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Category:Cranial Nerve Examination - Horse (view source)
Revision as of 16:05, 9 March 2011
, 16:05, 9 March 2011Created page with "* The cranial nerves are numbered 1-12 from the most rostral to the most caudal. * A systematic examination of the cranial nerves can aid accurate identification of the site of ..."
* The cranial nerves are numbered 1-12 from the most rostral to the most caudal.
* A systematic examination of the cranial nerves can aid accurate identification of the site of a lesion.
===Cranial Nerve I===
* Cranial nerve I is the olfactory nerve.
** Abnormalities are rarely detected in this nerve.
===[[Neurological Eye Examination - Horse]]===
===[[Face Sensation]]===
* 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]]
===[[Vestibular System Examination]]===
====The Vestibulocochlear Nerve====
* Cranial nerve VIII is the vestibulocochlear nerve.
* The vestibulocochlear nerve carries
** Auditory, or cochlear, signals.
** Balance, or vestibular, signals.
* Signals from CN VIII are relayed to the vestibular nuclei in the brainstem.
** The nuclei in turn relay information to
*** The eyes
*** The body and limbs
*** Higher centres.
* Many efferent signals are controlled in part by cerebellar input.
====Unilateral Vestibular Disease====
* Horses with unilateral vestibular lesions often have a head tilt towards the side of the lesion.
* If nystagmus is absent, determining whether a horse with a head tilt is also weak is helpful in deciding whether vestibular disease is central or peripheral.
** In peripheral diease, the horse may be ataxic but weakness is not normally seen.
=====Acute=====
* In the acute stages of vestibular disease, spontaneous nystagmus may be present.
** The appearance of nystagmus is different depending on the type of vestibular disease present.
*** Central vestibular disease
**** Nystagmus often is variable; i.e. rotary, horizontal and vertical.
*** Peripheral vestibular disease
**** The fast phase of the nystagmus is away from the side of the lesion.
=====Chronic=====
* Nystagmus may resolve in more chronic lesions.
** However, it may return with changes in head position.
*** I.e. positional nystagmus.
* Visual accomodation improves ataxic movements.
** However, these may return dramatically on blindfolding.
====Bilateral Vestibular Disease====
* An observable head tilt may not be present.
* Movements are likely to be markedly ataxic.
** This is probably due in part to involvement of ascending proprioceptive and descending motor pathways that run through the brainstem.
[[Category:Cranial Nerve Examination - Horse]]
===[[Pharyngeal and Laryngeal Function]]===
* The pharynx and larynx are innervated by:
** CN IX - the glossopharyngeal nerve
** CN X - the vagus nerve
** CN XI - the accessory nerve
* Pharyngeal and laryngeal function is best studied by:
*# Observing the horse eat and swallow
*# Endoscopy
====Laryngeal Dysfunction====
* Left recurrent laryngeal hemiplegia is the most common dysfunction in horses.
** The left recurrent laryngeal nerve is a branch of the vagus nerve.
** Horses are known as "roarers".
====Pharyngeal Dysfunction====
* Pharyngeal paralysis in horses is commonly associated with peripheral disease.
** Especially guttural pouch disease.
*** Endoscopy of the guttural pouches should be therefore be performed in horses that are dysphagic.
[[Category:Cranial Nerve Examination - Horse]]
===[[Tongue Movement]] ===
* The hypoglossal nerve, CN XII provides motor innervation to the [[Tongue - Anatomy & Physiology|tongue]].
* Normally, a horse resists the [[Tongue - Anatomy & Physiology|tongue]] being retracted from the mouth.
** The horse will quickly return the tongue after it is pulled out to the side.
* Horses with hypoglossal weakness appear differently.
** The [[Tongue - Anatomy & Physiology|tongue]] may protrude from the mouth.
** Chronic unilateral hypoglossal lesions may result in unilateral tongue atrophy.
** Bilateral hypoglossal lesions may result in difficulty prehending food.
* Horses with cerebral dysfunction may have signs corresponding to tongue weakness.
** However, [[Tongue - Anatomy & Physiology|tongue]] atrophy is not present in these animals.
[[Category:Cranial Nerve Examination - Horse]]
[[Category:Neurological Examination - Horse|C]]
* A systematic examination of the cranial nerves can aid accurate identification of the site of a lesion.
===Cranial Nerve I===
* Cranial nerve I is the olfactory nerve.
** Abnormalities are rarely detected in this nerve.
===[[Neurological Eye Examination - Horse]]===
===[[Face Sensation]]===
* 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]]
===[[Vestibular System Examination]]===
====The Vestibulocochlear Nerve====
* Cranial nerve VIII is the vestibulocochlear nerve.
* The vestibulocochlear nerve carries
** Auditory, or cochlear, signals.
** Balance, or vestibular, signals.
* Signals from CN VIII are relayed to the vestibular nuclei in the brainstem.
** The nuclei in turn relay information to
*** The eyes
*** The body and limbs
*** Higher centres.
* Many efferent signals are controlled in part by cerebellar input.
====Unilateral Vestibular Disease====
* Horses with unilateral vestibular lesions often have a head tilt towards the side of the lesion.
* If nystagmus is absent, determining whether a horse with a head tilt is also weak is helpful in deciding whether vestibular disease is central or peripheral.
** In peripheral diease, the horse may be ataxic but weakness is not normally seen.
=====Acute=====
* In the acute stages of vestibular disease, spontaneous nystagmus may be present.
** The appearance of nystagmus is different depending on the type of vestibular disease present.
*** Central vestibular disease
**** Nystagmus often is variable; i.e. rotary, horizontal and vertical.
*** Peripheral vestibular disease
**** The fast phase of the nystagmus is away from the side of the lesion.
=====Chronic=====
* Nystagmus may resolve in more chronic lesions.
** However, it may return with changes in head position.
*** I.e. positional nystagmus.
* Visual accomodation improves ataxic movements.
** However, these may return dramatically on blindfolding.
====Bilateral Vestibular Disease====
* An observable head tilt may not be present.
* Movements are likely to be markedly ataxic.
** This is probably due in part to involvement of ascending proprioceptive and descending motor pathways that run through the brainstem.
[[Category:Cranial Nerve Examination - Horse]]
===[[Pharyngeal and Laryngeal Function]]===
* The pharynx and larynx are innervated by:
** CN IX - the glossopharyngeal nerve
** CN X - the vagus nerve
** CN XI - the accessory nerve
* Pharyngeal and laryngeal function is best studied by:
*# Observing the horse eat and swallow
*# Endoscopy
====Laryngeal Dysfunction====
* Left recurrent laryngeal hemiplegia is the most common dysfunction in horses.
** The left recurrent laryngeal nerve is a branch of the vagus nerve.
** Horses are known as "roarers".
====Pharyngeal Dysfunction====
* Pharyngeal paralysis in horses is commonly associated with peripheral disease.
** Especially guttural pouch disease.
*** Endoscopy of the guttural pouches should be therefore be performed in horses that are dysphagic.
[[Category:Cranial Nerve Examination - Horse]]
===[[Tongue Movement]] ===
* The hypoglossal nerve, CN XII provides motor innervation to the [[Tongue - Anatomy & Physiology|tongue]].
* Normally, a horse resists the [[Tongue - Anatomy & Physiology|tongue]] being retracted from the mouth.
** The horse will quickly return the tongue after it is pulled out to the side.
* Horses with hypoglossal weakness appear differently.
** The [[Tongue - Anatomy & Physiology|tongue]] may protrude from the mouth.
** Chronic unilateral hypoglossal lesions may result in unilateral tongue atrophy.
** Bilateral hypoglossal lesions may result in difficulty prehending food.
* Horses with cerebral dysfunction may have signs corresponding to tongue weakness.
** However, [[Tongue - Anatomy & Physiology|tongue]] atrophy is not present in these animals.
[[Category:Cranial Nerve Examination - Horse]]
[[Category:Neurological Examination - Horse|C]]