Its dysfunction is implicated in Parkinson's disease. Substantia nigra pars compacta: This is a concentration of neurons in the ventral portion of the midbrain that uses dopamine as its neurotransmitter and is involved in both motor function and emotion.Red nucleus: This is a motor nucleus that sends a descending tract to the lower motor neurons.Trochlear nerve nucleus: This is the fourth cranial nerve.Oculomotor nerve nucleus: This is the third cranial nerve nucleus.When stimulated by a signal, the synaptic connections activate neurons in the nucleus raphe magnus the pathway then projects down into the posterior grey column of the spinal cord which prevents pain sensation transmission. Periaqueductal gray: The area of gray matter around the cerebral aqueduct contains various neurons involved in the pain desensitization pathway.These transmit axons of upper motor neurons. The ventral tegmental area (VTA) is composed of paired cerebral peduncles. Several nuclei, tracts, and the reticular formation are contained here. The tegmentum which forms the floor of the midbrain, is ventral to the cerebral aqueduct. It is involved in the special sense of vision and sends its superior brachium to the lateral geniculate body of the diencephalon. The superior colliculus is positioned above the inferior colliculus, and marks the rostral midbrain. Its inferior brachium (arm-like process) reaches to the medial geniculate nucleus of the diencephalon.

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. The tectum comprises the paired structure of the superior and inferior colliculi and is the dorsal covering of the cerebral aqueduct. The midbrain is further subdivided into three parts: tectum, tegmentum, and the ventral tegmental area. View of the midbrain showing covering tectum and tegmental floor Superior shown in green and inferior in orange. Main article: Midbrain Diagram showing the position of the colliculi. The brainstem extends from just above the tentorial notch superiorly to the first cervical vertebra below the foramen magnum inferiorly. The parts of the brainstem are the midbrain, the pons, and the medulla oblongata the diencephalon is sometimes considered part of the brainstem. These pathways include the corticospinal tract (motor function), the dorsal column-medial lemniscus pathway ( fine touch, vibration sensation, and proprioception), and the spinothalamic tract ( pain, temperature, itch, and crude touch). 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. Other roles include the regulation of the central nervous system and the body's sleep cycle. Ten pairs of cranial nerves come from the brainstem.

It also provides the main motor and sensory nerve supply to the face and neck via the cranial nerves. : 195 It has the critical roles of regulating cardiac, and respiratory function, helping to control heart rate and breathing rate. The brainstem is very small, making up around only 2.6 percent of the brain's total weight. : 152 The midbrain is continuous with the thalamus of the diencephalon through the tentorial notch. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The brainstem (or brain stem) is the stalk-like : 152 part of the brain that interconnects the cerebrum and diencephalon with the spinal cord. A 3D medical animation still shot showing different parts of the midbrain.

Brain stem definition