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Electrical Signaling in the Nervous System and Behavior

Related concepts: receptor, process, causality, subject. Related mechanism: hormonal signaling.

Purpose of This Document

This document describes electrical signaling in the nervous system as a biological mechanism for transmitting and transforming influences.

Acknowledging the existence of nerve impulses and their causal involvement in behavior does not require identifying, in advance:

nerve impulse
= decision
= action of the subject
= subject

These are different levels of description, and the relationships between them must be demonstrated, not presumed.

A Nerve Impulse Is an Electrochemical Process

The expression “electrical impulse” is convenient but incomplete.

An action potential arises through:

  • a difference in electrical potential across the membrane;
  • unequal distribution of ions;
  • changes in membrane permeability;
  • movement of ions through membrane channels;
  • successive changes in adjacent regions of the membrane.

Thus, a nerve impulse is not abstract electricity moving along a wire, but a reproducible wave of membrane-potential change based on ion movement.

Simplified diagram:

change in membrane potential
→ opening of voltage-gated channels
→ movement of ions
→ further potential change
→ propagation of an action potential

The classic experiments by Hodgkin and Huxley demonstrated how changes in sodium and potassium conductance allow quantitative description of the generation and propagation of action potentials in the squid giant axon.

Transmission Between Cells Cannot Be Reduced to Electricity

At many synapses, an action potential does not jump to the next cell as a continuous electrical current.

Usually, a sequence occurs:

an action potential reaches the axon terminal
→ calcium channels open
→ calcium enters the terminal
→ neurotransmitter is released
→ neurotransmitter binds to receptors of another cell
→ its membrane potential or internal state changes

Experiments by Katz and Miledi demonstrated the critical temporal involvement of calcium in neurotransmitter release at the neuromuscular junction.

Consequently, even the so-called electrical channel constantly transitions between electrical and chemical processes.

Electrical synapses also exist, where current passes between cells through intercellular junctions. But their existence does not turn the entire nervous system into one electrical wire.

From Receptor to Response

A minimal biological chain can be represented as:

influence
→ transduction at a receptor
→ change in nerve-cell activity
→ synaptic transmission
→ change in neural-network states
→ signals to motor or autonomic systems
→ observed response

But this diagram is not one linear route. At each level, there may be:

  • amplification or attenuation of the signal;
  • inhibition;
  • feedback;
  • arrival of other signals;
  • changes in sensitivity;
  • competition between motor programs;
  • termination of transmission;
  • absence of an externally observable response.

Thus, the presence of a sensory signal does not yet imply an inevitable motor response.

An Impulse Does Not Contain Ready-Made Meaning

An action potential is a physical event. It does not contain a ready-made statement:

be frightened;

trust;

choose this option;

perform this action.

The functional significance of an impulse depends on:

  • which cell it arose in;
  • where it comes from and where it goes;
  • which other signals coincide with it in time;
  • the state of the receiving network;
  • which synaptic connections are active;
  • the level at which an observer describes the result.

The same physical form of an action potential can participate in different sensory, motor, and regulatory processes. Significance arises from an event’s place within an organized network of relations, not from an electrical impulse considered in isolation.

The Nervous System and the Selection of a Response

In a biological model, the nervous system receives numerous signals, transforms and compares them within networks, and generates activity associated with possible responses.

It is justified to say that neural processes:

  • are necessary for many forms of perception and movement;
  • causally participate in preparing and performing actions;
  • can amplify one response and suppress another;
  • can preserve traces of previous experience;
  • change with learning and injury.

But it does not yet follow that a recorded impulse is itself the choosing subject, or that describing the entire chain of impulses already explains the existence of a subject.

Even the absence of an outward response is biologically compatible with ongoing internal activity: inhibition of motor output, changes in attention, maintenance of posture, or preparation for an alternative action. Observing that “the person did not respond outwardly” does not by itself prove either the absence of neural processing or the reduction of a decision to that processing.

Hormonal and Neural Processes Are Not Two Opponents

The formula

hormones compete to produce an emotional response
against
nerve impulses producing a rational response

is biologically inaccurate.

Hormonal and neural processes form an interacting circuit:

neural activity
→ can trigger the release of hormones and neuropeptides

hormonal signaling
→ can change neuronal excitability and synaptic transmission

altered neural network
→ changes subsequent signal processing and possible responses

For example, oxytocin is a chemical signaling molecule, but it is synthesized by neurons and acts on neural circuits. In prairie vole experiments, the effect of oxytocin on excitatory synaptic transmission depended on previous social experience. In other experiments, the formation of partner preference depended on the interaction of oxytocin and dopamine systems.

Emotional and deliberative processes use neuronal electrical activity, chemical synaptic transmission, and modulation. They cannot be allocated to two isolated physical channels.

What Can Compete

The nervous system can indeed involve competition between:

  • different sensory signals;
  • excitation and inhibition;
  • alternative motor responses;
  • different stable patterns of activity;
  • an immediate reaction and its suppression;
  • processes operating on different timescales.

But this is not the same as competition between “hormones” and “electricity.” A hormonal signal can change the neural network itself, within which alternative responses compete.

A more precise formulation is:

Different biological processes jointly change the state of a system within which the observed response takes shape.

Response and Action

We must distinguish:

change in cellular state
→ physiological response
→ motor response
→ action of the organism
→ action of the subject

Establishing a causal relationship at one transition does not automatically explain all subsequent levels.

For example, stimulation of a neural structure can cause a muscle contraction. This demonstrates a causal pathway from intervention to movement. It does not follow, however, that every human action is exhausted by the same linear scheme or that a description of movement already explains its meaning for the subject.

Levels of Assertion

Observation:
particular states and responses correspond to neural activity.

Causal experiment:
intervention in a specific part of the chain changes a measurable result.

Biological model:
neural networks integrate signals and participate in selecting and implementing responses.

Additional ontological hypothesis:
a complete description of neural activity exhaustively explains the decision and the subject.

Moving to the last hypothesis requires a separate argument. The very existence of nerve impulses does not provide one.

Final Formulation

Electrical signaling in the nervous system is the electrochemical propagation of changes in membrane potential, linked through synapses to transformations in the states of other cells and networks.

In brief:

A nerve impulse is a mechanism for transmitting and transforming an influence, but is not itself a ready-made decision or the subject making that decision.

Studies

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