DB - cranial nerves Flashcards
What is the name of each of the cranial nerves? What is the pneumonic to help remember them?
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Olfactory, optic, oculomotor, trochlear, trigeminal, abducen, facial, vestibulocochlear, glossopharyngeal, vagus, accessory and hypoglossal nerves.
What is the function of each cranial nerve? What is the pneumonic to help remember them?
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S - sensory
M- motor
B - both
Where do the afferent fibres of CNI run from?
Vomeronasal organ and olfactory mucosa
Where does CNI synpase?
Olfactory bulb
Olfactory tubercle, which projects to the piriform cortex
Limbic system
Hypothalamus and brainstem reticular formation
Where do the olfactory nerve fibres run?
Olfactory tract
How do you test the function of CNI?
Hide a treat and see if the dog can seek it out.
What is the function of CNII?
Visual pathway
Coordinating of eye movements
Pupillary constriction, which is consensual
Reflex response to a visual stimuli
What is the neuronal arrangement of CNII?
Neurone 1 - bipolar cell of the retina - special somatic efferent fibres.
Neurone 2 - retinal ganglion cell - forms the optic nerve.
Nerve tracts then unite at the optic chiasm, cross over occurs, and the fibres continue in optic tracts.
Neurone 3 - lateral geniculate nucleus of the thalamus - for conscious reception of light.
Projects to occipital cortex via internal capsule.
Which cranial nerve does not relay through the thalamus?
Olfactory nerve
What are the visual reflexes of CNII?
Reflex response to bright light.
Eye movement.
Head turning in response to stimuli.
Describe the menace test.
Causes eyelid closure.
Sensory - CNII
Motor - CNVII
Positive response - normal functioning eyes, intact visual pathway and cortex, intact facial nerve.
Describe the pupillary reflex test.
Some optic nerve fibres are relayed to the parasympathetic nucleus of CNIII, then to the ciliary ganglion.
Post-ganglionic fibres cause constriction in both eyes.
CNII - sensory
CNIII - motor
What tests are used to test CNII?
Menace test and pupillary reflex test
What muscles of the eye does CNIII innervate?
Dorsal rectus, medial rectus, ventral rectus and ventral oblique
What muscles of the eye does CNIV innervate?
innervates the dorsal oblique muscle
What muscles of the eye does CNVI innervate?
Lateral rectus and retractor bulbi muscles
How are CNIII, CNIV and CNVI tested?
Assessed by relating eye movements to the vestibulo-ocular reflexes.
Swiftly move the head in a horizontal/dorsal plane from side to side.
Eye movements should be fixed and this occurs even if blind.
Also, damage to these nerves, may cause abnormal eye position.
What is the slow phase of eye movement?
Eye movement can follow an object slowly
What is the fast phase of eye movement?
Eye movement has returned to its original position.
Where does CNV arise?
From the junction between the pons and the trapezoid body.
What are the branches of the CNV and what is their function?
1 - opthalmic branch - sensory
2 - maxillary branch - sensory
3 - mandibular branch - motor and sensory
How is each of the CNV branches tested?
1 - with the corneal and palpebral reflexes.
2 - with the palpebral and vibrissae reflexes.
3 - look for muscle asymmetry in the mandible.
Describe how to test the palpebral reflex.
CNV1, CNV2 and CNVII
Touch the medial canthus of the eye.
Blink should be complete.
Describe how to test the cornual reflex.
CNV1, CNVII
Cornea is lightly touched with a moist cotton tip applicator.
Eye should retract.
Describe how to test the vibrissae reflex.
CNV2 and CNVII
Touch the lip.
Patient may move the lip or turn it’s head away.
What is the origin of CNVIII?
Junction between the pons and the trapezoid body
What is the function of CNVIII and what are the different components?
Vestibular apparatus consists of 3 semicircular canals. Fluid running through the canals deform the hair cells depending on rotation and position of the head. This fires an AP to transduce balance to the brain.
The cochlear system contains hair cells and endolymph. Arriving sounds cause vibrations of the tympanic membrane, which is amplified across the ossicles. Hair cells are deformed by the movement of endolymph. This fires an AP to transduce the sound to the brain.
What are the symptoms of a dysfunctional CNVIII?
Head tilt/circling
Abnormal nystagmus
Vomiting
Incoordination
What are the inputs associated with the vestibular nuclei?
Cerebellar inputs for feedback control of movement.
Vestibular ganglion, which has receptors in semicircular canals and macula.
What are the outputs of the vestibular nuclei?
Thalamus -> cerebral cortex for conscious awareness of balance.
Medial longitudinal fasciculus -> control of extrinsic eye muscles.
Vestibulospinal tract -> reflex control of ipsilateral muscles.
Medullary reticular formation -> control of vomiting and responses to motion.
What is the neuronal pathway for perceiving an auditory stimulus?
Neurone 1: cochlear component of the vestibulocochlear nerve.
Neurone 2: cochlear nuclei
Lateral lemniscus
Neurone 3: caudal colliculi
Neurone 4: medial geniculate nucleus of the thalamus
Internal capsule
Auditory cortex
How is CNVIII tested?
Startle test - absent if the animal is bilaterally deaf. Presumes the tegmentum is intact.
How is CNIX and CNX tested?
Gag reflex - causes reflex contraction of pharyngeal muscles.
Sensory - glossopharyngeal
Motor - vagus
What are the sensory innervations of the CNIX?
Pharynx, tonsils, middle ear, rostral 1/3 of tongue, carotid bodies (chemoreceptors) and carotid sinus (baroreceptors)
What are the motor innervations of CNIX?
Stylopharyngeus muscle
What are the sensory innervations of CNX?
Somatic and visceral sensation via parasympathetic branches.
What are the motor innervations of CNX?
Pharyngeal and laryngeal muscles.
How is CNXI tested?
Assess muscle asymmetry of trapezius, sternomastoideus, cleidomastoideus, cleidocervalicus and omotransversarius
how is CNXII tested?
Assess the size and shape of the tongue. Touch the tongue and note the response.
