Neural Coding

The nervous system must interpret and pass along both quantitative and qualitative information about its environment—whether a light is dim or bright, red or green; whether a taste is mild or intense, salty or sour; whether a sound is loud or soft, high-pitched or low. Considering the complexity of information to be communicated about conditions in and around the body, it is a marvel that it can be done in the form of something as simple as action potentials—particularly since all the action potentials of a given neuron are identical. Yet when we considered the genetic code in chapter 4, we saw that complex messages can indeed be expressed in simple

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

12. Nervous Tissue

Text

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Chapter 12 Nervous Tissue 471

Signal in presynaptic neuron

No activity in inhibitory -neuron

No neurotransmitter -release here

Neurotransmitter

Excitation of postsynaptic neuron

Signal in presynaptic neuron

EPSP

Figure 12.24 Presynaptic Inhibition. (a) In the absence of inhibition, neuron S releases neurotransmitter and stimulates neuron R. (b) In presynaptic inhibition, neuron I suppresses the release of neurotransmitter by S, and S cannot stimulate R.

Signal in presynaptic neuron

EPSP

Signal in inhibitory neuron

Neurotransmitter

Inhibition of presynaptic neuron

No neurotransmitter release here

No response in postsynaptic neuron

Chapter 12 Nervous Tissue 471

Signal in presynaptic neuron

Signal in inhibitory neuron

Neurotransmitter

Inhibition of presynaptic neuron

Figure 12.24 Presynaptic Inhibition. (a) In the absence of inhibition, neuron S releases neurotransmitter and stimulates neuron R. (b) In presynaptic inhibition, neuron I suppresses the release of neurotransmitter by S, and S cannot stimulate R.

10 g

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Action potentials

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