BBS in a Box 7/BBS in a Box - Macintosh - Volume VII (BBS in a Box) (January 1993).iso/Files/Hyper/N-O/Ocular Anatomy Tutor.cpt/Ocular Anatomy Tutor/card_10000.txt

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XIV. Efferent nervous system:

     A.   (See diagram 1)

          1. Parasympathetic:
               a. From CNS to iris sphincter and ciliary body.
                    1. Preganglionic fibers originate in the Edinger Westphal nucleus (Accessory III nucleus) in
                        the tegmentum at the level of the superior colliculus (mesencephalon).
                    2. Fibers travel in III. nerve through superior orbital fissure, follow inferior branch of III.
                        nerve, branch off and form motor root of of the ciliary ganglion.
                    3. Fibers synapse in ciliary ganglion.
                    4. Postganglionic fibers via short ciliary nerves in suprachoroid to anterior eye, ciliary
                        muscle and iris sphincter.
               b. From CNS to lacrimal gland (increased tear film):
                    1. Preganglionic fibers from lacrimal nucleus in the pons, join sensory root of VII. nerve,
                        pass through facial ganglion (no synapse), enter great petrossal, join with deep petrossal
                        nerve to form the vidian nerve, enters sphenopalatine ganglion and synapses.
                    2. Postganglionic fibers enter zygomatic branch of maxillary V. nerve, a mixed nerve,
                        connecting branch to lacrimal nerve, terminates in the lacrimal gland.
          2. Sympathetic:
               a. Preganglionic fibers originate in cervical 18 (C-18) to thoracic 3 (T-3) vertebrae. Come out
                   of ventral roots of the spinal cord. Go superior, to superior cervical ganglion in neck and
                   synapse.
               b. Postganglionic fibers run up neck into skull on wall of internal carotid artery and branch in
                   skull.
                    1. Branch I.: Through gasserian ganglion to ophthalmic V. to nasociliary nerve to long ciliary
                        nerve to dilator muscle.
                    2. Branch II.: Sensory root of ciliary ganglion to short ciliary nerves to blood vessels of
                        choroid (vasoconstriction).
                    3. Branch III.: Through deep petrossal nerve to vidian nerve through sphenopalantine
                        ganglion to zygomatic nerve to lacrimal gland (vasodilation).
                    4. Branch IV.: Via oculomotor III. nerve superior branch to levator to Muller's muscle of
                        eyelid.
               c. Pathology:
                    1. Horner's syndrome: Trauma at the level of the superior cervical ganglion, damages
                        sympathetic system, causes miosis, ptosis, and anhydrosis, usually unilateral.
          3. Summary of ocular reflex pathways:
               a. Direct/consensual pupillary response:
                    1. Afferent: Retina to pretectal nuclei.
                    2. Intracranial:
                         a. Tectotegmental tract: From pretectal to EW nucleus on same side.
                         b. Posterior commissure: Crossover from pretectal to opposite EW nucleus. The
                             pretectal nuclei are not connected.
                    3. Efferent: EW to iris sphincter.
                         a. Preganglionic fibers follow III. nerve to ciliary ganglion and synapse.
                         b. Postganglionic fibers go to sphincter via short posterior ciliary nerves (
                             parasympathetic).
               b. Accommodation/convergence pupillary response:
                    1. Near response or reflex: Ciliary muscle contracts, medial recti contract, sphincter
                        contracts (accommodation, convergence, miosis).
                    2. AC/A: Ratio between accommodative convergence and amount of accommodation, usually
                        3.5 diopters.
                    3. Ways to separate accommodation/convergence/pupil:
                         a. Presbyopia: Accommodation = zero, AC/A increases.
                         b. Mydratic (sympathomimetic): Affects dilator muscle, no pupillary response.
                         c. Cycloplegic (parasympatholytic): Blocks innervation to ciliary and sphincter muscles,
                             convergence without accommodation or miosis.
                              1. Afferent pathway: Visual pathway to 17.
                              2. Intracranial: 17 to 18,19,22 to midbrain to EW and III. nerve     nucleus.
                              3. Efferent:
                                   a. Autonomic (parasympathetic) to EW to iris sphincter and ciliary muscle.
                                   b. Somatic: III. nucleus to medial rectus.
               c. Pathology:
                    1. Argyll Robertson pupil: Loss of direct and consensual response with retension of near
                         point miosis, results from lesion after branch off to optic tract to EW nucleus.
                         a. Can be unilateral or bilateral.
                         b. Remember that the near response goes directly to EW, but direct/consensual goes to
                             the pretectal first.  (See diagram 2)
                d. Example lesions:
                     1. Sever optic nerve of left eye:
                         a. Direct: left no, right yes.
                         b. Consensual: left yes, right no.
                     2. Damage to fibers of left optic nerve:
                         a. Loss of direct in left eye.
                         b. Swinging flashlight test more sensitive than fields.
                         c. Called Marcus Gunn or Relative afferent pupillary defect (RAPD).
                     3. Saggital section through chiasm:
                         a. Bitemporal hemianopsia.
                         b. Pupillary response unaffected.
                     4. Section left optic tract:
                         a. Right homonymous hemianopsia.
                         b. Pupillary response unaffected.
                     5. Cut after LGN, but before superior brachia:
                         a. Right homonymous hemianopsia.
                         b. Pupillary response unaffected.
                     6. Cut fibers from both PT to one EW:
                         a. Argyll Robertson in one eye on affected EW.
                     7. Cut both PT to both EW:
                         a. Argyll Robertson on both eyes.
                         b. Associated with tertiary syphillus, tumor, hemorrhage.
                     8. Cut III. nerve:
                         a. Droopy lid and slight abduction, ipsi.
                         b. Motor loss from MR, SR, IR, IO, levator.
                         c. Parasympathetic loss of sphincter and ciliary body.
                         d. No pupillary response, no accommodation, no miosis on ipsilateral side.
                     9. Postganglionic fiber damage:
                         a. Loss of ciliary body and sphincter.
                         b. Loss of choroidal blood vessels and dilator.
                     10. Adie's tonic pupil: Affects postganglionic fibers, after ciliary ganglion, after they
                            branch from III. nerve.
                         a. Eye movements are normal.
                         b. Pupillary responses are slow or absent.
                         c. Accommodation is hindered.
          4. Trigeminal or corneal reflex:
               a. Corneal pain results in lacrimation, blinking and miosis.  (See diagram 3)
          5. Sleep reflex:
               a. Parasympathetic system takes over and miosis results.
          6. Role of the superior colliculus:
               a. In other animals: Visual reflex system.
               b. In man: Integration of eyes, ears, head, trunk, and limbs to fixate on a visual target.
               c. Connections to superior colliculus:
                    1. Afferent: (going to):
                         a. A few from the optic tract.
                         b. From cortex area 17, 18, 19 via the optic radiations.
                         c. From the spinal tectal tract.
                    2. Efferent:
                         a. Oculomotor nuclei.
                         b. Through tectal spinal tract.
                         c. Moves head and neck.
     B. Somatic system: Eye movements.
          1. Oculomotor nucleus: In tegmentum at the level of the superior colliculus in mesencephalon,
              adjacent to the EW nucleus (parasymp.), each muscle innervated has a section in the III. nerve
              nucleus.
               a. Oculomotor nerve (III.) contains fibers from the III. nerve (somatic) and fibers from the EW
                   (parasymp.).
                    1. Superior branch: SR and levator.
                    2. Inferior branch: MR, IR, IO, and motor root of ciliary ganglion.
          2. IV. nucleus: In tegmentum at level of the inferior colliculus in midbrain.
               a. Trochlear nerve (IV.): Innervates SO.
          3. VI. nucleus: In tegmental portion of the pons in midbrain.
               a. Abducens nerve (VI.): Innervates LR.
          4. Medial longitudinal vasiculus: Coordinates eye movements, for balance, connects III., IV., VI.
              and vestibular nuclei (VIII.).
          5. Supranuclear control mechanisms:
               a. Smooth tracking or pursuit, maintains image on fovea, fixation movements.
               b. Rapid eye movements, saccadic, usually involuntary, originates in contralateral frontal eye
                   fields (8), stimulus on one side produces contralateral conjugate eye, head, and neck
                   movements.

XV. Innervation of the eye:

     A. Definitions:
          1. Neuron: Nerve cell.
          2. Synapse: Junction between nerve cells.
          3. Nervous system: Sequence of neurons connected by synapses.
          4. Neuroglia: Support cells among neurons.
          5. Myelin: Fatty sheath surrounding most nerve fibers, (myelinated = medullated).
          6. Nucleus: Group of neuron cell bodies in CNS with common connections/functions.
          7. Tract: Group of nerve fibers running together from one part of CNS to another part of the CNS.
          8. Ganglion: Group of nerve cell bodies outside of the CNS.
          9. Information into CNS: Sensory-afferent-centripetal.
          10. Information out of CNS: Motor-efferent-centrifugal.
          11.  (See diagram 4)
               a. Types of autonomic:
                    1. Sympathetic: Dilator muscle, blood vessels.
                    2. Parasympathetic: Sphincter, lacrimal, ciliary body.
     B. Sensory information:
          1. General: Almost all sensory information is via the (V) Trigeminal sensory root arising from the
              trigeminal ganglion.
               a. The sensory root has dendrites to surface, axons to the CNS.
               b. Trigeminal ganglion: Gasserian ganglion, contains the cell bodies of three divisions of the V.
                    nerve (ophthalmic, maxillary, mandibular).
          2. Branches of (V.) Trigeminal nerve:
               a. Ophthalmic:
                    1. Travels through lateral wall of cavernous sinus.
                    2. Just superior orbital fissure it takes three branches:
                         a. Lacrimal nerve: Above annulus of Zinn, runs along upper border of LR to lacrimal
                             gland, also branches to lateral lid.
                         b. Frontal nerve: Above annulus of Zinn, runs forward above levator and branches into:
                              1. Supratrochlear nerve: To trochlear area, conjunctiva, medial upper      lid,
                                  forehead, corrugator, and frontalis.
                              2. Supraorbital nerve: Parallels supraorbital artery, leaves orbit at     SOF, to upper
                                  lid, conjunctiva, forehead, frontal muscle.
                         c. Nasociliary nerve: Through Annulus of Zinn, passes below SR and SO to medial orbit.
                              1. Long or sensory root of ciliary ganglion: Sensory info passes     through, no
                                  synapse, exits via short ciliary nerves to suprachoroid, sclera, cornea, iris,
                                  ciliary body, and choroid.
                              2. Long ciliary nerves (2): Pierce sclera and run in suprachoroid to      cornea, iris,
                                  and ciliary body.
                              3. Anterior ethmoidal nerve: Parallel to anterior ethmoidal artery,     through
                                  ethmoidal sinus and mucous membrane of nose.
                              4. Posterior ethmoidal nerve: To ethmoidal and sphenoid sinuses.
                              5. Infratrochlear nerve: Medial conjunctiva, lids and nose, lacrimal     sac, and
                                  caruncle.
               b. Maxillary Division:
                    1. Travels in lateral wall of cavernous sinus.
                    2. Exits skull through foramen rotundum, enters orbit through IOF, with two important
                        branches in orbit:
                         a. Infraorbital nerve:
                              1. Parallels infraorbital artery.
                              2. Serves lower lid and face.
                         b. Zygomatic:
                              1. Serves lateral side of orbit and lateral face.
                         c. Mandibular Division:
                              1. Exits skull through foramen ovale.
                              2. Serves lower half of face and jaw.
     C. Visual pathway:
          1. Definition: A series of five cells and four synapses, activated during vision (perception of an
              image in the field of view).
               a. Photoreceptor cell: Absorbs light energy and converts it to chemical energy.
               b. Bipolar cell.
               c. Ganglion cells: Axons transverse nerve fiber layer, optic nerve, chiasm, optic tract, and
                   LGN.
               d. LGN cells: Axons transverse optic radiations to visual cortex.
               e. Visual cortex cells: Perception, Broadman area #17.
          2. Anatomy of the visual pathway:
               a. Retina: Not a typical sensory nerve, it is an extension of the CNS.
               b. Optic nerve:
                    1. types of fibers:
                         a. Visual pathway fibers: Axons of ganglion cells going to LGN.
                         b. Afferent pupillary fibers: Axons of ganglion cells going to the tectum, pupillary
                             response to light.
                         c. Efferent fibers.
                    2. Length is 40 to 50 mm.
                         a. Intraorbital: 24 mm.
                         b. Intracanal: 5 mm. (in optic canal).
                         c. Intracranial: 10 mm. (pre-chiasm).
                    3. Arrangement of fibers in the optic nerve:  (See diagram 5)
               c. Chiasm:
                    1. Location:
                         a. Anterior wall and floor of third ventricle, surrounded by cerebral spinal fluid.
                         b. Internal carotid artery is lateral.
                         c. Pitutary (hypophysis) is inferior.
                         d. Anterior cerebral and anterior communicating arteries are superior to anterior
                             chiasm.
                    2. Passage of fibers through chiasm:
                         a. Temporal fibers do not cross over.
                         b. Lower nasal retinal quadrant: Long loops forward (knees of Wilbrand) after crossing.
                         c. Upper nasal retinal quadrant loops posterior before crossing.
                         d. Nasal macular crossover, no loops.
                         e. Temporal macular straight through, no crossover.
               d. Lateral geniculate nucleus (LGN):
                         1. Part of thalamus: In thalamus each sensory system has an important system of
                             synaptic connections, LGN for vision which alters information.
                              a. Six cone-like layers of cells:
                                   1. Four upper layers are the Parvocellular layers.
                                          a. These are the most inferior layers.
                                   2. Two lower layers are the Magnocellular layers.
                              b. Each layer receives tract fibers from only one eye.
                                   1. Layers 1,4,6, receive from contra eye.
                                   2. Layers 2,3,5, receive from ipsilateral eye.
                              c. Each ganglion cell axon goes only to one layer.
                              d. Within layers they branch five to six times, each synapse with a different LGN cell.
                              e. Lower retina to lateral part, upper retina to medial part, macular retina to
                                  posterior part.
               e. Optic radiations: Axons of LGN cells (geniculo-calcarine pathway).
                    1. Fibers from medial LGN (upper retina) form upper portions of radiations, go to upper half
                        of visual cortex (cuneus gyrus).
                    2. Fibers from lateral LGN (lower retina) form lower part of radiations, loops of Meyer, go
                        to lower half of visual cortex (lingual gyrus), (loops of Meyer are from the lower
                        radiations forward into temporal lobe).
                    3. Fibers from posterior LGN (macular retina) go in middle of radiations to posterior cortex,
                        upper to cuneus gyrus, lower to lingual gyrus.
               f. Visual cortex: Primary visual cortex, striate cortex, broadman #17, occipital cortex.
                    1. Location: Inner medial surface, both hemispheres, extends around tip and a little on outer
                        surface.
                    2. Divided on medial surface by the calcarine fissure:
                         a. Above: Cuneus gyrus, upper retina.
                         b. Below: Lingual gyrus, lower retina.
                    3. Midway up and down is striae of Gennari, a thick visually distinct band of axons and
                        dendrites in the region of layer four.
                    4. In layer four: Axons from LGN.
                    5. Connections:
                         a. To other visual cortex via commissural fissure.
                              1. Right visual cortex: Left half of visual field.
                              2. Left visual cortex: Right half of visual field.
                         b. To frontal eye fields, keeps image on fovea.
                         c. With parastria (18) and peristria (19), psychovisual areas associated with memory.
                         d. With superior colliculus.
                         e. With oculomotor nuclei: Descending fibers in optic radiations in occipital
                             mesencephalic tract.
               g. Field changes: Backwards.
                    1. Retinal loss: Usually isolated, monocular scotoma, may be binocular if systemic.
                    2. Severed optic nerve: Blindness, also results from total retinal degradation or opaque
                        cornea, lens, and vitreous.
                    3. Saggital cut at chiasm: Nasal fibers, bitemporal heteronymous hemianopsia.
                    4. Pituitary tumor: Pressure on chiasm, bitemporal heteronymous hemianopsia.
                    5. Aneurism of right internal carotid artery: Pressure on right side of chiasm, loss of left
                        field in right eye, loss of temporal field in both eyes.
                    6. Sever geniculo calcarine tract: Opposite homonymous hemianopsia.
                    7. Affect loops of Meyer: Affects lower retina, opposite superior homonymous
                        quadrantanopsia.
                    8. Damage to posterior cortex: Central field loss.