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The right atrium

The right atrium is one of the four heart chambers, located in the anteromedial aspect of the heart, forming the right heart border. Inside, it has a ridged anterior wall formed by musculi pectinati and a smooth posterior wall with the fossa ovalis, the remnant of the foramen ovale.

The lateral boundary between the smooth posterior and rough anterior wall is the crista terminalis. The medial wall contains the tricuspid valve, through which blood flows into the right ventricle. The inferior wall contains the IVC and opening of the coronary sinus, while the superior wall contains the SVC and auricle, next to the sinoatrial node. 

Key terms:

  • right atrium
  • right auricle and right atrial appendage
  • crista terminalis
  • sulcus terminalis (terminal sulcus)
  • musculi pectinate (pectinate muscles)
  • foramen ovale
  • fossa ovalis
  • tricuspid valve
  • superior vena cava (SVC)
  • inferior vena cava (IVC)
  • sinoatrial node, SA node
Circle of Willis

The circle of Willis is a loop of arteries from which blood is supplied to the brain. It is located at the level of, and anterior to, the midbrain, and extends forward on the under-surface of the frontal lobe.

We follow the arteries for one half of the circle starting at its most posterior aspect, the top of the basilar artery and follow the arteries forward:

  1. posterior cerebral artery (PCA)
  2. posterior communicating artery (PCOM)
  3. internal carotid artery (ICA)
  4. anterior cerebral artery (ACA)
  5. anterior communicating artery
Transpyloric Plane

The transpyloric plane (Addison’s plane), is one of several imaginary axial planes slicing through the abdomen. It can be used to understand the location of abdominal viscera. Its surface marking is halfway between the umbilicus and the xiphisternum. Anteriorly this is at the level of the ninth costal cartilage. It passes backwards to end posteriorly at the lower edge of the L1 vertebral body. The plane transects many important structures as it crosses the abdomen.

Listed, loosely from anterior to posterior

  • Ninth costal cartilage
  • Gallbladder
  • First part of the duodenum, and the duodeno-jejunal flexure
  • Pylorus and body of the stomach
  • Hepatic and splenic flexures of the colon
  • Root of the transverse mesocolon
  • Pancreas
  • Origin of the portal vein from the splenic and superior mesenteric veins
  • Superior mesenteric artery (origin off the aorta)
  • Hila of the kidneys (remembering that the left kidney is just above and the right just below)
  • Lower edge of the L1 vertebral body
  • End of the spinal cord (conus medullaris at the level of L1/L2 in adults)
Transthoracic plane (thoracic plane, plane of Ludwig)

The transthoracic plane (thoracic plane, plane of Ludwig) is an imaginary axial plane the runs from the manubrial sternal joint (or angle of Lewis) anteriorly to the base of the T4 vertebral body posteriorly. It divides the superior and inferior mediastinum; so above the plane is the superior mediastinum, and below is the inferior mediastinum.

The plane crosses several anatomical structures which can be remembered using the RAT PLANT mnemonic, which loosely follows the structures from anterior to posterior.

  • R - Costal cartilage of the second rib.
  • A - Arch of aorta
  • T – Tracheal bifurcation (with the carina as the cartilage at the base of the division).
  • P - Pulmonary artery bifurcation - with the right running under the arch of the aorta.
  • L - Ligamentum arteriosum – a remnant from the foetal circulation, in the adult it is a ligament linking the arch of the aorta to the left pulmonary artery.
  • A - Azygos vein entering the superior vena cava
  • N – nerves - Superficial and deep cardiac plexus, and the left recurrent laryngeal nerve looping around the aortic arch.
  • T - The thoracic duct moves from the right to left side of the thorax
Introduction to the heart

Learn about the heart, a muscular organ in the mediastinum of the thorax that is responsible for blood circulation. You will learn about the atria, ventricles and the position of the four valves of the heart; the tricuspid, pulmonary, mitral and aortic.

The cardiac cycle

Learn about the the flow of blood through the heart, known as the cardiac cycle. Follow the flow of blood through the atria, ventricles and valves of the heart. You will learn about diastole, systole and the difference between arteries and veins. 

The coronary arteries

Learn the coronary arteries; the right coronary with its branches the sinoatrial, marginal and posterior interventricular arteries, and the left coronary artery with its branches the anterior interventricular artery (or left anterior descending, LAD) and the circumflex artery.

Introduction to the cranial nerves

The cranial nerves carry motor and sensory signals from the brainstem to and from the body.

There are twelve cranial nerves. In this episode we go through the names of each of them, and a simplified view of their function. We label each nerve by category of function; “motor”, “sensory” or “both motor and sensory”.

In the next episode we go through a mneumonic to help remember these categories and in future episodes we will look at the cranial nerves in greater individual detail.

Brainstem rule of fours

The brainstem rule of fours was developed by Dr Gates to help understand the effect of lesions in different parts of the brainstem. Fittingly, there are four parts to his rule of fours. In this episode we discuss one of these parts, which helps to localise the level of the cranial nerve nuclei in the brainstem.

To learn more about the rule of fours; check out "life in the fast lane" and search rule of fours, or click on this link: https://lifeinthefastlane.com/brainstem-rules-of-4/ or review the original article by Dr Gates. “The rule of 4 of the brainstem: a simplified method for understanding brainstem anatomy and brainstem vascular syndromes for the non-neurologist, P. Gates, Internal Medicine Journal 2005; 35: 263–266".

The foramen ovale

The foramen ovale is one of the prominent spaces in the base of skull, that allow structures to enter and exit the cranial vault. The contents of the foramen ovale are remembered using the ovale mnemonic (O V A L E).

  • O – Otic gangion (inferior to the foramen in the infratemporal fossa)
  • V – V3 branch of the trigeminal nerve
  • A – Accessory meningeal artery
  • L – Lesser petrosal nerve
  • E – Emissary vein
Branches of the axillary artery

The axillary artery arises from the subclavian artery at the outer boarder of the first rib. It runs to the lower boarder of teres major where it becomes the brachial artery. 

It gives off 6 branches in relation to pectoralis minor (pec minor), which passes anterior to the artery. They are in a 1,2,3 pattern; one branch before, two behind and three after.

They can be remembered using the mnemonic "skip the lawyer, save a patient."

Before pectoralis minor:

  • S: superior thoracic artery

Behind pectoralis minor:

  • T: thoracoacromial artery
  • L: lateral thoracic artery

 After pectoralis minor:

  • S: subscapular artery
  • A: anterior humeral circumflex artery
  • P: Posterior humeral circumflex artery

 

The subclavian artery and its branches

The subclavian artery arises from the brachiocephalic trunk on the right, and directly from the aorta as its third branch on the left. It runs posterior to the anterior scalene muscle, infront of the brachial plexus and middle scalene muscle, to end at the outer edge of the first rib.

It has five branches which can be remembered in using the mnemonic "VIT CD" in relation to scalenus anterior which runs anterior to the artery. This is a 3,2,0 pattern - with three branches before scalenus anterior (V I T), two behind (C D) and zero afterwards.

Branches before scalenus anterior:

  • V - vertebral artery
  • I - Internal thoracic artery
  • T - Thyrocervical trunk

Branches behind scalenus anterior:

  • C - Costocervical trunk
  • D - Dorsal scapular artery

Branches after scalenus anterior:

  • Zero!
Branches of the external carotid artery

The external carotid artery is one of the main arterial supplies to the neck. In this episode we go through "some anatomists like freaking out poor medical students" the mnemonic to remember the eight branches of the external carotid.

In ascending order from the carotid bifurcation:

  • Superior thyroid artery (anterior)
  • Ascending pharyngeal artery (posterior)
  • Lingual artery (anterior)
  • Facial artery (anterior)
  • Occipital artery (posterior)
  • Posterior auricular artery (posterior)

Terminal branches:

  • Maxillary artery
  • Superior temporal artery
Introduction to the upper limb

The upper limb is what is commonly referred to as the arm. It is the area between the shoulder and the fingers, including the shoulder, elbow and wrist joints. In this episode we introduce some of the key areas and structures of the upper limb. 

For further detail, you should listen to our extend episodes.

Carpal bones

There are eight carpals bone in the hand. The proximal row is the scaphoid, lunate, triquetrum and pisiform, and the distal row is the trapezium, trapezoid, capitate and hamate. To help remember the order, we go through the mnemonic "some lovers try positions that they can't handle".