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What are the main parts of the brainstem?
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nervous system
In a myelinated axon, the myelin sheath prevents the local current (small black arrows) from flowing across the membrane. This forces the current to travel down the nerve fibre to the unmyelinated nodes of Ranvier, which have a high concentration of ion channels. Upon stimulation, these ion channels propagate the action potential (large green arrows) to the next node. Thus, the action potential jumps along the fibre as it is regenerated at each node, a process called saltatory conduction. In an unmyelinated axon, the action potential is propagated along the entire membrane, fading as it diffuses back through the membrane to the original depolarized region.
The brainstem is anatomically divided into three primary sections in humans:12
- Midbrain (mesencephalon): The most superior portion of the brainstem.13
- Pons (metencephalon): Located beneath the midbrain.32
- Medulla oblongata (myelencephalon): The most inferior section, which connects to the spinal cord.132
While some anatomical descriptions include the diencephalon—comprising the thalamus, hypothalamus, epithalamus, and subthalamus—as structures rostral to the brainstem, the brainstem itself is specifically defined by these three core regions. Together, these parts serve as a vital communication pathway between the brain and the rest of the body, housing the nuclei for most cranial nerves and regulating essential involuntary functions such as breathing, heart rate, and blood pressure.312