Neurons are structures; they are the basic unit of the nervous system. It is estimated that the nervous system contains over 11 billion neurons. The neuron, which is covered by a cell membrane consist of: dendrites, cell body, and axons. Dendrites are branched appendages that carry information the cell body. The cell body contains the nucleus. An axon conveys information away from the cell body. Some axons are covered with myelin sheath. The myelin sheath is interspersed with spaces called nodes of Ranvier. The nodes of Ranvier help aid in the neural transmission. Neurons are surrounded by glial cells. Glial cells nourish the neurons and hold them in place; these cells are the basis of the myelin sheaths. Axon terminals are branched and contain terminal buttons. Terminal buttons are tiny swellings that in turn contain synaptic vesicles. Synaptic vesicles are filled with chemicals called neurotransmitters. Neurotransmitters assist in transmission of information to other neurons.
Types of neurons
There are three types of neurons; including: Sensory neurons, Motor neurons, and Interneurons. Sensory neurons are located in the body’s sense organs, such as, the eye, ear or nose. Sensory neurons send information from these organs to the brain. Motor neurons convey information from the nervous system to the body’s organs, glands, and muscles. Interneurons transmit information from one neuron to another within the nervous system.
Components of Neural Transmission
The function of a neuron is to transmit information within the nervous system. Neural transmission occurs when a neuron is activated, or fired. Activation of the neuron takes place when the neuron is stimulated by pressure, heat, light, or chemical information from other cells.
The fluid inside a neuron is separated from the outside by a polarized cell membrane that contains electrically charged particles known as ions. When a neuron is sufficiently stimulated to reach the neural threshold depolarization, or a change in cell potential occurs.
The term potential refers to a difference in electrical charges. Neurons have two types of potentials, a resting potential and a action potential. The neural threshold must be reached before a change from a resting to action potential occurs.
The resting potential is the potential maintained by the inactive neuron. When unstimulated, a neuron is like a small battery and has a measurable negative electrical charge called the resting potential (70 millivolts).
The action potential is the potential produced when appropriate stimulation is high enough to reach the neural threshold and causes the neuron to fire. Alteration of membrane permeability allows a change of electrical charges this is known as polarization, (from negative to more positive). These charges run along the entire cell membrane.
The rate of neural transmission is independent of the level of stimulation. That means, if the neural threshold is not reached, the neuron will not fire. Also, if the threshold is reached or exceeded, the amplitude of the action potential is the same regardless of the level of stimulation. This idea is known as the all or none principle. Once the neuron is triggered to fire (its action potential has reached 65 millivolts) the action potential continues the length of the axon without diminishing because the action potential depends upon cell membrane permeability, a cell characteristic, and not upon the strength of the triggering stimulus.
After the neuron reaches its action potential, however there is a short period of time called, refractoriness, which affects neuron firing. During the first part of the refractory period, the neuron will not fire again no matter how great the stimulation. This is known as the absolute refractory period. During this period a stronger than usual stimulus is required to trigger the action potential before the neuron returns to its resting state. After the refractory period, the neuron will fire when it reaches its neural threshold.
Components of Synaptic Transmission
The synapse is the name given for the junction between the neurons where information is exchanged. The action potential causes information to be transmitted from the axon of the first neuron called the presynaptic neuron to the dendrites or cell body of the second neuron called the postsynaptic neuron by secreting chemicals called neurotransmitters.
Where The Neurotransmitters Stored
Neurotransmitters are stored in small containers called vesicles located in knoblike structures called terminal buttons on the tip of the axons. The axon of the presynaptic neuron does not touch the dendrites or the postsynaptic neuron. It is separated from them by a space called the synaptic cleft. Stimulation of the presynaptic neuron produces an action potential and causes the release of neurotransmitters into the synaptic cleft. Most neurotransmitters combine with special sites called receptor sites located on the dendrites and cell body of the postsynaptic neuron. Left over neurotransmitters are taken up by the presynaptic, a process called reuptake.
Combining Neurons with Receptor sites
The combination of the neurotransmitters molecules to the receptor sites in the postsynaptic cell membrane produces a change of potential in the postsynaptic neuron, called postsynaptic potential. The postsynaptic potential allows ions to enter or leave the cell membrane. When ions move in and out of the postsynaptic neuron it changes the polarity of the neuron. Thus increasing or decreases the probability of the neuron reaching its action potential.
Two Different Types of Postsynaptic Potentials
There are two types of Postsynaptic Potentials, excitatory and, inhibitory. Excitatory Postsynaptic Potentials increase the likelihood that the postsynaptic neuron will reach its action potential, thus causing it to fire. The inhibitory postsynaptic potential decreases the likelihood that the postsynaptic neuron will reach its action potential, thus inhibiting it from firing. Excitatory adds positive charged ions and Inhibitory add negative charged ions in to the cell body of the postsynaptic neuron.
The synapse is the name given for the junction between the neurons where information is exchanged. The action potential causes information to be transmitted from the axon of the first neuron called the presynaptic neuron to the dendrites or cell body of the second neuron called the postsynaptic neuron by secreting chemicals called neurotransmitters.
Where The Neurotransmitters Stored
Neurotransmitters are stored in small containers called vesicles located in knoblike structures called terminal buttons on the tip of the axons. The axon of the presynaptic neuron does not touch the dendrites or the postsynaptic neuron. It is separated from them by a space called the synaptic cleft. Stimulation of the presynaptic neuron produces an action potential and causes the release of neurotransmitters into the synaptic cleft. Most neurotransmitters combine with special sites called receptor sites located on the dendrites and cell body of the postsynaptic neuron. Left over neurotransmitters are taken up by the presynaptic, a process called reuptake.
Combining Neurons with Receptor sites
The combination of the neurotransmitters molecules to the receptor sites in the postsynaptic cell membrane produces a change of potential in the postsynaptic neuron, called postsynaptic potential. The postsynaptic potential allows ions to enter or leave the cell membrane. When ions move in and out of the postsynaptic neuron it changes the polarity of the neuron. Thus increasing or decreases the probability of the neuron reaching its action potential.
Two Different Types of Postsynaptic Potentials
There are two types of Postsynaptic Potentials, excitatory and, inhibitory. Excitatory Postsynaptic Potentials increase the likelihood that the postsynaptic neuron will reach its action potential, thus causing it to fire. The inhibitory postsynaptic potential decreases the likelihood that the postsynaptic neuron will reach its action potential, thus inhibiting it from firing. Excitatory adds positive charged ions and Inhibitory add negative charged ions in to the cell body of the postsynaptic neuron.
Types of Neurotransmitters
Many different types of drugs can affect the level of neurotransmitters. Some disorders are associated with either neurotransmitter deficiencies or excesses. There several types of neurotransmitters, which include: Acetylholine, Biogenic amines, GABA, Glycine, Endorphins, and Substance P.
Looking At Acetylholine
Acetylcholine is a neurotransmitter that occurs throughout the nervous system and is the only neurotransmitter found in the synapses between the motor neurons and voluntary muscle cells. There are theories that claim that the Degeneration of the cells that produe Acetylcholine is associated with Alzheimer’s disease.
Looking At Biogenic Amines
This type of neurotransmitters include three neurotransmitters, which are: norepinephrine, dopamine, and serotonin. Some theories in the scientific community suggest that the deficiency of dopamine is associated with Parkinson’s disease. In addition certain types of depression is related with having low levels of norepinephrine. It does not seem that much is known about serotonin, except that when taking LCD the levels of serotonin is increased.
Looking at GABA
Gamma aminobutyric acid appears to produce only inhibitory postsynaptic potentials. Many tranquilizers work by increasing the inhibitory actions of GABA.
Looking at Endorphins
Endorphins modulated the activity of other neurotransmitters and are called neuromodulators. They tend to function in the same way as opiates such as morphine. In other words, when someone is walking really fast and they feel high, the cause tends to be related to an increase their endorphins.
Looking at Substance P
Substance P is a neurotransmitter in many neural circuits. Substance P has been associated with causing pain.
Many different types of drugs can affect the level of neurotransmitters. Some disorders are associated with either neurotransmitter deficiencies or excesses. There several types of neurotransmitters, which include: Acetylholine, Biogenic amines, GABA, Glycine, Endorphins, and Substance P.
Looking At Acetylholine
Acetylcholine is a neurotransmitter that occurs throughout the nervous system and is the only neurotransmitter found in the synapses between the motor neurons and voluntary muscle cells. There are theories that claim that the Degeneration of the cells that produe Acetylcholine is associated with Alzheimer’s disease.
Looking At Biogenic Amines
This type of neurotransmitters include three neurotransmitters, which are: norepinephrine, dopamine, and serotonin. Some theories in the scientific community suggest that the deficiency of dopamine is associated with Parkinson’s disease. In addition certain types of depression is related with having low levels of norepinephrine. It does not seem that much is known about serotonin, except that when taking LCD the levels of serotonin is increased.
Looking at GABA
Gamma aminobutyric acid appears to produce only inhibitory postsynaptic potentials. Many tranquilizers work by increasing the inhibitory actions of GABA.
Looking at Endorphins
Endorphins modulated the activity of other neurotransmitters and are called neuromodulators. They tend to function in the same way as opiates such as morphine. In other words, when someone is walking really fast and they feel high, the cause tends to be related to an increase their endorphins.
Looking at Substance P
Substance P is a neurotransmitter in many neural circuits. Substance P has been associated with causing pain.
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