the brainstem (or brain stem) is the posterior part of the brain, continuous with the spinal cord. In the human brain the brainstem includes the midbrain, the pons and medulla oblongata of the hindbrain. The midbrain continues with the thalamus of the diencephalon through the tentorial notch,[1] and sometimes the diencephalon is included in the brainstem.[2]

The brainstem is a very small component of the brain, making up only around 2.6 per cent of the total weight of the brain.[3] It is though, a crucial part of the brain providing the main motor and sensory nerve supply to the face and neck via the cranial nerves. Ten pairs of cranial nerves come from the brainstem. It is also of prime importance in the conveyance of motor and sensory pathways from the rest of the brain to the body, and from the body back to the brain. These pathways include the corticospinal tract (motor), the dorsal column-medial lemniscus pathway (fine touch, vibration sensation, and proprioception), and the spinothalamic tract (pain, temperature, itch, and crude touch).