Making head & neck muscle innervation easy

studyYes, I know, what a catchy title! Trust me this post says what it does on the tin. I came across these rules when I was a medical student (the days when using a tablet meant chiselling into stone) from Robert Whitaker’s book Instant Anatomy, a superb book which I thoroughly recommend. Essentially the innervation of the muscles of the head & neck can be broadly covered by six rules; each rule explains how a group of muscles all share the same innervation except for one exception per rule. In life, there are always exceptions! So let’s get started:

Rule 1 Muscles of the pharynx. 

All muscles of the pharynx are innervated by the pharyngeal plexus* except stylopharyngeus which is innervated by the glossopharyngeal nerve CN IX.

Rule 2 Muscles of the palate.

All muscles of the palate are innervated by the pharyngeal plexus* except tensor veli palatini, which is innervated by the nerve to the medial pterygoid (A branch of the mandibular branch of the trigeminal nerve CN V).

Rule 3 Muscles of the larynx.

All muscles of the larynx are innervated by the recurrent laryngeal nerve (a branch of the Vagus nerve CN X), except cricothyroid which is innervated by the external laryngeal nerve (another branch of the vagus).

Rule 4 Muscles of facial expression.

All muscles of facial expression are innervated by the facial nerve CN VII except levator palpebrae superiors which is innervated by the oculomotor nerve CN III and the sympathetic.

Rule 5 Muscles of mastication.

All muscles of mastication are innervated by branches of the mandibular decision of the trigeminal nerve, except buccinator** which is innervated by the facial nerve CN VII.

Rule 6 Muscles of the tongue.

All muscles of the tongue are innervated by the hypoglossal nerve CN XII except palatoglossal which is innervated by the pharyngeal plexus.

*The pharyngeal plexus consists of sensory and motor inputs from the glossopharyngeal CN IX and vagus CN X (axons from cell bodies of the nucleus ambiguus) cranial nerves respectively. Sympathetics from the superior cervical ganglion also contribute to the plexus. Some sources state that the accessory nerve CN XI also contributes to the pharyngeal plexus via the vagus. However, this is not supported by current evidence.

**Buccinator is innervated by the facial nerve and usually therefore characterised as a muscle of facial expression, however functionally it behaves like a muscle of mastication by pushing food from the vestibule into the oral cavity proper.

References:

Instant Anatomy, Robert Whitaker
Clinical Anatomy By Regions, Richard Snell
Colour Atlas of Head and Neck Anatomy, Robert McMinn
Gray’s Anatomy: The Anatomical Basis of Clinical Practice,  Susan Standring

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