1.4 The Brain and the Functioning of Nerve Cells

౪

35

There are similar mechanisms for ion-channels not gated by voltage but by other forces.

For example, ion channels in the inner ear are opened by having the “plug” pulled

away by mechanical forces. And for heat sensing neurons, the ion channel is opened

by a structure change initiated by temperature. Other channels open when a specific

compound binds (ligand-gated ion channel). In all cases, the opening (or closing) of the

channels changes the membrane potential, which either directly creates an action po-

tential in the following neuron, or sometimes first releases a compound that then re-

leases a neurotransmitter, which then generates an action potential in the following

neuron.

To fully understand that last paragraph one has to know how the signal is trans-

ferred from one neuron to the next, or more specifically, from a neuron’s axon to the

next neuron’s dendrite (Figure 1.38). That end of the axon, the gap between the two neu-

rons called the synaptic cleft, and the beginning of the following neuron’s dendrite to-

Figure 1.38: How information is transmitted from

one neuron to the next by the synapse.