The brain and spinal cord are protected by the skull and vertebrae the meninges

The brain and spinal cord are protected by the skull and vertebrae, the meninges, and thecerebrospinal fluid. Three layers of meninges surround the brain and spinal cord, assisting in theproduction and drainage of cerebrospinal fluid (Fig. 23.1).Cerebrospinal fluid circulates betweenan interconnecting system of ventricles in the brain and around the brain and spinal cord, servingas a shock absorber.The cerebellum aids the motor cortex of the cerebrum in the integration of voluntarymovement. It processes sensory information from the eyes, ears, touch receptors, andmusculoskeletal system. In concert with the vestibular system, the cerebellum uses the sensorydata forreflexive control of muscle tone, balance, and posture to produce steady and precisemovements. The cerebellum’s hemispheres have ipsilateral (same side) control of the body.Cranial nerves are peripheral nerves that arise from the brain rather than the spinal cord.Each nerve has motor or sensory functions, and four cranial nerves have parasympatheticfunction (p. 569)..39

29. Upper and Lower BrainstemThe brainstem is the pathway between the cerebral cortex and the spinal cord, and it controlsmany involuntary functions (Table 23.1). Its structures includethe medulla oblongata, pons,midbrain, and diencephalon. The nuclei of the 12 cranial nerves arise from these structures. Thediencephalon is the central core of the cerebrum and includes the thalamus, hypothalamus, andepithalamus. The thalamus is divided into several nuclei. It receives specific sensory input forinterpretation and transmission and plays a role in motor function. The hypothalamus regulatestemperature, food and water intake, aggressive behavior, and autonomic responses (Rhoads, p.409). The thalamus is the major integrating center for perception of various sensations such aspain and temperature (along with the cortical processing for interpretation). The thalamus alsorelays sensory aspects of motor information between the basal ganglia and cerebellum. Thepons transmits information between the brainstem and the cerebellum, where motor informationfrom the cerebral cortex is relayed to the contralateral cerebellar hemisphere. The medullaoblongata is the site where the descending corticospinal tracts decussate (cross to thecontralateral side) (Siedels, p. 569).30. Causes of cerebral vasoconstriction/vasodilation & Causes of decreased PCO2Changes in the diameter of the vascular bed are influenced by auto-regulation ofarterioles by means of vasoconstriction or vasodilation. Increases in PaCO2 cause vasodilationand decreases in PaCO2 cause vasoconstriction, leading to increases or decreases in CerebralBlood Flow (CBF), respectively. Hypoxemia leads to vasodilation of cerebral arteries, albeit to alesser extent than PaCO2 changes.