Structure and function of neurons
In Biology, we often use model organisms that allow us to study simple biological systems.
To study nervous systems, the animal model that we use is at the University of Bristol is the African clawed frog (Latin name: Xenopus laevis). It is often easier to study biological systems when they are at the early stages of development and therefore young animals are often used. We therefore use hatchling Xenopus laevis tadpoles that are just a few days old.
Neurons are nerve cells, the basic building blocks of the nervous system. Neurons carry information to and from the central nervous system (CNS: the brain and spinal cord) and to the peripheral nervous system (PNS).
These specialised cells carry messages throughout the body and make up the nervous system.
Neurons are capable of carrying electrical signals along their axons and release chemical signals at synapses between neurons. Different types of neurons have different properties depending on their function and these different types of neurons link together to form a neural network.
Different types of neurons include sensory neurons, motor neurons and interneurons.
Below is typical diagram of a neuron, with the main features labelled. In reality neurons are much more variable in shape, but follow this general structure, including an elongated axon with branching terminals and a cell body with branching dendrites.
Schwann cells wrap around the axon many times and form an insulated layer, called the myelin sheath. The area between these cells, where there is no insulation of the axon are called nodes of Ranvier.
Electrical signals propagating down a neurone from cell body to axon terminal can jump between these gaps from node to node, speeding up the propagation of the signal in what is called saltatory conduction. Most animals have a myelin sheath surrounding their neurones, however some invertebrates have a different system of myelination and some even lack it all together.
Below is a diagram showing how a nerve impulse travels along a myelinated axon.