through what structure would you expect the reflex arc of the consensual reflex to travel

Chapter vii: Ocular Motor Organisation

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vii.ane Introduction

The simplicity of the motor systems involved in controlling eye musculature make them platonic for illustrating the mechanisms and principals yous have been studying in the preceding material on motor systems. They involve the action of few muscles and of well divers neural circuits.

Nosotros use our optics to monitor our external environment and depend on our ocular motor systems to protect and guide our eyes. The ocular motor systems command eye lid closure, the amount of light that enters the middle, the refractive backdrop of the eye, and centre movements. The visual organisation provides afferent input to ocular motor circuits that employ visual stimuli to initiate and guide the motor responses. Neuromuscular systems command the muscles within the eye (intraocular muscles); the muscles attached to the eye (extraocular muscles) and the muscles in the eyelid. Ocular motor responses include ocular reflexes and voluntary motor responses to visual and other stimuli. The complexity of the circuitry (the chain or network of neurons) controlling a ocular motor response increases with the level of processing involved in initiating, monitoring, and guiding the response.

In this chapter we will start at the level of reflex responses and move onto more complex voluntary responses in the following lecture. The middle blink reflex is the simplest response and does not require the interest of cortical structures. In contrast, voluntary heart movements (i.e., visual tracking of a moving object) involve multiple areas of the cerebral cortex as well every bit basal ganglion, encephalon stalk and cerebellar structures.

7.2 Ocular Reflex Responses

The ocular reflexes are the simplest ocular motor responses. Ocular reflexes recoup for the condition of the cornea and for changes in the visual stimulus. For case, the eye glimmer reflex protects the cornea from drying out and from contact with foreign objects. The pupillary lite reflex compensates for changes in illumination level, whereas the adaptation responses compensate for changes in eye-to-object-viewed distance. Note that reflex responses are initiated by sensory stimuli that activate afferent neurons (e.g., somatosensory stimuli for the center blink reflex and visual stimuli for the pupillary light reflex and adaptation responses).

In general, ocular reflexes are consensual (i.eastward., the response is bilateral involving both optics). Consequently, a light directed in 1 eye elicits responses, pupillary constriction, in both eyes. In this affiliate you volition learn of the structures normally involved in performing these ocular responses and the disorders that issue from damage to components of neural circuit controlling these responses.

A. The Middle Glimmer Reflex

Tactile stimulation of the cornea results in an irritating awareness that ordinarily evokes eyelid closure (an middle blink). The response is consensual (i.eastward., bilateral) - involving automatic eyelid closure at both eyes.

The corneal middle blink reflex neural circuit: This neural circuit (Figure 7.one) is relatively simple, consisting of the

• trigeminal1° afferent (gratis nervus endings in the cornea, trigeminal nerve, ganglion, root, and spinal trigeminal tract), which end on
  
• trigeminal 2° afferent in the spinal trigeminal nucleus, some of which send their axons to
  
• reticular formation interneurons, which send their axons bilaterally to
  
• facial motor neurons in the facial nucleus, which send their axons in the facial nervus to
  
• orbicularis oculi, which functions to lower the eyelid
  

Figure vii.1 The corneal eye blink reflex is initiated past the free nervus endings in the cornea and involves the trigeminal nerve and ganglion, the spinal trigeminal tract and nucleus, interneurons in the reticular germination, motor neurons in the facial nucleus and nerve, and the orbicularis oculi. Equally the afferent information from each cornea is distributed bilaterally to facial motor neurons by the reticular formation interneurons, the heart blink response is consensual, that is, both eye lids will shut to stimulation of the cornea of either middle.

B. Pupillary Light Reflex

The pupillary calorie-free reflex involves adjustments in educatee size with changes in light levels.

• The reflex is consensual: Unremarkably lite that is directed in one eye produces student constriction in both optics.
  
• The direct response is the alter in pupil size in the eye to which the lite is directed (e.k., if the light is shone in the right eye, the correct pupil constricts).
  
• The consensual response is the change in pupil size in the eye opposite to the eye to which the light is directed (due east.yard., if the light is shone in the correct centre, the left pupil also constricts consensually).
  

The pupillary light reflex allows the heart to adjust the amount of light reaching the retina and protects the photoreceptors from bright lights. The iris contains two sets of smooth muscles that control the size of the pupil (Figure seven.ii).

• The sphincter muscle fibers form a ring at the educatee margin then that when the sphincter contracts, information technology decreases (constricts) pupil size.
  
• The dilator musculus fibers radiate from the pupil aperture and then that when the dilator contracts, it increases (dilates) student size.

Both muscles human activity to control the amount of light entering the eye and the depth of field of the centre^ane.

• The iris sphincter is controlled by the parasympathetic system, whereas the iris dilator is controlled past the sympathetic system.
  
• The action of the dilator is antagonistic to that of the sphincter and the dilator must relax to allow the sphincter to decrease student size.
  

Unremarkably the sphincter action dominates during the pupillary low-cal reflex.

Effigy seven.ii Iris dilator and sphincter muscles and their actions.

The pupillary light reflex neural circuit: The pathway decision-making pupillary light reflex (Effigy seven.3) involves the

• retina, optic nervus, optic chiasm, and the optic tract fibers that bring together the
  
• brachium of the superior colliculus, which terminate in the
  
• pretectal surface area of the midbrain, which sends most of its axons bilaterally in the posterior commissure to terminate in the
  
• Edinger-Westphal nucleus of the oculomotor complex, which contains parasympathetic preganglionic neurons and sends its axons in the oculomotor nerve to terminate in the
  
• ciliary ganglion, which sends its parasympathetic postganglionic axons in the
  
• short ciliary nerve, which ends on the
  
• iris sphincter
  

Figure 7.3 The pupillary light reflex pathway. The lines ending with an arrow betoken axons terminating in the construction at the tip of the arrow. The lines commencement with a dot betoken axons originating in the structure containing the dot. Bilateral impairment to pretectal area neurons (e.g., in neurosyphilis) will produce Argyll-Robertson pupils (not-reactive to light, active during adaptation).

Recall that the optic tract carries visual data from both eyes and the pretectal area projects bilaterally to both Edinger-Westphal nuclei: Consequently, the normal pupillary response to light is consensual. That is, a low-cal directed in one eye results in constriction of the pupils of both optics.

C. Pupillary Dark Response

The pupils unremarkably amplify (increase in size) when it is dark (i.due east., when light is removed). This response involves the relaxation of the iris sphincter and contraction of the iris dilator. The iris dilator is controlled by the sympathetic nervous arrangement.

The pupillary dark reflex neural circuit: The pathway controlling pupil dilation involves the

• retina and the optic tract fibers terminating on neurons in the hypothalamus and the
  
• axons of the hypothalamic neurons that descend to the spinal cord to end on the
  
• sympathetic preganglionic neurons in the lateral horn of spinal string segments T1 to T3, which send their axons out the spinal cord to end on the
  
• sympathetic neurons in the superior cervical ganglion, which ship their
  
• sympathetic postganglionic axons in the long ciliary nerve to the
  
• iris dilator.
  

Axons from the superior cervical ganglion also innervate the face up vasculature, sweat and lachrymal glands and the eyelid tarsal muscles. When the superior cervical ganglion or its axons are damaged, a constellation of symptoms, known as Horner's syndrome, result. This syndrome is characterized by miosis (pupil constriction), anhidrosis (loss of sweating), pseudoptosis (mild eyelid droop), enopthalmosis (sunken eye) and flushing of the face.

D. The Accommodation Response

The accommodation response is elicited when the viewer directs his optics from a afar (greater than 30 ft. away) object to a nearby object (Nolte, Figure 17-40, Pg. 447). The stimulus is an "out-of-focus" image. The accommodation (almost point) response is consensual (i.east., it involves the deportment of the muscles of both optics). The adaptation response involves three deportment:

Student accommodation: The activeness of the iris sphincter was covered in the section on the pupillary light reflex. During accommodation, pupil constriction utilizes the "pin-hole" effect and increases the depth of focus of the heart by blocking the calorie-free scattered by the periphery of the cornea (Nolte, Figure 17-39, Pg. 447). The iris sphincter is innervated by the postganglionic parasympathetic axons (short ciliary nervus fibers) of the ciliary ganglion (Figure vii.three).

Lens adaptation: Lens accommodation increases the curvature of the lens, which increases its refractive (focusing) ability. The ciliary muscles are responsible for the lens accommodation response. They control the tension on the zonules, which are attached to the rubberband lens capsule at one end and anchored to the ciliary body at the other cease (Figure 7.4).

Figure vii.4 The ciliary muscles, which command the position of the ciliary processes and the tension on the zonule, control the shape of the lens. The ciliary muscles part as a sphincter and when contracted pull the ciliary body toward the lens to decrease tension on the zonules (encounter Figure 7.five). The decreased tension allows the lens to increment its curvature and refractive (focusing) ability. When the ciliary musculus is relaxed, the ciliary trunk is not pulled toward the lens, and the tension on the zonules is college. High tension on the zonules pulls radially on the lens capsule and flattens the lens for altitude vision. The ciliary muscles are innervated by the postganglionic parasympathetic axons (short ciliary nerve fibers) of the ciliary ganglion

Effigy vii.v The accommodation response of the lens: comparison the lens shape during near vision (contraction of the ciliary muscle during accommodation) with lens shape during distance vision (relaxation of the ciliary muscle).

Convergence in accommodation: When shifting one'due south view from a distant object to a nearby object, the optics converge (are directed nasally) to keep the object's paradigm focused on the foveae of the ii eyes. This activeness involves the wrinkle of the medial rectus muscles of the two eyes and relaxation of the lateral rectus muscles. The medial rectus attaches to the medial aspect of the eye and its contraction directs the eye nasally (adducts the centre). The medial rectus is innervated past motor neurons in the oculomotor nucleus and nerve.

The accommodation neural circuit: The circuitry of the accommodation response is more complex than that of the pupillary low-cal reflex (Figure 7.6).

The afferent limb of the excursion includes the

• retina (with the retinal ganglion axons in the optic nerve, chiasm and tract),
  
• lateral geniculate trunk (with axons in the optic radiations), and
  
• visual cortex.
  

Ocular motor control neurons are interposed betwixt the afferent and efferent limbs of this circuit and include the

• visual association cortex, which
  
  • determines the image is "out-of-focus"
    
  • sends cosmetic signals via the internal capsule and crus cerebri to the
    
• supraoculomotor nuclei, which
  
  • is located immediately superior to the oculomotor nuclei
    
  • generates motor control signals that initiate the adaptation response
    
  • sends these control signals bilaterally to the oculomotor complex.
    

The efferent limb of this arrangement has 2 components: the

• Edinger-Westphal nucleus, which
  
  • sends its axons in the oculomotor nerve to
    
  • command the ciliary ganglion, which
    
    • sends it axons in the brusque ciliary nervus to
      
    • control the iris sphincter and the ciliary muscle/zonules/lens of the centre
      
• oculomotor neurons, which
  
  • sends its axons in the oculomotor nerve to
    
  • command the medial rectus
    
  • converge the 2 optics.
    

Figure 7.6 The accommodation pathway includes the afferent limb, which consists of the entire visual pathway; the college motor command structures, which includes an area in the visual association cortex and the supraoculomotor area; and the efferent limb, which includes the oculomotor nuclei and ciliary ganglion. The lines ending with an pointer indicate axons terminating in the construction at the tip of the arrow. The lines kickoff with a dot indicate axons originating in the structure containing the dot. During accommodation three motor responses occur: convergence (medial rectus contracts to directly the eye nasally), pupil constriction (iris sphincter contracts to decrease the iris aperture) and lens accommodation (ciliary muscles contract to decrease tension on the zonules).

7.3 Clinical Examples

An excellent way to test your knowledge of the cloth presented thus far is by examining the furnishings of damage to structures within the ocular motor pathways. The observed motor loss(s) provide clues to the pathway(s) affected; and the musculus(s) and eye afflicted provide clues to the level of the damage.

Cranial nerve damage: Impairment to cranial nerves may issue in sensory and motor symptoms. The sensory losses would involve those sensations the cranial nerve normally conveys (eastward.k., gustation from the anterior two thirds of the tongue and somatic sensations from the skin of the ear - if facial nerve is damaged). The motor losses may be astringent (i.e., a lower motor neuron loss that produces total paralysis) if the cranial nerve contains all of the motor axons controlling the muscles of the normally innervated area.

The cranial fretfulness involved in the eye blink response and pupillary response are the optic, oculomotor, trigeminal and facial nerves.

• The optic nerve carries visual information from the heart.
  
• The oculomotor nerve contains
  
  • lower motor axons innervating
    
    • extraocular muscles: the medial, superior and inferior rectus muscles, the inferior oblique muscle,
      
    • eyelid muscle: the superior levator palpebrae,
      
  • equally well as parasympathetic preganglionic axons to the ciliary ganglion.
    
• The trigeminal nervus contains
  
  • the 1° somatosensory afferents for the face, dura, oral and nasal cavities
    
  • the lower motor axons for the jaw muscles.
    
• The facial nervus contains
  
  • the lower motor neurons innervating the superficial muscles of the face,
    
  • the 1° gustatory afferents to the anterior tongue
    
  • the parasympathetic preganglionic axons to parasympathetic ganglia for the lachrymal and salivary glands.
    

7.4 Clinical Example #1

Symptoms. The patient, who appears with a bloodshot left eye, complains of an disability to close his left eye. When asked to rise his eyebrows, he can only elevate the right countenance. When asked to close both optics, the right eyelid closes only the left eyelid is only partially airtight. Touching the right or left cornea with a wisp of cotton elicits the heart blink reflex in the right centre, just not the left center (Figure 7.7). Notwithstanding, the patient reports he can feel the cotton when it touches either eye. He can smile, whistle and show his teeth, which indicates his lower facial muscles are functioning usually. Concrete examination determines that impact, vibration, position and hurting sensations are normal over the entire the trunk and face. There are no other motor symptoms.

Figure 7.7 Find the reaction to a wisp of cotton touching the patient's left and correct cornea.

Ascertainment: Y'all observe that the patient

• has not lost cutaneous sensation in the upper left face up expanse
  
• does not blink when his left cornea is touched
  
• cannot close his left eye voluntarily
  

You lot conclude that his left center'south functional loss is

• not sensory
  
• a lower motor neuron dysfunction
  

Pathway(s) affected: You conclude that structures in the following motor pathway accept been affected

• the eye blink pathway (Figure 7.8)
  

Effigy 7.8 The eye blink pathway involves the trigeminal nervus, spinal trigeminal tract and nucleus, the reticular formation, and the facial motor nucleus and nervus.

Side & Level of harm: As the middle glimmer loss involves

• merely motor function
  
• both reflex and voluntary motor functions
  
• the upper office of the face
  
• merely 1 eye lid
  
• eyelid closure
  

Conclusion: You lot conclude that the damage involves

• the facial nervus
  
• a branch of the nerve innervating the upper confront
  
• a lower motor neuron paralysis of the left orbicularis oculi
  
• motor innervation on the left side (i.due east., the symptoms are ipsilesional)
  

When lower motor neurons are damaged, there is a flaccid paralysis of the muscle normally innervated. The action of the musculus will exist weakened or lost depending on the extent of the damage. There will be a weakened or no reflex response and the muscle will be flaccid and may atrophy with fourth dimension.

The Facial Nerve. Section of the facial nerve on one side will result in paralysis of the muscles of facial expression on the ipsilesional side of the face up. There will be an disability to close the denervated eyelid voluntarily and reflexively. The eyelids may have some mobility if the oculomotor innervation to the levator is unaffected.

7.5 Clinical Case #2

Symptoms. The patient complains of a badly infected left eye. When he is asked to close both eyes, both eyelids close. Touching the right cornea with a wisp of cotton elicits the eye blink reflex in the both eyes (Effigy seven.ix, Right). However, touching the left cornea with a wisp of cotton does not elicit the eye glimmer reflex in the either eye (Effigy 7.9, Left). The patient cannot detect pinpricks to his left forehead. However, he reports that pinpricks to rest of his face are painful. He tin can blink, wrinkle his brows, smile, and whistle and evidence his teeth, which indicates his facial muscles are functioning normally. Physical examination determines that bear on, vibration, position and hurting sensations are normal over the entire the body and over the lower left and right side of his face.

Figure seven.9 Find the reaction to a wisp of cotton touching the patient'due south left and right cornea.

Observation: You observe that the patient

• responds with direct and consensual eye blink when his correct cornea is touched
  
• can close his left eye voluntarily
  
• has lost cutaneous sensation in the upper left face up area
  
• does non blink when his left cornea is touched
  

You lot conclude that his left eye's functional loss is

• not motor
  
• sensory
  

Pathway(southward) affected: You conclude that structures in the following reflex pathway have been afflicted

• the heart blink pathway (Figure 7.8)
  

Side & Level of damage: As the eye blink loss involves

• only one heart
  
• a sensory loss
  
• the upper part of the confront
  

Conclusion: Yous conclude that the damage involves

• a loss of the afferent limb of the eye blink response
  
• the trigeminal nerve
  
• a branch of the nerve innervating the upper face
  
• the innervation of the left side (i.due east., the symptoms are ipsilesional)
  

The Trigeminal Nerve. Section of the trigeminal nervus will eliminate somatosensory sensation from the face up and the eye blink reflex (eastward.g., with section of the left trigeminal nerve, low-cal touch of the left cornea volition not produce an eye blink in the left or right middle). Nonetheless, calorie-free touch of the right cornea will elicit a bilateral heart blink. The result of sectioning the trigeminal nerve is to remove the afferent input for the eye blink reflex.

7.6 Clinical Example #3

Symptoms. The patient complains of pain in her left eye. Her left pupil appears dilated and is not reactive to low-cal directed at either the left or right middle (Effigy vii.10). The right educatee appears normal in size and reacts to calorie-free when it is directed in the correct or left center. Both eyelids can exist elevated and lowered and both eyes exhibit normal move. Bear upon, vibration, position and pain sensations are normal over the unabridged the trunk and confront. There are no other motor symptoms.

	Figure 7.x Observe the reaction of the patient'south pupils to light directed in the left or right centre.

Observation: You observe that the patient has

• a left pupil that does not react to light directly or consensually
  
• a right educatee that reacts to lite straight and consensually
  
• normal eye movements
  

You lot conclude that his left eye's functional loss is

• not sensory (the right pupil reacts to light directed at the left heart)
  
• a motor dysfunction
  

Pathway(due south) affected: Yous conclude that structures in the following motor pathway have been affected

• the pupillary lite reflex pathway (Figure vii.xi)
  

	Figure 7.11 The pupillary light reflex pathway involves the optic nerve and the oculomotor nerve and nuclei.

Side & Level of damage: As the pupillary light reflex loss

• involves merely i eye
  
• involves merely motor function
  
• does non involve eyelid or ocular move
  
• is limited to pupil constriction in the left eye
  

Conclusion: You conclude that the damage

• involves the motor innervation of the left iris sphincter²
  
• involves structures peripheral to the oculomotor nucleus (i.e., eye movement unaffected)
  
• does not involve the oculomotor nerve
  
• involves the ciliary ganglion or the curt ciliary nerve
  
• is on the left side (i.e., the symptoms are ipsilesional)
  

Parasympathetic Innervation of the Eye. Section of the parasympathetic preganglionic (oculomotor nerve) or postganglionic (short ciliary nerve) innervation to one heart will outcome in a loss (motor) of both the direct and consensual pupillary low-cal responses of the denervated center. Section of the left brusque ciliary nerve or a benign lesion in the left ciliary ganglion volition result in no direct response to light in the left eye and no consensual response in the left centre when lite is directed on the right eye (a.k.a., tonic pupil). When the harm is limited to the ciliary ganglion or the short ciliary nervus, eyelid and ocular mobility are unaffected.

seven.7 Clinical Case #four

Symptoms. The patient presents with a left eye characterized by ptosis, lateral strabismus, and dilated pupil. When asked to rise his eyelids, he can only raise the lid of the right heart. When asked to close both eyes, both eyelids close fully. His left pupil does not react to light directly or consensually (Figure seven.12). When asked to look to his right, his left eye moves to a central position, merely no further. The right eye is fully mobile. When the patient is asked to look direct alee, you annotation his left centre remains directed to the left and depressed. Concrete examination determines that touch, vibration, position and pain sensations are normal over the entire the body and confront. There are no other motor symptoms.

	Figure 7.12 The patient presents with a left eye characterized by ptosis, lateral strabismus and dilated pupil. Detect the reaction of the patient's pupils to light directed in the left or right middle.

Observation: You observe that the patient

• has non lost cutaneous awareness in the face surface area
  
• has a left ptosis
  
• cannot adduct his left centre (i.e., move it toward the nose)
  
• has a left dilated pupil that is non reactive to lite in either center
  

You conclude that his left eye'southward functional loss is

• not sensory
  
• a lower motor neuron dysfunction
  
• involving an autonomic dysfunction
  

Pathway(s) affected: You conclude that structures in the post-obit motor pathway accept been affected

• the pupillary/oculomotor pathway (Figure seven.11)
  

Side & Level of harm: As the ocular loss involves

• only motor function
  
• both reflex and voluntary motor functions
  
• both somatic and autonomic functions
  
• but the left eye
  

Decision: You conclude that the damage

• involves the oculomotor nerve
  
• is a lower motor neuron paralysis of the superior levator palpebrae
  
• is a lower motor neuron paralysis of the medial, superior & inferior rectus muscles and inferior oblique muscles of the heart
  
• is an autonomic disorder involving the axons of the Edinger-Westphal nucleus
  
• is on the left side (i.eastward., the symptoms are ipsilesional)
  

The Oculomotor Nerve. Section of the oculomotor nerve produces a not-reactive pupil in the ipsilesional side as well as other symptoms related to oculomotor nerve damage (e.grand., ptosis and lateral strabismus). Section of the oculomotor nervus on 1 side will result in paralysis of the superior levator palpebrae, which commonly elevates the eyelid. Information technology will also paralyze the medial, superior & inferior rectus muscles and the junior oblique, which volition let the lateral rectus to deviate the eye laterally and the superior oblique to depress the eye. The parasympathetic preganglionic axons of the Edinger-Westphal nucleus, which normally travel in the oculomotor nerve, will be cut off from the ciliary ganglion, disrupting the excursion normally used to control the iris sphincter response to calorie-free.

7.8 Clinical Instance #5

Symptoms. The patient complains of reduced vision in the left eye. Pupil size in both eyes appears normal. However, both pupils do not appear to constrict equally speedily and strongly when light is directed into his left centre (Figure seven.13). That is, compared to the response to light in the left centre, calorie-free in the right middle produces a more than rapid constriction and smaller student in both eyes. Physical exam determines that touch, vibration, position and pain sensations are normal over the unabridged the body and over the lower left and correct side of his confront.

	Figure seven.13 Discover the reaction of the patient's pupils to light directed in the left or right eye.

Ascertainment: You discover that the patient'southward pupils

• respond when light is directed into either eye
  
• has weaker direct and consensual responses to light directed in the left eye
  

Y'all conclude that his left center'due south functional loss is

• not motor
  
• sensory (because the responses in both eyes are weaker when light is directed in the left eye)
  

Pathway(southward) affected: You conclude that structures in the post-obit motor pathway have been afflicted

• the pupillary low-cal reflex pathway (Figure seven.11)
  

Side & Level of impairment: As the pupillary light response arrears involves

• only stimulation of ane eye
  
• a sensory loss
  
• the left middle
  

Conclusion: You conclude that the damage

• is in the afferent limb of the pupillary light response
  
• involves the optic nerve or retina
  
• is on the left side (i.east., the symptoms are ipsilesional)
  
• produced a left pupillary afferent defect
  

The Optic Nerve. Fractional damage of the retina or optic nerve reduces the afferent component of the pupillary reflex circuit. The reduced afferent input to the pretectal areas is reflected in weakened directly and consensual pupillary reflex responses in both eyes (a.k.a., a relative afferent pupillary defect).

Section of one optic nervus volition outcome in the complete loss of the direct pupillary lite reflex just non the consensual reflex of the blinded eye. That is, if the left optic nerve is sectioned, light directed on the left (blind) center will not elicit a pupillary response in the left heart (direct reflex) or the correct eye (consensual response). Yet, light directed in the right heart will arm-twist pupillary responses in the right eye and the left (bullheaded) heart. The consequence of sectioning one optic nerve is to remove the afferent input for the direct reflex of the blinded middle and the afferent input for the consensual reflex of the normal heart. Department of one optic tract will not eliminate the direct or consensual reflex of either eye every bit the surviving optic tract contains optic nervus fibers from both eyes. However, the responses to light in both eyes may be weaker because of the reduced afferent input to the ipsilesional pretectal surface area.

7.ix Clinical Instance #half dozen

Symptoms. A patient who is suffering from the late stages of syphilis is sent to you for a neuro-ophthalmological work-up. His vision is normal when corrected for refractive errors. He has normal ocular mobility and his eyelids tin can be elevated and depressed at will. Examination of his pupillary responses indicates a loss of the pupillary light reflex (no pupil constriction to light in either eye) just normal pupillary adaptation response (pupil constricts when the patient's eyes are directed from a distant object to one nearby).

Observation: You observe that the patient has normal vision just that his pupils

• do not respond when lite is directed into the either of his eyes
  
• practice reply during accommodation
  

You lot conclude that his heart's functional loss is

• not sensory (his vision is normal)
  
• motor (the pupillary light responses in both eyes are absent)
  
• higher-order motor (because he has a normal pupillary adaptation response)
  

Pathway(south) affected: You conclude that construction(southward) in the

• adaptation pathway take not been damaged (Figure 7.fourteen)
  
• pupillary light reflex pathway accept been damaged (Effigy 7.11)
  

Side & Level of damage: As the pupillary response deficit

• does not involve a sensory loss
  
• does not involve the pupil accommodation response
  
• involves only the pupillary light reflex response
  

Conclusion: You conclude that the damage

• involves the pretectal area bilaterally
• spared the supraoculomotor expanse
  
• produced the Argyll Robertson response
  

	Figure 7.14 The accommodation pathway includes the supraoculomotor area, which functions as a "higher-social club" motor control stage controlling the motor neurons and parasympathetic neurons (i.due east., the Edinger-Westphal neurons) of the oculomotor nucleus. This area was spared by syphilis.

In the Argyll Robertson response, at that place is an absenteeism of the pupillary light reflex with a normal pupillary accommodation response. The Argyll Robertson response is attributed to bilateral damage to pretectal areas (which command the pupillary lite reflex) with sparing of the supraoculomotor area (which controls the pupillary adaptation reflex).

The adaptation response involves many of the structures involved in the pupillary light response and, with the exception of the pretectal area and supraoculomotor area, damage to either pathway will produce mutual the symptoms. The most mutual complaint involving the accommodation response is its loss with aging (i.eastward., presbyopia). Call up that presbyopia virtually commonly results from structural changes in the lens which impedes the lens accommodation response.

7.ten Summary

This affiliate described three types of ocular motor responses (the eye blink, pupillary calorie-free and accommodation responses) and reviewed the nature of the responses and the effectors, efferent neurons, college-gild motor control neurons (if any), and afferent neurons normally involved in performing these ocular responses. Tabular array I summarizes these structures and the function(s) of these ocular motor responses. Readers should understand the anatomical ground for disorders that result from damage to components of neural circuit controlling these responses.

Table I Classification of Consensual Ocular Responses & Their Motor Command Structures
Ocular Responses	Part	Afferent Input* & Motor Command Structures
Eye Blink Reflex	Protects cornea from contact with strange objects	Costless Nerve Endings in cornea that are afferent endings of the Trigeminal Nerve, Ganglion, Root & Spinal Trigeminal Tract* Spinal Trigeminal Nucleus* Reticular Formation (bilaterally to) Facial Motor Nuclei & Facial Nerves Orbicularis Oculi
Pupillary Light Reflex	Decreases pupil size (constriction) – reduces the amount of light that enters the eye.	Retina, Optic Nervus, Chiasm & Tracts and Brachium of Superior Colliculus* Pretectal Areas of Midbrain (bilaterally to) Edinger-Westphal Nuclei & Oculomotor Nerves Ciliary Ganglia & Short Ciliary Nerves Iris Sphincters
Pupillary Accommodation Lens Adaptation	Increases depth of focus of center lens system Increases refractive power of lens	Visual Organisation* including Visual Association Cortex Supraoculomotor Nuclei (bilaterally to) Edinger-Westphal Nuclei & Nerve Three Ciliary Ganglia & Brusque Ciliary Fretfulness Iris Sphincters & Ciliary Muscles
Convergence	Eyes directed nasally during accommodation	Visual System* including Visual Clan Cortex Supraoculomotor Nuclei (bilaterally to) Oculomotor Nuclei Medial Rectus Muscles
* Afferent structures proving sensory input.

Test Your Cognition

• Question 1
• A
• B
• C
• D
• Due east

A patient is capable of pupillary constriction during accommodation but not in response to a light directed to either eye. The lesion is virtually likely present in the...

A. optic nerve

B. abducens nucleus

C. Edinger-Westphal nucleus

D. pretectal areas

E. supraoculomotor nucleus

A patient is capable of pupillary constriction during adaptation but non in response to a calorie-free directed to either centre. The lesion is nigh likely present in the...

A. optic nerve This answer is INCORRECT.

Optic nerve is incorrect equally department of i nerve would not obliterate the consensual response to stimulation of the contralesional middle.

B. abducens nucleus

C. Edinger-Westphal nucleus

D. pretectal areas

E. supraoculomotor nucleus

A patient is capable of pupillary constriction during adaptation only non in response to a light directed to either eye. The lesion is almost likely nowadays in the...

A. optic nerve

B. abducens nucleus This answer is Incorrect.

Abducens nucleus is incorrect as information technology is non involved in pupillary responses. Its motor neurons innervate the lateral rectus muscle.

C. Edinger-Westphal nucleus

D. pretectal areas

Eastward. supraoculomotor nucleus

A patient is capable of pupillary constriction during accommodation but not in response to a calorie-free directed to either eye. The lesion is most likely present in the...

A. optic nervus

B. abducens nucleus

C. Edinger-Westphal nucleus This respond is INCORRECT.

Edinger-Westphal is wrong equally damage to this nucleus would diminish the pupil response both to light and during accommodation.

D. pretectal areas

Due east. supraoculomotor nucleus

A patient is capable of pupillary constriction during accommodation but non in response to a light directed to either heart. The lesion is most likely nowadays in the...

A. optic nerve

B. abducens nucleus

C. Edinger-Westphal nucleus

D. pretectal areas This reply is CORRECT!

The pretectal area provide bilateral input to the Edinger-Westphal nucleus for the straight and consensual pupillary light response.

E. supraoculomotor nucleus

A patient is capable of pupillary constriction during accommodation but not in response to a light directed to either eye. The lesion is most probable nowadays in the...

A. optic nerve

B. abducens nucleus

C. Edinger-Westphal nucleus

D. pretectal areas

E. supraoculomotor nucleus This answer is Wrong.

Supraoculomotor nucleus is incorrect considering it is involved in the pupillary accommodation response and not in the pupillary light reflex response.

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Source: https://nba.uth.tmc.edu/neuroscience/m/s3/chapter07.html

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