Summary of basic mechanisms

The basic processes of sensory action, illustrated by the campaniform organ, can now be reviewed by reference to Fig. 4.4. The incoming energy is coupled to the sensory ending by means of highly specialised accessory structures and is transduced in the sensory neuron terminal into a receptor potential. This is a smoothly graded potential which spreads passively

Figure 4.4 Summary of the events that occur when a sensory receptor responds to a stimulus. The normal sequence of processes is shown by the arrows in the centre of the figure, and the structures in which these processes occur are shown on the right. The arrows on the left indicate the extent to which these events are specific to a particular modality (details in text). Where the receptor cell works without trains of spikes, the receptor potential spreads passively down the axon to the synapse with second-order neurons.

Figure 4.4 Summary of the events that occur when a sensory receptor responds to a stimulus. The normal sequence of processes is shown by the arrows in the centre of the figure, and the structures in which these processes occur are shown on the right. The arrows on the left indicate the extent to which these events are specific to a particular modality (details in text). Where the receptor cell works without trains of spikes, the receptor potential spreads passively down the axon to the synapse with second-order neurons.

along the neuron membrane. When it spreads to a special region at the start of the axon called the spike-initiation zone, the receptor potential is converted into a digital code of spikes. The spikes propagate along the axon towards the central nervous system.

As indicated on the left of Fig. 4.4, the more central processes, such as coding, are not specific to the particular type of receptor. Indeed, the coding of passive potentials into spikes is not specific even to sensory neurons, but is common to all neurons that employ trains of spikes. The more peripheral processes are modality-specific: the transduction process determines the sensory modality, and the coupling process, effected by the accessory structures, narrows down the modality and sharpens the receptive field.

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.

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