Anatomy & Physiology

Anatomy & Physiology Study Guide

12.4 Protection and Support of the Brain The cranial meninges, cerebrospinal fluid, and the blood–brain barrier protect and support the brain. The cranium, cranial meninges, and CSF protect the delicate tissues of the brain from mechanical forces. The Cranial Meninges The cranial meninges protect the brain, and the spinal meninges protect the spinal cord. There are three layers that formulate the meninges: the dura mater, arachnoid, and the pia mater. The cranial dura mater consists of outer and inner fibrous layers. The outer layer is joined to the periosteum of the cranial bones. The outer (endosteal) and inner (meningeal) layers of the cranial dura mater are divided by a small space that contains tissue fluids and blood vessels, including several large venous sinuses. The veins of the brain open into these sinuses, which deliver the venous blood to the internal jugular veins of the neck. The cranial arachnoid mater consists of the arachnoid membrane (an epithelial layer) and provides a smooth surface on top of the brain that does not follow the underlying folds. The inner epithelial layer of the dura mater is in contact with this membrane. The subarachnoid space widens between the arachnoid membrane and the pia mater. The pia mater attaches to the surface of the brain extending into every fold. It also accompanies the branches of cerebral blood vessels that travel deep into the brain to reach internal structures. Dural Folds In particular regions of the brain, the inner layer of the dura mater extends into the cranial cavity and forms a sheet that folds inward. These dural folds provide stability and support to the brain. The falx cerebri, the tentorium cerebelli, and the falx cerebelli are the three biggest dural folds. The falx cerebri projects into the longitudinal fissure between the cerebral hemispheres. The posterior border of the falx cerebri intersects the tentorium cerebelli . The falx cerebelli divides the two cerebellar hemispheres along the midsagittal line inferior to the tentorium cerebelli. The overall shape of the brain roughly corresponds to that of the cranial cavity. The massive cranial bones provide mechanical protection by cradling the brain. The tough, fibrous dural folds act like seat belts that hold the brain in position. The cerebrospinal fluid in the subarachnoid space represents a cushion against sudden jolts and shocks. Cerebrospinal Flui Cerebrospinal fluid (CSF) surrounds and bathes the exposed surfaces of the CNS. The CSF functions in cushioning delicate neural structures, supporting the brain, and transporting chemical messengers, nutrients, and waste products. The CSF communicates chemically with the interstitial fluid that surrounds the neurons and neuroglia of the CNS. The Formation of CSF The choroid plexus consists of a combination of specialized ependymal cells and permeable capillaries involved in the production of cerebrospinal fluid. Specialized ependymal cells surround the capillaries of the choroid plexus. The ependymal cells secrete CSF into the ventricles, and they also remove waste products from the CSF and adjust its composition over time.

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