The brainstem is similar to the spinal cord in two ways: there are peripheral axons entering and exiting horizontally from nerves that are attached at certain levels, and there are vertical axons connecting the cerebrum above to the spinal cord below, as well as to connections to parts of the cerebellum and the brainstem itself. Instead of spinal nerves, the nerves attached to the brainstem are cranial nerves, and in addition to somatosensory, lower motor neuron, and autonomic functions, some of these nerves also perform other sensory functions, such as hearing and taste.
Abnormalities of the brainstem may cause many kinds of sensory, motor, or autonomic dysfunction of almost any part of the body. Areas of the brainstem also connect to the cerebrum to play a role in the higher nervous system functions, so that brainstem lesions may also cause dysfunction of aspects of cognition, emotion, or consciousness. The neuroanatomy of the brainstem is complex, so that focal lesions may cause many different syndromes.