PCB3743 Vertebrate Physiology Summer 2014 Exam #2 Study Guide 1 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 motionPCB3743 Vertebrate Physiology Summer 2014 Exam #2 Study Guide 2 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)PCB3743 Vertebrate Physiology Summer 2014 Exam #2 Study Guide 3 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 cochleaPCB3743 Vertebrate Physiology Summer 2014 Exam #2 Study Guide 4 • Basilar membrane is thinner 5. Understand the receptive field of an auditory nerve fiber. 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)PCB3743 Vertebrate Physiology Summer 2014 Exam #2 Study Guide 5 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 o Grayscale, low-light level o Night vision o Peripheral vision • Cones: Contain photopigment photopsins 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 nervePCB3743 Vertebrate Physiology Summer 2014 Exam #2 Study Guide 6 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 cellsPCB3743 Vertebrate Physiology Summer 2014 Exam #2 Study Guide 7 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 in the dark 4. Light activates rhodopsin in the disk membranes by altering configuration of retinal (vitamin A) 5. Rhodopsin is a G-protein coupled receptor – activated by light & not a ligand a. Activated G-proteins activate a phosphodiesterase that breaks down cGMP 6. In light, cGMP levels fall & cGMP-gated Na+ channels close 7. Photoreceptor cell becomes hyperpolarized, so it releases less neurotransmitter 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 acuityPCB3743 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 9 optic tract, or visual cortex on the visual field of a patient. Damage to left visual
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