Activated rhodopsin triggers a signal transduction cascade

Reminder on Ion Distribution and Transport in Cells

Cells (eukaryotes) divided into a number of membrane-bound compartments.Concentrations in different compartments can be orders of magnitude different.Proteins (ion channels, transporters) mediate these concentration gradients.Membrane proteins central to huge range of processes – cell signaling, nerve impulses, nutrient transport, etc.

Ion Channels and Transient Permeability

Channels open in response to a variety of different stimuli.Key mechanisms are voltage gating, ligand binding-induced gating and mechanical tension in the membrane.

Mwc models of ligand-gated channels

Light-induced hyperpolarization of the rod cell membrane

Hydrolysis of cGMP causes cation channels to close

Rod cell membrane hyperpolarizes

cGMP

Electrical consequences of illumination

http://www.d.umn.edu/~jfitzake/Lectures/DMED/Vision/Retina/ReceptorPotential.html

Each dot in the figure below represents delivery of a very dim pulse of light containing only a few quanta. Voltage responses appear to come in 3 sizes: none, small, and large, representing the detection of 0, 1 or 2 quanta in each flash. The granularity of response to dim light stimuli is evident.

http://webvision.med.utah.edu/book/part-ii-anatomy-and-physiology-of-the-retina/photoreceptors/

Synapse diffusion

http://www.colorado.edu/intphys/Class/IPHY3430-200/008sensory.htm

Other examples of synaptic communication

Other examples of synaptic communication

Other examples of synaptic communication

Other examples of synaptic communication

Other examples of synaptic communication

Other examples of synaptic communication

Other examples of synaptic communication

Other examples of synaptic communication

Other examples of synaptic communication