Neurological Disorders

Parkinson's Disease: Progressive degeneration of dopaminergic neurons in the substantia nigra depletes the nigrostriatal pathway. Reduced dopamine in the basal ganglia (striatum) causes loss of smooth voluntary motor control. Clinical features: resting tremor (pill-rolling), cogwheel rigidity, bradykinesia (slowness), festinating gait, flat affect. Treatment: L-DOPA (dopamine precursor that crosses the blood-brain barrier and is converted to dopamine in the CNS). Directly relevant to NEET: dopamine = motor control neurotransmitter; its deficiency = Parkinson's.

Multiple Sclerosis (MS): Autoimmune destruction of CNS myelin sheaths formed by oligodendrocytes. Demyelination converts myelinated axons to effectively unmyelinated fibres, disrupting saltatory conduction. Symptoms reflect which CNS white matter tracts are affected — optic neuritis (visual), limb weakness, cerebellar ataxia, sensory loss. Young adults, relapsing-remitting pattern, more common in females.

Myasthenia Gravis: Autoimmune production of antibodies against nicotinic ACh receptors at the NMJ. Insufficient ACh binding → impaired neuromuscular transmission → fatigable muscle weakness. Ptosis (drooping eyelid) and diplopia (double vision) are typical. Treated with acetylcholinesterase inhibitors (e.g., pyridostigmine), which increase ACh availability by slowing its degradation.

Organophosphate Poisoning: Irreversible inhibition of acetylcholinesterase causes ACh accumulation at all cholinergic synapses — NMJ (muscle spasm, then paralysis), parasympathetic (SLUDD syndrome: salivation, lacrimation, urination, defecation, diarrhoea), CNS (seizures). Treatment: atropine (blocks muscarinic receptors) and pralidoxime (if given early, reactivates AChE).

Sensory Organ Pathologies

Cataract: Opacification (clouding) of the lens, most commonly from aging, UV exposure, or diabetes. Light scattering prevents clear image formation. Treatment: surgical lens replacement — most common elective surgery globally; most common cause of reversible blindness.

Glaucoma: Elevation of intraocular pressure (from impaired aqueous humour drainage) compresses the optic nerve at the optic disc, causing progressive irreversible loss of peripheral vision (arcuate scotoma → tunnel vision → blindness). Most common cause of irreversible blindness worldwide. Treatment: eye drops to reduce aqueous production (beta-blockers: timolol) or laser/surgery to improve drainage.

Night Blindness (Nyctalopia): Vitamin A deficiency depletes retinal (derived from Vitamin A), impairing rhodopsin synthesis in rods. The rods cannot function without adequate rhodopsin, particularly in dim light conditions. Treatment: Vitamin A supplementation. Note: this directly connects nutrition (micronutrient) to neural function (photoreceptor function), which is a commonly integrated topic in NEET.

Otosclerosis: Abnormal bone remodelling fixing the stapes footplate to the oval window, preventing vibration transmission to the cochlea. Causes progressive conductive hearing loss. Treated by surgical stapedectomy (replacement of stapes with prosthesis).