The musculocutaneous nerve is a terminal branch of the lateral cord of the brachial plexus. Uniquely, it travels a relatively short distance compared to other branches of the brachial plexus. It includes fibers from only three nerve roots (C5, C6, and C7) and innervates only three muscles (biceps, brachialis, and coracobrachialis). The major function of the musculocutaneous nerve is to flex the elbow, thus flexing the biceps muscle (showing others your “guns”).

The lingual gyrus is the portion of medial occipital lobe just inferior to the calcarine sulcus, and so named because of its tongue-like shape. The lingual gyrus functions as a part of the primary visual cortex, as its superior border (the inferior bank of the calcarine sulcus) houses synapsing fibers from Meyer’s loop. This part of the primary visual cortex analyzes visual information from the contralateral superior quadrant of both visual fields.

The middle cerebral artery branches from the internal carotid artery and travels laterally, branching several times to perfuse the frontal, parietal, and temporal lobes unilaterally. If occluded proximally, it can result in the infarction of ~half of the cerebral hemisphere, which is seen as a hypodense region on a non-contrasted CT scan.

Weinberg takes a summer job in the Atomic Beam Group at Princeton, calculating the trajectories of beam particles through the experimental equipment. He describes the culture of close relations of graduate students in physics with the younger faculty and its emphasis on research rather than course work. He details the various courses he took, along with the personalities of the Princeton professors at the time. Sam Treiman agrees to be his PhD advisor for a thesis on strong interactions in decay processes.

The parietal lobe is located posterior to the frontal lobe, anterior to the occipital lobe, and superior to the temporal lobe. The central sulcus separates the parietal lobe from the frontal lobe. Inferiorly, the sylvian fissure separates the parietal lobe from the temporal lobe anteriorly. Posteriorly, the distinction between parietal lobe and temporal lobe is less clear. The parieto-occipital sulcus separates the parietal lobe from the occipital lobe. The mesial part of the parietal lobe is called the precuneus. The lateral surface is split into the superior parietal lobule and the inferior parietal lobule by the intraparietal sulcus.

The denticulate ligaments are triangular extensions of the pia mater (Latin meaning “tender mother”), which project laterally through the subarachnoid space from the surface of the spinal cord to the dura mater. The primary function of the denticulate ligaments is to brace the spinal cord in place within the dural sac.

Generalized Baumslag-Solitar groups are a class of combinatorially interesting groups. Their group theory is also closely associated to a the topology of a class of 2-dimensional spaces. These 2-dimensional spaces are Seifert fibred. We develop the basic topology of these fibrations and derive some of the most immediate group theoretic consequences of this topology.

Weinberg returns to the “The Cosmological Constant Problem” and suggests an anthropic principle solution. Anthropic reasoning could make it possible for us to calculate the effective vacuum energy. Observations of dark energy in 1998 show that the expansion of the universe is accelerating. This observational result is not inconsistent with the notion of a possible multiverse – the issue has not been settled.

The axillary nerve is one of the terminal branches of the brachial plexus. A branch of the posterior cord, the axillary nerve is composed of nerve fibers originating from C5 and C6 roots. From the brachial plexus, the axillary nerve courses inferolaterally anterior to the subscapularis muscle, just posterior to the axillary artery and beneath the glenohumeral joint, ultimately passing through the quadrangular space. Here, it terminally divides into its anterior and posterior branches.

The saphenous nerve is a terminal branch of the femoral nerve and functions as a pure sensory nerve, providing cutaneous innervation to the medial knee, leg, ankle, and foot. It originates from the posterior division of the femoral nerve in the femoral triangle, lateral to the femoral artery and vein. Exiting the femoral triangle, it enters the adductor canal and travels inferiorly with the femoral artery and vein. The saphenous nerve then exits the canal, just superior to the knee, travels superficially, and gives off its first branch, the infrapatellar branch, which travels through the inferior portion of the sartorius muscle and provides sensory innervation to the skin of the inferomedial knee.

The vertebral arteries are the main source of the posterior cerebral circulation. Each vertebral artery originates as a branch of the subclavian artery in the thorax. The vertebral artery has four segments. V1 is the segment from the origin to the point where the artery enters the transverse foramen of the C6 vertebra.

The C7 nerve root is the third root from the top in the brachial plexus. The word root is derived from Latin radix. The C7 dermatome provides sensation to the middle finger and a thin strip of sensation on the back of the arm.

The raphe nuclei are a group of nuclei clustered in the brainstem that get their name from the Greek word for “seam” due to their midline position. The more rostral group of raphe nuclei have extensive cortical projections and play a role in sleep–wake regulation, modulation of behavior, and emotion. The more caudal nuclei project mainly to the spinal cord and play a significant role in pain modulation.

The dorsal root ganglion (DRG) is a collection of sensory nerve cell bodies located outside the spinal cord at each vertebral level. These are pseudounipolar neurons with an axon that bifurcates and travels in two directions. The peripheral part of this axon receives distal sensory information from elsewhere in the body and projects it proximally to the DRG, which is located in or just distal to the intervertebral foramen at each spinal level, corresponding to the dermatome of that sensory area. From there, the central axon transmits the signal to the spinal cord.