Nervous System Part TwoS Y N A P S E S A N D N E U R A L I N T E G R A T I O N
The Nervous System
Junction between
Adjacent neurons
Mediates information transfer
Postsynaptic neuron
Copyright © 2010 Pearson Education, Inc.
Dendrites
Axosomatic synapses
Axon of presynaptic
Neurons are electrically coupled (joined by gap junctions)
Communication is very rapid
Important in
Embryonic tissue
Unidirectional
Copyright 2009 John Wiley & Sons, Inc. 8
Signal transmission at the chemical synapse
The Synapse
Excitatory Postsynaptic Potentials (EPSP)
Inhibitory Postsynaptic Potentials (IPSP)
Excitatory Postsynaptic Potentials (EPSP)
Depolarizes postsynaptic cell membrane
Copyright © 2010 Pearson Education, Inc. Figure 11.18a
An EPSP is a local depolarization of the postsynaptic membrane that brings the neuron closer to AP threshold. Neurotransmitter binding opens chemically gated ion channels, allowing the simultaneous pas- sage of Na+ and K+.
Time (ms)
Threshold
Stimulus
Inhibitory Postsynaptic Potentials (IPSP)
Hyperpolarizes postsynaptic cell membrane
An IPSP is a local
hyperpolarization of the
Time (ms)
Threshold
Stimulus
Thought Question
Strychnine is a pesticide that is used against small vertebrates. This chemical is an antagonist to glycine, what symptoms might an animal or human experience if they ingest this substance?
The Synapse
Action potential
Ca2+ entry causes neurotransmitter- containing synaptic vesicles to release their contents by exocytosis.
Chemical synapses
Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane.
Binding of neurotransmitter opens ion channels, resulting in graded potentials.
Neurotransmitter effects are terminated by reuptake through transport proteins, enzymatic degradation, or diffusion away from the synapse.
Ion movement
Graded potential
Neuroplasticity
Idea that the brain is not hardwired. Following injury or changes in use, the brain is able to changes its neural circuits. Neurons can adapt and change their functions dependent on need.
Synaptic plasticity
Changes in the use of a neuronal connection can lead to changes at the synapse.
Increased/decreased amount of calcium released at the axon terminal (this changes the amount of NT released)
Altering the number of receptors on the postsynaptic cell membrane (happens by triggering a second messenger system which affects gene transcription for the receptors)
Neural Integration
EPSP’s can summate to reach threshold
IPSP’s can also summate with EPSP’s
Cancel each other out
Excitatory synapse 1 (E1)
Excitatory synapse 2 (E2)
add together.
One or more presynaptic neurons transmit impulses in rapid-fire order
Spatial summation
Postsynaptic neuron is stimulated by a large number of terminals at the same time
Neuronal Circuits
May consist of thousands of neurons
Often include excitatory and inhibitory neurons
Copyright © 2010 Pearson Education, Inc. Figure 11.21
Presynaptic
Neuronal Circuits
Diverging circuit
May affect a single pathway or several
Common in both sensory and motor systems
Figure 11.22a
Figure 11.22b
Neuronal Circuits
Converging circuit
Figure 11.22c, d
We’ll come back to this when we cover reflexes
Questions?
Don’t forget homework for lab, due at the beginning…
Lab Exercise 17 pg.’s 265 (all) and 265 #9 & 10 only (top)
PreLab 1