Neurons

For reference to help you with this assignment, please read below before answering the questions. Each worksheet has a word bank to help you answer the questions as well.

Nerve Cells

Although the nervous system is very complex, nervous tissue consists of just two basic types of nerve cells: neurons and glial cells. Neurons are the structural and functional units of the nervous system. They transmit electrical signals, called nerve impulses.

Neuron Structure

As shown in Figure below, a neuron consists of three basic parts: the cell body, dendrites, and axon.

• The cell body contains the nucleus and other cell organelles.

• Dendrites extend from the cell body and receive nerve impulses from other neurons.

• The axon is a long extension of the cell body that transmits nerve impulses to other cells. The axon branches at the end, forming axon terminals. These are the points where the neuron communicates with other cells.

Communication Between Neurons

Neurons communicate with each other at specialized junctions called synapses. Synapses are also found at junctions between neurons and other cells such as muscle cells (see below).

There are two types of synapses:

• Chemical synapses use chemical signaling molecules as messengers. We are focusing on this type of synapse.

• Electrical synapses use ions as messengers.

At a chemical synapse, the axon terminal of one neuron usually does not touch the other cell; the gap is called a synaptic cleft. The transmitting cell is called the presynaptic neuron, and the receiving cell is called the postsynaptic cell or, if it is another neuron, the postsynaptic neuron.