A hair follicle or HF is a small part of the skin that produces the hair shaft. Paul Gerson Unna was the first to observe a bulge in the human hair follicle's outer root sheath (ORS). The bulge is present between the sebaceous gland and the arrector pili muscle and is the niche for hair follicle stem cells (HFSCs). The bulge is also a niche for melanocyte stem cells, and their loss results in graying of hair. The HFSCs express Sox9 and Lhx2, which help them maintain stemness and prevent...

The trachea, commonly known as the windpipe, is a vital part of the human respiratory system. It serves as a passageway for air to travel between the larynx and the bronchi, allowing oxygen to reach the lungs. Let's explore its anatomical features, dimensions, layers of the tracheal wall, associated muscles, and the functions of its parts.
Anatomical Features:
Location: About half of the trachea is situated in the neck, anterior to the esophagus, and extends from the larynx (at the level of...

Nerve plexuses are networks of interlacing nerves that serve as communication hubs to distribute and organize nerve action across various body regions. The nerve plexuses are organized into the cervical plexus located in the neck region, brachial plexus in the shoulder area, lumbar plexus found in the lower back, sacral plexus situated in the pelvis, and coccygeal plexus located in the coccygeal region.
The Cervical Plexus
The cervical plexus, formed by the anterior rami of the first four...