Head Injury: ANATOMY AND PHYSIOLOGY A. The skull is particularly thin in the temporal region and thick in the occiput. The floor of the cranial cavity is divided into three regions: anterior (frontal lobes), middle (temporal lobes), and posterior (lower brainstem and cerebellum). B. The meninges cover the brain in three layers: dura mater (fibrous membrane that adheres to the internal surface of the skull), arachnoid membrane, and pia mater (attached to the surface of the brain). Cerebrospinal fluid (CSF) circulates between the arachnoid and pia mater in the subarachnoid space. C. The brain is composed of the cerebrum, cerebellum, and the brainstem. The brain-stem consists of the midbrain, pons, and medulla. The reticular activating system (responsible for state of alertness) is within the midbrain and upper pons. The car-diorespiratory centers reside in the medulla. Small lesions in the brainstem can cause profound neurologic deficit. D. The Monro-Kellie doctrine states that the total volume of intracranial contents must remain constant because of the rigid bony cranium. With an expanding mass lesion, the intracranial pressure (ICP) is generally within normal limits. As cerebral edema worsens and brain swelling increases, CSF and blood volume within the skull decrease to compensate until the point of decompensation on the pressure-volume curve is reached; ICP then dramatically increases.
Posted on: Sat, 24 Aug 2013 11:55:40 +0000
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