8: nerves to the eye & nervous system

where does information of the nervous system go into

information comes into the central nervous system via afferent fibres

afferent fibres have specialised nerve endings that respond to sensations as touch, pressure and temp

what 2 categories are in the nervous system

sensory ( afferent): ascending, transmits information to the cns.

motor ( efferent): descending impules from cns to the peripheral organs to cause an effect

optic nerve II

origin is retinal ganglion cells

destination: LGN

function: sensory; sight

oculomotor , inferior division III

origin: midbrain

destination: medial rectus muscle, inferior rectus muscle,inferior oblique muscle and ciliary ganglion

function: motor- abduction, eleevation, extorsion , also motor to the iris sphincter and ciliary muscle in miosis

oculomotor, superior division III

origin: midbrain

destination: superior rectus muscle and superior palpebral levator muscle

function: elevation, abduction, intorsion, and elevation of eyelid

trochlear IV

origin is midrbrain

destination: superior oblique muscle

function: motor- depression, abduction and intorsion

abducens VI

origin is the pons

destination is the lateral rectus muscle

function is motor absuction

facial VII

origin is the pons

destination is the frontalis, orbicularis muscles

function is facial expressions, closure of eyelids and secretor to lacrimal gland

subdivisions of sensory afferent systems

visceral ( autonomic)

special ( somatic)

central ( comatic)

motor efferent systems subdivision

somatic motor

visceral motor: subdivided into parasympathetic and sympathetic

afferent

somatic afferent: general sensory eg pain touch and special sensory eg vision, smell , hearing

autonomic afferent: visceral sensory eg internal organs, vessels and special sensory

efferent

somatic motor

visceral motor

brachial motor - skeletal muscles, derived from branchial arteries

CN I & 2 emerge from the cerebrum

rest emerge from the brain stem

the optic nerve CN II

afferent - special sensory

conducts signals from the eye to the brain

made up of retinalganglion cell axons

axon bundles exit eye as optic nerve and runs nasal and posterior to the optic foramen , through canal in sphenoid bone

optic nerve visual pathway

after the 2 optic nerves pass through the canals they merge at chiams, and cross over at nasal fibres

forms optic tract where moves to LGN

follow throgh as optic radiations where enters V1

what are the extraocular muscles of the eye- muscles that move the eye: somatic

levator palpebrae superioris

superior oblique

inferior oblique

superior rectus

medial rectus

lateral rectus

inferior rectus

what nerves innervate the extraocular muscles

oculomotor: innervates all rectus, inferior palp and inferior oblique

trochlear; innervates the superior oblique

adbucens: innervates lateral rctus muscles

what does the oculomotr nerve CNIII innervate

superior rectus, medial rectus, inferior rectus, inferior oblique and superior palp levator muscles

also provides a route along which the autonomic fibres travel to innervate iris sphincter , ciliary and smoth muscles of the eyelind

where does the paired oculomotor nerve arise from

from the large nuclei - axons arise from a subnuclesu within this nucleus

located within the midbrain at level of superior colliculus

extends in a column from posterior edge of floor of third ventricle to the trochlear nucleus

subnucleus of the oculomotor nerve

controls each muscle

nucleus of medial rectus is located toward lower border of oculomotor nucleus

nucleus of levator muscle is in the centre

oculomotor nerve pathway

fibres from each of the indv nuclei join, forming fascicular part of nerve that passes through red nucleus and decussating fibres of superior cerebellar peduncle

these fibres merge as oculor motor nerve

nerve passes between superior cerebellar and post cerebral arteries to the artery

nerves pierce roof of sinus and run within 2 dural layers above trochlear nerve

where does oculomotor nerve exit

eits the sinus and enters the orbit through superior orbital fissure havog divdided into sup and inf diivisions

where does the superior oculomotr branch move into

this ranch runs medially above optic nerve and enters the superior rectus on its inferior surface , another goes to the levator

where does the inferior banch of oculomotor move to

this branch runs below optic nerve and divides into 3 branches

one branch enters medial rectus

another enters inferior rectus

third branch gives off parasympathetic fibres that form the parasymp root extending to ciliary ganglion, then runs along inferior rectus to enter inferior oblique muscle

what do the parasympathetic fibres innervate

innervates the sphincter and ciliary muscle

reaches the eye via short ciliary nerve

oculo motor nerve route from midbrain to eye

1. nucleus

2. passes posterior cerebral, sup cerebellar and posterior communicating artery

3. into sinus

4. divides into superior and inferior branches

5. into edinger westpal nucleus

6. and then either paraymp supply to iris sphincter and ciliary muscle or travels with inferior branch then inferior oblique and into ciliary ganglion

trochlear nerve CN IV

innervates superior oblique muscle

located in midbrain at level of inferior colliculus

run backwards/ dorsally to inf colliculus

only nerve to cross so innervates the contralateral superior oblique muscle

the 2 trochlear nerves cross the superior cerebellar arteries to contralateral side before emerging on posteriior side of brain stem

trochlear nerve pathway

only nerve to leave dorsal aspect of cns

as trochlear nerve emerges from dorsal midbrain, it decussates and curves around cerebral peduncle at pons , between sup and post cerebral arteries

passes between these vessels and runs to oculomotor nerve

where does the trochlear nerve go to affter passing to oculor motor nerve

enters cavernous sinus and lies between oculomotor nerve and opthalamic division of trigeminal nerve

whilst in sinus the nerve sends sensory fibres to opthalmic nerve

how does the trochlear nerve enter the orbit

enters orbit through the superior orbital fissure above the tendinous ring

runs with frontal neve to medial side of orbit and enters the superior oblique muscle

what does adbucens nerve CN VI innervate

inervates the lateral rectus muscle

abducens nucleus

located near the inferior dorsal midline of the pons beside floor of the 4th ventricle , below cerebellum

fibres from nucleus pass through pons and lie next to corticospinal tract

exit in the groove between pons and medulla oblongata

what does the abducens nerve also contain

contains internucleur neurons that communicate with the nucleus for contralateral medial rectus muscle in oculomotor complex

this is the pathway for conjugate horizontal eye movements

this pathway recieves information from higher cns centres

abducens nerve pathway

runs along occipital bone and along temporal bone, and bends over to enter sinus

within sinus it lies near wall of internal carotid artery

small sympathetic branches leave internal carotid plexus and travel with abducens nerve

nerve carries autonomic fibres into the opppthalmic division of trigeminal nerve

how does abducens nerve enter the orbit

enters orbit through the superior orbital fissure within tendinous ring and innervates lateral rectus muscle on medial surface

what 3 nerves innervate the extraocular muscle

oculomotor

trochlear

abducens

trigeminal nerve CN V

originate in the innervated structures

join to become larger nerves and come together in the ganglion of CN V , and then exit the ganglion and enter pons

opthalmic division of trigeminal nerve: nasociliary nerve

sensory fibres form structures of medial canthal area, lacrimal sac, join to form infratrochlear nerve

this nerve penetrates orbital septum , and enters orbit below trochlea

where does motor nucleus lie in trigeminal nerve

lies medial to sensory nucleus near horizontal midline of pons where the nerve emerges from the brainstem

sensory nucleus extends veetically above and below its main section in the pons

how is nasociliary nerve formed

joining infratrochlear nerve, the anterior and posterior ethmoid nerves, long ciliary nerves and the sensory root of ciliary ganglion

where does trigeminal nerve exit

exits through 2 routes

sensory root and motor root

where does nasociliary nerve exit

exits the obit by passing through the oculomotor foramen within the common tendionous ring and superior orbital fissure and into the cranial cavity

opthalmic divi of trigeminal nerve V1: frontal nerve

sensory fibres form skin and muscles and upper eyelid come to form supratrochlear nerve

this enters orbit by piercing superior medial corner of orbital septum

frontal nerve: supraorbital nerve

sensory fibres form skin and muscles form the supraorbital nerve

this nerve enters orbit as one or two branches:

one enters supraorbital notch other supraorbital artery

the supraorbital nerve joins supratrochlear and forms frontal nerve

frontal exits the orbit through superior orbital fissure above the ring

innervates skin and conjunctiva of the central eyelid

opthalmic div of trigeminal nerve : lacrimal nerve

sensory fibres from lateral aspect of upper eyelid form lacrimal gland

jon sensory fibres that serve the gland to form lacrimal nerve

runs along lateral rectus muscle and exit through superior orbital fissure

goes to lacrimal gland, and can innervate lateral eyelid

opthalmic nerve formation

after exiting orbit, nasociliary, lacrimal and frontal nerve join and form trigeminal nerve opthal div

this then enters lateral walls of sinus

maxillary V2 of trigeminal nerve

sensory, from nose, cheeks and upper jaw

infraorbital nerve and zygomatic nerve and nerves from roof of mouth form the maxillary nerve

enters the skull via foramen rotundum

innervates skin, sinuses of maxilla and mucous membrane

what is the pterygopalatine ganglion

largest of the parapsympathetic ganglia

contains post ganglionic, para and symp fibres of maxillary nerve

mainly controls secretion of glands in the face

mandibular division of trigeminal nerve V3

innervates the lower face ad contains both sensory and motor fibres

enters skull via foramen ovale

from cheeks, side of head lower haw mouth tongue and motor to lower jaw

trigeminal nerve formation

as opth and max divisions enter the skull and run within sinus

mandibular division lies below the sinus

the sensory fibres from all 3 divisions enter the trigeminal ganglion where they synapse

fibres then leave and enter the pons as either the sensory or motor root

zygomatic nerve branches provide sensory innervation of temporal and zygomatic regions

facial nerve: CN VII

has 2 roots: large motor root innervates the facial muscles

smaller root contains sensory and parasymp fibres

sensory fibres carry taste sensations from tongue

parasymp fibres supply secretomotor fibres to various glands of face

facial nucleus

motor nucleus of facial nerve is located in reticular formation of pons

upper segment supplies frontalis, orbicularis muscles and supplies remaining facial muscles

facial nerve pathway

fibres leave facial nucleus, arch around abducens nucleus and emerge as facial nerve from brain stem

enters acoustic foramen and runs through canal in temporal bone

the parasymp fibres here run to lacrimal and give off as petrosal nerve

morot fibres emerge through stylomastoid foramen, pass below external auditory canal and divide into several branches

what branches do the facial nerve divide into

upper two: temporal and zygomatic

they supply the frontalis, procerus, corrugator and orbicularis muscle

segment of the facial nerve

extratemporal: exits temporal bone via stylomastoid foramen

orbicularis muscle recieves innervation from temporal nerve and zygomatic nerve

what is the other segment of the facial nerve

labyrinthine segment goes to the greater petrosal nerve

made up of parasympathetic nerve fibres and joined by deep petrosal nerve

pupil light reflex

light shon onto the pupil, light signal stramsits via optic nerve to the chiasm

nerve fibres go to contralateral side, temp goes to ipsilateral side

at the optic tract, 90% of fibres end at LG, 10% leave V1 and follow pupil pathway

those signals go to the pretectal nucleus

from there, it send signals to the edinger wheshal nuclei

efferent: other way to the sphincter muscle

dim light

pupillary dilator muscle fibres contract and widne ppil

post ganglionic parasymp fibres from long ciliary nerve innervate the dilator muscle

pupil near response

accom, convergence and pupil constriction

pre tectal nucleus plays role in light near