We have 12 pairs of cranial nerves: the olfactory nerve, optic nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, glossopharyngeal nerve, vagus nerve, accessory nerve, and hypoglossal nerve. A common mnemonic to remember these is: "On old Olympus' towering top a Fin and German viewed some hops." We have 31 pairs of spinal nerves.

This question sounds complicated, but the key lies in the first sentence: we are to identify the vessel that normally carries oxygen-rich blood. The pulmonary veins fit this description; they return oxygen-rich blood from the lungs back to the heart. In contrast, the pulmonary arteries carry oxygenated-poor blood from the heart to the lungs (to be oxygenated). The portal vein carries oxygenated-poor blood with nutrients to the liver from the intestine. Lastly, the superior vena cava carries oxygenated-poor blood to the right atrium of the heart.

Visceral efferent (autonomic) and somatic efferent axons are found in the ventral roots of spinal nerves. The ventral root is the efferent motor root of a spinal nerve, distally it joins with the dorsal root to form a mixed spinal nerve, whose postertior branch innervates skin and muscles of the back, while the anterior branch supplies skin and muscles of the front and sides of the trunk and limbs.

The C6 spinal nerve passes through the intervertebral foramen between the fifth and sixth cervical vertebrae. There are eight cervical spinal nerves that exit above their associated vertebrae. In this case C6 exits between the vertebrae C5 and C6 (above C6 vertebrae). This is unique in comparison to the thoracic and lumbar spine where the nerves exit below their associated vertebrae. 

The deep brachial artery travels with the radial nerve, around the spiral/radial groove of the humerus. The anterior interosseous artery travels with the anterior interosseous branch of the median nerve, not the radial nerve, and passes through the dorsal surface of the interosseous membrane. The recurrent branch of the median nerve branches off the median nerve in the hand, not in the arm. The ulnar artery travels with the ulnar nerve at various points in its pathway, not the deep brachial artery.

Although all of these nerves arise from the cervical plexus, and supply sensation to the head and neck, the supraclavicular nerves do not receive C2 segmental innervation. They receive C3, C4 segmental innervation. Anteriorly, they supply sensation to the skin superolateral to the sternum, and posteriorly to the skin over the supraspinous fossa, and the adjacent area.

The thoracodorsal nerve innervates the latissimus dorsi, which is not one of the rotator cuff muscles. The suprascapular nerve innervates the supra- and infraspinatus muscles, the upper and lower subscapular nerves innervate the subscapularis, and the axillary nerve innervates the teres minor. These muscles make up the rotator cuff. Accordingly, the nerves that innervate them are associated with the rotator cuff.

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.