What is neurons ? Structure or parts of Neuron , What is Neurotransmitters ? Types of Neurotransmitters ,

 

 What is Neurons ?

The nervous system is composed of more than 100 billion cells known as neurons. A neuron is a basic building block of the central nervous system. It is also known as nerve cells . This are the fundamental units of the brain and nervous system, the cells which are responsible for receiving sensory input from the external world, for sending motor commands to our muscles. This are the cells that transmit chemical and electrical signals in the brain. 

At birth, the human brain consists of an estimated 100 billion neurons. Unlike other cells, neurons don't reproduce or regenerate. They aren't replaced once they die.

Structure or parts of Neuron

Neurons vary in their structure, but almost all neurons have four basic parts. These include a soma{cell body}, dendrites, an axon and terminal buttons.

Soma- It contains the nucleus of the cell {the central portion that performs metabolic and reproductive functions for the cell}. It is responsible for the life of the neuron and connects the dendrites to the axon.

Dendrites- Branch like structures that receive information from other neurons.

Axon-It is a long, thin tube that extends from the soma and responds to the information, when appropriate, by transmitting an electrochemical signal, which travels to the terminus[end] where the signal can be transmitted to other neurons.

Terminal buttons-Small knobs found at the ends of the branches of an axon that do not directly touch the dendrites of the next neuron.

Some other parts are-

Myelin- It is a white, fatty substance that surrounds some of the axons of the nervous system, which accounts for some of the whiteness of the white matter of the brain.

Nodes of Ranvier-This are small gaps in the myelin coating along the axon, which serve to increase conduction speed even more by helping to create electrical signals, also called action potentials, which are then conducted down the axon.

Synapse-It serves as a junction between the terminal buttons of one or more neurons and the dendrites[or sometimes the soma] of one or more other neurons.[Carlson,2006].

Functional classification of Neurons:

 1). Sensory neurons :- Convey information from tissues and organs into the central nervous system and are sometimes also called afferent neurons.

 

2). Motor neurons :- Transmit signals from the central neurons system to effecter cells.

 

3). Relay neurons or inter neurons :- Connect neurons within specific regions of the central nervous system. 

What is Neurotransmitters ?

The transmitter of signals from one neuron to another, across the synapse was earlier through to be electrical.

The communication takes place through a change in chemical concentration and these chemicals are called neurotransmitter.

Neurotransmitter was first discovered by "Otto loewi" in 1921.

Neurotransmitters are the chemicals which allow the transmission of signals or nerve impulses from one neuron to next accesses of  synapses. Neuromitter regulate the physical and emotional processes.

Neurotransmitters are the chemical messengers for transmission of information across the synaptic gap to the receiving dendrites of the next neuron [ Von Bohlen and Halbach and Dermietzel ,2006].Some neurotransmitters are excitatory in nature while some are inhibitory in nature.

Types of neurotransmitters:-

1.      Amino acid.

2.     Monoamines.

3.     Peptides.

1). Amino acid :- Neurotransmitter like glutamate, glycine, serine, & gamma aminobutyric acid (GABA).

2). Monoamines :- Dopamine, serotonin, melatonin, epinephrine & norepinephrine are the monoamines neurotransmitters.

3). Peptides :- Calcitonin, glucagon, vasopressin, oxytocin, & beta-endorphin are some of the neuroactive peptides. There are about 50 neuroactive peptides till now, with new ones being discovered regularly.

 

There are more than 40 neurotransmitters in the human nervous system: Some important neurotransmitters are acetylcholine, gamma aminobutyric acid [GABA] , dopamine, norepinephrine, glutamate, serotonin .

Acetylcholine - It is associated with memory functions, and the loss of acetylcholine through Alzheimer's disease has been linked to impaired memory functioning in Alzheimer's patient's [Hasselmo, 2006] . Acetylcholine also plays an important role in sleep and arousal. When someone awakens, there is an increase in the activity of so-called cholinergic neurons in the basal forebrain and the brainstem [ Rockland, 2000] . 

Dopamine - It is associated with attention, learning, and, movement coordination. Dopamine also involved in motivational processes, such as reward and reinforcement. Schizophrenics show very high levels of dopamine. This fact has led to the "dopamine theory of schizophrenia" which suggests that high levels of dopamine may be partially responsible for schizophrenic conditions. Drugs used to combat schizophrenia often inhibit dopamine activity [ von Bohlen und Halbach and Dermietzel , 2006].

In contrast, patients with Parkinson's disease show very low dopamine levels, which leads to the typical trembling and movement problem associated with Parkinson's. When patients receive medication that increases their dopamine level, they [as well as healthy people who receive dopamine] sometimes show an increase in pathological gambling. Gambling is a compulsive disorder that results from impaired impulse control. When dopamine treatment is suspended, these patients no longer exhibit this behavior [ Drapier et al.., 2006 ; Voon et al., 2007; Abler et al., 2009] . These findings support the role of dopamine in motivational processes and impulse control. 

Serotonin - It play an important role in eating behavior and body- weight regulation. High serotonin levels play a role in some types of anorexia resulting from illness or treatment of illness. For example, patient suffering from cancer or undergoing dialysis often experience a severe loss of appetite [ Agulera et al., 2000; Davis et al., 2004]. This loss of appetite is related, in both cases, to high serotonin levels, Serotonin is also involved in aggression and regulation of impulsivity [ Rockland, 2000]. Drugs that block serotonin tend to result in an increase in aggressive behavior.

Epinephrine and norepinephrine - It involves in diverse effects on body related to fight-or-flight reactions, anger, and fear. It also involve in regulation of alertness.

GABA [ gamma aminobutyric acid ] - It influence certain mechanisms for learning and memory [ lzquierdo and Medina, 1997].

Glutamate - It influence certain mechanisms for learning and memory [ Rledel, Platt and Micheau, 2003].

Neurotransmitter effects:-

• Control the appetite center of the brain.
• Stimulates corticotropin releasing factor, Cortisol regulate mole & female sex hormones.
• Regulates sleep.
• The mind body connection.

 

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