V665 Cranial Nerves

What is the difference in the beginning of firing for cells with low thresholds versus high thresholds?

-Cells with *low thresholds* begin firing when the cell is in the off field of the muscle. -Cells with high thresholds begin to fire after the eye has moved past the primary position by as much as 10 degrees into the on field of the muscle.

What is the function of Spinal Accessory? (XI)

-Controls trapezius & sternocleidomastoid -Controls swallowing movements

What is the function of the vestibulocochlear (VIII)?

-Hearing -Vestibular (equilibrium) sensation

Which muscles are innervated ipsilaterally versus contra laterally from the oculomotor nuclei?

-Ipsilateral: medial rectus, inferior rectus, and inferior oblique. -Contralateral: superior rectus

What is the function of the vagus? (X)

-Motor -pharynx, heart, lung, bronchi, & GI tract -Sensory - heart, lungs, bronchi, trachea -Taste of epiglottis

What is the function of the Facial (VII)?

-Muscles of facial expression & stapedius (inner ear) -Secretion of submandibular, sublingual, and lacrimal glands -Taste - anterior 2/3 tongue -Sensation - external auditory meatus and nasopharynx.

What is the function of the trigeminal nerve (V)?

-Muscles of mastication -Sensation of face, mouth touch and pain

What is the relationship among omnipause cells, bust cells, and neural integrator cells in the generation of the saccadic pulse and step?

-Omnipause cells cease discharging just before each saccade, allowing the burst cells to generate the pulse. - The pulse is integrated by the neural integrator to produce the step. - The pulse and step combine to produce the innervation charge on the ocular motoneurons (OMN) that produces the saccadic eye movement (E).

What would likely result if you have damage to oculomotor nerve? (and oculomotor palsy)

-Ptosis (drooping lid) -Downward and lateral gaze deviation in the affected eye -Diplopia (in the absence of complete ptosis) -Mydriasis -Accommodation difficulties

What is the function of glossopharyngeal (IX)?

-Taste: posterior 1/3 tong - Sensory: tonsils, pharynx, middle ear, and soft palate -Motor: stylopharyngeus, pharyngeal musculature.

What would likely result if you have damage to the trochlear nerve?

-The affected eye is higher and is also deviated medially because the inferior oblique (responsible for elevation and abduction) becomes dominant due to loss of the superior oblique -Affected eye is deviated medially -Diplopia

Firing rate can be plotted as a function of eye position. What does the slope of these functions describe?

-The cell's sensitivity.

Muscles can increase their *contractile force* by two different mechanisms, what are they?

1. *Increasing firing rate* of individual motoneurons 2. *Recruitment* of more motoneurons to stimulate the muscle.

All motoneurons have 4 characteristics to them, what are they?

1. Clear on-off directions (they increase their firing rate in the direction of agonist activity) 2. *Participate in all classes* of eye movements (steady fixation, and in the primary position of gaze) 3. Each cell (especially tonic) has an *eye position threshold* at which it begins to fire. 4. Increase in contraction is achieved by increasing frequency of spike potentials for a given neuron.

List the 12 cranial nerves.

1. Olfactory 2. Optic 3. Oculomotor 4. Trochlear 5. Trigeminal 6. Abducence nerve 7. Facial Nerve 8. Vestibulocochlear 9. Glossopharyngeal 10. Vagus 11. Accessory 12. Hypoglossal

Overall which 2 muscles are innervated contra- laterally?

1. Superior oblique 2. Superior rectus

What are the three categories of motoneurons?

1. Tonic 2. Burst 3 Burst-tonic (Burst and Burst-Tonic are referred to as phasic)

Know all of the nerves of the ophthalmic division (1st division of the trigeminal nerve)

1st branch: recurren meningeal branch. 2nd. Lacrimal 3rd. Frontal 4th. Nasociliary

What is cranial nerve VI? and where is it's nuclei located?

Abducens Nuclei located in the Pons

A general observation for most motoneurons (especially tonic) is that sensitivity and threshold tend to be correlated. What does this mean for cells with low thresholds?

Cells with *low thresholds* have *low sensitivities* -They don't change their firing rates dramatically ad the eye moves into their field of action.

What is the function of the hyoglossal? (XII)

Controls tongue movements

The anterior portion of the oculomotor nucleus contains innervation for pupil and accommodation in a specialized region called what?

Edinger Westphal Nucleus.

What is the function of oculomotor nerve (III)?

Eyelid and eyeball movement

True or False. Is specialization of neuron type for: saccades, versus pursuits, versus convergence, versus VOR and OKN.

False! *There is no specialization of neuron type and type of eye movement* Important note: *Classes of eye movements prior to the cranial nerves in the premotor nuclei*

True or false. It takes a lot of change in innervation to move the eye away from its off position.

False. It takes *little change in innervation* to move the eye away from its off position because of the *elastic force* of the stretched agonist and slackened position of the antagonist.

True or false. The trochlear (IV) nerve innervates the ipsilateral superior oblique.

False. It innervates the contralateral superior oblique. *The acronym LR6SO4 may help memorize the name of the nucleus and its associated number.

True or False. Fibers to the *IR, IO, and MR* supply the contralateral eye.

False. Ipsilateral eye! *Fibers innervating *SR* muscle supply the contralateral eye.

The 7th cranial nerve is the Facial. Where does it go and what does it do?

Goes to the lacrimal gland, also responsible for blinking.

What is the function of the trochlear nerve? (IV)

Innervates superior oblique - turns eye downward and laterally

Cells who firing rate increase slowly with eye position have what kind of sensitivity?

Low sensitivity to eye position whereas cells that increase their firing rate abruptly have high sensitivities.

Random point: The summed activity of all motoneurons as the eye moves from its off field to the upper limit of its of field increases exponentially as a result of recruitment.

More info: This exponential increase is necessary because different amounts of force are needed to make small changes in eye position starting from different orbital positions.

What is the term used to describe the cells within each of the nuclei that project axons along the cranial nerves?

Motorneurons -they are the final common pathway for all classes of eye movements, and their main function is to control the position of the eye, that is they encode position info that can change in time to result in changes in eye position. -This is true for pursuits and saccades where position signals are varied over time.

What is the function of the more phasic or burst cells?

Moving the eyes *rapidly* *Tonic-burst have both tonic and phasic properties

What is cranial nerve III? and where is its nuclei located?

Oculomotor Nuclei located in Mesencephalon (midbrain)

What nerve innervates the all the oculomotor nerves not covered by abducens and trochlear?

Oculomotor nerve! -It's nucleus is the most complex of the cranial nuclei associated with eye movements.

What fibers synapse in the ciliary ganglion?

Parasympathetic fibers.

Position signals are derived by what?

Supranuclear regions that transform velocity to position in regions called neural integrators.

Afferent fibers from the Edinger Westphal nuclei synapse where prior to enervating their target muscles?

Synapse in the Ciliary ganglion.

When fibers must *decussate* from their nucleus, were do they do it at?

They pass through the opposite superior rectus nucleus; thus damage to the right oculomotor nucleus might have bilateral superior rectus muscle involvement.

Information: For rapid movements (saccade), the contraction requires a phasic increase, or burst of neural activity in the ocular motor nuclei. Once at its new position, the eye must be held there against elastic restoring forces that would pull the glove back to its central position.

To hold the eye in an eccentric position requires a steady contraction of extra ocular muscles arising from a new tonic level of neural activity - the step of innervation. When the combined pulse-step of innervation is appropriately programmed, the eye is moved rapidly to its new position and held there steadily.

What is cranial nerve IV? and where is its nuclei located?

Trochlear Nuclei located in Mesencephalon (midbrain)

Contraction is increased by increasing the frequency of spike potentials for a given neuron. Once their threshold is exceeded all cells increase their firing rate as the eye moves further along in the on direction of the muscle. True or False. Different cells increase their firing rate linearly as the eye moves into the on field.

True.

True or False. Abducens (VI) nerve innervates the ipsilateral lateral rectus.

True. *The acronym LR6SO4 may help memorize the name of the nucleus and its associated number.

True or false. A definitive area or sub-nuclear within the oculomotor nucleus controls each muscle.

True. -Each of these sub nuclei are found in the right and left oculomotor nucleus. *The nucleus for the elevator muscle is single and is located centrally in the caudal area.

True or false. Cells with high thresholds tend to have high sensitivities.

True. -This means that once their threshold is exceeded, their fringing rate increases abruptly with change in eye position. *The net effect of t hs is that contraction ^ mainly as a result of recruitment when staring from the off position of a muscle, and it increases meinly as a result of increased firing rates of individual motoneurons when it moves beyond the primary position of gaze into the on field of the muscle.

True or False. It takes greater change in innervation to move the eye the same amount when starting from a position near the full limits of its potential contraction.

True. This is due to the *spring force of the stretched* antagonist and the loss of strectch of the agonist. *Thus the innervation pattern compensates for the mechanical properties of the agonist-antagonist pair of muscles they innervate*

What is cranial nerve VIII? and where is it's nuclei located?

Vestibular nerve. Nuclei is located in the Medulla Oblongata

What is the function of tonic cells?

They are responsible for holding the *eyes steady or moving them slowly*

The oculomotor nerve innervates the pupillary sphincter and ciliary muscle, what path does it take to get there?

*Visceral efferents: Parasympathetic* preganglionic efferents from *Edinger-Westphal* nucleus snaps with the neurons int he ciliary ganglion an then innervate those two muscles.

What is the function of abducens (VI)?

Turns eye laterally