Excitatory Chemical Synapses

At an excitatory synapse, the postsynaptic response to the neurotransmitter is a depolarization, bringing the membrane potential closer to threshold. The usual effect of the activated receptor on the postsynaptic

Presynaptic Fiber

FIGURE 8-26

Synapses appear in many forms as demonstrated here in views (a) to (d). The presynaptic fiber contains synaptic vesicles.

Redrawn from Walmsley et al.

FIGURE 8-26

Synapses appear in many forms as demonstrated here in views (a) to (d). The presynaptic fiber contains synaptic vesicles.

Redrawn from Walmsley et al.

PART TWO Biological Control Systems

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

PART TWO Biological Control Systems

Excitatory Postsynaptic Potential

Threshold

10 20

FIGURE 8-27

Excitatory postsynaptic potential (EPSP). Stimulation of the presynaptic neuron is marked by the arrow.

Threshold

Inhibitory Postsynaptic Potential

Threshold

10 20

FIGURE 8-28

Inhibitory postsynaptic potential (IPSP). Stimulation of the presynaptic neuron is marked by the arrow.

Threshold

10 20

FIGURE 8-27

Excitatory postsynaptic potential (EPSP). Stimulation of the presynaptic neuron is marked by the arrow.

10 20

FIGURE 8-28

Inhibitory postsynaptic potential (IPSP). Stimulation of the presynaptic neuron is marked by the arrow.

membrane at such synapses is to open postsynaptic-membrane ion channels that are permeable to sodium, potassium, and other small, positively charged ions. These ions then are free to move according to the electrical and chemical gradients across the membrane.

There is both an electrical and a concentration gradient driving sodium into the cell, while for potassium, the electrical gradient is opposed by the concentration gradient. Opening channels nonspecifically to all small positively charged ions, therefore, results in the simultaneous movement of a relatively small number of potassium ions out of the cell and a larger number of sodium ions into the cell. Thus, the net movement of positive ions is into the postsynaptic cell, and this slightly depolarizes it. This potential change is called an excitatory postsynaptic potential (EPSP, Figure 8-27).

The EPSP is a graded potential that spreads decre-mentally away from the synapse by local current. Its only function is to bring the membrane potential of the postsynaptic neuron closer to threshold.

Was this article helpful?

0 0
Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Post a comment