The posterior auricular muscle is a

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

behind the auricle of the

outer ear The outer ear, external ear, or auris externa is the external part of the ear, which consists of the auricle (also pinna) and the ear canal. It gathers sound energy and focuses it on the eardrum ( tympanic membrane). Structure Auricle The ...

. It arises from the mastoid part of the temporal bone, and inserts into the lower part of the cranial surface of the auricle of the

. It draws the auricle backwards, usually a very slight effect.

Structure

The posterior auricular muscle is found behind the auricle of the

. It consists of two or three fleshy

fasciculi Fascicle or ''fasciculus'' may refer to: Anatomy and histology * Muscle fascicle, a bundle of skeletal muscle fibers * Nerve fascicle, a bundle of axons (nerve fibers) ** Superior longitudinal fasciculus *** Arcuate fasciculus ** Gracile fasc ...

. These arise from the mastoid part of the

temporal bone The temporal bone is a paired bone situated at the sides and base of the skull, lateral to the temporal lobe of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples where four of the cranial bone ...

by short aponeurotic fibers. They insert into the lower part of the cranial surface of the auricle of the

. The posterior auricular muscle is supplied by branches of the

posterior auricular artery The posterior auricular artery is a small artery that arises from the external carotid artery. It ascends along the side of the head. It supplies several muscles of the neck and several structures of the head. Structure Origin The artery ar ...

, which continues deep to the muscle. It is drained by the

posterior auricular vein The posterior auricular vein is a vein of the head. It begins from a plexus with the occipital vein and the superficial temporal vein, descends behind the auricle, and drains into the external jugular vein. Structure The posterior auricula ...

that accompanies the artery.

Nerve supply

The posterior auricular muscle is supplied by the posterior auricular nerve, a branch of the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...

(VII).

Function

The posterior auricular nerve draws the auricle of the outer ear backwards. This effect is usually very slight, although some people can wiggle their ears due to a more significant muscle movement. Electromyographic signals in humans suggest the posterior auricular muscle may be part of an ancient system for monitoring sounds we can't see.

Postauricular reflex

The postauricular reflex is a

vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

myogenic muscle response in humans that acts to pull the ear upward and backward. Research suggests neural circuits for auricle orienting have survived in a vestigial state for over 25 million years. It is often assumed the reflex is a vestigial Preyer reflex (also known as the pinna reflex). A study on auriculomotor activity found that in the presence of sudden, surprising sounds, the muscles around the ear closest to the direction of the sound would respond by moving involuntarily, causing the pinna to be pulled backwards and flatten.

Clinical significance

If the posterior auricular muscle inserts into an unusual part of the auricle of the

, this can cause protruding ears. In one study, the muscle was found to be absent in 5% of people.

References