Comparative Vertebrate Physiology Communication between neurons The synapse

Synapses Types Electrical & chemical Membranes presynaptic & postsynaptic Synaptic cleft

Electrical synapse Gap junctions An all electrical event

Chemical synapse An all chemical event

Chemical synapse ion influx presynaptic binding exocytosis diffusion neurotransmitter breakdown and recycling postsynaptic binding extracellular ion influx

Postsynaptic membrane Events Ion influx (Na+, Cl-) Ion efflux (K+) Ach degradation (acetylcholinesterase) Protein channel closes

Synaptic delay 0.3 - 5.0 msec Delay caused by fusion and diffusion Reducing delay reduce pathway length reduce number of synapses Start Finish

Neurotransmitters Major categories Acetylcholine Amino acids (glutamate, aspartate, glycine) Biogenic amines (dopamine, norepinephrine, epinephrine)

Postsynaptic transmission EPSP: a single depolarization Na+ influx

Postsynaptic transmission IPSP: a single hyperpolarization K+ efflux or Cl- influx

Summation Temporal: PSP’s occur at different times Spatial: PSP’s occur at the same time

Neural integration Facilitation: neurons facilitate communication at the synapse using Ca++ Synaptic inhibition (pre- and post-)

Synaptic sensitivity pH Hypoxia Drugs Alkalosis leads to hyperexcitability Acidosis leads to coma Hypoxia Leads to unconsciousness Drugs Caffeine increases excitability Strychnine increases excitability Anesthetics decrease excitation