Tuesday, June 30, 2009

The brainstem is the lower extension of the encephalon (brain). It is made up of the cerebral peduncles, the pons, and the medulla oblongata. The brainstem is structurally continuous with the spinal cord and provides the main motor and sensory innervation to the face and neck via the cranial nerves as it is the pathway for all fiber tracts passing up and down from peripheral nerves and spinal cord to the highest parts of the brain. The nerve connections of the motor and sensory systems from the main part of the brain to the rest of the body pass through the brainstem. This includes the corticospinal tract (motor), the posterior column-medial lemniscus pathway (fine touch, vibration sensation and proprioception) and the spinothalamic tract (pain, temperature, itch and crude touch). The brainstem controls vital functions such as breathing and instructing the heart to beat.

All information related from the body to the cerebrum and cerebellum and vice versa, must go through the brainstem. The ascending pathways that come from the body to the brain are the sensory pathways, and include the spinothalamic tract for pain and temperature sensation and the dorsal column, fasciculus gracilis, and cuneatus for touch, proprioception, and pressure sensation (both of the body). (The facial sensations have similar pathways, and will travel in the spinothalamic tract and the medial lemniscus also). Descending tracts are upper motor neurons destined to synapse on lower motor neurons in the ventral horn and intermediate horn of the spinal cord. In addition, there are upper motor neurons that originate in the brain stem's vestibular, red, tactile, and reticular nuclei, which also descend and synapse in the spinal cord.