Nerve Cells
Parts of Nerve Cells
All nerve cells have three parts:
- a portion of cytoplasm immediately surrounding the cell nucleus, which is called the cell soma
- multiple processes that extend from the cell soma, which are called dendrites
- a single, thinner process called an axon
Cell Soma
The cell soma of a nerve cell has several characteristic features. The cell nucleus of a neuron is typically very large, spherical, and light-staining. Also, it contains an unusually prominent, dark-staining dot called a nucleolus. The cytoplasm of a nerve cell also has many dark-staining patches, which we know represent an unusually abundant rough endoplasmic reticulum (or rough ER). As it turns out, it is no accident that all of these features are found in nerve cells somas, because they all are related to each other.
A pale-staining nucleus signifies that the DNA and the chromosomes are unusually active. Many genes in nerve cells are active, and many types of mRNA molecules are being produced. For this to happen, the DNA and chromosomes must be spread out, or dispersed, so that cell machinery can read the information on the DNA. Dispersed DNA stains lightly.
To produce proteins from the information on the mRNA, many extra ribosomes are needed. The nucleolus functions as a factory for the creation of ribosomes, so it makes sense that it is unusually large in nerve cells. When the ribosomes leave the nucleus and enter the cytoplasm, they attach to membranes of the rough ER, which are correspondingly very abundant.
Other cells in the body have an appearance different from that of nerve cells. If such cells have a small, dark-staining nucleus, a small nucleolus, and very little rough endoplasmic reticulum, this means that they have few active genes and produce only a small amount of mRNA molecules. So, you can tell a lot about the activity of genes in a cell simply by looking at the cell.
Dendrites
Dendrites carry information from other nerve cells towards the cell soma, in the form of altering electrical voltages. The pattern of dendrites extending from the soma differs greatly between different types of nerve cells and makes the activity of nerve cells different from one another in different parts of the nervous system. Most nerve cells are found within the brain, although fewer numbers of nerve cells can be found in the walls of the intestines, near glands that they control. The nerve cells of the cortex of the brain have unusually large numbers of dendrites.
Axons and Synaptic Boutons
Axons end as small, button-shaped structures called synaptic boutons. Synapses attach to target cells such as other neurons, muscle cells, or glands. Each synapse contains many bubbles, or vesicles, that contain chemicals called neurotransmitters. When an electrical impulse reaches the synapse, it causes membrane pores called calcium channels to open. This causes calcium atoms to rush into the cytoplasm of the synapse. Calcium binds to a protein called synaptotagmin. This protein, in turn, then interacts with other proteins called snare proteins, which bring synaptic vesicles close to the cell membrane. When these vesicles fuse with the cell membrane, they release their chemical contents into the environment. These chemicals bind to receptors on the target cell’s membrane, they stimulate the target cell to change its function.
Related Topics
Parts of Nerve Cells
All nerve cells have three parts:
- a portion of cytoplasm immediately surrounding the cell nucleus, which is called the cell soma
- multiple processes that extend from the cell soma, which are called dendrites
- a single, thinner process called an axon
Cell Soma
The cell soma of a nerve cell has several characteristic features. The cell nucleus of a neuron is typically very large, spherical, and light-staining. Also, it contains an unusually prominent, dark-staining dot called a nucleolus. The cytoplasm of a nerve cell also has many dark-staining patches, which we know represent an unusually abundant rough endoplasmic reticulum (or rough ER). As it turns out, it is no accident that all of these features are found in nerve cells somas, because they all are related to each other.
A pale-staining nucleus signifies that the DNA and the chromosomes are unusually active. Many genes in nerve cells are active, and many types of mRNA molecules are being produced. For this to happen, the DNA and chromosomes must be spread out, or dispersed, so that cell machinery can read the information on the DNA. Dispersed DNA stains lightly.
To produce proteins from the information on the mRNA, many extra ribosomes are needed. The nucleolus functions as a factory for the creation of ribosomes, so it makes sense that it is unusually large in nerve cells. When the ribosomes leave the nucleus and enter the cytoplasm, they attach to membranes of the rough ER, which are correspondingly very abundant.
Other cells in the body have an appearance different from that of nerve cells. If such cells have a small, dark-staining nucleus, a small nucleolus, and very little rough endoplasmic reticulum, this means that they have few active genes and produce only a small amount of mRNA molecules. So, you can tell a lot about the activity of genes in a cell simply by looking at the cell.
Dendrites
Dendrites carry information from other nerve cells towards the cell soma, in the form of altering electrical voltages. The pattern of dendrites extending from the soma differs greatly between different types of nerve cells and makes the activity of nerve cells different from one another in different parts of the nervous system. Most nerve cells are found within the brain, although fewer numbers of nerve cells can be found in the walls of the intestines, near glands that they control. The nerve cells of the cortex of the brain have unusually large numbers of dendrites.
Axons and Synaptic Boutons
Axons end as small, button-shaped structures called synaptic boutons. Synapses attach to target cells such as other neurons, muscle cells, or glands. Each synapse contains many bubbles, or vesicles, that contain chemicals called neurotransmitters. When an electrical impulse reaches the synapse, it causes membrane pores called calcium channels to open. This causes calcium atoms to rush into the cytoplasm of the synapse. Calcium binds to a protein called synaptotagmin. This protein, in turn, then interacts with other proteins called snare proteins, which bring synaptic vesicles close to the cell membrane. When these vesicles fuse with the cell membrane, they release their chemical contents into the environment. These chemicals bind to receptors on the target cell’s membrane, they stimulate the target cell to change its function.
