Download Comparative Vertebrate Physiology

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
• postsynaptic binding
• extracellular ion influx
• neurotransmitter breakdown
and recycling
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


Alkalosis leads to hyperexcitability
Acidosis leads to coma
Leads to unconsciousness
Drugs



Caffeine increases excitability
Strychnine increases excitability
Anesthetics decrease excitation