KIN 460 Spring 2014 Practice Questions for Final Exam 1 Visual System a Describe how the eye is able to form images on the retina Include in your answer clearly the function of the key structures Key Structures Cornea white part of the eye Iris colored part of the eye Ciliary muscles involved in accommodation of the lens works with zonule fibers to change shape of lens in order to let more or less light into the pupil Lens pupil where light enters the eye Anterior chamber aqueous humor front part of the eye regulates the pressure in the eye by replenishing the liquid Posterior chamber vitereous humor back part of the eye largest region of the eye floaters can occur here collection of debris that can interfere with vision Fovea central region of retina where highest density of cones are located and no rods are found high visual acuity Retina lateral region of the fovea Optic disc blind spot location of no photoreceptors no rods or cones Optic nerve where are nerves meet Process of Image Formation Light hits the cornea gets refracted bent then enters the pupil through the lens where it is further refracted The size of the pupil can be adjusted to let more or less light in by contraction relaxation of the ciliary muscles The shape of the lens can also be adjusted by a combination of the ciliary muscles and the zonule fibers working together to adjust how light hits the back of the eye this ability is known as accommodation If the object being viewed is far away the lens will be flattened there will be a smaller refraction angle and in turn less refraction If the object being viewed is near by the lens will be rounded there will be a larger refraction angle and in turn more refraction The goal is for light to hit the back of the eye at the center of the retina called the fovea fovea has mostly cones no rods because this is where the optimal visual acuity is reached Some light may not hit the fovea directly and may hit the lateral parts of the back of the eye called the retina which has cones and rods the farther from the fovea the more rods you get Info from the photoreceptors located on the fovea and retina goes down the optic nerve location of no photoreceptors no rods or cones blind spot and is transmitted to the brain for processing Cones Color and visual acuity Rods Night vision Blind Impairment of Cones Night Blindness Impairment of Rods b What parts of the retina provide 1 visual acuity and 2 night vision Explain your answer 1 Visual acuity Provided by the fovea center region Fovea is where the highest density of cones are located Cones provide visual acuity 2 Night vision Provided by the lateral regions of the retina These regions have high densities of rods Rods are used in low light situations but do not provide high levels of visual acuity c Draw a graph with the changes in distribution of rods and cones on the retina clearly label the axes d Explain either in words or through a diagram how the left optic tract comes to represent images from the right visual field and the right optic tract images from the left visual field At the fovea 0 degrees we have the highest density of cones and no rods This is where the highest degree of visual acuity can be found The farther from the fovea we get the more rods we see and the less cones we see Nasal indicates closer to the nose temporal indicates closer to the lateral sides of the heads Note that the optic disc has NO photoreceptors no rods or cones this is the optic nerve and also considered a blind spot Everything in the left visual field hits nasal retina of the left eye and the temporal retina of the right eye which both filter into the right optic tract Conversely everything in the right visual field hits the nasal retina of the right eye and the temporal retina of the left eye which both filter into the left optic tract Note All temporal information from one side stays on that side while nasal information from one side crosses over to the opposite side 2 Somatosensory System a Describe the different kind of cutaneous receptors and their function in the skin that are sensitive to mechanical deformations Sensory Receptors Proprioceptors give information about where our limbs are in space largest diameters fastest conduction velocity Mechanoreceptors touch next largest diameters 5 types Free nerve endings Meissner corpuscle Merkel cell neurite complex Ruffini ending Pacinian corpuscle Pain temperature receptors smallest diameters slowest conduction velocities Mechanoreceptors Free nerve endings pain temperature Meissner corpuscle grip control slippage rapid Merkel cell neurite complex form and texture resolution high slow Ruffini ending skin stretch slow Pacinian corpuscle vibration rapid Deformation in the skin results in depolarization and action potentials b Describe how we can assess the sensitivity of cutaneous receptors in the skin What factors may influence this sensitivity Sensitivity of cutaneous receptors in skin can be assessed using the two point discrimination threshold test Factors that may influence the sensitivity of cutaneous receptors Receptive field density the more receptors in a given area the more receptor dense that specific field the more sensitive the response of the receptors Intensity of stimuli the more intense the stimuli the more sensitive the reponse There is no difference in nature of receptors c Explain how the somatosensory cortex is organized according to receptor density Larger areas of the cortex are represented by the areas of the body that have high sensitivity of receptors high receptive field densities 3 Vestibular System a What is the function of the two different components of the vestibular system namely the otoliths and the semicircular canals Otolith organs 2 give information about linear accelerations and static head positions tilting head forward or back or when head moves with entire body These don t work in outer space disorientation Semicircular canals 3 give information about angular accelerations rotation of head depolarization in direction of head turn b How is neural activity generated in these two systems Otolith organs Covered in hair cells separated into bundles made up one large hair cell kinocilium and many smaller hair cells stereocilia As movement occurs hair cells move if stereocilia move toward kinocilium depolarization neurotransmitter is released excitation of vestibular nerve if stereocilia and kinocilium move away from one another hyperpolarization