Brainstem

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, and the pons and medulla oblongata of the hindbrain. Sometimes the diencephalon, the caudal part of the forebrain, is included.Cross-section of the midbrain at the level of the superior colliculus.Cross-section of the midbrain at the level of the inferior colliculus.Cross-section of the middle pons (at the level of cranial nerve V).Cross-section of the inferior pons (at the level of the facial genu).Cross-section of the rostral (superior) medulla.Cross-section of the middle medulla.Cross-section of the inferior medulla.The midbrain, pons, and medulla oblongata are labelled on this coronal section of the human brain. 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, and the pons and medulla oblongata of the hindbrain. Sometimes the diencephalon, the caudal part of the forebrain, is included. The brainstem provides the main motor and sensory nerve supply to the face and neck via the cranial nerves. Of the thirteen pairs of cranial nerves, ten pairs (or twelve, if the diencephalon is included in the brainstem) come from the brainstem. The brainstem is an extremely important part of the brain as 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 dorsal column-medial lemniscus pathway (fine touch, vibration sensation, and proprioception), and the spinothalamic tract (pain, temperature, itch, and crude touch). The brainstem also plays an important role in the regulation of cardiac and respiratory function. It also regulates the central nervous system, and is pivotal in maintaining consciousness and regulating the sleep cycle. The brainstem has many basic functions including heart rate, breathing, sleeping, and eating. The midbrain is divided into three parts: tectum, tegmentum, and the ventral tegmentum. The tectum (Latin:roof), which forms the ceiling. The tectum comprises the paired structure of the superior and inferior colliculi and is the dorsal covering of the cerebral aqueduct. The inferior colliculus, is the principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei, as well as inputs from the auditory cortex. Its inferior brachium (arm-like process) reaches to the medial geniculate nucleus of the diencephalon. Superior to the inferior colliculus, the superior colliculus marks the rostral midbrain. It is involved in the special sense of vision and sends its superior brachium to the lateral geniculate body of the diencephalon. The tegmentum which forms the floor of the midbrain, is ventral to the cerebral aqueduct. Several nuclei, tracts, and the reticular formation are contained here. The ventral tegmental area (VTA) is composed of paired cerebral peduncles. These transmit axons of upper motor neurons.