Neuroanatomy: Reflexes and Cranial Nerves

Study Notes

Corneal Reflex: Involves cranial nerves V (ophthalmic branch of trigeminal) and VII (facial).
Pupillary Light Reflex: Involves cranial nerves II (optic), III (oculomotor), and V (trigeminal).
Monosynaptic Reflex: One synapse, one neuron (e.g., knee-jerk reflex).
Polysynaptic Reflex: Multiple synapses and neurons (e.g., reflex arc like touching something hot).
Babinski's Sign: Normal in infants under one year; abnormal in adults, indicating upper motor neuron (UMN) lesion, specifically in the corticospinal tract.

Optic Nerve (CN II): Sensory nerve responsible for vision.
Oculomotor Nerve (CN III): Motor nerve controlling pupil constriction and other eye muscles.
Trochlear Nerve (CN IV): Motor nerve controlling the superior oblique muscle of the eye.
Trigeminal Nerve (CN V): Mixed nerve for facial sensation and mastication. Mandibular branch is a mixed nerve.
Abducens Nerve (CN VI): Motor nerve controlling the lateral rectus muscle of the eye.
Facial Nerve (CN VII): Motor nerve controlling facial expressions. Clinical notes: UMN lesions cause contralateral lower facial weakness (forehead spared); LMN lesions cause ipsilateral complete paralysis (e.g., Bell's palsy).
Glossopharyngeal Nerve (CN IX): Responsible for the gag reflex, taste from the posterior 1/3 of the tongue, and motor to palate elevators and pharynx
Vagus Nerve (CN X): Lesions cause soft palate/uvula deviation to the healthy side; controls tongue movement.
Hypoglossal Nerve (CN XII): Controls tongue movements; lesions cause tongue deviation to the affected side.

Upper Motor Neuron (UMN): Located in the brain/spinal cord; symptoms include hypertonia, hyperreflexia, and spasticity. Lesion above facial nucleus spares forehead and upper eye muscles.
Lower Motor Neuron (LMN): Located in nerve roots, peripheral nerves, or neuromuscular junctions; symptoms include hypotonia, hyporeflexia, and flaccidity.
Lesion above facial nucleus spares forehead and upper eye muscles, whereas lesion below the nucleus leads to complete ipsilateral facial paralysis.

Dorsal Column-Medial Lemniscus (DCML): Transmits fine touch, vibration, and proprioception.
Spinothalamic Tract (Anterolateral): Transmits crude touch, pain, and temperature.
Spinocerebellar Tract: Carries unconscious proprioception to the cerebellum.
Corticospinal Tract: Involved in voluntary motor control from the neck down.

Glasgow Coma Scale (GCS): Scores range from 3 (deep coma) to 15 (fully alert); asses eye, verbal, and motor responses.
Two-Point Discrimination: Measures ability to distinguish two simultaneous stimuli on the skin.
Point Localization: Tests ability to pinpoint where the body is being touched with eyes closed.
Double Simultaneous Stimulation: Tests recognition of bilateral stimuli pressed simultaneously.
Folstein Mini-Mental Status Exam: Evaluates cognitive decline; a score of ≤23 indicates potential cognitive impairment.

Bell's Palsy: Ipsilateral facial droop, dry eyes, decreased taste, hyperacusis, and differentiation from stroke.
Trigeminal Neuralgia: Severe facial pain; treated with carbamazepine or surgery.
Cavernous Sinus Thrombosis: Odontogenic/sinus infections potentially causing associated immunocompromised states.
Extrapyramidal Symptoms: Drug-induced movement disorders (dystonia, akathisia, Parkinsonism, tardive dyskinesia).