Doctor-Reviewed Health Guides: Conditions, Procedures & Health News

The vestibulocochlear nerve, cranial nerve VIII, is a sensory nerve that carries electrical impulses from the inner ear to the brain. It has two branches: the cochlear nerve, which carries sound signals from the cochlea for hearing, and the vestibular nerve, which transmits information about head movement and position for balance. It is essential for hearing and navigating the environment.

The vertebral artery is a major neck artery that runs from the subclavian artery through the cervical vertebrae into the skull, where it joins its partner to form the basilar artery. It supplies 20% of the blood flow to the brain. Narrowing, a tear or compression can reduce flow and lead to TIA or stroke.

Vellus hair is thin, light hair that grows on most of the body, including the face, arms, legs and trunk, but not the palms, soles, lips or eyelids. It insulates, wicks sweat, protects the skin and helps sense light touch. At puberty, androgens turn some into terminal hair. A noticeable increase is worth discussing with a provider.

Uterus involution is the postpartum process in which the uterus shrinks from its expanded pregnancy size back to its nonpregnant size. Starting with delivery of the placenta, regular contractions reduce blood flow to the placental site and shed lochia. Over about six weeks, the uterus descends back into the pelvis, shrinking from roughly grapefruit size to pear size.

Vaginal delivery is giving birth through the vagina, which accounts for approximately 80% of births worldwide. Providers favor it for its low-risk profile and benefits such as faster maternal healing and the transfer of beneficial bacteria to the newborn. It involves cervical opening, pushing and birth, then delivery of the placenta, typically within a few hours to a day.

The thigh muscles are powerful skeletal muscles between the hip and knee that enable lower-body movement, stability and weight-bearing. They are divided into the quadriceps at the front, adductors on the inside and hamstrings at the back, and together they support balance and align the hips and legs. Warm-ups, adequate protein and resting when painful help protect them.

The vas deferens is a long, fibromuscular tube, 30 to 45 centimeters in length, that carries sperm from the epididymis to the ejaculatory duct through rhythmic muscle contractions during sexual arousal. It is essential for male fertility and is the site targeted during a vasectomy for permanent contraception.

The uvula is a teardrop-shaped piece of tissue hanging from the soft palate at the back of the roof of the mouth. It moistens the throat with saliva and moves backward during swallowing to block the nasal passage. It also plays a role in speech and triggers the gag reflex, helping prevent foreign objects from entering the airway.

The uterus is a pear-shaped, muscular organ in the pelvis between the bladder and rectum. It sheds its lining during menstruation, hosts a fertilized egg for implantation and expands to nourish and protect a growing fetus during pregnancy. Its muscles contract during labor to deliver the baby. When not pregnant, it is roughly fist-sized and weighs about one ounce.

The urinary system is a network of organs and tubes that filters blood and removes liquid waste as urine. It consists of two kidneys that filter blood, two ureters that carry waste, a bladder for storage and a urethra for elimination. By separating toxins from vital nutrients, it maintains the body's internal balance and protects overall health.

The urothelium is a unique type of epithelial tissue that lines the inside of the urinary system. It acts as a barrier that keeps urine and germs from entering the bloodstream or surrounding muscles. Unlike other body linings, it stretches and contracts as the bladder fills and empties, and it helps signal the nervous system when the bladder is full.

The sphenoid sinus is one of the four pairs of paranasal sinuses, located farthest back in the skull behind the upper nasal cavity. It produces mucus that clears germs and humidifies air, reduces skull weight and may protect against head injury. Infections are rare but need immediate treatment because of its closeness to the optic nerve and brain.

The tympanic membrane, or eardrum, is a thin, semi-transparent layer of connective tissue that separates the outer ear from the middle ear, measuring approximately one centimeter across. It vibrates when sound waves strike it and passes those vibrations to the middle ear's tiny bones. It also protects the middle ear from bacteria and foreign debris.

Ureters are two narrow, muscle-lined tubes in the urinary system. Their primary function is to carry urine produced in the kidneys down to the urinary bladder for storage. Through rhythmic muscle contractions known as peristaltic waves, the ureters actively propel liquid waste, maintaining a one-way flow that protects the kidneys from backflow and potential infection.

The trigeminal nerve, or cranial nerve 5 (CN V), is the largest of the twelve pairs of cranial nerves. It carries touch, pain and temperature sensation from the face and head and controls the chewing muscles. It splits into three branches: the ophthalmic, maxillary and mandibular nerves. Its function is critical for eating, speaking and facial sensation.

The ulnar nerve is one of the main nerves of the arm, running from the brachial plexus in the neck to the hand. It powers small muscles needed for fine motor tasks like writing and gripping and provides sensation to the pinky and half of the ring finger. Bumping it at the elbow causes the funny bone tingle.

The thyroid is a small, butterfly-shaped gland at the base of the neck, just below the Adam's apple, and a key part of the endocrine system. Its main role is regulating metabolism, how the body converts food into energy. It produces hormones, mainly thyroxine (T4) and triiodothyronine (T3), which influence nearly every organ, including the heart and brain.

The obturator nerve is a peripheral nerve formed from the L2, L3 and L4 nerve roots that runs from the lower back through the pelvis to the inner thigh. It controls the adductor muscles and provides feeling to the skin, hip and knee. Damage can cause groin or thigh pain, numbness and weakness.

The spinal cord is a cylinder-shaped bundle of nerves and cells running from the brainstem to the lower back and is a core part of the central nervous system. It carries messages that control voluntary movement, involuntary functions and sensation, and manages reflexes on its own. It is protected by the vertebrae and meninges, and damage can cause paralysis.

The ulnar artery is a major forearm blood vessel that carries oxygenated blood from the elbow to the hand. A branch of the brachial artery, it runs along the forearm's pinky-finger side. Its main role is supplying circulation to the muscles, bones and nerves of the forearm and hand, supporting sensation and movement in the fingers and palm.

The medulla oblongata is a funnel-shaped structure at the base of the brain that connects the brainstem to the spinal cord. It regulates life-sustaining autonomic processes such as heartbeat, breathing and blood pressure. It is also a major crossover point for motor nerves and a pathway for cranial nerves controlling swallowing and speech. Damage can cause severe neurological symptoms.

The inner ear is a dual-purpose organ in the temporal bone of the skull, just beyond the middle ear. The snail-shaped cochlea converts fluid ripples into electrical signals the brain perceives as sound, while the vestibular system senses head and body movement to keep you balanced. Protecting it from loud noise and treating problems early supports hearing and balance.

The hymen is a flexible tissue membrane around the vaginal opening that naturally thins and stretches over time. Contrary to popular belief, it is not a solid seal and usually does not block the vagina. Most people do not notice when it tears, though some have light spotting or minor discomfort. Its shape varies, and imperforate types are rare.

The human immune system is the body's first-line defense against germs and other invaders, made up of organs such as the spleen, thymus and bone marrow, white blood cells and protective proteins. It works through innate immunity, which gives immediate non-specific protection, and acquired immunity, which learns to recognize and remember specific threats over time.