Nervous and sensory systems

Cerebral hemisphere

Cerebral hemisphere: one of the two halves of the cerebrum, separated by the longitudinal fissure and joined by the corpus callosum. Divided into frontal, parietal, temporal, occipital lobes, and insula; lateralized for language (left) and spatial/face processing (right).

Cerebral hypoxia

Cerebral hypoxia (hypoxic/anoxic encephalopathy) is insufficient oxygen delivery to the brain, causing cell death within minutes; causes include cardiac arrest, drowning, and carbon monoxide poisoning, treated with oxygen, ventilation, and cooling.

Cerebrum

Cerebrum: the largest brain division, two hemispheres joined by the corpus callosum, four lobes each, folded cerebral cortex, basal nuclei, and higher functions like language, memory, and vision.

Cervical spinal nerves

The cervical spinal nerves are the eight pairs of neck nerves, C1 to C8, exiting above their same-numbered vertebrae and forming the cervical and brachial plexuses.

Chemical senses

Chemical senses: olfaction (smell), gustation (taste), and trigeminal chemesthesis, the sensory systems detecting airborne, ingested, and irritant chemicals, their receptors, brain integration into flavor, and clinical dysfunction.

Chemosis

Chemosis (conjunctival chemosis) is edema and ballooning of the conjunctiva, usually from infection, allergy, injury, or eyelid surgery such as blepharoplasty; treated by addressing the cause, with cold packs, lubrication, and medications.

Chiari malformation

Chiari malformation (Arnold-Chiari malformation): hindbrain defect where cerebellar tonsils herniate ≥3-5 mm below the foramen magnum, type 1 most common, prevalence 0.24-2.6%, treated by posterior fossa decompression with or without duraplasty.

Cholecystokinin receptor

Cholecystokinin receptors (CCK1R/CCKAR, CCK2R/CCKBR): class A GPCRs for CCK and gastrin. CCK1R needs sulfated CCK, couples Gs/Gq; CCK2R is the gastrin receptor, couples Gq; cloned 1992, cryo-EM structures 2022.

Cholesteatoma

Cholesteatoma: a benign keratin cyst of the middle ear and mastoid that erodes bone. Also called pearly tumor; treated surgically by canal wall up or down mastoidectomy, with 39% cumulative recurrence at 15 years.

Cholesteatoma of external auditory canal

External auditory canal cholesteatoma (EACC), also called canal cholesteatoma, is a rare keratin-filled, bone-eroding ear canal lesion, distinguished from keratosis obturans by osteonecrosis and treated by debridement or surgery.

Cholesteatoma of middle ear

Middle ear cholesteatoma: benign but destructive keratin squamous epithelium cyst in the middle ear, also called acquired or congenital cholesteatoma, causing bone erosion, hearing loss, and treated by mastoidectomy surgery.

Cholinergic

Cholinergic: relating to acetylcholine, the first identified neurotransmitter. Covers cholinergic neurons, nicotinic and muscarinic receptors, ChAT/VAChT/CHT-1 machinery, basal forebrain Ch1-Ch4 groups, and the cholinergic hypothesis of Alzheimer's disease.

Cholinergic neuron

Cholinergic neurons are nerve cells that synthesize and release acetylcholine (ACh) as their neurotransmitter; cell bodies are mainly located in the basal forebrain, brainstem, and striatum.

Chorda tympani

Chorda tympani: branch of the facial nerve (CN VII) crossing the middle ear between malleus and incus, joining the lingual nerve; carries anterior two-thirds tongue taste and parasympathetic fibers to submandibular and sublingual glands.

Choroid

The choroid is the pigmented vascular middle layer of the eye (part of the uvea) supplying the outer retina and RPE, with five layers from Bruch's membrane to the suprachoroid, fed by posterior ciliary arteries and drained by 4-7 vortex veins.

Choroid plexus

Choroid plexus: secretory epithelial tissue in the brain's four ventricles that produces most cerebrospinal fluid, forms the blood-CSF barrier via tight junctions, and aids immune surveillance.

Choroid plexus cyst

Choroid plexus cyst (CPC), a fluid-filled cyst in the choroid plexus, found in 0.5–2.5% of second-trimester fetuses; usually resolves by 26–28 weeks; isolated cysts are benign, but CPCs can mark trisomy 18 risk when other findings are present.

Choroidal rupture

Choroidal rupture: a traumatic break in Bruch's membrane, choriocapillaris, and RPE after blunt ocular trauma (ICD-11 NA06.61). Direct or indirect (countercoup) forms; main complication choroidal neovascularization treated with anti-VEGF.

Choroideremia

Choroideremia, also called progressive tapetochoroidal dystrophy (TCD), is an X-linked recessive retinal degeneration caused by CHM gene mutations, causing childhood night blindness, tunnel vision, and late blindness in males.

Christopher and Dana Reeve Foundation

Christopher & Dana Reeve Foundation, also called the Reeve Foundation, is a Short Hills, New Jersey 501(c)(3) nonprofit founded in 1982 as the Stifel Paralysis Research Foundation, merged with the American Paralysis Association, funding spinal cord injury research and the National Paralysis Resource Center.

Chronic atticoantral suppurative otitis media

Chronic atticoantral suppurative otitis media (ICD-11 AA91.1, ICD-10 H66.2) is the unsafe CSOM subtype with posterosuperior pars tensa or pars flaccida marginal perforation, attic and mastoid disease, cholesteatoma risk, bone erosion, and mastoidectomy treatment.

Chronic bilateral vestibulopathy

Chronic bilateral vestibulopathy (BVP, bilateral vestibular hypofunction) is a chronic vestibular syndrome with bilaterally reduced angular VOR causing unsteadiness, oscillopsia, and worsening in darkness; diagnosed by vHIT gain <0.6 or caloric sum <6°/sec, treated mainly with vestibular rehabilitation.

Chronic inflammation of postmastoidectomy cavity

Chronic inflammation of postmastoidectomy cavity (ICD-11 AB93; ICD-10-CM H95.11) is persistent inflammation of the open mastoid cavity after canal wall down mastoidectomy, causing therapy-resistant otorrhea in over 20% of open-cavity patients, treated topically or by revision obliteration surgery.

Chronic mastoiditis

Chronic mastoiditis (ICD-11 AB11.1, ICD-10 H70.1) is persistent or recurrent inflammation of the mastoid bone lasting over a month, usually a complication of chronic suppurative otitis media or cholesteatoma, treated with IV antibiotics and mastoidectomy.

Chronic myringitis

Chronic myringitis, also called granular myringitis or myringitis granulosa, is persistent inflammation and epithelial loss of the tympanic membrane lasting over one month without middle ear disease, causing painless otorrhea and treated with topical agents, laser, or surgery.

Chronic otitis media

Chronic otitis media (COM, chronic suppurative otitis media, CSOM) is persistent middle ear inflammation with eardrum perforation, discharge, and hearing loss, affecting about 3.8% of people worldwide, mostly in low- and middle-income countries.

Chronic suppurative otitis media

Chronic suppurative otitis media (CSOM), also called chronic otitis media, is a chronic middle ear infection with discharge through a perforated eardrum and hearing loss; about 297 million people are affected, mostly in low- and middle-income countries, and treatment centers on ear cleaning and topical quinolone drops.

Chronic tubotympanic suppurative otitis media

Chronic tubotympanic suppurative otitis media (CSOM, tubotympanic type, ICD-11 AA91.0) is a chronic middle ear infection with a persistent pars tensa perforation, recurrent ear discharge, and 20-60 dB conductive hearing loss, treated with topical quinolones and surgery.

Cicatricial lagophthalmos

Cicatricial lagophthalmos, a mechanical form of lagophthalmos (ICD-11 9A03.40), is incomplete eyelid closure caused by scarring after eyelid surgery, trauma, or burns, treated with lubrication and scar release with grafting.