Changes

==Trochlear nerve (IV)==

==Trochlear nerve (IV)==

The trochlear nerve is part of the cranial nerve group responsible for innervation of the [[Skull and Facial Muscles - Anatomy & Physiology#Facial_Muscles|muscles of the head]]. The trochlear nerve originates from the dorsal midbrain and is a motor nerve. It is composed of '''general somatic efferent fibres''' and is the smallest of the cranial nerves.

The trochlear nerve is part of the cranial nerve group responsible for innervation of the [[Skull and Facial Muscles - Anatomy & Physiology#Facial_Muscles|muscles of the head]]. The trochlear nerve originates from the dorsal [[Equine Brain - Horse Anatomy#Midbrain|midbrain]] and is a motor nerve. It is composed of '''general somatic efferent fibres''' and is the smallest of the cranial nerves.

After leaving the dorsal midbrain, its axons decussate (cross) and then run in a rostral direction through the cavernous sinus before exiting the skill via the [[Skull and Facial Muscles - Anatomy & Physiology#Major Foramen and Canals|'''orbital fissure''']].  In the horse, it may also exit via a seperate trochlear foramen.  Finally, it runs to innervate the 'dorsal oblique muscle' muscle of the contralateral eye.

After leaving the dorsal midbrain, its axons decussate (cross) and then run in a rostral direction through the cavernous sinus before exiting the skill via the [[Skull and Facial Muscles - Anatomy & Physiology#Major Foramen and Canals|'''orbital fissure''']].  In the horse, it may also exit via a seperate trochlear foramen.  Finally, it runs to innervate the ''dorsal oblique'' muscle of the contralateral eye.

During a clinical examination, a dorso-lateral strabismus may indicate a problem with this nerve.

During a clinical examination, a dorso-lateral strabismus may indicate a problem with this nerve.

==Trigeminal nerve (V)==

==Trigeminal nerve (V)==

The trigeminal nerve is part of the cranial nerve group responsible for innervation of structures originating from branchial arches. The trigeminal nerve nuclei is in the area of the '''pons''' and '''medulla oblongata''' and is the nerve of the 1st branchial arch. The trigeminal nerve provides sensory innervation of cutaneous elements of the face, cornea, mucosa of the nasal septum and mucosa of the oral cavity.  It also provides motor fibres to structures also associated with the 1st branchial arch, which are the muscles of mastication (''temporalis'', ''masseter'', ''medial and lateral pterygoids'' and ''rostral digastricus''. There are three primary branches of the trigeminal nerve; the '''Opthalmic nerve (V1)''', the ''' Maxillary nerve (V2)''' and the '''Mandibular nerve (V3)'''.

The trigeminal nerve is part of the cranial nerve group responsible for innervation of structures originating from branchial arches. The trigeminal nerve nuclei is in the area of the '''[[Equine Brain - Horse Anatomy#Hindbrain|pons]]''' and '''[[Equine Brain - Horse Anatomy#Hindbrain|medulla oblongata]]''' and is the nerve of the 1st branchial arch. The trigeminal nerve provides sensory innervation of cutaneous elements of the face, cornea, mucosa of the nasal septum and mucosa of the oral cavity.  It also provides motor fibres to structures also associated with the 1st branchial arch, which are the muscles of mastication (''temporalis'', ''masseter'', ''medial and lateral pterygoids'' and ''rostral digastricus''. There are three primary branches of the trigeminal nerve; the '''Opthalmic nerve (V1)''', the ''' Maxillary nerve (V2)''' and the '''Mandibular nerve (V3)'''.

===Opthalmic nerve (V1)===

===Opthalmic nerve (V1)===

The opthalmic nerve is a sensory nerve composed of '''general somatic afferent fibres'''.  It passes along the cavernous sinus and exits via the [[Skull and Facial Muscles - Anatomy & Physiology#Major Foramen and Canals|'''orbital fissue''']]. As it enters the orbit of the eye, it splits further into the '''lacrimal nerve''', the '''frontal nerve''', the '''nasociliary nerve''' and the '''infratrochlear nerve'''.  

The opthalmic nerve is a sensory nerve composed of '''general somatic afferent fibres'''.  It passes along the cavernous sinus and exits via the [[Skull and Facial Muscles - Anatomy & Physiology#Major Foramen and Canals|'''orbital fissue''']]. As it enters the orbit of the eye, it splits further into the '''lacrimal nerve''', the '''frontal nerve''', the '''nasociliary nerve''' and the '''infratrochlear nerve'''.  

* The '''lacrimal nerve''' containes postganglionic parasympathetic fibres from the pterygopalatine ganglion that innervate the lacrimal gland. The lacrimal nerve also contains general somatic afferents that provide sensation to the lateral part of the upper eyelid.  

* The '''lacrimal nerve''' containes postganglionic parasympathetic fibres from the pterygopalatine ganglion that innervate the lacrimal gland. The lacrimal nerve also contains general somatic afferents that provide sensation to the lateral part of the upper eyelid.  

*In the horse, the '''frontal nerve''' exits the medial aspect of the orbit via the '''supraorbital foramen''', becoming the '''supraorbital nerve''', and innervates the upper eyelid and forehead.  

*In the horse, the '''frontal nerve''' exits the medial aspect of the orbit via the '''supraorbital foramen''', becoming the '''supraorbital nerve''', and innervates the upper eyelid and forehead.  

*The '''infratrochlear nerve''' innervates the medial aspects of the eyelids, third eyelid and frontal sinus.

*The '''infratrochlear nerve''' innervates the medial aspects of the eyelids, third eyelid and [[Equine Upper Respiratory Tract - Horse Anatomy#Paranasal Sinuses|frontal sinus]].

* '''Nasociliary nerves''', which carry parasympathetic fibres from the oculomotor nerve to the iris, also provide sensory innervation to the globe.

* '''Nasociliary nerves''', which carry parasympathetic fibres from the oculomotor nerve to the iris, also provide sensory innervation to the globe.

==Facial nerve (VII)==

==Facial nerve (VII)==

The facial nerve is part of the cranial nerve group responsible for the innervation of structures originating from the branchial arches. It originates from the '''medulla oblongata''' and from the second branchial arch. It has a common dura sheet with the opthalmic (V1) branch of the trigeminal nerve. The facial nerve is of a mixed composite, made up of a number of different fibre types. It has a '''general somatic efferent fibre''' within the ear canal, a '''general visceral efferent fibre''' acting under parasympathetic control to some salivary glands, lacrimal glands, nasal cavity and palate, a '''special visceral afferent fibre''' providing taste to the rostral 2/3 of the tongue and finally it has a '''general somatic efferent fibre''' supplying motor function to the muscles of facial expression and ''caudal digastricus''.

The facial nerve is part of the cranial nerve group responsible for the innervation of structures originating from the branchial arches. It originates from the [[Equine Brain - Horse Anatomy#Hindbrain|medulla oblongata]] and from the second branchial arch. It has a common dura sheet with the opthalmic (V1) branch of the trigeminal nerve. The facial nerve is of a mixed composite, made up of a number of different fibre types. It has a '''general somatic efferent fibre''' within the ear canal, a '''general visceral efferent fibre''' acting under parasympathetic control to some salivary glands, lacrimal glands, nasal cavity and palate, a '''special visceral afferent fibre''' providing taste to the rostral 2/3 of the tongue and finally it has a '''general somatic efferent fibre''' supplying motor function to the muscles of facial expression and ''caudal digastricus''.

The facial nerve enters the petrosal bone via the [[Skull and Facial Muscles - Anatomy & Physiology#Temporal Bone (os_temporale)|'''internal acoustic meatus''']] along with the vestibulocochlear nerve. The facial nerve also runs inside the '''facial canal'''. There are a number of intermediate branches which separate from the main facial nerve inside the facial canal including the '''greater petrosal nerve''', '''stapedial nerve''' (motor) and the '''chorda tympani'''. These then emerge via the [[Skull and Facial Muscles - Anatomy & Physiology#Major Foramen and Canals|'''stylomastoid foramen''']] at the caudoventral aspect of the skull. The chorda tympani of the facial nerve represents the '''special visceral afferent fibre''' supplying taste to the rostral 2/3 of the tongue.

The facial nerve enters the petrosal bone via the [[Skull and Facial Muscles - Anatomy & Physiology#Temporal Bone (os_temporale)|'''internal acoustic meatus''']] along with the vestibulocochlear nerve. The facial nerve also runs inside the '''facial canal'''. There are a number of intermediate branches which separate from the main facial nerve inside the facial canal including the '''greater petrosal nerve''', '''stapedial nerve''' (motor) and the '''chorda tympani'''. These then emerge via the [[Skull and Facial Muscles - Anatomy & Physiology#Major Foramen and Canals|'''stylomastoid foramen''']] at the caudoventral aspect of the skull. The chorda tympani of the facial nerve represents the '''special visceral afferent fibre''' supplying taste to the rostral 2/3 of the tongue.

==Accessory nerve (XI)==

==Accessory nerve (XI)==

The accessory nerve is part of the group of cranial nerves responsible for innervation of structures derived from the branchial arches. It is also part of a group, together with the glossopharyngeal and vagus, nerves that passes through the '''jugular foramen''' which is termed the '''vagus group'''. The accessory nerve supplies structures related to the fourth branchial arch. The accessory nerve has cell bodies that are referred to as '''nucleus ambiguus''' and originate in the '''medulla oblongata'''. The cranial root of the accessory nerve actually contributes to the vagus nerve and to the striated muscles of the pharynx, larynx, palate and oesophagus.

The accessory nerve is part of the group of cranial nerves responsible for innervation of structures derived from the branchial arches. It is also part of a group, together with the glossopharyngeal and vagus, nerves that passes through the '''jugular foramen''' which is termed the '''vagus group'''. The accessory nerve supplies structures related to the fourth branchial arch. The accessory nerve has cell bodies that are referred to as '''nucleus ambiguus''' and originate in the '''medulla oblongata'''. The cranial root of the accessory nerve actually contributes to the vagus nerve and to the striated muscles of the pharynx, [[Equine Upper Respiratory Tract - Horse Anatomy#Larynx|larynx]], [[Alimentary System - Horse Anatomy#Palate|palate]] and [[Alimentary System - Horse Anatomy#Oesophagus|oesophagus]].

   

   

However, the accessory nerve also contributes to the cervical spinal cord and spinal root through the '''foramen magnum'''; providing innervation to muscles of the neck. The spinal root of the accessory nerve branches into the '''dorsal branch''' and the '''ventral branch'''. The dorsal branch innervates the ''brachiocephalicus'', ''trapezius'' and ''omotransversarius'' muscles of the dorsal neck. The ventral branch innervates the ''sternocephalicus'' muscle.

However, the accessory nerve also contributes to the cervical [[Equine Spinal Cord - Horse Anatomy|spinal cord]] and spinal root through the '''foramen magnum'''; providing innervation to muscles of the neck. The spinal root of the accessory nerve branches into the '''dorsal branch''' and the '''ventral branch'''. The dorsal branch innervates the ''brachiocephalicus'', ''trapezius'' and ''omotransversarius'' muscles of the dorsal neck. The ventral branch innervates the ''sternocephalicus'' muscle.

During clinical examination any difficulties in turning the neck or muscle atrophy around the dorsal and ventral neck may indicate a problem with the accessory nerve.

During clinical examination any difficulties in turning the neck or muscle atrophy around the dorsal and ventral neck may indicate a problem with the accessory nerve.

==Hypoglossal nerve (XII)==

==Hypoglossal nerve (XII)==

The hypoglossal nerve is part of the group of cranial nerves responsible for the control of muscles of the head. It is in part a cervical nerve due to its caudal position on the [[Hindbrain - Anatomy & Physiology|brain stem]]. The nerve is composed of '''general somatic efferent fibres''' which control the intrinsic and extrinsic muscles of the tongue (together with other nerves including the lingual nerve, facial nerve, lingual branch of the glossopharyngeal nerve and the vagus nerve). The nucleus of the nerve is located within the ''medulla oblongata'' of the brain stem and it passes through the '''hypoglossal canal'''.

The hypoglossal nerve is part of the group of cranial nerves responsible for the control of muscles of the head. It is in part a cervical nerve due to its caudal position on the [[Equine Brain - Horse Anatomy#Hindbrain|brainstem]]. The nerve is composed of '''general somatic efferent fibres''' which control the intrinsic and extrinsic muscles of the tongue (together with other nerves including the lingual nerve, facial nerve, lingual branch of the glossopharyngeal nerve and the vagus nerve). The nucleus of the nerve is located within the ''medulla oblongata'' of the [[Equine Brain - Horse Anatomy#Hindbrain|brainstem]] and it passes through the '''hypoglossal canal'''.

During a clinical examination any deviation of the tongue may indicate a problem with this nerve. Deviation of the tongue is always to the side of the lesion initially.

During a clinical examination any deviation of the tongue may indicate a problem with this nerve. Deviation of the tongue is always to the side of the lesion initially.