PCB3743 Vertebrate Physiology Summer 2014 Exam 2 Study Guide Audition and Vestibular System 1 Understand the mechanism by which the membrane potential of hair cells changes in response to vibration Stereocilia Tufted projections that stick into endolymph and gelatinous tectorial membrane bend with vibration Bending of the stereocilia causes a change in membrane potential regulates release of neurotransmitter onto afferent nerve o Bending opens K channels o Because endolymph is high in K K rushes into hair cell to cause depolarization Depolarization more neurotransmitter release more action potentials Hyperpolarization less neurotransmitter release fewer action potentials 2 Know the difference between the utricle and semicircular canals in terms of responding to linear vs rotational acceleration Utricle Saccule detect linear acceleration Uses otoliths calcium carbonate crystals Inertial mass of otoliths used to detect gravity starting stopping during linear motion 1 PCB3743 Vertebrate Physiology Summer 2014 Exam 2 Study Guide Semicircular Canals detect rotational acceleration in each of the 3 planes Sloshing of endolymph around the canal deforms the cupula which bends hair cell 3 Know the basic anatomy of the outer middle and inner ear Fox Figure 10 12 10 18 2 PCB3743 Vertebrate Physiology Summer 2014 Exam 2 Study Guide 4 Understand the frequency response of the basilar membrane and how it translates sound frequency into a location within the cochlea The greater the frequency of a sound the higher the pitch High frequency high pitch Low frequency low pitch Vibrations of oval window vibrations in endolymph vibration of basilar membrane Response of the basilar membrane varies across its length Low frequency sounds vibrate the apex of the cochlea Basilar membrane is thicker High frequency sounds vibrate the base of the cochlea 3 PCB3743 Vertebrate Physiology Summer 2014 Exam 2 Study Guide Basilar membrane is thinner 5 Understand the receptive eld of an auditory nerve ber Receptive field of neuron position of hair cells in cochlea Each auditory neuron responds best to characteristic frequency A neuron s response rate of action potentials reflects the intensity of sound at characteristic frequency 6 Understand how a cochlear implant can substitute for loss of hair cells in the cochlea Cochlear Implant Electrodes threaded into the cochlea a receiver implanted in the temporal bone and an external microphone processor transmitter Reproduce function of basilar membrane hair cells Stimulate auditory nerve endings at appropriate point in cochlea to reproduce tonotopic mapping of missing hair cells Some neurons can be electrically stimulated to produce action potentials convey information of low medium and high sound frequencies to the brain Ex Sound of voice music if only a small number of frequencies are restored 4 PCB3743 Vertebrate Physiology Summer 2014 Exam 2 Study Guide Vision 7 Know the basic anatomy of the retina fovea optic disk and the cells of the retina Fox Figures 10 43 10 44 You do NOT need to know the detailed anatomy of the eyeball Retina Layer of photoreceptor cells neurons and ganglion cells at back of the eye Photoreceptors are at the back of the retina o Light passes through neural layers of retina to reach photoreceptors Fovea Center of the visual field with the highest acuity Highest density of photoreceptors In fovea one photoreceptor transmits to one ganglion cell Optic Disk Blind Spot Point where optic nerve cranial nerve II leaves eye and central artery vein enter eye Interrupts retina no photoreceptor cells here Photoreceptor Cells Synapse onto bipolar cells neurons Rods Contain light sensitive photopigment protein rhodopsin Cones Contain photopigment photopsins o Grayscale low light level o Night vision o Peripheral vision o High light level o High density in fovea o Detailed vision o Either S short blue M medium green L long red Bipolar Cells Synapse onto ganglion cells neurons Ganglion Cells Project to brain via optic nerve 5 PCB3743 Vertebrate Physiology Summer 2014 Exam 2 Study Guide 8 Understand the mechanism by which photoreceptor cells detect photons how visual pigments work and the G protein cascade that modulates the dark current in the rod outer segment Photoreceptors are activated when light produces a chemical change in molecules of pigment contained within the membranous discs of the outer segments of the receptor cells 6 PCB3743 Vertebrate Physiology Summer 2014 Exam 2 Study Guide Dark Current and Activation of Rhodopsin 1 Rods have cGMP gated Na channels on their plasma membranes 2 In the dark cGMP levels are high Na channels are open 3 Influx of Na depolarizes photoreceptor cell so it releases more neurotransmitter 4 Light activates rhodopsin in the disk membranes by altering configuration of 5 Rhodopsin is a G protein coupled receptor activated by light not a ligand a Activated G proteins activate a phosphodiesterase that breaks down 6 In light cGMP levels fall cGMP gated Na channels close 7 Photoreceptor cell becomes hyperpolarized so it releases less neurotransmitter in the dark retinal vitamin A cGMP in the light 9 Understand the difference between on center and off center ganglion cells On Center Ganglion Cells Ganglion cells that are stimulated by light at the center of their visual fields Respond to light surrounded by dark Off Center Ganglion Cells Ganglion cells that are inhibited by light in the center and stimulated by light in the surround Respond to dark surrounded by light A small spot of light can be a more effective stimulus than a larger area of light Activity of each ganglion cell is a result of the difference in light intensity between the center surround of its visual field Helps accentuate the contours of images improve visual acuity 7 PCB3743 Vertebrate Physiology Summer 2014 Exam 2 Study Guide 8 10 Be able to interpret the effects of transecting or lesioning the optic nerve PCB3743 Vertebrate Physiology Summer 2014 Exam 2 Study Guide optic tract or visual cortex on the visual field of a patient Damage to left visual cortex causes loss of sight in right visual field Damage to right visual cortex causes loss of sight in left visual field Lesions in the dorsal pathway can t pick up or orient objects Lesions in the ventral pathway can t recognize or describe objects orientations but visually guided motor responses left intact 9 PCB3743 Vertebrate Physiology Summer 2014 Exam 2 Study Guide Taste and Smell Although I did not cover
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