UNFIGURE 16.1.

FIGURE 16.1. The ionotropic glutamate receptor is an ion channel that opens when glutamate in the extracellular medium binds.

FIGURE 16.2. Noradrenaline activates Gq and hence phospholipase C in many cells including smooth muscle.

FIGURE 16.3. Opening of ionotropic glutamate receptors depolarizes the postsynaptic cell.

FIGURE 16.4. Spatial summation at a synapse.

FIGURE 16.5. Temporal summation at a synapse.

FIGURE 16.6. Inhibition by a GABAergic synapse.

FIGURE 16.7. Motoneurons release the transmitter acetylcholine that binds to nicotinic receptors on skeletal muscle cells. The plasma membrane of the muscle cell is depolarized to threshold and fires an action potential.

FIGURE 16.8. Transmitters regulate the blood supply to muscles.

FIGURE 16.9. Bicoid signalling in the Drosophila embryo.

FIGURE 16.10. Numb signalling in the vertebrate retina.

FIGURE 16.11. Cell division in the retina. The micrograph shows part of the develo-ping retina. The tissue was fixed and then stained with propidium iodide, a dye that, like Hoechst, stains DNA, but fluoresces red. Four stem cells in the field of view have divided and are in telophase/cytokinesis, with the chromosomes still conden-sed and visible as independent structures (page 299). Three of the cell divisions, generating the daughter cells indicated by yellow arrows,were symmetrical divisions in the plane of the retina, but one, generating the daughter cells indicated by the green arrows, was an asymmetric one at 90 degrees to the plane of the retina. Ima-ge by Professor David Becker, University College London; used with permission.