For clinical purposes, and particularly in general medicine, the extreme complexity of neuroanatomy must be reduced to its core elements. The following sections cover:

• cranial nerves
• three systems of motor control:
• corticospinal or pyramidal system
• extrapyramidal system
• cerebellum
• motor unit
• reflex arc
• sensory pathways and pain
• control of the bladder and sexual function.

Table 21-4. Causes of the amnestic syndrome

Alcohol (Wernicke-Korsakoff syndrome)

Head injury (severe)

Anoxia

Posterior cerebral artery occlusion (bilateral)

Herpes simplex encephalitis

Chronic sedative and solvent abuse

Bilateral invasive tumours

Arsenic poisoning

Following hypoglycaemia

Disorders of memory follow damage to the medial surfaces of both temporal lobes and their brainstem connections – the hippocampi, fornices and mammillary bodies. Bilateral lesions are necessary to cause amnesia. It is characteristic of all organic memory disorders that more recent events are recalled poorly, in contrast to the relative preservation of distant memories.

Memory loss (the amnestic syndrome) is part of dementia, but also occurs as an isolated entity (see Table 21.4).