Specialised Cells

The sperm cell comprises of three sections, the head, the mid piece and the tail which is kept in shape by the plasma membrane. The head of the sperm is round in shape and contains the nucleus and acrosome. The nucleus is the control centre of the cell and holds the Deoxyribonucleic acid (DNA); this is what makes this cell a eukaryotic cell. The acrosome is an organelle that forms on the outside of the head; they derive from the Golgi apparatus and contain digestive enzymes. Acrosome’s are needed to break down the outer membrane of the egg, so that the two nucleuses’ can fuse together thus producing a zygote (fertilized egg).

The mid piece holds the centriole and mitochondrion. The centriole is necessary for the first mitotic division of the zygote; this is where the zygote undergoes rapid cell division, producing a cluster of cells with no significant growth. The mitochondria is simply the energy centre or the cell, this is the power plant and is wrapped around the mid piece of the sperm cell.

The tail consists of the axial filament or the flagella; this is what propels the human sperm cell at about 1 to 3 mm per minute by rotating like a propeller (http://www.newworl dencyclopedia.org/entry/Spermatozoon accessed 01/11/09).

 (Accessed 01/11/09)

Having investigated the sperm cell, we will now look at a motor neuron cell. This is a specialized cell in the nervous system that processes and transmits information around the body by nerve impulses. There are two types of nerve cell in the human body; sensory which control touch, sound, light and motor which receive signals from the brain and spinal cord also causing muscle contractions.

The cell body forms the grey matter of the nervous system, it is found at the periphery of the brain and in the centre of the spinal cord (Waugh and Grant, 2006. P143). Within the cell body are all the organelles that would be found in a normal cell including the nucleus, mitochondria, Golgi body and is bound by a cell membrane. In addition to these organelles are the ‘tree like branches’ called dendrites, these receive and carry the incoming impulses towards the cell body.

        The long sausage like tail contains the axon which is made up of postganglionic fibres; these carry impulses away from the cell body. The nodes of ranvier are breaks in the chain that speed up these impulses. Surrounding the axon is the Schwann cells, these are named after their founder Theodor Schwann; they have their own nucleus and produce the myelin sheath (fatty membranes) that insulates and prevents the information from jumping to other axons. At the end of the cell is the axon terminals, these are fibrous branches that deliver the messages to the muscle.

        

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The diagram above is of a goblet cell. These are found along the internal surface of the intestinal and respiratory tracts. There sole purpose is to secrete mucus from the body and in the case of the small intestine, to absorb all the good stuff the body needs from food and fluids. The Microvilli are lots of fur like fingers that moves the mucus and also traps dust and debris. The cell, like any other is controlled by the nucleus which houses the DNA. As the picture illustrates above, this is a very energetic cell so needs lots of mitochondria to supply the cell with energy.

        The ribosomes are tiny granules made from Ribonucleic acid (RNA) and protein. They are found around the rough endoplasmic reticulum and are responsible for synthesizing proteins that are to be exported. The rough endoplasmic reticulum of the goblet cell will also help with this. The Golgi body is the packaging centre and once the RER and ribosomes have synthesised the protein, the Golgi body will package it into membrane bound vesicles called secretory granules.

Having now looked at three specialised cells, we will investigate our final one. The diagram below shows human erythrocytes otherwise known as red blood cells (RBC). The only organelle red blood cells contain is a plasma membrane; this is so that they have more room for the haemoglobin, the large pigmented protein responsible for gas transport (Waugh and Grant, 2006, p59) which is the main function of RBC. These cells are flexible so that they can squeeze through narrow capillaries.

 (accessed 02/11/09).

Red blood cells are produced in red bone marrow and go through several stages of development before entering the blood stream. When these cells mature (roughly 1 – 2 days in the blood stream), they lose their nucleus and become incapable of cell division. Their main job is to transport oxygen with some traces of carbon dioxide around the body.

In conclusion, there are many cells within the human body with some being specialised cells. They are constantly repairing and producing new cells through the process of mitosis. The four cells mentioned above all have their own specialised functions and a very important part to play in the human body’s day to day life.

Bibliography

Reference Books,

• Boyle, M. and Senior, K., 2002. Human Biology 2nd Edition. Collins
• Waugh, A. and Grant, A., 2006. Anatomy and Physiology in health and illness, 10th Edition. Ross and Wilson

Electronic Sources,

•  

(Accessed 01/11/09)

Diagram Links,

• Spermatozoon cell,  

(Accessed 30/10/09)

• Neuron cell,

 

(Accessed 01/11/09)

• Small intestine goblet cell,

 (Accessed 01/11/09)

• Erythrocyte (Red blood cell)

(Accessed 02/11/09)