Hering's law of equal innervation

Now to study this law, we need to know clinical function diagram of eye muscles.

So according to this diagram,

Right SR is responsible for elevating right eye to right side.
Similarly, Left IO is responsible for elevating left eye to right side.

Since both the muscles are performing same action on two different eyes using two different muscles they are called yoke muscles of each other.
This is Hering's law of equal innervation.

Now, here is a trick to solve problem without looking into the diagram:

Right gets converted to Left.
S (Superior) gets converted to I (Inferior)
O (Oblique) gets converted to R (Rectus)

So the mnemonic for remembering muscle change is

ROSI (You can remember it as ROSS from friends!)
R gets converted to O.
S gets converted to I.

-Demotional bloke

Movements of eye muscles.

This post is actually the primary post for squint studies. Just basic post so we can explore squint in easy and simplified manner.

So there are seprate diagrams for anatomical and clinical functions. In this post we will go for former part.

Anatomical functions diagram.

Note: Don't use this diagram when you are studying squint. This diagram is used only for movements of eye muscles.

So every muscle has 3 actions except medial and lateral rectus.
Actions are divided into three types Primary, secondary and tertiary.

We know the basic or primary action of superior and inferior rectus is to elevate and depress the eyeball respectively.

According to the diagram given you also know that superior rectus can intort and adduct. Similarly, inferior rectus can extort and adduct the muscles.

How to remember this?
1) Through diagram.
2) Trick: Recti muscles are adductors

Now comes to SO(Superior oblique) and IO(Inferior oblique). Now this is also basic which we fail to notice often. These muscles are coming to tarsus part of eye obliquely. So, primary action is intortion and extortion respectively. Now go to diagram and you will notice that IO actually corresponds to SR hence it performs elevation and SO corresponds to IR so it performs depression.

Also, both the muscles are "Abductors"

How to remember this?
1) Diagram off course!
2) Trick: Superior muscles are Intorters and inferior muscles are extorters.

To keep the things in apple pie order I have made this chart. Hope it helps.

-Demotional bloke

Warfarin and Newer Oral Anticoagulants (NOACs) notes

Hey guys!
These are my notes from Harrison on Warfarin and Newer Oral Anticoagulants (NOACs).

Stop Antibiotic Abuse!

Hello Everyone,

It's been really long since the last post! Well it's been hectic all the way to and through residency.

I was recently researching on the topic of antibiotics while I stumbled upon this excellent piece of information cum approach by Dr.Strong on starting Anbiotics.

Well everyone should ask themselves these 12 questions before starting any antibiotic for one's patient and trust me you'll end up choosing the most appropriate one.
This is how we don't contribute to the Antibuse- "Antibiotic Abuse"( my personal neologism)

So now coming back to the questions, ask yourself these questions before you start any antibiotics,

1) What condition is being treated?
2) What are the commonly known bacterial species causing that condition?
3) Which antibiotic group is typically active against those?
4) What are the local resistance patterns for the chose antibiotic?
5)Will there be adequate organ penetration?
6) What is the preferred route of administration?
7)Any specific contraindication of the antibiotic to look out for?
8) Any required dose adjustment for coexisting renal or hepatic diseases?
9) Any specific drug interactions to be considered?
10) When on therapy anything that needs periodic monitoring?
11) How can the therapy be narrowed once bacterial sensitivities are available?
12) What will be the anticipated duration of the therapy?

Let's take a step towards stopping the rampant Antibuse.

That's all for now.

Let's learn Together!
-Medha Vyas.

Ring-enhancing lesion in an immunocompromised host

Hello everyone,

If it is a ring-enhancing lesion in an immunocompromised host, the most commonly seen etiologies are Cerebral toxoplasmosis (50%) and Primary central nervous system (CNS) lymphoma (30%).

But let's talk about the uncommon etiologies -

ECG quiz: ST elevation in aVR and ST depression in other leads

Quiz question: ST elevation in aVR and ST depression in other leads is suggestive of?

Trapezius and pericarditis.

Suppose a patient of 40 years of age male comes to you with complaints of  chest pain which is often heavy, squeezing and crushing.

You make up the diagnosis of MI based upon the symptoms in your mind. Proceeding for proper history of case you ask patient if the pain is radiating type.
Patient explains you that the pain is radiating and he is eventually experiencing pain in to the back of this some muscle. You find out that he is pointing towards the "Trapezius muscle" .

Now, this should raise an alarm in your mind. You should stop thinking about MI.

Reason?

Both NSTEMI and STEMI shows pain which is radiating in nature. Pain involves the central portion of the chest, sometimes epigastrium and occasionally it radiates to the arms. Less common involves back, neck, lower jaw. Pain can radiate as high as occipital area but never below umbilicus.
but it never radiates to trapezius.

Depicting exact lines of Harrison textbook of medicine.

"Radiation of discomfort to the trapezius is not seen in patients with STEMI and is  useful in correct diagnosis of pericarditis"

Now, why pain radiates to trapezius?

Pericarditis, as name suggests inflames the pericardial sac of the heart. This causes irritation of the vagus nerve supplying heart. Vagus nerve is affected because it is closely related to pericardial sac. Vagus nerve acts as the afferent nerve fibers. These fibers reaches nucleus tractus solitarius in the medulla oblongata. From there it comes downwards reaches cervical plexus C2, C3 and C4. From there, the nerve fibers formed supplies lower part of trapezius.

Trapezius nerve supply:
Upper part is supplied by the spinal accessory nerve.
Lower part is supplied by the nerves from C3 and C4 only.

Hence pain radiates to trapezius in pericarditis.

-Vipul and Ojas.

Update from IkaN: It's wrong to say that the pain of MI "never" radiates to the trapezius (which is in the back) because occasionally, pain of MI can radiate to the back. Also, pain radiating to the back should alarm you to a more serious diagnosis - aortic dissection. 

Can you find Asterixis in Non-Hepatic disorders?

Hello Awesomites! :D

This doubt came to my mind when I saw a case of COPD with asterixis.

 I used to think of asterixis with respect to hepatic disorders only.

 So let see is it so?

"Asterixis"is a non-specific sign. It is also known as flapping tremor.

It is a non-specific neurologic finding which may accompany organic delirium in a variety of metabolic or toxic disorders which interfere with cerebral metabolism.

It can be found in the cases with:-

1. Chronic pulmonary insufficiency

2. Uremia

3. Drug induced electrolyte imbalance

4. Arterial hypoxemia

5. Other reasons of electrolyte imbalance.

 Stay Awesome!

Upasana Y. :)

Authors' diary: Ponder

We were discussing a case today and learnt how important it is to take a second to think before we do something when dealing with patients.

Before you get a CT scan on the patient in the ER, stop and think - does the patient really need a CT scan? Will it get me the answers I'm looking for? Or will I need additional testing? Think of the harms of radiation exposure. Unless you don't want to rule out a hemorrhage that requires immediate intervention, do not order it STAT.

Dentinoenamel Junction

• DEJ appears as a scalloped line.
• The convexities of scallop are directed towards the dentine 
• The surface of dentine appears pitted
• DEJ provides strength to the union between enamel and dentin

Clinical Significance:

• Prevents shearing of enamel when functioning.
• Scalloping of the junction is seen more in the occlusal portion where masticatory stresses are high.

- Written by Anisha Valli

Enamel Lamellae

Thin, leaf-like structure that extends from enamel surface towards DEJ
Sometimes, they penetrate towards DEJ
They consist of organic material but with a little amount of mineral content.

Types of enamel lamellae:

• Type A: Lamelle composed of poorly calcified rod segments
• Type B: Lamelle consists of degenerated cells
• Type C: Lamelle arising in erupted teeth where cracks are filled with organic material, originating from saliva

Type A is restricted to enamel
Type B and C are restricted to dentine

Clinical Significance: 

• It is a site of weakness in a tooth.
• It forms a road of entry for bacteria to initiate caries.

Written By Anisha Valli

Hunter-Schrengar bands

The change in the direction of rods is responsible for Hunter Schregar bands.

These bands are the functional adaptation to occlusal masticatory forces.

Alternating, light and dark bands of varying width that can be seen in longitudinal cross-section under the obliquely reflected light.

Dark bands: Parazones
Light Bands: Diazones

The angle between the bands is 40 degrees

- Written by Anisha Valli

Zone Of Weil

Zone of Weil is present below the odontoblastic zone.

• Its a layer of 40um.
• It is also known as the sub-odontoblastic layer.
• It doesn't consist of cells.
• This zone is prominently seen in the coronal pulp.
• Cell-free zone decreases in size when dentin formation occurs at a rapid rate.
• The cell-free zone consists of a network of nerve fibres which lost their myelin sheath. This is known as Plexus of Rashkow.

Written by Anisha Valli