The central nervous system (CNS) allows the coordination and integration of neural signals that control activities of the body, such as respiration. The CNS is also involved in higher cognitive functions such as memory and learning. The CNS comprises the brain and spinal cord (Figure 52.1), which are composed of a large number of excitable nerve cells (neurones) and specialised tissue (neuroglia). Neuronal cell bodies are located within grey matter and the processes of the neurones occupy white matter of the CNS.
Brain
The brain and its membranous coverings are protected by the surrounding neurocranium. The brain is composed of an inner core of white matter surrounded by grey matter. Some specialised grey matter masses (nuclei) are located deep within the white matter.
Cerebrum
The left and right cerebral hemispheres form the largest component of the brain. The cerebral surfaces are thrown into multiple folds (gyri), grooves (sulci) and clefts (fissures). The major sulci separate each hemisphere into frontal, parietal, temporal and occipital lobes, named according to the bones they lie beneath (Figure 52.2). The pattern of gyri and sulci is anatomically important, as some demarcate functional areas of the cortex. For example, the pre-central gyrus corresponds to the primary motor area (Chapter 54) and the post-central gyrus is associated with the primary sensory area of the cortex (Chapter 53). The left and right hemispheres are connected by a large mass of white matter, the corpus callosum. The diencephalon forms the central core of the cerebrum and includes the thalamus and hypothalamus (Figure 52.3 and Chapter 55).
Brainstem
The brainstem is composed of the midbrain (rostral), pons and medulla oblongata (caudal). Cranial nerves III–IV (midbrain), V (pons), VI–VII (pons-medulla junction) and VIII–XII (medulla oblongata) are associated with the brainstem (Figures 52.3 and 52.4).
Cerebellum
This lies posterior to the pons and medulla and is composed of two hemispheres, thrown into folds (folis) united by the vermis (Figure 52.3 and 52.4). The cerebellum connects to the midbrain, pons and medulla oblongata via large bundles of nerve fibres called the superior, middle and inferior cerebellar peduncles, respectively.
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