Nervous System

The brain is the center of neural activity and integrates all sensory information; it initiates responses , controls the neuroendocrine system, it is the site for cognitive processes (learning, memory, reasoning etc.) and it creates our concept of self, our individual person.

What do we need to know about nerve tissue? The nervous system contains nerve cells and glia cells. While glia cells serves the function of nutrition and immune response within the nervous system, nerve cells (also called neurons) are information processing devices. The architecture of each neuron is rather uniform. It consists of the cell body, the dendrite and the axon. The cell body (soma) contains the nucleus of the neuron and is, thus , the site of gene expression and protein synthesis. The main pathways are located within the brain or in the spinal cord. In both regions they are protected by bones, for example the vertebral bodies of the backbone. Neurons are electrically active, because they have an excitable cell membrane. Information is encoded in the nervous system in the form of electrical energy, held in the membrane potential. Dendrites transmit this potential toward the cell body. In the axon the membrane potential is transformed into a nerve impulse, called action potential. This action potential runs along the axon to the dendrite of the next neuron. Most axons in the CNS and PNS are ensheathed by specialized glia cells, which produce membrane layers – the myelin sheaths. Their function is to electrically insulate the axon and speed up action potential propagation. In the PNS, myelin is produced by the Schwann cells . The myelin sheaths are interrupted at regular intervals by the Nodes of Ranvier . These are un-isolated spaces between Schwann cells and they are necessary for action potential propagation. The nucleus and cytoplasm of the Schwann cells lie outside the myelin sheath. They are called neurolemma and are important after injury of the peripheral nerves. Unlike in the CNS, Schwann cells are actually able to stimulate regeneration of the PNS axons after injuries. This regeneration takes months, but afterwards patients may regain their sensation and movement in the affected limb.

The myelin sheaths around axons of the CNS axons are produced by glia cells called oligodendrocytes. Severing the spinal cord or brain areas induces permanent function loss, because oligodendrocytes are unable to trigger neuronal regeneration. This is the reason why spinal cord injury patients often remain paraplegic.

What is the function of synapses? Most neurons are not electrically connected to each other. There is a small gap between the axon of one neuron and the dendrite of the next neuron. To pass information from one neuron to the other specialized contact zones exist where the two cells communicate chemically with each other. The contacts are called synapses .

The electrical impulse that runs into the axon terminal is there translated into a chemical signal. For this, a chemical neurotransmitter is released by the axon (of the presynaptic cell) and diffuses across the synaptic gap. It then binds to its specific receptor on the dendrite of the next cell (the postsynaptic neuron). This neurotransmitter binding produces a membrane potential again, which is transmitted via the dendrite to the cell body. The whole process is called synaptic transmission . It is terminated by rapid enzymes that quickly inactivate the neurotransmitter. An example of a neurotransmitter is acetylcholin, a neurotransmitter found at neuromuscular junctions, where the nerve impulse excites muscle cells and causes muscle contraction. Acetylcholin is released from motor neurons onto muscle cells. The specialized receptor on the human muscle cell is called the nicotinic acetylcholine receptor. When this receptor binds to acetylcholine the muscle cell changes its potential and the muscle contracts. The enzyme that degrades the neurotransmitter within the neuromuscular junction is acetylcholine esterase. There are many other neurotransmitters in our nervous system, e.g., glutamate, GABA, dopamine, norepinephrine, or serotonin.

One consequence of the chemical synaptic transmission is that the information transfer is unidirectional: the signal can only be transmitted from the presynaptic neuron to the postsynaptic neuron and not the other way round. Neurotransmitters can only be released by a neuron’s axon. Therefore, the information flows from our CNS to the muscles to produce movements. Then signals flow from the sense organs to our brain, which receives information about the external world.

Sie finden die Lösung des Rätsels aus Heft 12/2017 hier .

BIBLIOGRAPHY 1. Greenberg DA, Aminoff MJ, Simon RP: Clinical Neurology. 8 th edition, Mc Graw Hill Lange 2012.

2. http://dict.leo.org.

3. www.dict.cc.

4. www.webster-dictionary.org.

EXERCISE: 1. Myelin sheaths on the outsides of many axons in the peripheral nervous system are constructed by ______________________. a. axons b. Schwann cells c. secretory vesicles

2. A nerve is formed through collection of a. nerve fibers b. neurons c. spinal cords

3. The junction between two neurons is called a a. synapse b. loop of Henle c. Node of Ranvier

You’ll find the answer on: http://tinyurl.com/weiterbildung-englisch

Die Autorin: Carmen Lobitz mail@lobitz-seminare.de www.lobitz-seminare.de

Carmen Lobitz ist freie Trainerin, Lehrerin und MTA. Sie gründete 1998 in Berlin lobitz seminare, die u.a. Englischseminare für Health Professionals anbieten.

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Lösung für Exercise:

Answer: 1. b Answer: 2. a Answer: 3. a

Nervous System

What do we need to know about nerve tissue?

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Nervous System

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