Cranial Nerves and Reflexes PDF

**Reflexes** - **Corneal Reflex:** Involves CN V (Ophthalmic branch of Trigeminal) and CN VII (Facial). - **Pupillary Light Reflex:** Involves CN II (Optic), CN III (Oculomotor), and CN V (Trigeminal). - **Monosynaptic Reflex:** One synapse, one neuron (e.g., stretch reflex and...

**Reflexes** - **Corneal Reflex:** Involves CN V (Ophthalmic branch of Trigeminal) and CN VII (Facial). - **Pupillary Light Reflex:** Involves CN II (Optic), CN III (Oculomotor), and CN V (Trigeminal). - **Monosynaptic Reflex:** One synapse, one neuron (e.g., stretch reflex and the knee jerk rxn). - **Polysynaptic Reflex:** Involves multiple synapses and neurons, including relay neurons(e.g. reflex arc like touching something hot). - **Babinski's Sign:** - Normal in infants under one year old. - Abnormal in adults; indicates Upper Motor Neuron (UMN) lesion, particularly corticospinal tract. **Cranial Nerves** 1. **Optic Nerve (CN II):** Sensory, vision. 2. **Oculomotor Nerve (CN III):** Motor; parasympathetic functions include pupil constriction. 3. **Trochlear Nerve (CN IV):** Motor; controls superior oblique muscle. 4. **Trigeminal Nerve (CN V):** - **Sensory:** Face sensation, including cornea. - **Motor:** Mastication. - **Mixed Branch:** Mandibular nerve (only mixed branch of CN V). 5. **Abducens Nerve (CN VI):** Controls lateral rectus muscle. 6. **Facial Nerve (CN VII):** - **Motor:** Facial expression. - **Clinical Notes:** - UMN lesion: Contralateral weakness of lower face; forehead spared due to bilateral innervation. - **LMN lesion**: Ipsilateral complete paralysis, as seen in Bell's Palsy. 7. **Glossopharyngeal Nerve (CN IX (9)):** - Gag reflex. - Taste from posterior 1/3 of tongue. 8. **Vagus Nerve (CN X):** - Motor to palate elevators and pharynx. - Lesion results in deviation of soft palate/uvula to the healthy side. 9. **Hypoglossal Nerve (CN XII):** - Controls tongue movement. - Lesion: Tongue deviates toward affected side. **Motor Neurons** - **Upper Motor Neuron (UMN):** - Found in brain/spinal cord. - Symptoms: Hypertonia, hyperreflexia, spasticity. - Lesion above facial nucleus spares forehead and upper eye muscles. - **Lower Motor Neuron (LMN):** - Found in nerve roots, peripheral nerves, or neuromuscular junctions. - Symptoms: Hypotonia, hyporeflexia, flaccidity. - Lesion results in complete ipsilateral facial paralysis. **Sensory Pathways** 1. **Dorsal Column-Medial Lemniscus (DCML):** - Fine touch, vibration, proprioception. 2. **Spinothalamic Tract (Anterolateral):** - Crude touch, pain, temperature. - Two components: Anterior (crude touch/pressure) and lateral (pain/temperature). 3. **Spinocerebellar Tract:** - Unconscious proprioception. - Ipsilateral function, crucial for cerebellar inputs. 4. **Corticospinal Tract:** - Voluntary motor control, from neck to foot. **Clinical Assessments** 1. **Glasgow Coma Scale (GCS):**https://lh7-rt.googleusercontent.com/docsz/AD\_4nXcyFHwxbuGeQDCTgk4jupLXduw2ZIAy2zfmLxPoRmsG6bnyispWcXbvYZpHotY1cCenNgVJYXtbIy6ZCfFmElQVPqSqdk7sBL4MPwEAdoN2wbl2kmSKyxir03laqLUd3gqTw2B7xmgBMC0LjeK0j4Y?key=vtOHud927IHaSxKZWYGj-iuI - Score range: 3 (deep coma) to 15 (fully alert). - Assesses eye, verbal, and motor responses. 2. **Two-Point Discrimination:** - Measures ability to distinguish two stimuli applied simultaneously to the skin. 3. **Point Localization:** - Tests patient's ability to identify where they've been touched with their eyes closed. 4. **Double Simultaneous Stimulation:** - Tests recognition of bilateral stimuli applied simultaneously. 5. **Folstein Mini-Mental Status Exam:** - Evaluates cognitive decline (e.g., dementia). - Maximum score: 30; score ≤23 indicates cognitive impairment. **Key Pathologies** - **Bell's Palsy:** - Symptoms: Ipsilateral facial droop, dry eye, decreased taste, hyperacusis. - Differentiation from Stroke: Stroke spares forehead. - **Trigeminal Neuralgia:** - Symptoms: Severe facial pain. - Treatment: Carbamazepine; surgery (Microvascular Decompression) for persistent cases. - **Cavernous Sinus Thrombosis:** - Causes: Odontogenic/sinus infections. - Associated with immunocompromised states. - **Extrapyramidal Symptoms:** - Drug-induced movement disorders, including dystonia, akathisia, Parkinsonism, and tardive dyskinesia. **Drug Effects** - **Pupil Dilation:** Cocaine. - **Pupil Constriction:** Opiates, clonidine. **Additional Notes** - Reflexes bypass the brain; responses occur via spinal cord. - **Extrapyramidal Tracts:** Involved in stress responses and involuntary control of posture and movement. - **Extraocular Muscles:** Require all cranial nerves except CN IV (superior oblique) and CN VI (lateral rectus). - Always offer patients a second opinion.