754 articoli pubblicati
This nerve may anastomose with a branch from the upper division of the oculomotor nerve. In one case, a branch from a communication between the supra- and infratrochlear nerves pierced the orbital plate, ran beneath the dura, pierced the frontal bone, and supplied the overlying skin. Reference Cushing, H. (1904) The sensory distribution of the fifth cranial nerve. Johns Hopkins Hospital Bulletin 15:213-232.
In about 54% of cases, a middle alveolar nerve arises from the infraorbital, 28% show significant variation, and in 18% the middle alveolar nerve is absent. The branch supplying the upper lip may run independently in the floor of the orbital cavity; other branches of the nerve arise earlier and enter another canal medial to the main channel. The nerve may be doubled.
This nerve arises from S3, S4, and occasionally S2. It may arise from the sacral plexus directly rather than being one of the three terminal branches (inferior rectal, perineal, and dorsal nerve of the clitoris or penis) of the pudendal. The inferior rectal nerve may pierce the sacrospinous ligament medial to the ischial spine as reported in 20% of body halves. The inferior rectal nerve may arise in common with the perineal nerve.
See also: Vagus Nerve Superior Laryngeal Nerve
This nerve is frequently joined in the early part of its course with the posterior femoral cutaneous nerve. It may also be joined with the nerve to the short head of the biceps. The inferor gluteal nerve frequently provides a communicating branch that joins the posterior femoral cutaneous nerve.
The inferior cervical ganglion is irregular in shape and usually larger than the middle ganglion. It is frequently combined with the first thoracic and is named the stellate (cervicothoracic) ganglion. A direct communication to the phrenic nerve is often derived from the inferior ganglion, less frequently from the middle cervical ganglion. The sympathetic chain on the left side may split and encircle the subclavian artery.
The inferior alveolar nerve may form a single trunk with the lingual nerve, extending as far as the mandibular (dental) foramen. It may be separated from the lingual nerve by an accessory ligament extending from the lateral pterygoid plate and spine of the sphenoid to the lateral side of the pterygospinous ligament. The inferior alveolar nerve is sometimes perforated by the internal (medial) maxillary artery. It may have accessory roots from other divisions of the mandibular nerve.
This nerve may be small and terminate near the iliac crest by joining the iliohypogastric nerve, which sends branches to replace the absent terminal part of the ilioinguinal nerve. When present, the nerve is replaced by either the genital (more commonly) or the femoral branches of the genitofemoral nerve. The ilioinguinal may provide a lateral cutaneous or iliac branch to supply the skin in the region of the anterior superior iliac spine. It may partially or completely replace the genital branch of the genitofemoral nerve or the lateral femoral cutaneous nerve.
The iliac branch of the iliohypogastric nerve may be absent, replaced by the lateral cutaneous branch of the twelfth thoracic nerve. The hypogastric branch may supply the pyramidalis muscle and may be joined with the twelfth thoracic nerve. The iliohypogastric nerve is sometimes derived from the twelfth thoracic nerve and may also receive a root from the eleventh thoracic nerve.
A number of variations in the course and branches of this nerve have been reported. The nerve may have a posterior (dorsal) root bearing a ganglion reminiscent of its embryologic origin (like a spinal nerve). The hypoglossal nerve has been reported to exit from the posterior surface of the medulla oblongata instead of its usual exit anteriorly.
The greater splanchnic is usually formed from the seventh, eight, and ninth thoracic ganglia, but the upper and lower limits are variable. The nerve arises symmetrically in only 12% of bodies (100 cadavers). So-called normal nerves (T7-T9) occurred in 23%; only 9% of these were symmetric bilaterally.
This nerve may supply the mylohyoid and the anterior belly of the digastric nerve. A communicating branch sometimes arises between the glossopharyngeal and facial nerves. A tympanic branch of the glossopharyngeal may arise from two roots, one of which may come from the vagus. The glossopharyngeal may receive fibers from the hypoglossal just distal to the hypoglossal foramen.
This nerve is considered by some authors as the most variable nerve of the lumbar plexus. The genital and the femoral (crural) branches of the nerve may arise as separate offshoots of the lumbar plexus. Either of them may be derived from the first or second lumbar nerves and occasionally from the third. The genital branch sometimes receives fibers from the twelfth thoracic nerve. The genitofemoral or either of its branches (genital or femoral) may be absent.
A variation has been reported in which the frontal nerve divides at a variable point before leaving the orbit to form supratrochlear and supraorbital branches. In such cases, the supraorbital branch passes through the supraorbital foramen, through which the undivided nerve ordinarily passes. When the foramen is absent, it may have a special groove, the frontal notch (Henle). The frontal nerve runs, at first forward, in a roughly a sagittal direction. In approximately 90% of subjects it divides during its course within the orbit, but in 10.5% it remains undivided.
See also: Fissures Sulci Calcarine Fissure Central Sulcus Fissure Collateral Fissure Cingulate Sulcus Parietal Occipital Fissure Inferior Frontal Sulcus Rolando Fissure Intraparietal Sulcus Sylvian Fissure Middle Frontal Sulcus Middle Temporal Sulcus Olfactory Sulcus Orbital Sulcus Postcentral Sulcus Precentral Sulcus Superior Frontal Sulcus Image 07A Image 07B Image 07C Image 07D Image 07E Image 07F
The first thoracic is usually larger than the others and is variable in shape (ovoid or semilunar). It may be fused with the inferior cervical (stellate) or second thoracic ganglion.
This nerve usually has variable connections with both the subcostal (T12) nerve and the second lumbar nerve. This contributes to the right/left asymmetry of the lumbosacral plexuses.
See Trigeminal (CN V) Nerve
In its course to the thigh, the femoral nerve may pierce m. iliacus. The nerve has been reported to enter the thigh between the femoral artery and vein. The anterior cutaneous branch of the femoral nerve may arise from the beginning of the femoral nerve or directly from the lumbar plexus. It may partly or completely replace the femoral branch of the genitofemoral nerve. The posterior branch of the medial cutaneous nerve may be small or absent, in which case its usual area of supply is provided by the obturator or saphenous nerve.
A pattern of variation has been established for the facial nerve (see Illustrations). However, the clear separation of the nerve into five main terminal branches (temporal, zygomatic, buccal, mandibular, and cervical) may be difficult or impossible. The posterior auricular and occipital branches may arise before their exit from the stylomastoid foramen. Branches from the facial nerve have been observed to replace those from the glossopharyngeal (CN IX) in supplying the root of the tongue and palate.