase into 5-HIAA.[6] The end product is then excreted through the urine. When the body is producing excess levels of serotonin, one may expect to see increased levels of 5-HIAA in the urine or blood.

Clinical Significance

Serotonin plays a critical role in the human body. Over the last 70 years, researchers have been able to obtain a great understanding of which disease processes are influenced by this neurotransmitter, as well as its therapeutic properties in potential medical interventions.

It appears to play an essential role in the central nervous system (CNS) and the body's general functioning and, in particular, the gastrointestinal (GI) tract. Studies have shown links between serotonin and bone metabolism, the production of breast milk, liver regeneration, and cell division.

Serotonin influences the brain cells both directly and indirectly.

Bowel Function

Most of the body's serotonin is in the GI tract, where it regulates bowel function and movements. The human digestive tract is composed of several layers of enterochromaffin cells. These cells sense food in the stomach and release serotonin as a response. Increased serotonin levels in the gut cause digestive processes to increase in speed, which often occurs as a result of digesting toxins or noxious substances. It also plays a part in reducing appetite while eating.[2]

Mood

Serotonin plays a significant role in the nervous system and, therefore, largely affects mood. In the brain, serotonin changes mood, anxiety, and happiness by increasing nerve stimulation and electrical impulses. Drugs like ecstasy and LSD increase the levels of serotonin in the brain to produce effects like increased appetite, increased sexual drive, euphoria, and even hallucinations.[7]

Clotting

When serotonin is released into the blood, it is often absorbed by platelets rather than remaining free serotonin. The effect serotonin has on the platelets is similar to those produced by the interaction of platelet factor 2 and platelets. Serotonin accelerates the metabolism of fibrinogen to fibrin. This action causes platelet aggregation leading to vasoconstriction, and the result is a reduction in the blood flow and an increase in clot formation; this is one of the earliest defined functions of serotonin.[8]

Nausea

When serotonin is released into the gut faster than it can be digested, it is oven reabsorbed into the bloodstream. In the bloodstream, the neurotransmitter can interact with 5-HT3 receptors, which in turn activate chemoreceptor trigger zones. The activation of these sites causes stimulation of the brain to cause expulsion of the substance eaten; this is perceived as nausea by us.[6]

Bone Density

Several research studies have shown that it may have links to a decrease in bone density, but the relationship lacks sufficient proof. This correlation has been hypothesized by an early study that measured the changes in mice that lacked brain serotonin. The researchers found that these mice have severe osteopenia, while mice that only lack intestinal serotonin have regular bone density. Humans with increased levels of blood serotonin have been linked to increased or regular bone density. The belief is that the 5-HT1B receptor is the link between blood serotonin and bone density.[9]

Sexual Function

Serotonin has been linked to increased sexual drive but decreased sexual function; this can be rather detrimental to patients who have received a prescription for selective serotonin reuptake inhibitors (SSRIs). As these drugs are commonly given to patients suffering from depression, they can often exacerbate the underlying problem due to sexual tension. The main course of serotonin's role in decreased sexual function is increasing retrograde ejaculation and erectile dysfunction. The cause of these symptoms is due to overstimulation of the 5-HT2C receptors, which promote erection and inhibit ejaculation, and the under-stimulation of the 5-HT1A receptor, which has the inverse functions.[10]

References

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5.

Coleman JA, Yang D, Zhao Z, Wen PC, Yoshioka C, Tajkhorshid E, Gouaux E. Serotonin transporter-ibogaine complexes illuminate mechanisms of inhibition and transport. Nature. 2019 May;569(7754):141-145. [ PMC free article: PMC6750207 ] [ PubMed: 31019304 ]

6.

Weaver SR, Xie C, Charles JF, Hernandez LL. In utero and lactational exposure to the Selective Serotonin Reuptake Inhibitor fluoxetine compromises pup bones at weaning. Sci Rep. 2019 Jan 18;9(1):238. [ PMC free article: PMC6338725 ] [ PubMed: 30659249 ]

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Disclosure: Arjun Bakshi declares no relevant financial relationships with ineligible companies.

Disclosure: Prasanna Tadi declares no relevant financial relationships with ineligible companies.

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Serotonin is a monoamine neurotransmitter that plays a role in several complex biological functions.[1][2] Its common abbreviation is 5-HT because of its chemical name: 5-hydroxytryptamine.

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Hello,

In the lecture, you mention that grey matter consists of myelinated neurones and white matter non-myelinated neurones. However, in one of the textbooks and on google it states that grey matter consists of the cell bodies of neurones and white matter consists of the axons and dendrites of neurones. I wanted to check whether both of these statements are the case or whether I have misinterpreted the textbook.

Thanks

Hello, thank you for this! There is a slide (the last one we got to in Lecture 2 (slide 8) that shows the correct arrangement - which shows that it is myelinated axons that form white matter. I think I mentioned this is due to the lipids in the Schwann Cells or Oligodendrocytes which form an insulating layer around the axon. Meanwhile, grey matter is non-myelinated regions of the neuron which are ususally the cell bodies and the dendrites.

[Although there may also be a some neurons that have myelinated dendrites (but these are not very common!)]

So basically white matter is composed of mostly axons of myelinated neurons and grey matter is non-myelinated parts of neurons - which are mainly cell bodies and dendrites, (or sometimes may also just be non-myelinated axons).

Generally in the CNS, the white matter regions are myelinated axons transporing the impulses in the axons quickly - up and down the outside of the spinal column, and through some of the middle areas of the cerebrum. Meanwhile the grey matter (such as the cortex) is where the cell bodies, axon terminals and dendrites are found. These tend to be non-myelinated and are important for all the important communication that occurs between the neurons that arrive at and leave the cortex. There are some important areas of grey matter in the spinal column too.

If I said the opposite in the lecture (white matter= non-myelinated) then that was an error on my part and apologies for any confusion.

Best wishes

Rosalyn

Rosalyn

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Hello.
I was wondering if both of these processes take place during the formation of tissue fluid and lymph?
If so can we use the terms interchangeably?
Thank you.

Hello, thank you for this.
The term oncotic pressure is sometimes called Colloid Osmotic Pressure (COP). This is actually a more precise term than osmosis to describe the force that draws water back into a solution containing proteins (such as the blood). So to answer your question, no the terms 'osmosis' and 'oncotic pressure' are not used interchangably. Oncotic pressure is due to the principle of osmosis (water moving from where it is in higher concentration to a lower concentration) but is specifcally used to describe water moving back into the blood capillaries from the tissues due to the pull of proteins (and also the red blood cells). I have added this term to the lecture slides now as well. Thank you!
Rosalyn

'The proteins in the blood plasma create an osmotic force that attracts water from the surrounding tissues, helping to maintain the proper balance of fluids in the body.'

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The Atkinson and McHanwell book have given different descriptions/functions for the specific white blood cells to the ones in the slides.
The book says that Basophils are the WBCs of allergic reactions whereas the slides say that Eosinophils do this.
Which one should we note as correct?

Hi, thanks for spotting this. It's true- the basophils are usually more involved in allergic reactions (although they also can be involved in eliminating parasites). It's best to go with the textbook - Basophils - allergic reactions. I have changed the slides accordingly and re-uploaded.
Many thanks for this,
Rosalyn

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Hi, just reading more into the cardiovascular system in the Atkinson and McHanwell textbook and came across this diagram of circulation on page 54. Maybe i'm confused but I was under the impression that oxygenated blood was red and deoxygenated blood was blue?

Hi - thank you for spotting this! It looks like there must be a mistake with the key - the oxygenated blood is definitely in the red vessels and the deoxygenated in blue in this diagram, so the colours in the legend need to be the other way around...!
Thanks again and hope this helps,
Rosalyn

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Are all the answers to the quiz questions correct?
For example, one question asks about the opening of valves during ventricular systole, and it has given the answer the atrioventricular valves as the valves that open during this process.

Obviously I could be very wrong.

Hi - thanks for spotting this. The wrong answer was selected in the quiz, but I have changed this now.
Rosalyn

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Is pseudo stratified ciliated columnar epithelium the same as ciliated epithelium?

Hi, thanks for this.
Psuedostratified ciliate columnar epithelium is a type of ciliated epithelium.
It means the nuclei are at unequal heights.
There is also just ciliated columnar epithelium (found in the fallopian tubes) where the nuclei are at the same level, and this is just called ciliated columnar epithelium (not pseudostratified).
I hope this helps,
Rosalyn

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I'm not sure on what neuron excitability is and how this links to sodium regulating the membrane potential of cells. Please could you help?

Hi there, thanks for this question. We'll study this in more detail when we start the nervous system. Excitiability means that a neuron can respond quickly to changes in its environment (a stimulus), and start an action potential (flow of ions) to comminicate with another neuron or a muscle cell. For this to happen, there needs to be a high concentration of sodium ions outside the cell to start with, which is what is seen when the cell is at its resting membrane potential - more negative on the inside than the outside, due to there being less positive charges (ions) on the inside of the cell relative to the outside.

When there's a big enough stimulus, enough sodium ions will rush into the cell down their concentration gradient to start an action potential. Once the action potential starts (flow of charges along the neuron) it will keep moving along the neuron until reaches the end of the neuron, where another neuron is stimulated (or if the neuron is attached to a muscle, it will cause a muscle cell to contract).

I hope this helps! best wishes
Rosalyn

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In the slide covering passive transport, you wrote that facilitated diffusion involves carrying large or charged molecules across the cell membrane...what are some of the charged molecules that the proteins carry  without the use of ATP? Because i thought that charged molecules like potassium and sodium required active transport.

Hello, thanks for this question! You are right in that ATP is used to pump charged molecules such as Na+ and K+ across the membrane in certain situations. For example, in the situation when they are being moved from where they are in lower concentration outside the cell to where they are in higher concentration inside the cell, so against their concentration gradient. The Na+K+ATPase pump is a good example of this occuring.

However, active transport can also be used to pump non-charged molecules like glucose, from where they are in lower concentration to where they are in higher concentration, if necessary. For example, there are cells lining the small intestine that can do this with an active transport ptotein and ATP, to ensure that even small amounts of glucose remaining in the digestive tract can still be absorbed by the cells of the intestine.

With regards to facilitated diffusion, this process helps to move molecules down their concentration gradient from high concentration to low concentration across the phospholipid bilayer. This could be glucose (on the other side of the intestine cells facing the bloodstream, where glucose moves into the bloodstream from high concentration to low concentration using a carrier protein, without ATP). This also could be the movement of Na+ ions down their concentration gradient into the cell rapidly down a gated channel protein, to start activation of a neuron signal.  The gated Na+ protein channel is gated (closed) most of the time, but when the neuron activation starts, the gate opens and all the Na+ ions built up outside the cell rush into the cell down their concentration gradient using the channel protein by faciliated diffusion (without the need for ATP).

Another example of a charged molecule which also crosses the membrane by facilitated diffusion is some amino acids (building blocks of proteins); some of these have positive charges and others have negative charges.

I hope this helps.
Best wishes
Rosalyn
This article on Facilitated Diffusion may also be helpful.