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| 1 | +--- |
| 2 | +sidebar_position: 2 |
| 3 | +sidebar_label: 'Anatomy of the Nervous System and Principles of Localization' |
| 4 | +--- |
| 5 | + |
| 6 | +:::danger |
| 7 | +This article is automatically translated and has not yet been reviewed by an expert! |
| 8 | +::: |
| 9 | + |
| 10 | +# Anatomy of the Nervous System and Principles of Localization |
| 11 | + |
| 12 | +## Peripheral Nervous System |
| 13 | + |
| 14 | +### Cranial Nerves |
| 15 | + |
| 16 | +- **Definition**: Cranial nerves are peripheral nerves connected to the brain. |
| 17 | +- **Number**: 12 pairs. |
| 18 | + |
| 19 | +| Cranial Nerve | Exit from Skull | Brain Connection | Function | |
| 20 | +|--------------------------|-----------------------------------------------------------|-----------------------------------------------|------------------------------------------------------| |
| 21 | +| Olfactory (I) | Olfactory Foramen | Cerebrum (olfactory sulcus) | Olfaction | |
| 22 | +| Optic (II) | Optic Canal | Diencephalon (optic chiasm) | Vision | |
| 23 | +| Oculomotor (III) | Superior Orbital Fissure | Midbrain (interpeduncular fossa) | Eye movement, pupil constriction | |
| 24 | +| Trochlear (IV) | Superior Orbital Fissure | Midbrain (superior medullary velum) | Control of upward eye deviation | |
| 25 | +| Trigeminal (V) | Superior Orbital Fissure, Foramen Rotundum, Foramen Ovale | Pons (pons peduncle) | Facial sensation, mastication | |
| 26 | +| Abducens (VI) | Superior Orbital Fissure | Pons (middle of pontomedullary sulcus) | Lateral eye movement | |
| 27 | +| Facial (VII) | Internal Acoustic Meatus | Pons (lateral pontomedullary sulcus) | Facial expression, taste | |
| 28 | +| Vestibulocochlear (VIII) | Internal Acoustic Meatus | Pons (lateral pontomedullary sulcus) | Hearing and balance | |
| 29 | +| Glossopharyngeal (IX) | Jugular Foramen | Medulla oblongata (posterior groove of olive) | Taste, pharyngeal sensation | |
| 30 | +| Vagus (X) | Jugular Foramen | Medulla oblongata (posterior groove of olive) | Visceral control, pharyngeal muscles | |
| 31 | +| Accessory (XI) | Jugular Foramen | Medulla oblongata (posterior groove of olive) | Control of sternocleidomastoid and trapezius muscles | |
| 32 | +| Hypoglossal (XII) | Hypoglossal Canal | Medulla oblongata (anterolateral sulcus) | Tongue movement | |
| 33 | + |
| 34 | +> - One for smell, two for sight, three for eye movement, four for tilt, five for touch and chew, six for lateral gaze, seven for face and taste, eight for hearing and balance, nine for tongue and throat, ten for vagus, eleven for accessory, twelve for hypoglossal. |
| 35 | +> - Sensory nerves: I, II, VIII (Dad really dares). |
| 36 | +> - Mixed nerves: V, VII, IX, X (My wife is mixed). |
| 37 | +> - Without parasympathetic component: II, V, VI, XI (Second grade math problem 5+6=11). |
| 38 | +
|
| 39 | +### Olfactory Nerve (Olfactory Nerve, 1) |
| 40 | + |
| 41 | +- **Origin**: Olfactory epithelium in the upper nasal cavity. |
| 42 | +- Bipolar neurons pass through the cribriform plate into the anterior cranial fossa, terminating at the olfactory bulb, whose neurons send fibers through the olfactory tract to the olfactory center. |
| 43 | +- Special visceral sensory fibers; sensory nerve conducting olfaction. |
| 44 | +- **Localization Diagnosis**: |
| 45 | + - Nasal mucosa: Local lesions affecting both sides can cause decreased or absent sense of smell. |
| 46 | + - Olfactory nerve, bulb, and tract: Abnormalities (decreased or absent sense of smell); tumors in the frontal lobe or olfactory sulcus can cause unilateral or bilateral loss of smell. |
| 47 | + - Olfactory center: Lesions generally do not cause loss of smell but may cause olfactory disturbances (parosmia). |
| 48 | + |
| 49 | +### Optic Nerve (Optic Nerve, 2) |
| 50 | + |
| 51 | +- **Origin**: Axons of retinal ganglion cells. |
| 52 | +- The retina has three layers of neurons: |
| 53 | + - Outermost: Rods and cones. |
| 54 | + - Middle: Bipolar cells. |
| 55 | + - Innermost: Retinal ganglion cells. |
| 56 | +- Pathway: Ganglion cells → optic canal → middle cranial fossa → above the sella turcica forming the optic chiasm → nasal half fibers cross to the contralateral side, temporal half remains ipsilateral → form the optic tract → lateral geniculate nucleus → decussate → posterior limb of internal capsule → optic radiation → occipital visual cortex. |
| 57 | +- **Localization Diagnosis**: |
| 58 | + |
| 59 | +| Affected Area | Clinical Presentation | Common Causes | |
| 60 | +|-------------------------|------------------------------------------------------------------------------------------------------------|----------------------------------------------------| |
| 61 | +| Optic nerve | Unilateral blindness, direct pupillary reflex (-), consensual reflex (+) | Optic neuritis, optic atrophy, tumor compression | |
| 62 | +| Optic chiasm | Bitemporal hemianopia | Pituitary adenoma, craniopharyngioma, aneurysm | |
| 63 | +| Optic tract | Contralateral homonymous hemianopia in both eyes, direct pupillary reflex (-) on the affected side | Stroke, brain tumor, head trauma | |
| 64 | +| Optic radiation | Upper quadrantanopia if damaged in the parietal lobe, lower quadrantanopia if damaged in the temporal lobe | Stroke, brain tumor, head trauma | |
| 65 | +| Occipital visual center | Contralateral homonymous hemianopia, macular sparing, visual agnosia | Occipital infarction, occipital tumor, head trauma | |
| 66 | + |
| 67 | +### Oculomotor, Trochlear, and Abducens Nerves (Oculomotor Nerve, Trochlear Nerve, Abducens Nerve, 3, 4, 6) |
| 68 | + |
| 69 | +- **Origins**: |
| 70 | + - Oculomotor: Oculomotor nucleus located below the aqueduct in the periaqueductal gray matter. |
| 71 | + - Trochlear: Originates from the trochlear nucleus in the inferior colliculus. |
| 72 | + - Abducens: Originates from the abducens nucleus in the midline of the pons. |
| 73 | +- The oculomotor, trochlear, and abducens nerves, through their innervated muscles, collectively control eye movements and various reflexes. |
| 74 | +- **Localization Diagnosis**: |
| 75 | + - **Ocular Muscle Paralysis and Diplopia**: |
| 76 | + - **Causes**: When the oculomotor, trochlear, abducens nerves and their nuclei, or connecting fibers are diseased. |
| 77 | + |
| 78 | +| Type | Ocular Muscle Paralysis | Description | Clinical Presentation | Possible Causes | |
| 79 | +|------------------------------|------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------| |
| 80 | +| Peripheral nerve paralysis | | | | | |
| 81 | +| ⤷ Oculomotor nerve paralysis | Motor fiber damage | Ptosis, paralysis of levator palpebrae superioris, superior rectus, medial rectus, inferior oblique, and inferior rectus; paralysis of the sphincter pupillae | Ptosis, restricted eye movement inward, upward, and downward, dilated pupil, loss of light reflex | Intracranial aneurysm, tuberculous meningitis | |
| 82 | +| ⤷ Trochlear nerve paralysis | Paralysis of the superior oblique muscle | Restricted downward and outward eye movement | Restricted downward and outward eye movement on the affected side, diplopia when looking down or descending stairs | - | |
| 83 | +| ⤷ Abducens nerve paralysis | Paralysis of the lateral rectus muscle | Esotropia, limited or no lateral eye movement | Esotropia, limited or no lateral eye movement on the affected side | Nasopharyngeal cancer intracranial infiltration, diabetes | |
| 84 | +| Nuclear paralysis | Brainstem lesion | Ocular motility disorder | Similar to peripheral ocular muscle paralysis, selective damage to individual nuclei, often accompanied by other brainstem lesions, can be bilateral | Brainstem lesion | |
| 85 | +| Internuclear paralysis | | | | | |
| 86 | +| ⤷ One-and-a-half syndrome | Pontine tegmental lesion | Horizontal gaze limitation | The affected eye cannot move medially or laterally; the contralateral eye cannot move medially but can move laterally with nystagmus | Pontine lesion | |
| 87 | +| Pupillary changes | | | | | |
| 88 | +| Pupillary phenomena | Pupillary size regulation | The oculomotor nerve parasympathetic fibers innervate the sphincter pupillae; postganglionic fibers from the cervical sympathetic ganglia innervate the dilator pupillae | Normal pupil diameter 3-4 mm in ordinary light; less than 2 mm is miosis, greater than 5 mm is mydriasis | Intracranial aneurysm compressing the oculomotor nerve; Horner's syndrome | |
| 89 | + |
| 90 | +### Trigeminal Nerve (Trigeminal Nerve, 5) |
| 91 | + |
| 92 | +- **Origin**: Pons trigeminal motor nucleus, exiting the brainstem ventrally, passing through the foramen ovale. |
| 93 | +- Mixed nerve: |
| 94 | + - Motor fibers innervate: Masseter, temporalis, medial and lateral pterygoid, and tensor tympani muscles. |
| 95 | + - Sensory nerve participation: |
| 96 | + - Originating structure: Trigeminal ganglion located at the trigeminal impression on the petrous apex, containing pseudounipolar neurons, divided into three peripheral branches. |
| 97 | + - Distribution |
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