疾病名隆突性皮肤纤维肉瘤课件.ppt

? 2013 Pearson Education, Inc. Light Transduction Reactions Light-activated rhodopsin activates G protein transducin Transducin activates PDE, which breaks down cyclic GMP (cGMP) In dark, cGMP holds channels of outer segment open ? Na+ and Ca2+ depolarize cell In light cGMP breaks down, channels close, cell hyperpolarizes Hyperpolarization is signal! ? 2013 Pearson Education, Inc. Information Processing In The Retina Photoreceptors and bipolar cells only generate graded potentials (EPSPs and IPSPs) When light hyperpolarizes photoreceptor cells Stop releasing inhibitory neurotransmitter glutamate Bipolar cells (no longer inhibited) depolarize, release neurotransmitter onto ganglion cells Ganglion cells generate APs transmitted in optic nerve to brain ? 2013 Pearson Education, Inc. Figure 15.18 Signal transmission in the retina (1 of 2). Slide 1 In the dark cGMP-gated channels open, allowing cation influx. Photoreceptor depolarizes. 1 Voltage-gated Ca2+ channels open in synaptic terminals. Neurotransmitter is released continuously. Neurotransmitter causes IPSPs in bipolar cell. Hyperpolarization results. Hyperpolarization closes voltage-gated Ca2+ channels, inhibiting neurotransmitter release. No EPSPs occur in ganglion cell. No action potentials occur along the optic nerve. Photoreceptor cell (rod) Bipolar Cell Ganglion cell Ca2+ ?40 mV ?40 mV 2 3 4 5 6 7 Ca2+ Na+ ? 2013 Pearson Education, Inc. Figure 15.18 Signal transmission in the retina. (2 of 2). Slide 8 ?70 mV No neurotransmitter is released. Depolarization opens voltage-gated Ca2+ channels; neurotransmitter is released. EPSPs occur in ganglion cell. Action potentials propagate along the optic nerve. cGMP-gated channels close, so cation influx stops. Photoreceptor hyperpolarizes. Lack of IPSPs in bipolar cell results in depolarization. Voltage-gated Ca2+ channels close in synaptic terminals. 1 Photoreceptor cell (rod) Bipo