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Created page with "* Nerve fibres giving sensation to the face are carried in cranial nerve V - the trigeminal nerve. ** The trigeminal nerve provides sensory innervation to: *** The skin of the fa..."
* Nerve fibres giving sensation to the face are carried in cranial nerve V - the trigeminal nerve.
** The trigeminal nerve provides sensory innervation to:
*** The skin of the face
*** The ears
*** The nasal mucosa
*** The cornea
** There are three divisions of the trigeminal nerve
*** The mandibular branch
*** The maxillary branch
*** The opthalmic branch
* Facial sensation is tested by observation for an avoidance response or reflex movement following stimulation.
** All the divisions of the trigeminal nerve should be tested. This is achieved by:
*** Stimulation within the nostrils
*** Stimulation within the ears
*** Stimulation between the mandibles
*** Testing the corneal reflex.
***# Pressure is exerted on the corneal surface through the eyelid.
***# The opthalmic branch of the trigeminal nerve provides sensory (afferent) input.
***# Efferent signals are sent via the abducens nerve (CN VI)
***# The retractor oculi muscle retracts the eye
====Masticatory muscles====
* The mandibular branch of the trigeminal nerve carries motor fibres.
** It is the only division of the trigeminal nerve that does so.
* The muscles of mastication are innervated by these fibres.
** The masseter and temporalis muscles are particulaly influenced by the mandibular brach of the trigeminal nerve.
*** These muscles of mastication are also the easiest to assess.
*** These muscles should be closely examined for signs of atrophy.
**** '''Atrophy of the temporalis and masseter muscle indicates damage to the mandibular branch of CN V.'''
====Facial Expression====
* The muscles of facial expression are innervated by branches of cranial nerve VII - the facial nerve.
* The facial nerve also carries the parasympathetic supply to the lacrimal glands.
** Horses with facial nerve dysfunction are therefore prone to corneal ulceration, due to :
*** An inability to blink
*** Poor or absent tear production
=====Facial Nerve Dysfunction=====
* Facial nerve dysfunction is common in the horse.
* It is readily identified by one or more of the following:
** A lip droop
** Muzzle deviation
*** Deviation is towards the normal side.
** An ear droop
* Early or mild dysfunction may be reflected by:
** Slight changes to nostril size
** Nostril flare
** Reduced ear movements in response to audible stimuli
* The branch of CN VII supplying the muzzle and nostrils crosses the vertical mandibular ramus and the surface of the masseter muscle.
** A lesion to that side of the face, for example a kick, may cause signs confined to the nose.
** Alternatively, a more central lesion will give both ear and nostril signs.
=====The Palpebral Reflex=====
* The palpebral reflex examines the function of both CN V (afferent) and CN VII (efferent).
* The reflex is elicited by lightly touching the eyelids and watching for reflex closure.
[[Category:Cranial Nerve Examination - Horse]]
** The trigeminal nerve provides sensory innervation to:
*** The skin of the face
*** The ears
*** The nasal mucosa
*** The cornea
** There are three divisions of the trigeminal nerve
*** The mandibular branch
*** The maxillary branch
*** The opthalmic branch
* Facial sensation is tested by observation for an avoidance response or reflex movement following stimulation.
** All the divisions of the trigeminal nerve should be tested. This is achieved by:
*** Stimulation within the nostrils
*** Stimulation within the ears
*** Stimulation between the mandibles
*** Testing the corneal reflex.
***# Pressure is exerted on the corneal surface through the eyelid.
***# The opthalmic branch of the trigeminal nerve provides sensory (afferent) input.
***# Efferent signals are sent via the abducens nerve (CN VI)
***# The retractor oculi muscle retracts the eye
====Masticatory muscles====
* The mandibular branch of the trigeminal nerve carries motor fibres.
** It is the only division of the trigeminal nerve that does so.
* The muscles of mastication are innervated by these fibres.
** The masseter and temporalis muscles are particulaly influenced by the mandibular brach of the trigeminal nerve.
*** These muscles of mastication are also the easiest to assess.
*** These muscles should be closely examined for signs of atrophy.
**** '''Atrophy of the temporalis and masseter muscle indicates damage to the mandibular branch of CN V.'''
====Facial Expression====
* The muscles of facial expression are innervated by branches of cranial nerve VII - the facial nerve.
* The facial nerve also carries the parasympathetic supply to the lacrimal glands.
** Horses with facial nerve dysfunction are therefore prone to corneal ulceration, due to :
*** An inability to blink
*** Poor or absent tear production
=====Facial Nerve Dysfunction=====
* Facial nerve dysfunction is common in the horse.
* It is readily identified by one or more of the following:
** A lip droop
** Muzzle deviation
*** Deviation is towards the normal side.
** An ear droop
* Early or mild dysfunction may be reflected by:
** Slight changes to nostril size
** Nostril flare
** Reduced ear movements in response to audible stimuli
* The branch of CN VII supplying the muzzle and nostrils crosses the vertical mandibular ramus and the surface of the masseter muscle.
** A lesion to that side of the face, for example a kick, may cause signs confined to the nose.
** Alternatively, a more central lesion will give both ear and nostril signs.
=====The Palpebral Reflex=====
* The palpebral reflex examines the function of both CN V (afferent) and CN VII (efferent).
* The reflex is elicited by lightly touching the eyelids and watching for reflex closure.
[[Category:Cranial Nerve Examination - Horse]]