Nervi craniales
The 12 pairs of cranial nerves emerge directly from the brain and brainstem and are responsible for sensory, motor, and parasympathetic functions of the head and some viscera. In horses, several cranial nerves have unique clinical significance: the vagus nerve (CN X) gives rise to the recurrent laryngeal nerve critical for laryngeal function; CN VII (facial) is vulnerable to external trauma; and CN IX, X, XI, XII are at risk from guttural pouch disease; a condition unique to equids. The guttural pouches are diverticula of the auditory tubes that surround the internal carotid artery and major cranial nerves, making guttural pouch infections potentially life-threatening.
There are 12 pairs of cranial nerves. A systematic cranial nerve exam evaluates: CN I (olfaction), CN II (menace response, PLR), CN III/IV/VI (pupil, strabismus, eye movement), CN V (facial sensation, jaw tone), CN VII (facial symmetry, ear/eyelid/lip movement), CN VIII (vestibular function, hearing), CN IX/X (swallow, laryngeal function, guttural pouch), CN XI (trapezius/brachiocephalic), CN XII (tongue symmetry/tone). The guttural pouches are unique to equids and are clinically critical because CN IX, X, XI, XII, and the internal carotid artery traverse their walls.
Dysfunction of the facial nerve, commonly from halter pressure (at the facial crest), guttural pouch disease, temporohyoid osteoarthropathy, or EPM. The facial nerve is superficial where it crosses th
Fungal infection of the guttural pouch, potentially eroding into the internal carotid artery.
Dysfunction of the vestibulocochlear nerve causing balance disturbances. Peripheral (inner ear, nerve) causes include THO, otitis media/interna, and guttural pouch disease. Central causes include EPM
Inflammation of the trigeminal nerve, which may occur with polyneuritis equi or idiopathically. Causes denervation of the muscles of mastication.
Progressive proliferative osteoarthropathy of the temporohyoid joint that may cause fusion of the joint and fracture of the petrous temporal bone, damaging CN VII and CN VIII as they traverse the bone
Dysfunction of the facial nerve, commonly from halter pressure (at the facial crest), guttural pouch disease, temporohyoid osteoarthropathy, or EPM. The facial nerve is superficial where it crosses the mandible, making it vulnerable to external compression. Signs include: Lip droop on affected side; ear droop; inability to close eyelid (exposure keratitis risk); feed accumulation in cheek; muzzle deviation to unaffected side
Fungal infection of the guttural pouch, potentially eroding into the internal carotid artery. Signs include: Epistaxis (can be fatal); nasal discharge; difficulty swallowing; cranial nerve deficits
Dysfunction of the vestibulocochlear nerve causing balance disturbances. Peripheral (inner ear, nerve) causes include THO, otitis media/interna, and guttural pouch disease. Central causes include EPM and EHV-1. Signs include: Head tilt toward affected side; horizontal or rotary nystagmus; circling; ataxia with falling/leaning to affected side; strabismus (ventral deviation of ipsilateral eye)
Inflammation of the trigeminal nerve, which may occur with polyneuritis equi or idiopathically. Causes denervation of the muscles of mastication. Signs include: Bilateral masseter and temporalis atrophy ('sunken face'); inability to close mouth (dropped jaw); difficulty prehending and chewing feed; weight loss
Progressive proliferative osteoarthropathy of the temporohyoid joint that may cause fusion of the joint and fracture of the petrous temporal bone, damaging CN VII and CN VIII as they traverse the bone. Signs include: Consult veterinarian for specific symptoms.; Head shaking; difficulty eating; ear rubbing; acute onset vestibular signs (head tilt, nystagmus, circling); facial nerve paralysis; keratitis (corneal ulceration from inability to blink)
There are 12 pairs of cranial nerves. A systematic cranial nerve exam evaluates: CN I (olfaction), CN II (menace response, PLR), CN III/IV/VI (pupil, strabismus, eye movement), CN V (facial sensation, jaw tone), CN VII (facial symmetry, ear/eyelid/lip movement), CN VIII (vestibular function, hearing), CN IX/X (swallow, laryngeal function, guttural pouch), CN XI (trapezius/brachiocephalic), CN XII (tongue symmetry/tone). The guttural pouches are unique to equids and are clinically critical because CN IX, X, XI, XII, and the internal carotid artery traverse their walls.
See the Cranial Nerves on our interactive 3D horse model. Open 3D Model