USMLE - Some Points To remember about Brachial Plexus

If you are preparing for your USMLE Step 1 exams, ignoring studying Anatomy may be a wrong strategy as this is a branch that is sure to score you a few easy points. Don’t we know what difference a mere 5 or 7 points makes to your score? So instead of focusing just on Pharmacology and Pathology, spend time studying this branch as well. A very high yield USMLE Step 1 topic is the injuries that are related to the Brachial Plexus. Here are 4 injuries you should definitely know about.

1. The Median Nerve Injury: This is a kind of injury that occurs due fracture of the supracondyle of the humerus. What it results in is a loss of wrist flexion, thumb movements, finger flexion and forearm pronation. It may also result in the person losing his sensation in the lateral side of the palm and even the thumb.

 

2. The Ulnar Nerve Injury: This is a kind of injury that occurs when the medial epicondyle of the humerus is injured and may lead to the following troubles: impaired adduction of the thumb, the ulnar and two fingers and adduction of wrist and loss of flexion. The patient may also face loss of sensation to the medial half of the pinky and the ring finger as well as to the medial way of the palm.

 

3. The Radial Nerve Injury: This is a kind of injury which may result from the shaft of the humerus to be injured. It may cause the following problems: loss of carpi radialis longus, loss of brachioradialis reflex and loss of triceps reflex. Other than these, the patient may face something called the ‘wrist drop’ and the loss of sensation to posterior brachial cutaneous nerves and posterior antebrachial cutaneous.

 

4. The Axillary nerve Injury: This is a kind of injury that occurs due to two causes: firstly, if there is anterior dislocation of the shoulder or/and if the surgical neck of the shoulder gets injured. When this happens, the deltoid muscle loses its sensation and the movement of the deltoid muscle is completely lost.

 

The above is a basic idea about the 4 common injuries of the Brachial Plexus. 

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The Conduction System of the Heart

The conduction system of the heart is made up of specialized conducting tissue. Human heart works as an electrically timed pump. The electrical stimulation of the heart originates from SA node (Sinoatrial Node). The location of this node is in the right atrium near the opening of superior venacava. SA node is collection of specialized cells which are capable of producing automatic electrical activity. The SA node is also known as pacemaker of the heart.
The electrical stimulus generated by SA node in the right atrium travels to left atrium. The right and and left atrium  are activated in the first phase of electrical stimulation. As a result both of these chambers contract and pump the blood to right and left ventricle through Tricuspid and Mitral valve.
The electrical signal generated by SA node further travels to AV junction through specialized conducting tissue. The AV junction consists AV node, bundle of his and, right and left bundle branches. The bundle branches are located in the interventricular septum. The right and left bundle branches transmit the electrical stimulus to right and left ventricles respectively with the help of purkinje fibers. These specialized fibers are located in the ventricular myocardium.
Under normal circumstances the SA node serves as the primary pacemaker of the heart. But in some situations if SA node is unable to generate the impulses, the AV node acts as an escape pacemaker.