There are many types of specialized cells that exist in animal bodies. During development, cell differentiation occurs, giving rise to skin, muscle, nerve, immune, blood, and many other cell types, each with unique structures and functions. Nerve cells, for instance, relay information from one part of the body to another. They send electrical signals from the sites of stimuli to a receptor organ that produces some form of response. Certain drugs can impact the functioning of nerve cells, producing varied responses to stimuli and affecting the brain. Another form of specialized cells—immune cells—protects the body from disease, providing lines of defense against invading microorganisms and viruses. Certain cells of the immune system attack and digest foreign bodies that travel through the bloodstream.
At A Glance
- During animal development, changes in gene expression enable the formation of specialized cells.
- The nervous system relays information around the body using neurons that each consist of three parts: a cell body that contains the nucleus, dendrites attached to the cell body that receive signals, and the axon, which plays a role in the propagation of the signals.
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Neurons differ based on function, which includes afferent, efferent, and interneuron cells. Neurons also differ based on structure, which includes multipolar, bipolar, unipolar, and anaxonic cells. These cells are defined by the number and type of projections extending from the cell body.
- Oligodendrocytes, ependymal cells, microglia, and astrocytes are neuroglia found in the central nervous system (CNS), while Schwann cells and satellite cells are neuroglia found in the peripheral nervous system (PNS).
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Chemical substances that act upon the central nervous system to alter brain function, called psychoactive drugs, affect neurotransmission, the sending of nerve impulses between neurons or from a neuron to other tissue.
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Immune system cells identify invading pathogens and rally the body's defenses.
- There are five types of leukocytes, also called white blood cells—neutrophils, monocytes, eosinophils, basophils, and lymphocytes—with each having mechanisms to fight foreign invaders.
- Lymphocytes are specialized types of white blood cells that hunt and destroy pathogens in the body, such as bacteria.
