CNS
On this page 8 sections
One Liners
- While sudden violent, flinging movements of an entire limb = (hemiballismus) = subthalamic nucleus
- generalized erratic dance-like jerky movements (chorea) = basal ganglia
- Vector of Viral Enchepelitis = House Flies
- Autonomic Neuropathy = Postural Hypotension
- Most common brain tumor in children = Astrocytoma
- Route of tranmission for meningiococcal infections = Bloodstream
Meningitis
| Age Group | Primary Bacterial Etiologies |
| Neonates (<3 months) | 1. Group B Streptococcus (S. agalactiae) 2. Escherichia coli 3. Listeria monocytogenes |
| Children (3 months – 10 years) | 1. Streptococcus pneumoniae (Most common overall) 2. Neisseria meningitidis |
| Teens & Young Adults (10 – 19 years) | 1. Neisseria meningitidis (Highest incidence in teens/dorms) 2. Streptococcus pneumoniae |
| Adults & Elderly (>20 years) | 1. Streptococcus pneumoniae 2. Neisseria meningitidis (Adults) 3. Listeria monocytogenes (Elderly/Immunocompromised) |
Syndromes
| Syndrome | Cause / Lesion | Key structures involved | Classic findings / MCQ clues |
|---|---|---|---|
| Costen Syndrome | TMJ dysfunction | Temporomandibular joint | Facial pain Ear symptoms; no true nerve infiltration or palatal paralysis |
| Sluder Syndrome | Sphenopalatine ganglion neuralgia | Sphenopalatine ganglion | Severe facial pain nasal congestion lacrimation |
| Wallenberg Syndrome ⭐ | PICA infarction → lateral medulla | Spinal trigeminal nucleus, spinothalamic tract, nucleus ambiguus, sympathetic fibers, inferior cerebellar peduncle | Ipsilateral Horner + ipsilateral facial pain/temp loss contralateral body pain/temp loss ipsilateral ataxia dysphagia/hoarseness |
| Dejerine Syndrome ⭐ | ASA infarction → medial medulla | CN XII, pyramid, medial lemniscus | Ipsilateral tongue paralysis contralateral hemiparesis contralateral loss of vibration/proprioception |
| Ramsay Hunt Syndrome ⭐⭐⭐ | VZV reactivation in geniculate ganglion | CN VII ± CN VIII | Ipsilateral LMN facial paralysis painful vesicular ear/palatal rash severe otalgia; may have vertigo, tinnitus, hearing loss |
| Trotter Syndrome ⭐⭐⭐ | Nasopharyngeal carcinoma invading lateral nasopharynx / Sinus of Morgagni | Eustachian tube + V3 + palatal muscles/innervation | Ipsilateral conductive hearing loss ipsilateral facial pain/numbness ipsilateral palatal paresis |
| Parkinson Disease ⭐⭐⭐ | Degeneration of dopaminergic neurons | Substantia nigra pars compacta | Resting tremor rigidity bradykinesia/akinesia; Lewy bodies |
| Frey's Syndrome (Auriculotemporal Syndrome) ⭐⭐⭐ | Injury/surgery to parotid region, classically after parotidectomy | Damaged parasympathetic postganglionic secretomotor fibers sympathetic fibers supplying sweat glands and cutaneous blood vessels | Gustatory sweating + flushing over the parotid/cheek region during eating or anticipation of food |
| Dejerine–Roussy Syndrome (Thalamic Pain Syndrome) ⭐⭐⭐ | Thalamic stroke/infarctionVPL + VPM nuclei of thalamus | Sudden contralateral hemisensory loss + sensory ataxia | As sensation returns → severe, persistent central neuropathic pain, dysesthesia, paresthesia, sensory disturbances, emotional/behavioral changes |
| Gerstmann Syndrome ⭐⭐⭐, | Lesion of the dominant hemisphere (usually left)Angular gyrus, inferior parietal lobule | Brodmann area 39 | Agraphia + Acalculia + Finger agnosia + Left-right disorientationThe 4 A's → Angular gyrus |
Eye
| Feature | CN III (Oculomotor) | CN IV (Trochlear) | CN VI (Abducens) |
| Innervated Muscle(s) | Superior, Inferior, & Medial Recti; Inferior Oblique; Levator Palpebrae Superioris; Pupillary Sphincter | Superior Oblique | Lateral Rectus |
| Resting Eye Position | "Down and Out" (due to unopposed Lateral Rectus & Superior Oblique) | Normal or slightly elevated / extorted | Medially deviated (Esotropia / Inward) |
| Type of Diplopia | Horizontal & vertical diplopia | Vertical & torsional diplopia (worse when looking down/reading) | Horizontal diplopia (worse when looking toward side of lesion) |
| Compensatory Head Position | Head turned or tilted to side of lesion | Head tilt to the OPPOSITE side (chin tucked) | Head turned TOWARD side of lesion |
| Ptosis (Drooping Lid) | Severe ptosis (paralysis of levator palpebrae) | Absent | Absent |
| Pupil Deficit | Mydriasis (dilated, fixed pupil) & loss of accommodation | Normal | Normal |
| Key Clinical Sign | Inability to adduct, elevate, or depress eye + ptosis + dilated pupil | Difficulty walking down stairs or reading | Inability to abduct the eye (look laterally) |
Reflexes
Ear
Basal Ganglia Structures
| Structure | Main function / role | Lesion / Disease | Classic clinical finding | MCQ association |
|---|---|---|---|---|
| Substantia nigra pars compacta ⭐⭐⭐ | Produces dopamine → projects to striatum; facilitates movement | Parkinson disease | Bradykinesia/akinesia + resting tremor + rigidity + mask-like facies | ↓ Dopamine → Parkinson |
| Subthalamic nucleus ⭐⭐⭐ | Part of indirect pathway; increases inhibition of unwanted movements | Hemiballismus | Sudden, violent, flinging movements of contralateral limbs | Subthalamic lesion → contralateral hemiballismus |
| Caudate nucleus ⭐⭐⭐ | Part of striatum; motor planning + cognitive/procedural functions | Huntington disease | Chorea + behavioral changes + dementia | Caudate degeneration → Huntington |
| Putamen | Part of striatum; regulates motor execution | Lesions can cause movement disorders; degeneration with caudate in Huntington | Athetosis / dystonia | Putamen + caudate = striatum |
| Globus pallidus | Major output nucleus of basal ganglia; GPi inhibits thalamus, GPe regulates subthalamic nucleus | Lesions associated with dystonia / athetosis | Sustained muscle contractions, abnormal postures or slow writhing movements | CO poisoning / Wilson disease → basal ganglia injury |
Vagus
| Nerve | Target / Function | Clinical Deficit on Damage |
| External Laryngeal Nerve | Motor to cricothyroid muscle (tenses vocal cords to raise pitch) | Loss of high-pitched voice; inability to sing high notes |
| Recurrent Laryngeal Nerve | Motor to all other intrinsic laryngeal muscles | Hoarseness, breathy voice; stridor/airway obstruction if bilateral |
| Internal Laryngeal Nerve | Sensory above the vocal cords (epiglottis, laryngeal vestibule) | Loss of cough reflex above vocal cords (risk of aspiration) |