Download Neurons

Question: What Is a Neuron?
Answer:
A neuron is a nerve cell that is the basic building block of the nervous
system. Neurons are similar to other cells in the human body in a
number of ways, but there is one key difference between neurons and
other cells. Neurons are specialized to transmit information throughout
the body.
These highly specialized nerve cells are responsible for communicating
information in both chemical and electrical forms. There are also several
different types of neurons responsible for different tasks in the human
body.
Sensory neurons carry information from the sensory receptor cells
throughout the body to the brain. Motor neurons transmit information
from the brain to the muscles of the body. Interneurons are responsible
for communicating information between different neurons in the body.
Neurons vs. Other Cells
Similarities with other cells:
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Neurons and other body cells both contain a nucleus that holds
genetic information.
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Neurons and other body cells are surrounded by a membrane that
protects the cell.
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The cell bodies of both cell types contain organelles that support
the life of the cell, including mitochondria, Golgi bodies, and
cytoplasm.
Differences that make neurons unique:

Unlike other body cells, neurons stop reproducing shortly after
birth. Because of this, some parts of the brain have more neurons at
birth than later in life because neurons die but are not replaced.
While neurons do not reproduce, research has shown that new
connections between neurons form throughout life.

Neurons have a membrane that is designed to sends information to
other cells. The axon and dendrites are specialized structures
designed to transmit and receive information. The connections
between cells are known as a synapses. Neurons release chemicals
known as
The Structure of a Neuron
There are three basic parts of a neuron: the dendrites, the cell body and
the axon. However, all neurons vary somewhat in size, shape, and
characteristics depending on the function and role of the neuron. Some
neurons have few dendritic branches, while others are highly branched
in order to receive a great deal of information. Some neurons have short
axons, while others can be quite long. The longest axon in the human
body extends from the bottom of the spine to the big toe and averages a
length of approximately three feet!
Learn more about the structure of a neuron.
Neurotransmitters
Neurotransmitters are an essential part of our everyday functioning.
While it is not known exactly how many neurotransmitters exist,
scientists have identified more than 100 of these chemical messengers.
What effects do each of these neurotransmitters have on the body? What
happens when disease or drugs interfere with these chemical
messengers? The following are just a few of the major neurotransmitters,
their known effects, and disorders they are associated with.
Acetylcholine: Associated with memory, muscle contractions, and
learning. A lack of acetylcholine in the brain is associated with
Alzheimer’s disease.
Endorphins: Associated with emotions and pain perception. The body
releases endorphins in response to fear or trauma. These chemical
messengers are similar to opiate drugs such as morphine, but are
significantly stronger.
Dopamine: Associated with thought and pleasurable feelings.
Parkinson’s disease is one illness associated with deficits in dopamine,
while schizophrenia is strongly linked to excessive amounts of this
chemical messenger.
Communication Between Synapses
Once an electrical impulse has reached the end of an axon, the
information must be transmitted across the synaptic gap to the dendrites
of the adjoining neuron. In some cases, the electrical signal can almost
instantaneously bridge the gap between the neurons and continue along
its path.
In other cases, neurotransmitters are needed to send the information
from one neuron to the next. Neurotransmitters are chemical messengers
that are released from the axon terminals to cross the synaptic gap and
reach the receptor sites of other neurons. In a process known as
reuptake, these neurotransmitters attach to the receptor site and are
reabsorbed by the neuron to be reused.
Dendrites serve as the input region of the neuron and receive
information from other cells. Image: Kendra Cherry
Dendrites are treelike extensions at the beginning of a neuron that help
increase the surface area of the cell body. These tiny protrusions receive
information from other neurons and transmit electrical stimulation to the
soma. Dendrites are also covered with synapses.
Dendrite Characteristics
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Most neurons have many dendrites
However, some neurons may have only one dendrite
Short and highly branched
Transmits information to the cell body
The soma is where the signals from the dendrites are joined and passed
on. The soma and the nucleus do not play an active role in the
transmission of the neural signal. Instead, these two structures serve to
maintain the cell and keep the neuron functional.
The support structures of the cell include mitochondria, which provide
energy for the cell, and the Golgi apparatus, which packages products
created by the cell and secretes them outside the cell wall.
Axon Hillock
Image: Kendra Cherry
The axon hillock is located at the end of the soma and controls the
firing of the neuron. If the total strength of the signal exceeds the
threshold limit of the axon hillock, the structure will fire a signal (known
as an action potential) down the axon.
Image: Kendra Cherry
The axon is the elongated fiber that extends from the cell body to the
terminal endings and transmits the neural signal. The larger the axon, the
faster it transmits information. Some axons are covered with a fatty
substance called myelin that acts as an insulator. These myelinated
axons transmit information much faster than other neurons.
Axon Characteristics
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Most neurons have only one axon
Transmit information away from the cell body
May or may not have a myelin covering
The terminal buttons are located at the end of the neuron and are
responsible for sending the signal on to other neurons. At the end of the
terminal button is a gap known as a synapse. Neurotransmitters are used
to carry the signal across the synapse to other neurons.