The lateral antebrachial cutaneous nerve supplies sensation to the lateral forearm (both the palmar-lateral and dorsolateral surfaces), and stems from the musculocutaneous nerve, not the radial nerve. The inferior lateral brachial and posterior antebrachial cutaneous nerves are sensory branches of the radial nerve and supply sensation to parts of the dorsal arm and forearm, respectively. The posterior interosseous nerve is a motor branch of the radial nerve that innervates the finger extensors that cross the wrist (e.g. extensor digitorum).

When at rest, the neuron initially has a negative membrane potential. At the beginning of an action potential, voltage-gated sodium channels open, allowing sodium ions to enter the cell. This causes the cell to become positively charged compared to the outside of the cell. This process is called depolarization.

After depolarization occurs, the sodium channels close, initiating the absolute refractory period. Voltage-gated potassium channels then open and potassium ions exit the cell. This results in hyperpolarization and the relative refractory period. The potassium channels then close and the sodium-potassium pump returns the cell to its resting potential by removing sodium and collecting potassium.

There are five layers of the epidermis. From surface to base, the layers are the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum and stratum basalis.

The stratum corneum is composed of several layers of barrier cells and serves mostly for protection. The stratum lucidum is only found in the palms and soles and helps thicken the skin. The stratum granulosum contains lipids and fatty acids. The stratum spinosum contains some immune cells, as well as lipids. The stratum basalis contains melanocytes and mechanoreceptor cells attached to the basement membrane.

Lacrimal glands are located superior to and along the lateral half of both eyeballs, and are responsible for keeping the eyes moist and creating tears. The lacrimal fluid is drained via the lacrimal ducts into the nasal cavity, which is why there is increased nasal drainage when crying.

The atrium and ventricle on each side of the heart are separated from one another by the atrioventricular valves. There is also another pair of valves that separate the ventricles from the arteries exiting the ventricles, known as the semilunar valves. The semilunar valves are the pulmonary and aortic valves, which separate the ventricles from the pulmonary trunk and aorta respectively. The tricuspid valve is found between the right atrium and ventricle, while the mitral (bicuspid) valve is found between the left atrium and ventricle.

T-lymphocytes mature in the thymus, where they interact with "self antigens." This process ensures that T-lymphocytes do not interact with antigens found in the body. If the immature cell interacts with self antigens, the T-lymphocyte will be destroyed. Mature T-lymphocytes that still react to self antigens can cause allergic reactions and autoimmune disease.

B-lymphocytes, in contrast, mature in the bone marrow. Both types of lymphocyte originate from stem cells in the bone marrow, but differ in their site of maturation.

The appendix is located in the lower right corner of the abdominopelvic cavity, of which there are nine regions. The lower corners are known as the iliac regions, named after the adjacent coxal section. The lumbar regions are located directly superior of the iliac regions, and the hypochondriac regions are directly superior to the lumbar regions. Medial to the hypochondriac, lumbar, and iliac regions are (from superior to inferior) the epigastric, umbilical and hypogastric regions.

Orientation of abdominopelvic regions:

The body can be divided into two main cavities: the dorsal cavity and the ventral cavity. The ventral cavity contains several subdivision, namely the thoracic, abdominal, and pelvic cavities. Of these, only the thoracic cavity can be further divided.

Within the thoracic cavity are the two pleural cavities, separated by a central pericardial cavity. The pleural cavities are defined by the pleural space and membranes around the lungs. This is the region that must expand in order to generate the negative pressure that is necessary for inspiration.

The diaphragm is a muscle that separates the thoracic cavity from the abdominal cavity. The rectum is located in the pelvic cavity. The heart has its own cavity called the pericardial, which is another subset of the thoracic cavity. The brain is in the cranial cavity, a subset of the dorsal body cavity. 

The skin is made up of two major components: the superficial epidermis layer and the deep dermis layer. The epidermis is essentially made up of four layers, however, there is an additional layer found in regions of thick skin. The four principle epidermal layers, going from superficial to deep, are the stratum corneum, stratum granulosum, stratum spinosum, and stratum basale. In regions of thick skin (namely the soles of the feet and palms of the hands) there is an additional layer of cells located between the stratum corneum and stratum granulosum, known as the stratum lucidum, which serves to enhance protection and cushioning of these areas.

A hair has two principle parts: the shaft and the root. The shaft is seen above the skin and the root stays deep within the skin surface. The shaft and the root are made of keratinized epithelial cells, which have ceased to divide and are considered non-living. The cells of the hair are organized into three layers. The cuticle is the outermost layer, which wraps around the hair exterior. The next layer is the cortex, which surrounds the innermost layer, the medulla. The root sheath structure is separate from the actual hair and is constructed from living epithelial cells that anchor and nourish the hair.