Our vagus nerve, one of the longest in our bodies, governs our immune systems, endocrine systems, and nervous systems. It has a newly evolved (relatively) branch that works with social engagement. There's also an older branch that is more primitive, which works with shutdown and collapse states.
There are chapters in this video. Somatic Practices start at 12:55.
In this video I define what somatics are and what we mean by trauma. Understanding what these words and concepts mean is important. This is part of our foundational education for our healing journey.