Lecture 5 - Cranial Nerves Flashcards
How do Cranial Nerves compare to other peripheral nerves? What is similar about their structure, and what is unique?
- most CN target structures are located ipsilaterally (some have contralateral structures)
- motor branches are multipolar
- somatosensory branches are psuedounipolar
- most special sensory are bipolar
What are the major components of a peripheral nerve?
- epineurium (outermost) - contains blood vessels
- Perineurium (middle) - bind groupings of axons into fascicles
- Endoneurium (connective tissue) - surrounds nerve fiber
What is the function of the olfactory nerve?
smell
What can be found in the olfactory epithelium, and what are their functions?
- olfactory sensory receptor cells (hair cells) - help dissolve odor
- supporting cells - nourish, insulate, detoxify olfactory cells
- basal stem cells - regulate new olfactory receptor cells
- olfactory glands - create mucous that covers surface of epithelium
What transfers smells into electrical signals?
olfactory epithelium - sensory organ of nose
Describe the olfactory pathway, including neuroanatomical structures involved and areas of synapse between first, second, and third order neurons.
1st - Olfactory Nerve
- odor enters and dissolved in surface mucus, then odor molecules bind to ligand-gated chemoreceptors on CN 1 in neuroepithelium, then synapse with 2nd order neuron, CN 1 goes through cribiform plate in ethmoid bone and synapses w/ olfactory bulb
2nd - Olfactory Bulb
- travels rostrally to synapse w/ olfactory tract
3rd - Olfactory tract
- projects to ipsilateral and contralateral limbic structures
What is the function of the optic nerve?
- vision
- carries information about visual input from retina to brain
What are accessory structures of the eye?
- eye lid
- eyebrow
- eye lashes
- muscles
- lacrimal apparatus
What are structures of the eye?
- fibrous outer layer (avascular)
- vascular middle layer
- retinal layer
- lens
- vitreous humor
- anterior cavity
What are the major structures found in fibrous outer layer of eye? What do they do?
Sclera - attaches eye w/ eyelid, dural sheath of CN 2, and tendons of extra-ocular muscles
Cornea - outermost lens of eye - controls and focuses incoming light
What is the function of the vascular middle layer? What are its major components and their function?
- provide vascularization and suspend lens
- Choroid - contains blood vessels
- Ciliary body - contains ciliary processes which contain capillaries and attach to ligaments that help suspend lens, and ciliary muscle
- Iris - contains smooth muscle fibers that act on pupil
What are they layers of the retinal inner layer of eye?
7 layer dip 1) pigment epithelium 2) photoreceptor layer (rods and cons) 3/4) outer and inner nuclear layers 5/6) outer and inner synaptic layers 7) ganglion cell layer
Where are rods and cones found? What are their functions?
- photoreceptor layer
Rods - dim light vision, no color, low acuity
Cones - bright light, color, high acuity
What is found in the ganglion cell layer of retinal inner layer?
ganglia (cluster of gray mater) - cell bodies of optic nerve
What is the optic disc? Can you see via the optic disc?
- site where optic nerve and blood vessels enter/exit the eye
- No, blind spot
Where is the highest visual resolution in the eye found? Is it made up of rods or cones?
- macula lutea that contains central fovea (cones only)
What is the function of the lens?
- bend light to focus image on retina
What is the function of vitreous humor? Where is it found? What does it contain?
- between lens and retina
- holds retina in place
- contains phagocytes to remove debris
What is the function of anterior cavity? Where is it found? What does it contain?
- between cornea and lens
- contains aqueous humor that filters blood plasma that nourishes lens and cornea
Describe the optic pathway, including neuroanatomical structures involved and the areas of synapse between first, second, and third order neurons.
1st order - retinal cells
- photoreceptor cells send impulses to retinal cell layers where signal is processed, impulses gather at optic disc, AP propagated through CN 2
2nd order - Optic Nerve
- Optic nerve travels through optic canal and converges w/ contralateral optic nerve at optic chiasm, nerve exits optic chiasm via optic tract and goes to thalamus (lateral geniculate nuclei) or midbrain (superior colliculus and pretectal nuclei), synapse w/ 3rd order neuron
3rd order - Optic radiations
- thalamus projects to primary visual cortex of contralateral side in occipital lobe via optic radiations
What fibers cross contralaterally at optic chiasm? Ipsilaterally?
contralaterally - nasal visual fibers
ipsilaterally - temporal visual fibers
What part of the visual field does the right vs left primary visual cortices process?
contralateral side
right visual field - left primary visual cortex
left visual field - right primary visual cortex
What are the functions of the oculomotor, trochlear, and abducens nerve?
motor efferents to 6 sets of extraocular muscles
- move the eye
What specific muscles and associated eye movements are innervated by the oculomotor nerve?
- medial rectus - adduction
- superior rectus - elevation and intorsion
- interior rectus - depression and extorsion
- inferior oblique - extorsion and elevation
What specific muscles and associated eye movements are innervated by the trochlear nerve?
superior oblique - intorsion and depression
What specific muscles and associated eye movements are innervated by the abducens nerve?
lateral rectus - abduction
Describe the oculomotor pathway, including how it exits the skull, neuroanatomical structures involved and the areas of synapse between first and second order neurons.
1st order neuron - oculomotor nerve travels from nuclei in midbrain, exits skull via superior orbital fissure and splits into superior and inferior divisions, then synapses in ciliary ganglion
2nd order - ciliary ganglion neurons project to muscles for accommodation and muscles for pupil constriction
What is the function of the Pupillary Response to Light reflex? What Cranial Nerves are involved? Describe the path taken during this loop.
- quick way to evaluate the integrity of parasympathetic relationship to visual and ocular motor input and output
- CN 2 & 3
- light enters pupil activating retinal ganglion cells (1st order), synapse with optic nerve (2nd order), temporal stay ipsilateral and nasal projections go contralateral, (skip lateral geniculate nucleus of thalamus) go to bilateral pre-tectal area of midbrain which neighbors Edinger-Westphal nuclei (parasympathetic) which projects ipsilaterally via CN 3 to ciliary ganglia which constricts pupils - both eyes constrict b/c of bilateral synapses
What is the function of visual accommodation? What cranial nerves are involved?
- maintain visual accuracy when visual object moves from far to near
- CN 2 & 3
What 3 things must happen during visual accommodation response?
1) pupillary constriction
2) accommodation of lens ciliary muscle
3) convergence of eyes by extraocular muscles
Describe the pathway of visual accommodation?
- go through entire optic pathway (end at occipital primary visual cortex)
- primary visual cortex needs help so it sends signal to visual association center
- association center projects down to midbrain (superior colliculus and pre-tectal area)
- midbrain sends signal to oculomotor nucleus and EW nucleus
- oculomotor and EW nucleus project to extraocular muscles, lens sphincter, and ciliary ganglion
Describe the trochlear pathway, including how it exits the skull and neuroanatomical structures involved.
- trochlear nucleus project contralaterally
- travels through superior orbital fissure to superior oblique muscles
Describe the abducens pathway, including how it exits the skull and the neuroanatomical structures involved.
- abducens nucleus exits dura via Dorello’s canal
- travels rostrally to exit via superior orbital fissure to lateral rectus muscle (abducts eye)
What is the function of the trigeminal nerve?
- sensation of face, mouth, anterior 2/3 of tongue, nasal sinuses and meninges
- motor for muscles of mastication and tensor tympani muscle of inner ear
What are the three sensory divisions of the trigeminal nerve, and where do they innervate?
V1 - Ophthalmic Division - forehead/scalp, upper eyelid, cornea, nose
V2 - Maxillary Division - Lower eyelid, cheeks, temples, upper lip region, upper teeth
V3 - Mandibular Division - part of external ear, lower lip, chin, anterior 2/3 of tongue, lower teeth
Where does Ophthalmic division (V1) enter the skull?
superior orbital fissure
Where does Maxillary division (V2) enter the skull
foramen rotundum
Where does Mandibular division (V3) enter the skull?
foramen ovale
Once V1, V2, V3 enter skull, what do they form? What type of neurons are they?
- form trigeminal ganglion (cluster of gray matter) that forms trigeminal nerve
- psuedo-unipolar neurons so there is no synapsing
Describe the trigeminal sensory pathway, differentiating between the major divisions of the nerve, how it enters back into the skull, neuroanatomical structures involved and the areas of synapse between first, second, and third order neurons
1st order
- V1, V2, V3 enter skull and form trigeminal ganglion that forms trigeminal nerve
- nerve travels caudally to trigeminal nuclear complex in brainstem
2nd order
- brainstem neurons project to ventral posteromedial (VPM) of thalamus
3rd order
- thalamus sends info to inferolateral postcentral gyrus
Describe the trigeminal motor pathway, including how it exits the skull, neuroanatomical structures involved and the area of synapse between first and second order neurons.
1st order
- upper motor neurons in precentral gyrus go down corticobulbar tract and split on motor nuclei
2nd order
- Mandibular division (V3) travels to muscles of mastication and tensor tympani
What are the 4 major nuclei of trigeminal nerve?
- motor trigeminal nuclei
- principle sensory trigeminal nuclei
- mesencephalic trigeminal nuclei
- spinal trigeminal nuclei
What information is sent through motor trigeminal nuclei?
efferent singles to muscles of mastication (masseter, temporalis, medial and lateral ptyergoid)
What information is sent through principle sensory trigeminal nuclei?
afferent discriminate touch, light touch, proprioception to face, and dental pressure
What information is sent through mesencephalic trigeminal nuclei?
afferent proprioception to jaw
What information is sent through spinal trigeminal nuclei?
afferent crude touch, pain, temperature of face
- somatotopically organized
What is the function of the facial nerve?
- somatomotor input to muscles of facial expression
- parasympathetic to lacrimal and salivary glands
- taste from anterior 2/3 of tongue
- somatosensory from external ear
What are the 5 major somatomotor branches of the facial nerve?
- temporal
- zygomatic
- buccal
- mandibular
- cervical
Which branch of the facial nerve receives bilateral integration?
- temporal
- bilateral integration goes to upper face (forehead)
Describe the facial motor pathway, including how it exits the skull, neuroanatomical structures involved and the area of synapse between first and second order neurons
1st order
- corticobulbar tract (UMN of precentral gyrus) projects bilaterally to upper face and contralaterally to lower face
2nd order
- UMN synapses w/ facial nerve
- facial nerve exits skull through stylomastoid foramen and innervates 5 major branches
Describe the facial autonomic pathway, including how it exits the skull, neuroanatomical structures involved and the area of synapse between first and second order neurons.
1st order
- facial nerve projects to lacrimal and salivary projections
2nd order Lacrimal
- lacrimal projections exit skull through pterygoid canal and form pterygopalatine ganglion
- neurons project to lacrimal gland
2nd order Salivary
- salivary projections exit skill through petrotympanic fissure and form submandibular ganglion
- neurons project to salivary glands
What is the function of the corneal reflex? What cranial nerves are involved?
- protective reflex to protect eye from debris and damage
- CN 5 and 7
Describe the pathway of the corneal reflex
- gentle sway to cornea
- ophthalmic division of trigeminal nerve
- sends signal to spinal trigeminal nucleus
- sends bilateral signal to facial nuclei
- facial nerve sends efferent signal to muscles of eye causing Bilateral eye blink
What is the function of the vestibulocochlear nerve?
hearing and vestibular sensation
Describe the Dorsal auditory pathway, including how it enters into the skull, neuroanatomical structures involved and the areas of synapse between first, second, third, fourth and fifth neurons when applicable.
1st order
- cochlear division of CN 8 enters skull via internal auditory meatus
- ventral and dorsal cochlear nuclei decussate at trapezoid body in pontine tegmentum
2nd order
- neurons ascend contralaterally via lateral lemniscus to inferior colliculus of caudal tectum in midbrain
3rd Order
- Neurons project to medial geniculate nuclei of thalamus
4th Order
- neurons project to primary auditory cortex of temporal lobe
Describe the Ventral auditory pathway, including how it enters into the skull, neuroanatomical structures involved and the areas of synapse between first, second, third, fourth and fifth neurons when applicable.
1st order
- cochlear division of CN 8 enters skull via internal auditory meatus
- ventral and dorsal cochlear nuclei decussate at trapezoid body in pontine tegmentum
2nd Order
- neurons ascend bilaterally to superior olivary nuclei
3rd Order
- neurons project to inferior colliculi via lateral lemniscus
4th Order
- neurons project to medial geniculate nuclei of thalamus
5th Order
- neurons project to primary auditory cortex of temporal lobe
What is the function of the glossopharyngeal nerve?
- somatomotor to stylopharyngeus muscle (pharynx elevation during talking and swallowing, gag reflex)
- somatosensory and taste to posterior 1/3 of tongue
- viscerosensory from carotid sinus and carotid body
Describe the glossopharyngeal motor pathway, including how it exits the skull, neuroanatomical structures involved and the area of synapse between first and second order neurons.
1st Order
- precentral gyrus
- corticobulbar tract to nucleus ambiguous of medulla
- decussates prior to 2nd synapse
2nd Order
- neuron exits skull via jugular foramen
- travels rostrally to stylopharyngeus
Describe the glossopharyngeal sensory pathway, including how it enters the skull, neuroanatomical structures involved and the areas of synapse between first , second and third order neurons.
1st Order
- Lingual branch (tongue) sends afferent fibers from receptors in tongue via spinal trigeminal tract
2nd Order
- neuron projects to ventral posteromedial (VPM) of thalamus
3rd Order
- neuron projects to lateral postcentral gyrus
Describe the glossopharyngeal viscerosensory pathway, including how it exits the skull and neuroanatomical structures involved.
1st Order
- pharyngeal branch receptors send afferent input from chemo- and baroreceptors from carotid body and sinus through jugular foramen to solitary nuclei of medulla
What is the function of the vagus nerve?
- somatomotor to pharyngeal muscles (swallowing) and laryngeal muscles (voice box)
- parasympathetics to heart, lungs, and digestive tract
- Viscerosensory from aortic arch
Describe the vagus motor pathway, including how it exits the skull, neuroanatomical structures involved and the area of synapse between first and second order neurons.
1st Order
- precentral gyrus
- corticobulbar tracts to nucleus ambiguous of rostral medulla
- decussate
2nd Order
- vagus nerve exits skull through jugular foramen to innervate muscles of pharynx, larynx, and palatoglossus
Describe the vagus autonomic pathway, including how it exits the skull and neuroanatomical structures involved.
1st order
- dorsal motor nucleus of CN X projects via superior and inferior vagal ganglia through jugular foramen
- walls of organs in neck, thorax, and abdominal regions
Describe the vagus visceral pathway, including how it exits the skull and neuroanatomical structures involved.
1st order
- solitary nucleus of medulla projects via superior and inferior vagal ganglia through jugular foramen
- aortic arch for reflexive cardiovascular control
What is the function of the gag reflex? What cranial nerves are involved? Describe the pathway taken by this loop.
- reflex to prevent the aspiration of solid food particles
- CN IX and X
- pressure on posterior structures of mouth
1st order
- CN IX excitatory afferent signal to medulla
2nd Order
- synapse w/ nucleus ambiguous (CN X)
- bilateral efferent projections via CN X to pharyngeal muscles
- gag response
What is the function of the spinal accessory nerve?
- somatomotor to SCM and upper trapezius muscle
Describe the spinal accessory pathway, including how it re-enters and then exits the skull, neuroanatomical structures involved, and the area of synapse between the first and second order neurons.
1st Order
- precentral gyrus
- corticospinal tract tp ventral horns of C1-6
- to spinal accessory nucleus in medulla
- decussate in medullary pyramids
2nd Order
- Spinal accessory nerve ascends into skull through foramen magnum and exits via jugular foramen
- innervate SCM and upper trapezius
Describe the hypoglossal pathway, including how it exits the skull, neuroanatomical structures involved, and the area of synapse between the first and second order neurons.
1st Order
- precentral gyrus
- corticobulbar tract to hypoglossal nuclei in medulla
- decussate
2nd Order
- Hypoglossal nerve travels through hypoglossal foramen
- innervates all intrinsic and extrinsic muscles of the tongue
