Your gameplay flows, but it takes a bit. Starting with an overview anchors the learner. Consider:
Gameplay:
"The player who was most recently unnerved goes first. Play proceeds clockwise." {I love this starting player method!}
"A turn consists of (in order): 1) Taking one Card, and 2) Playing one Card. Players may also, at any point in their turn: a) Connect Pathways, b) Innervate a Muscle, or c) Activate a Root Power. These optional steps may be taken in any order."
"Cards are played to form Pathways of Innervation cards leading to a Muscle card."
"Here is an example of a completed Pathway of 4 nerves and a muscle:"
--Showing how nerves count here is important, because there is some confusion later in the rules as to what length Pathway counts for what points.
--You can hopefully see how eliminating the Tableau label, and calling them Pathways, shortens and simplifies all the rules.
--Green section: calling this Taking instead of Drawing better describes your choices.
--Yellow: Again, look for wordiness issues. Long sentences and paragraphs are intimidating. "Any Innervation card may be played as a Singleton, even if a Pathway connection is available. Keep in mind that Singletons can be stolen by other players." 27 words instead of 53. This applies throughout your rules.
--Perhaps it would be useful for non-Neurology nerds to note that each card need only match a nerve color with the adjacent cards, and that nerve endings can only connect with muscles.
--Complete a Pathway: Players can add to a Pathway by connecting two incomplete Pathways or Singletons to each other:
--Innervate a Muscle: a Pathway of two or more Innervation cards may Innervate a Muscle to score points. The player either reveals their Secret Muscle card or takes one a Shared Muscle card from the table. After showing the other players that the Pathway is correct, the player places the Muscle card in front of them with the collected cards of the Pathway on top. The name and point value of the Muscle should be left visible.
--Unless the Innervation Pathway contains four cards, the Pathway is placed face-down.
--If the Pathway contains four cards, it is placed face up with the Root card on top, showing its Root Power.
--Muscle cards played, whether Secret or Shared, are immediately replaced from the Muscle deck.
--The terms for one-time Root powers should be labelled "One-Time" rather than Play, since the Root card was Played much earlier.
--How do you keep from miscounting Pathways with Anomalous Innervation cards? Suggestions: return them to the box when the Pathway is Scored, or place them sideways face down.
--Wow! Who is in love with the pronator teres muscle? What if two players (or no players) have innervated pronator teres Muscles?