Laboratory for Physiology EOG

Sensory motor integration A basic concept in the function of the nervous system defined as the PROCESSING OF SENSORY INPUTS LEADING TO THE PRODUCTION OF A MOTOR OUTPUT Last week we also looked at sensory inputs and sensory mapping. In this lab we are still using sensory INPUTS but now we are looking at MOTOR OUTPUTS or the ACTIVATION OF MUSCLE IN RESPONSE TO SENSORY INPUT

PUPILLARY LIGHT REFLEX Will be demonstrated in the first part of the lab For this reflex a light is shone in one eye and this stimulus initiates a reflex that results in CONSTRICTION OF THE PUPILS OF BOTH EYES Purpose of this reflex? To regulate the amount of light entering the eye so that the amount allowed in matches the light conditions. Helps keep photoreceptor activation equal and even in both eyes.

Neurocircuitry of the pupillary light reflex Figure 12.3. The circuitry responsible for the pupillary light reflex. This pathway includes bilateral projections from the retina to the pretectum and projections from the pretectum to the Edinger-Westphal nucleus. Neurons in the Edinger-Westphal nucleus terminate in the ciliary ganglion, and neurons in the ciliary ganglion innervate the pupillary constrictor muscles. Notice that the afferent axons activate both Edinger-Westphal nuclei via the neurons in the pretectum

HINT For part 1 of the lab: Hold your hand along the bridge of the subjects nose and shine the light in one eye while you watch for the reflex in the other eye. A blue or green eyed person will be easier to see the reflex on BUT ALL team members should serve as both tester and subject for this exercise.

EOG PART 2 The Vestibulo-occular reflex (VOR) Evoked by stimulation of the hair cells in the semi-circular canals (see figure) Within the ear you have THREE semi circular canals. Anterior, posterior and horizontal canals. Each of which has receptors called hair cells. These hair cells are innervated by the vestibular part of the 8th cranial nerve and are stimulated by head rotation.

Figure 10-23 - Overview

EOG PART 2 The Vestibulo-occular reflex (VOR) In the exercise you will rotate your lab partners while measuring eye movements. Rotation causes the hair cells to become activated and evoke eye muscle reflexes called VOR reflexes. Rotation in either the horizontal OR vertical plane will evoke responses however for ease of use, we will only be rotating in the horizontal plane and thus stimulate the hair cells of the horizontal semi circular canal. This will be accomplished by spinning in a chair evoking horizontal VOR eye movements measured by BIOPAC

EOG PART 2 The Vestibulo-occular reflex (VOR) Typically, the VOR causes your eyes to move in the OPPOSITE direction to the direction of rotation of the head. SO initially when you spin someone around, the VOR reflex causes the eyes to slowly drift in the opposite direction and then quickly flick back to center. If you record these eye movements it looks like those shown in your packet (slow vs fast phase). Slow drift is mediated by the vestibular system while the fast drift is due to a “reset” mechanism in the brain which moves your eyes back to center. Slow phase Fast Phase

EOG PART 2 The Vestibulo-occular reflex (VOR) Purpose of the VOR: TO STABILIZE YOUR VISUAL FIELD AS YOU ROTATE YOUR HEAD ALLOWING YOU TO VISUALLY FIXATE ON A TARGET WHILE YOUR HEAD MOVES IN SPACE. W/O the VOR you would be unable to see clearly whenever you walked as your head bobs as you walk. More so when you run or jump up and down. You will also see VOR movements AFTER the subject stops spinning. This is called POST ROTARY NYSTAGMUS and is also due to activation of the vestibular system. When you stop spinning the fluid in your ear canal has inertia and continues to flow for a short time, thus evoking PRN VOR movement. You will measure this in the lab today.

HINT HINTS for good VOR recordings: Lean forward at about 30 degrees. The subjects eyes must be CLOSED during the testing

EOG PART 3 Smooth pursuit movements To measure you will record the eye movements as the subject follows a moving object with their eyes. Voluntary eye movements involving very complex processing of information in the visual cortex including the superior colliculus and other brain centers. The stimulus for smooth pursuit movements is the movement of the object across your visual field.

EOG PART 4 SACCADIC EYE MOVEMENTS Very fast eye moments (ballistic like) in which the eyes jump from target to target in your visual field. SEM are used during reading as your eyes jump from word to word. For this exercise each group has reading samples that will be used to demonstrate these movements. HINT: Hold head level, upwards and steady. Have another student hold the paper up in front of the subjects face and hold it completely steady

Enjoy the lab HAVE FUN WITH IT DO NOT RUSH!!!!! QUESTIONS? Enjoy the lab HAVE FUN WITH IT DO NOT RUSH!!!!!