Anatomy And Physiology

Anatomy Physiology



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Neurons are cells of the nervous system which are specialized in the transmission of electric signals between cells of the nervous system, such as the sensory sensation of pain and the sensation of temperature changes in the skin.  This differentiates these cells from other cells of the nervous system which are called neuroglial cells.  These latter cells do not have any role in the transmission of sensory or motor innervation in the human body. They have a supporting function to neurons such as the cells astrocytes which help to form the blood-brain barrier. 


Neurons do not have the capacity to divide.  This is in contrast to neuroglial cells which have the ability to divide and regenerate.  For this reason, damage of the nervous system can be irreversible damage.  For example, an injury to the spinal cord can cause a permanent paralysis in an area of the body which depends on the site of injury in the spinal cord. the


Also, because neurons do not divide, they cannot undergo mutagenesis or cancer.  Neuroglial cells, on the other hand, can undergo mutagenesis due to their mitotic ability.  Therefore, cancer of the nervous system is relatively rare although it can occur due to the presence of the neuroglial cells which are the ultimate source of malignancy in the nervous system. 


Neurons are divided into three segments that are connected with each other to form the cell.  These include the dendrite which receives the electrical information from other neurons.  This is in addition to a body which contains the nucleus.  In addition there is an axon which is the site where information is passed to the other neurons.


Neurons are excitable cells in the body.  They are similar in this sense to muscle cells which are also excitable cells.  Neurons transmit electrical information to other cells through several methods.  The communication between two adjacent neurons can be performed in one of two ways.  The first includes the mediation of a neurotransmitter and the other uses an electrical contact between the neurons through special tubules that are called connexons.


The third way of communicating is through a neurotransmitter between a neuron and a muscle cell.  The first type of communication between two neurons is by the use of a neurotransmitter.  In this type of communication, one neuron receives a signal such as from a neurotransmitter which then opens voltage gated ion channels that leads to the depolarization of the electric potential of the cellular membrane of the neuron. 


If an action potential takes place, this neuron secretes in turn a neurotransmitter into the synaptic cleft between the neurons.  This neurotransmitter binds to receptors on the adjacent neuron and leads to opening of sodium ion channels.  This process continues until the information reaches the brain where it is processed and interpreted appropriately.  This manner of communication is the most common method of communication between neurons in the nervous system. 


The second type of communication occurs mainly in smooth muscle cells and in cells of the heart muscles. It involves neurons that are connected with each other using canals that are called connexons.  Once a neuron receives an impulse and an action potential occurs, sodium ions start to flow inside the cells and from there to the other neuron that is connected to it by the tubules.  As a result, electrical information starts to propagate from one neuron to another neuron and a process of contraction or relaxation occurs. 


The third type of communication between the cells is between neurons and muscle cells.  This involves an area which is called the neuromuscular junction which is located between the neuron and the muscle cell.  After the neuron receives a stimulus, it releases the neurotransmitter acetylcholine to the neuromuscular junction in the area between the cells.  It is called also the synaptic cleft. 


This neurotransmitter then binds to the muscle cell on the motor end plate and causes depolarization of the muscle cell which in turn initiates an action potential that leads to the release of calcium ions from the sarcoplasmic reticulum in the muscle cell.  This in turn initiates a process of muscle contraction.

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