Fascial Layers, Part 2 + Anatomy of a Nerve

For the most part, fascia can be classified as either superficial or deep, with the superficial layer being just beneath the skin and the deep layer being, well, everything else. As far as the deep layer goes, the “everything else” can be classified as either meningeal fascia or visceral fascia. 


Joint capsules, ligaments, tendons and the three layers that weave their way through each muscle (epimysium, perimysium and endomysium) make up the deep fascia. Aponeuroses are included in this classification as well. An aponeurosis is a broad, thick sheet of connective tissue that serves as an attachment site for muscles. A big one is the diamond-shaped thoracolumbar aponeurosis (where the latissimus dorsi originates) that spans across the lower back. I explained in Part 1 that fascia is rich in lots of sensory receptors. I’ll go into detail about each of those in a later post, but one of the sensory receptors found in fascia is called a nociceptor, otherwise known as a pain receptor. I once came across a study showing that people with lower back pain had a thickening of the thoracolumbar fascia compared to those in the trial who didn’t suffer from any LBP. This makes sense because with pain receptors being spread all throughout the fascial layers, a thickening of the fascia would equal an increase in pain receptors.


The visceral fascia is the layer that surrounds the heart (specifically called the pericardium) and lungs (pleura) as well as the abdominal organs. It also suspends the organs within their respective cavities (thoracic or abdominal) by way of ligaments that are meant to hold the organs against the body wall as well as allow for necessary physiological movement like breathing, the heart beating and peristalsis. 


This is the layer that surrounds the brain and the nervous system. To better understand this, we’ll look at the anatomy of a nerve. But first...


A nerve is a structured pathway that allows for the transmission of impulses to and from the brain and nervous system. Nerves either have one type of neuron, in which case they are classified as sensory or motor nerves, or like most nerves they have both motor and sensory neurons and are called mixed nerves. Nerves are structurally very similar to skeletal muscle in that each nerve has three separate layers of fascia, just like each muscle. 

Let’s look at the structure of a nerve from superficial to deep. The outer fascial covering of a nerve is called the epineurium (translates to on the nerve). Inside of that, nerve fibers (also called axons) are bundled together the same way muscle fibers are bundled, the layer that surrounds each bundle of axons is called the perineurium (around the nerve). Each individual axon that makes up the bundle is also surrounded by its own layer of fascia, this is called the endoneurium (within the nerve). 


Fascial Layers, Part 1 + Anatomy of a Muscle

While it’s true that the fascia is one big continuous and completely connected piece of tissue, it looks and acts differently depending on where it’s located in the body. In order to gain a better understanding of the fascial system as a whole and also have it be less overwhelming, we’ll break it down into more digestible bites. 

Just beneath your skin there is a layer of fatty tissue that provides the body with necessary insulation, blood and lymphatic flow and energy storage. Just beneath that is the superficial fascia. It anchors the skin to the tissues and organs below and is rich in blood and lymphatic vessels, nerves and some general sensory receptors which I’ll describe in detail in a later post. This thin and fibrous but highly elastic layer is classified as loose connective tissue. In this case loose just means it lacks any regular pattern or strong organization. 

Unlike the superficial fascia, the deep fascia is dense and well-organized. As far as I’m concerned, it’s the coolest layer of fascia because of the incredible and stunningly beautiful way it surrounds, supports and separates yet also connects every single structure in your body. The deep fascia is rich in sensory receptors that are sensitive to things like pressure and movement, which I will also cover in detail in another post. First let’s look at the anatomy of a muscle. Understanding the fascial anatomy of a muscle is essential for truly understanding how yoga and massage create change for people and actually really “work”.

Let’s consider a muscle from the outside in, or anatomically speaking, superficial to deep. Every muscle as a whole is wrapped in a sleeve of fascia called the epimysium. Epi- meaning on and my- meaning muscle. Epimysium means on the muscle.

Within each muscle are groups of muscle cells that have been bundled together into what’s called fascicles. Each fascicle is wrapped in its own layer of fascia called the perimysium. Peri- meaning around and my- meaning muscle. Perimysium means around the muscle. 

Each individual muscle cell also has its own layer of fascia called the endomysium. Endo- meaning within, my- meaning muscle. Endomysium meaning within the muscle. 

Each of these three layers comes together to form the tendons that connect muscle to bone. The layer of fascia that surrounds each bone is called the periosteum.

In part two we’ll look at the fascial layers that surround the brain, nerves and organs as well as the anatomy of a nerve.