Cranial Nerve Reflexes and Ocular Motility.pdf

Cranial Nerve Reflexes and Ocular Motility AN5203 Dr. Moira Jenkins What is a Reflex? Is an involuntary, unplanned sequence or action and nearly instantaneous movement in response to a stimulus. A reflex is made possible by neural pathways called reflex arcs which can act on an impulse before tha...

Cranial Nerve Reflexes and Ocular Motility AN5203 Dr. Moira Jenkins What is a Reflex? Is an involuntary, unplanned sequence or action and nearly instantaneous movement in response to a stimulus. A reflex is made possible by neural pathways called reflex arcs which can act on an impulse before that impulse reaches the brain. Different Types Deep tendon reflexes Superficial reflexes Cardiovascular reflexes Primitive reflexes Calming reflexes (5S’s- swaddle, suck, swing, shush, side-stomach) Reflexes associated with Cranial Nerves→ DTR Reflex , Monosynaptic Every reflex has 5 components 1. Receptor 2. Sensory afferent 3. Integration 4. Motor efferent 5. Effector target tissue Reflex Testing An easy way to screen test the nerve and/or cord Can be done on most muscles but typical ones are checked clinically Biceps – C5 Patellar – L4 Brachioradialis – C6 Achilles – S1 Triceps – C7 Hyporeflexia – suspect lower motor lesion Hyperreflexia – suspect upper motor lesion Jaw-jerk Reflex, Jaw-closing reflex Sensory and motor limbs- trigeminal V3 Pupillary Light Reflex Each eye will have a direct and indirect reflex Right Eye Direct- shine the light in the right eye, right pupil constricts Indirect- shine the light in the right eye, left pupil constricts Indirect is also known as consensual Left Eye Direct- shine the light in the left eye, left pupil constricts Indirect- shine the light in the left eye, right pupil constricts Denote normal response as a positive reflex Right direct pos Right indirect pos Pupillary Light Reflex Receptor-photoreceptors of the retina Sensory Afferent – Optic N. II (nerve, chiasm, tract) Central Integration- pretectal nucleus and posterior commissure Motor Efferent – Oculomotor N. (Edinger Westphal) Effector Target – constrictor pupillae muscle REFLEXES: Pupillary light reflex Near Response The near response involves 3 responses – accommodation, convergence, pupillary constriction Receptor-photoreceptors of the retina Sensory Afferent – Optic N. II Central Integration- chiasm, tract, LGN, optic radiation, visual cortex, *image is blurred Visual association are sends messages to midbrain Motor Efferent – Oculomotor N. (Edinger Westphal AND somatic motor= oculomotor complex) Effector Target – Constrictor pupillae muscles - Ciliary muscles (lens thickens) - Medial rectus muscles (eyes converge) REFLEXES: Accommodation-convergence reflex The pupillary constriction of near response involves a different part of the Edinger Westphal Nucleus (caudal) than the light reflex (rostral) Argyll Robertson Pupil Seen in neurosyphilis, systemic lupus, diabetes The pretectal area is damaged “Do not react but they do accommodate” Centers for Ocular Motility There are different kinds of eye movements 1. Convergence/Vergence (this is not conjugate) 2. Fast/Searching Saccades-rapid conjugate eye movements, eyes “jump”, looking for someone in a crowd. Frontal eye field 3. Smooth Pursuit/tracking- eyes are conjugate as they track an object, keeping your eyes on someone walking through a crowd. Occipital eye field 4. Vestibulo-ocular movement- gaze and image remains fixated on fovea despite movement of the head and neck Frontal eye field Centers for Ocular Motility • There are no direct fibers from the corticobulbar tract to the motor nuclei for Oculomotor, Trochlear, or Abducens • Gaze centers are under the control of higher cortical areas • Paramedian Pontine Reticular Formation- involved in voluntary horizontal lateral gaze, in the pons near the abducens nucleus, *horizontal gaze center • Stimulates the lateral rectus M. on the same side AND the medial rectus M. contralateral by way of the Medial Longitudinal Fasciculus (MLF) • Rostral internucleus/Nucleus of Cajal – involved in vertical gaze, found where the MLF meets the posterior commissure, midbrain *vertical gaze center Frontal Eye Field Saccadic movement, largely voluntary (smooth pursuit, mostly involuntary) Controls voluntary horizontal gaze to the contralateral side Want to look to the right, excite right lateral rectus muscle and left medial rectus muscle The frontal eye field will project to the contralateral PPRF→ stimulates the abducens nucleus on the same side as the PPRF PPRF→ also sends a projection to the contralateral MLF which goes to stimulate the medial rectus M. ** lesion in frontal eye field, cannot horizontally gaze to the opposite side Lesion in MLF Pt cannot laterally gaze with medial rectus muscle BUT they can converge If lesion is oculomotor N/N or medial rectus muscle Cannot adduct for lateral gaze AND cannot converge Conjugate lateral (horizontal) eye movements Conjugate Vertical Eye Movements (for left eye) Motor Nuclei of Extraocular Muscles Cranial Nerves 3, 4, 6 The Medial Longitudinal Fasciculus (MLF) ascending tract carries fibers from the vestibular nuclei to the Cranial nerve nuclei 3, 4, 6 Conjugate gaze which head and neck are moving Vestibulo-ocular Reflex, VOR – coordinate eye muscles so that image stays focused on retina/fovea even when head is moving (fixation/foveation) Head rotating to right, eyes move to left paired eye movement – conjugate gaze Tract – MLF (dotted circle in picture) Corneal Reflex Sensory limb/arc-Trigeminal V Motor limb/arc- Facial VII Chief/principle sensory nucleus of trigeminal Facial Motor Nucleus Reflexes • Efferents of the sensory trigeminal nuclei project to other brain stem nuclei in order to mediate reflex responses initiated by stimuli originating in the area of CN V distribution. Examples are: • Corneal reflex • Sneezing reflex Gag Reflex Sensory arc- Glossopharyngeal IX Motor arc- Vagus X Jaw opening “reflex” (this is not a reflex) Mandible deviates to side of lesion if LMN Due to weakness of lateral pterygoid M.