Somatic Cells

Somatic Cells Definition

Somatic cells are any cell in the body that are not gametes (sperm or egg), germ cells (cells that go on to become gametes), or stem cells. Essentially, all cells that make up an organism’s body and are not used to directly form a new organism during reproduction are somatic cells. The word somatic comes from the Greek word σὠμα (soma), which means body. In the human body, there are about 220 types of somatic cells.

Examples of Somatic Cells

There are many different kinds of somatic cells in the human body because nearly every cell found inside and on the surface of the human body, with the exception of cells that become sperm and eggs, is a somatic cell. In addition, mammals have many organ systems that specialize in specific functions, so there are many different specialized cells. The following is an overview of a few main types of cells in the human body.

Bone Cells

Old bone cells are constantly being replaced with new bone cells. The two broad categories of bone cells are called osteoblasts and osteoclasts. Osteoblasts form bone and help maintain it. They are cuboidal, or square-shaped, and they make proteins that form bone. They also communicate with each other and produce certain molecules such as growth factors, which promote bone growth. Osteoclasts, on the other hand, resorb, or dissolve, old bone. They are large cells that have multiple nuclei. When the work of an osteoblast or osteoclast is done, it undergoes a programmed cell death known as apoptosis.

Muscle Cells

Muscle cells are also known as myocytes. They are long, tube-shaped cells. There are three types of muscle which are each made up of specialized myocytes: smooth muscle, cardiac muscle, and skeletal muscle. Smooth muscle lines the walls of internal organs such as the bladder, uterus, and digestive tract. Cardiac muscle is only found in the heart, and it allows the heart to pump blood. Skeletal muscle is attached to bone and helps move the body.

The various parts of myocytes have special terminology because myocytes are so different from other types of cells. The cell membrane is called the sarcolemma, the mitochondria are called sarcosomes, and the cytoplasm is called the sarcoplasm. The sarcomere is the part of the cell that contracts and allows muscle movement, and they form long chains called myofibrils that run throughout each muscle fiber. Muscle cells cannot divide to form new cells. This means that even though muscles can get bigger through exercise, babies actually have more myocytes than adults.

Nerve Cells

Nerve cells are called neurons. Neurons are found throughout the body, but there is an especially high density in the brain and spinal cord, which control the body’s movements. Neurons send and receive information to and from other neurons and organs via chemical and electrical signaling. Neurons maintain a certain voltage, and when this voltage changes, it creates an electrochemical signal called an action potential. When an action potential occurs in a neuron, the neuron will release neurotransmitters, which are chemicals that affect target cells. Some examples of neurotransmitters are dopamine, serotonin, epinephrine (adrenaline), and histamine.

Neuron annotated

Neurons have a unique structure as shown in the diagram above. The main parts of a neuron are the soma, axon, and dendrites. The soma is the body of the cell and contains the nucleus. The axon is a long protrusion that transmits electrical impulses. The dendrites fan out from the soma and receive impulses from other neurons. The end of the axon branches out into axon terminals, which is where neurotransmitters are released.

Blood Cells

Blood cells are called hematopoietic cells or hemocytes. There are three general types of blood cells: red blood cells, known as erythrocytes, white blood cells, or leukocytes, and platelets, also known as thrombocytes or yellow blood cells. These cells, along with plasma, comprise the contents of blood.

Erythrocytes carry oxygen to cells via the molecule hemoglobin, and they collect the waste product carbon dioxide from cells. They make up 40 to 45 percent of the blood’s volume. Approximately one-fourth of the cells in the human body are erythrocytes. They live for around 100 to 120 days, and they do not have a nucleus when mature. Leukocytes defend the body against foreign substances and infectious disease agents like viruses and bacteria. They have a very short lifespan of only three to four days. Platelets are small cell fragments that help blood to clot after an injury. They also have a short lifespan, living for five to nine days.

Differences between Somatic Cells and Gametes

Somatic cells are produced through the cell division process of mitosis. They contain two copies of each chromosome, one from an organism’s mother and one from their father. Cells with two copies of each chromosome are called diploid. Sperm and egg cells, called gametes, are formed through meiosis, which is a slightly different cell division process that results in the cells having only one copy of each chromosome. These cells are called haploid. Gametes are haploid because a sperm and an egg fuse during fertilization to create a new organism with diploid cells.
Mutations in somatic cells can affect an individual organism, but they do not affect the offspring since they are not passed on during reproduction. However, mutations that occur in gametes can affect offspring since the gametes are passed down. When gametes fuse, they become the offspring’s first somatic cell, which subsequently divides to form all of their other somatic cells. Therefore, while mutations in somatic cells will not affect the next generation, mutations in gamete cells do and can sometimes have drastic effects. For example, if a large-scale mutation occurs and there is an extra chromosome in the fertilized egg, all the somatic cells will also have that extra chromosome when it divides. An extra chromosome 21 results in Down Syndrome.

Related Biology Terms

  • Cell – The basic biological unit of living things.
  • Gamete – A sperm or egg cell.
  • Apoptosis – Programmed cell death in which a cell self-destructs.
  • Diploid – A cell with two copies of each chromosome; somatic cells are diploid.

Quiz

1. Which type of cell is NOT a somatic cell?
A. Leukocyte
B. Myocyte
C. Osteoblast
D. Gamete

Answer to Question #1

2. What is the approximate lifespan of an erythrocyte?
A. 3-4 days
B. 5-9 days
C. 100-120 days
D. 365-395 days

Answer to Question #2

3. What is the function of an osteoclast?
A. To form and help maintain bone
B. To attach to bone and allow it to move
C. To resorb old bone
D. To release neurotransmitters

Answer to Question #3
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