The dural venous sinuses receive cerebral veins from the brain and drain the venous blood mainly into the internal jugular vein (Figures III-6-12 and III-6-13). The superior sagittal sinus is located in the midsagittal plane along the superior aspect of the falx cerebri. It drains into the confluence of the sinuses. Arachnoid granulations protrude through the walls of the superior sagittal sinus. The arachnoid granulations transmit CSJ from the subarachnoid space into the venous circulation. The superior sagittal sinus drains into the confluens of the sinuses.
vein of scalp
Galea aponeurotica Pericranium Skull (diploic bone) Dura mater Arachnoid mater Pia mater
Superior sagittal sinus Falx cerebri Subarachnoid space Inferior sagittal sinus
Figure III-6-12. Coronal Section of the Dural Sinuses
Faix Superior cerebri) sagittal sinus Inferior
Faix Superior cerebri) sagittal sinus Inferior
The inferior sagittal sinus is located in the midsagittal plane, near the inferior margin of the falx cerebri It terminates by joining with the great cerebral vein to form the straight sinus at the junction of the falx cerebri and tentorium cerebelli.
The straight sinus is formed by the union of the inferior sagittal sinus and the great cerebral vein. It usually terminates by draining into the confluens of sinuses (or into the transverse sinus).
The occipital sinus is found in the attached border of the tentorium cerebelli. It drains into the confluens of sinuses.
The confluens of sinuses is formed by the union of the superior sagittal, straight, and occipital sinuses. It drains into the two transverse sinuses.
The transverse sinuses drain venous blood from the confluens of sinuses into the sigmoid sinuses. Each sigmoid sinus joins with an inferior petrosal sinus to drain into the internal jugular vein below the jugular foramen.
Infection can spread from veins of the face into the cavernous sinuses, producing infection and thrombosis. Such infection may involve the cranial nerves, which course through the cavernous sinus. Cranial nerves III, IV, and VI and the ophthalmic and maxillary divisions of CM V, as well as the internal carotid artery and its periarterial plexus of postganglionic sympathetic fibers traverse the cavernous sinus. All of these cranial nerves course in the lateral wall of the sinus except for CN VI, which courses through the middle of the sinus. As 3 result, CN VI is typically affected first in a cavernous sinus thrombosis or by an aneurysm of the internal carotid artery, with the other nerves being affected later.
A subarachnoid hemorrhage results from a rupture of a berry aneurysm in the circle of Willis. The most common site is in the anterior part of the circle of Willis. A common site for an aneurysm is at the branch point of the anterior cerebral and anterior communicating arteries. Other common sites are in the proximal part of the middle cerebral artery, or at the junction of the internal carotid and posterior communicating arteries. A typical presentation associated with a subarachnoid hemorrhage is the onset of a severe headache.
A subdural hematoma results from head trauma that tears superficial ("bridging") cerebral veins at the point where they enter the superior sagittal sinus. A venous hemorrhage results between the dura and the arachnoid. If acute, large hematomas result in signs of elevated intracranial pressure such as headache and nausea. Small or chronic hematomas are often seen in elderly or chronic alcoholic patients. Over time, herniation of the temporal lobe, coma, and death may result if the venous blood is not evacuated.
An epidural hematoma results from trauma to the lateral aspect of the skull, which lacerates the middle meningeal artery. Arterial hemorrhage rapidly occurs in the space between the dura and the skull. The head trauma is associated with a momentary loss of consciousness followed by a lucid (asymptomatic) period of up to 48 hours. The patient then develops symptoms of elevated intracranial pressure such as headache, nausea, and vomiting, combined with neurologic signs such as hemiparesis. Herniation of the temporal lobe, coma, and death may result if the arterial blood is not evacuated.
contains the dilator pupillae (radial) muscle and the sphincter pupillae (circular) constrictor muscle, which have antagonistic effects on the diameter of the pupil. The dilator pupillae muscle is innervated by preganglionic sympathetic fibers from the upper thoracic spinal cord and postganglionic sympathetics from the superior cervical ganglion. The constrictor pupillae muscle is innervated by preganglionic parasympathetic fibers from the nucleus of Edinger Westphal, which exit the midbrain in CN III, and by postganglionic parasympathetic fibers from the ciliary ganglion.
The ciliary muscle is a smoodi muscle that, when contracted, relaxes the suspensory ligament of the lens, allowing the lens to "round up" for near vision. Contraction of the ciliary muscle is part of the accommodation reflex under control of parasympathetic fibers in the oculomotor (CN III) nerve.
The orbit also contains the lacrimal gland; parasympathetic innervation to the gland comes from the facial nerve by way of the pterygopalatine ganglion.
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