6. Brainstem and cranial nerves

The brainstem is the portal between the brain and the spinal cord, through which signals pass in both directions. The stem also acts as the ‘spinal cord’ for the cranial senses and muscles. Various biogenic amines are produced in the stem, which regulate mood, vigilance, attention and initiative. Of the twelve cranial nerves, ten lead to or emanate from the brainstem. Unlike the spinal cord nuclei, they are usually controlled by both cortex hemispheres. The brainstem performs various vital and autonomic motor system functions. Failure of the brainstem gives rise to a life-threatening condition. An EMV score provides an indication of brainstem function. Discrete failure can be associated with a wide variety of syndromes, in the context of which the problem can be localized on the basis of the combined clinical symptoms. The brainstem anatomy is described in the first section (sect. 6.1). This is followed by a description of the cranial nerves, grouped by function (sect. 6.2). Ample attention is paid to the supranuclear, nuclear/internuclear and infranuclear eye movements (sect. 6.2.3). The examination of all twelve cranial nerves is described systematically and in the physiological context in sect. 6.3. As coma is generally accompanied by loss of brainstem functions, and symptoms of cranial nerve dysfunction are important in the diagnosis of coma, this chapter also describes the coma examination and the Glasgow Coma Scale, also referred to as the ‘EMV’ (eye/motor/verbal) score (sect. 6.4). Many cerebral disorders that cause coma jeopardize respiration, as discussed in sect. 6.5. Analogous to supranuclear spinal cord disorders, there are supranuclear brainstem disorders, which are referred to as ‘pseudobulbar’. In contrast there are bulbar disorders, the subject of the penultimate section (sect. 6.6). Lastly, some brainstem syndromes are described, mainly because they give a good impression of the symptoms of brainstem dysfunction (sect. 6.7). Disorders of the cranial nerves are described in Chap. 16. Chapter 20 looks at coma in a clinical setting.