NEUROANATOMY - Nerves Flashcards
How long is each optic nerve segment?
1. intraocular
2. orbital
3. intracanalicular
4. intracranial
- 1mm (1squared)
- 25mm (5 squared)
- 6-9mm (3 squared)
- 16mm (4squared)
Which nerve is not covered by the neurilemma? What is this nerve covered by?
optic nerve, covered by the meninges
What is the average diameter of the optic nerve head? What happens at level of the sclera?
1.5mm. At the level of sclera it doubles to 3mm as there is now myelination of the fibres
What are the 4 subregions of the intraocular part of the optic nerve? What is their blood supply?
- Surface nerve fibre layer - nerve fibres (95%) plus astrocytes (5%)
–> branches of central retinal artery - Prelaminar region: higher number of astrocytes and neurons
–> short posterior ciliary artery - Laminar region : passing through lamina cribrosa through fenestrations
–> short posterior ciliary artery + arterial circle of zinn - Retrolaminar region: astrocytes decrease and oligodendrocytes increase to form myelin
–> pile plexus (centripetal branches) + centrifugal branches
When does the central retinal artery and vein enter the intraorbital part of the nerve?
About 10mm from the eyeball and passes inferomedially.
Where is the internal carotid artery in relation to the intracranial part of the optic nerve
Runs inferiorly and laterally to the optic nerve
What is the blood supply of the surface nerve fibre layer region of the optic nerve?
branches of CRA.
What is the ocular blood supply of the prelaminar region of intraocular part of optic nerve?
short posterior ciliary artery
What is the ocular blood supply for the laminar region of the intraocular part of the optic nerve?
Laminar region : passing through lamina cribrosa through fenestrations
–> short posterior ciliary artery + arterial circle of zinn
What is the ocular blood supply for the retrolaminar region of the optic nerve?
pile plexus (centripetal branches) + centrifugal branches
How thick are the optic nerve fibres?
2-10 microns
What is the route of the optic nerve?
Intraocular part passes through sclera and passes through lamina cribrosa, chorod and appears inside as the optic disc.
What is the average diameter of the optic nerve head? Why does it expand behind the sclera?
1.5mm, 3mm behind sclera due to presence of oligodendrocytes (which form myelin)
What is the route of the intraorbital part of the optic nerve?
extends from back of eyeball to the optic foramina. Sinous path (curved) to allow extraocular movement.
At what point does the central retinal artery enter the intraorbital part of the optic nerve and where does it pass in relation to optic nerve?
10mm posterior to eyeball. Passes inferomedially to nerve.
What are the structures that pass between optic nerve and lateral rectus muscle? (5)
- Ciliary Ganglion
- superior/inferior divisions of CN3
- Nasociliary nerve
- Sympathetic nerve
- CN6
What are the close relations of the intracanalicular part of optic nerve?
- ophthalmic artery
- sphenoid and ethmoid sinus
- thin bony lamina separates sinus from intracanalicular part
Where does the larger lateral root of the optic tract terminate?
Where does the smaller medial root of the optic tract terminate?
lateral root: LGN
medial root: subcortical targets (1) superior colliculus, (2) pretectal nucleus (3) suprachiasmatic nucleus (4) pulvinar nucleus (5) parvocellular reticular formation (6)
In the intracranial part of the optic nerve, what are its relations to the..
1) internal carotid artery
2) ophthalmic artery
3) anterior cerebral artery
1) ICA - medial
2) ophthalmic artery - superomedial
3) anterior cerebral artery - inferior
What is are the two routes of the optic nerve after the optic chiasm?
optic tracts —-> lateral geniculate body —-> optic radiation —> terminate at Brodmann area 17 of visual cortex
some fibres bypass LGB and terminate in either:
1) pretectal nucleus (pupillary light reflex)
2) superior colliculus (regulaton of saccadic eye movements)
What are the layers of optic radiations?
1, 4, 6 - contralateral fibres synapse
2, 3, 5 - ipsilateral fibres synapse
Where is the ciliary ganglion situated?
Between optic nerve and lateral rectus muscle.
Name the structures.
What are the 3 roots of the ciliary ganglion?
- Sensory
- Sympathetic
- Parasympathetic
What is the sympathetic pathway of the sympathetic root of ciliary ganglion?
PRE-GANGLIONIC:
1. Hypothalamus
2. Sympaethtic root (ciliospinal of budge)
3. Superior cervical ganglion
POST-GANGLIONIC:
1. pleuxs around ICA
2. sympathetic root –> short ciliary nerve (autoregulation of vascular tone of eye)
3. nasociliary nerve –> long ciliary nerve –> dilator pupillae –> DILATION.
What is the sensory route of the ciliary ganglion?
Trigeminal ganglion (PONS) –> ophthalmic division (V1) –> nasociliary nerve
Nasociliary nerve –> long ciliary nerve
–> sensory route through ciliary ganglion –> short ciliary nerve
SAME FUNCTION --> carry pain touch and temperature sensations of the eye
What is the parasympathetic route of the ciliary ganglion?
edinger westphal nucleus (subnucleus of CNIII in midbrain) –> travel superificially in ocularmotor nerve –> inferior division of CNIII –> relay in ciliary ganglion —> short ciliary nerve –>
—> SPHINCTER PUPILLAE - constriction
—> CILIARY MUSCLE - accomodation for near task
WHat is the afferent limb of the oculocardiac reflex?
stretch receptors in ocular tissues –> short/long ciliary nerve –> ciliary ganglion (no synapse) –> V1 –> trigeminal ganglion –> trigeminal nucleus –> CNS.
What is the efferent limb of the oculocardiac reflex?
internuerons between trigeminal sensory nucleus and visceral motor nucleus of vagus nerve –> myocardium to synapse –> sinoatrial node –> vagal motor response (bradycardia).
What is the route of the abducents nerve from its nucleus to its innervation? (CN6)
NUCLEUS:
medial to the facial nerve nucleus.
pure motor nucleus to the lateral rectus muscle.
1) the nerve leaves the brainstem at the junction of the pons and medulla and enters the subarchnoid space.
2) It runs upward in the subarachnoid space between the pons and the clivus, and then pierces the dura mater to run between the dura and the skull through Dorello’s canal.
3) At the tip of the petrous temporal bone it makes a sharp turn forward to enter the cavernous sinus. In the cavernous sinus it runs alongside just lateral to the internal carotid artery.
4) It then enters the orbit through the superior orbital fissure and innervates the lateral rectus muscle of the eye.
What are the two types of nuclei for the oculomotor nerve? Where is the location of the oculomotor nuclei?
- somatic/motor nucleus (efferent)
- parasympathetic (edinger-westphal) posterior to motor nucleus
located in the midbrain at the level of the superior colliculus
What is the route of the oculomotor nerve?
Originates at level of superior colliculus in midbrain.
Passes between cerebral (above) and superior cerebellar arteries (below) and parallel to posterior communicating artery pierces dura mater, and runs anteriorly in subarachnoid space, medial to larger trigeminal nerve and its ganglion
It passes through superolateral aspect/roof of cavernous sinus, lateral to ICA and in anterior portion of cavernous sinus, divides into superior and inferior branches prior to entering the orbit.
Both branches pass below anterior clinoid process of sphenoid bone to etner orbit within common tendinous ring and enter through SOF.
What is the route of the superior branch of oculomotor nerve?
Divides at anterior portion of cavernous sinus and superior branch passes medially ocver optic nerve. It supplies superior rectus and LPS
What is the route of the inferior branch of the oculomotor nerve?
Divides into three branches
1. beneath optic nerve to medial rectus
2. another to inferior rectus
3. third runs forward alongisde inferior rectus and reaches inferior oblique, gives off branch to ciliary ganglion for parasympathetic supply.
What is the route of the trochlea nerve?
Originates in trochlea nucleus inferiorly to origin of oculomotor nerve in posterior aspect of midbrain at level of inferior colliculus.
Trochlea nerve loops around to contralateral side and similarly to oculomotor, runs between superior cerebellar and posterior cerebral artery - RUNS BELOW OCULOMOTOR NERVE.
Runs anteriorly and inferiorly within subarachnoid space before piercing dura mater adjacent to posterior clinoid process of sphenoid bone.
Enters cavernous sinus and runs laterally and exits ABOVE AND LATERAL TO OCULOMOTOR NERVE and enters the SOF OUTSIDE the tendinous ring and passes around the LPS and loops medially to innervate the superior oblique muscle.
What is the route of the abducens nerve (Cranial nerve 6)?
Originates in the Pons at the floor of fourth ventricle at level of facial colliculus and exits the pons anteriorly and moves superiorly over the anterior inferior cerebellar artery.
It runs anterior and inferiorly within subarachnoid space before it enters the cavernous sinus at apex of petrous part of temporal bone.
It moves across the lateral wall (in between ICA and other nerves - an atheroma can compress nerve here) and then enters through common tendinous ring at medial end of SOF to innervate the lateral rectus.
What are the different nuclei of the trigeminal nerve and where do they arise from?
3 sensory nuclei
1. mesencephalic nucleus - midbrain - sensory info from muscles of mastications, facial expression and EOMs
2. spinal nucleus - medulla - tactile, nociceptive, thermal infro from face (pain and temperature)
3. principal sensory nucleus - touch and presssure
1 motor nuclei
motor nucleus of trigeminal nerve
What are the three main branches of V1? What are their sub-branches?
Frontal nerve - supraorbital and supratrochlear nerves
Lacrimal nerve
Nasociliary nerve - infratrochlear, anterior ethmoidal and posterior ethmoidal nerves
What are the route and the branches of V2?
lies in lateral wall of cavernous sinus, goes through foramen rotundum into pterygopalatine fossa to supply pterygopalatine ganglion
Becomes infraorbital nerve as it enters inferior orbital fissure, and passes through infraorbital groove, canal and foramen.
Main branches are zygomatic, superior alveolar nerves which anastomose with superior dental plexus
What is the route of the trigeminal nerve? (sensory root)
trigeminal nerve originates from three sensory nuclei extending from midbrain to medulla - they all merge at the level of the pons to form a sensory root.
second order nerve goes upwards from medulla (spinal nucleus) to Ventroposteromedial nucleus of thalamus (VPM), synapses with third order neuron here through internal capsule into somatosensory cortex.
The sensory root expands into the trigeminal ganglion in the middle cranial fossa. This is located lateral to cavernous sinous in a depression of temporal bone (trigeminal cave).
The peripheral part of trigeminal ganglion gives rise to 3 divisions, ophthalmic, maxillary and mandibular.
V1 and V2 travel laterally in cavernous sinus and exit for SOF and foramen rotundum. V3 exits via foramen ovale.
What is the route of the trigeminal nerve (motor root)
motor cortex transmits fibres to pons and dessucates here to contralateral side at the trigeminal motor nucleus, medial to sensory root.
The motor root enters trigeminal ganglion and branches as V3 (mandibular nerve) to supply the muscles of mastication.
V3 exits via foramen ovale into the infratemporal fossa.
What is the course of the ophthalmic nerve?
Starts from anterior aspect of the trigeminal ganglion and gives off meningeal branch before it enters and passes along lateral wall of cavernous sinus
divides into 3 branches, nasociliary, frontal and lacrimal branch and all 3 branches leave cranial cavity via SOF and enter the orbit.
What is the route of the frontal nerve?
What do its terminal branches supply?
Enters orbit through lateral part of SOF and passes forward between roof of orbit and above LPS
Divides into its terminal branches, the supratrochear (medially) and supraorbital nerve (laterally) which passes through supraorbital foramen at the orbital rim
supraorbital nerve - forehead, scalp, upper eyelid and frontal air sinus.
supratrochlear nerve - forehead, scalp and upper eyelid
What is the route of the lacrimal nerve?
What are the branches of the lacrimal nerve and what is its supply?
Smallest branch of ophthalmic nerve, passes lateral part of SOF and passes across lateral orbital wall at superior border of lacteral rectus muscle.
Penetrates lacrimal gland and orbital septum and terminating as sensory nerves that supply skin and conjunctiva of lateral upper eyelid.
Receives communicating branch from zygomaticotemporal nerve (from facial nerve) which conveys parasympathetic secretomotor fibres for lacrimal gland
What is the route of the nasociliary nerve?
What are its branches?
Passes through annulus of zinn and crosses above optic nerve from and then enters medial compartment of orbit passing between superior oblique and medial rectus and gives off branches
1. long ciliary nerves -2-3 nerves medial to optic nerve for sensory innervation to cornea, ciliary body and iris and sympathetic fibres to dilator pupillae
- posterior ethmoidal nerve - ethmoidal and sphenoid sinuses
- anterior ethmoidal nerve - ethmoidal sinus, nasal cavity, septum and skin of nose
- infratrochlear nerve - eyelids, conjunctiva, lacrimal sac and skin of nose.
What is the route of the facial nerve?
INTRACRANIAL AND EXTRACRANIAL ROUTE.
INTRACRANIAL
the motor and sensory fibres leave through pons enters through the internal auditory meatus (petrous part of temporal bone) and then enters Z shaped facial canal where the two roots fuse to form the facial nerve.
The nerve then forms geniculate ganglion and the nerve then gives rise to 3 nerves
1. greater petrosal nerve - parasympathetic fibres to mucous glands and lacrimal gland
2. nerve to stapedius - to stapedius muscle of middle ear
3. chorda tympani - special senory fibres to anterior 2/3rds of tongue and parasympathetic fibres to submandibular and sublingual gland
Exits via stylomastoid foramen (located posterior to styloid process of temporal bone)
EXTRACRANIAL
3 branches
1. posterior auricular nerve
2. nerve to digastric
3. nerve to stylohyoid
then main motor root continues anterior and inferiorly into the parotid gland to 5 terminal branches which innervate muscles of facial expression
1. temporal branch
2. zygomatic branch
3. buccal branch
4. marginal mandibular branch
5. cervical branch
TO ZANZIBAR BY MOTOR CAR
What are the nuclei of facial nerve?
1.facial proper nucleis - moves aroudn 6th nerve nucleus, creates facial colliculus and exits through pontomedullary junction/cerebellar pontine angle
2.superior salivatory nucleus -
- nucleus tractus solatarius - connects to anterior 2/3rd of tongue for taste.
They all exit through cerebellopontine angle.
What are the terminal branches of the facial nerve? What do they supply?
Temporal - frontalis, orbicularis, corrugator supercilli
Zygomatic - orbicularis oculi
Buccal - orbicularis oculi, baccinator, zygomaticus
Marginal mandibular - depressors, mentalis
Cervical - platysma
