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Nerve Signals
The nervous system is responsible for communication and coordination of all organ systems within a body. To
achieve this, the neurons – cells that make up the nervous system – must be able to pass signals from one to
another. To understand how a neuron transmits a signal, it is important be reminded of the structure of the neuron.
The dendrites receive chemical or electrical signals from the axon terminals of other neurons. The cell body
contains the nucleus, lysosomes and ribosomes. Most neurons have a single axon which sends signals to other
neurons. These signals are carried down the axon into the axon terminals which are small branches of the axon.
The axon terminals form synapses, or connections, with other cells. The space between two nerve cells is called the
synaptic cleft.
When a neuron is not transmitting a signal, it is at rest. During this rest period, the cytoplasm just inside
of the neuron contains two important molecules: positively charge potassium ions (K+) and negatively charged
protein molecules. (A positively charged ion occurs when an atom loses one or more electrons. Negatively
charged molecules form when the molecule gains extra electrons.) The cytosol contains more negatively charged
protein molecules than potassium ions, so the inside of the neuron is negative in charge. The fluid just outside of
the neuron is positively charged. This positive charge is due to the presence of positively charged ions, like
sodium (Na+). The cell membrane stores energy by holding these opposite charges apart. This difference in charge
is referred to as an electrical potential. When the neuron is at rest, this difference in charge is referred to as the
resting potential.
Sending a signal through a neuron – Action Potential
A stimulus (light, sound, touch or the presence of a chemical) can generate an electrical
nerve signal by reversing the charges inside and outside of the neuron’s membrane. c
Action potential occurs when specialized protein channels, called ion channels, open and
allow the positively charged sodium ions to diffuse into the cell. This influx of positive
ions causes the inside of the cell to become more positive than the outside of the cell. This
reversal of charge then triggers the sodium channels to close, blocking the diffusion of Na
. Meanwhile, another type of ion channel opens allowing potassium ions (K+) to diffuse
out of the cell. This causes
the charge on the inside of the cell to become negative again. The neuron has returned to
resting potential.
To transmit the signal throughout the neuron, the action potential must travel
the length of the neuron. The changes in charge in one area of the neuron trigger the
opening of
Na+ channels is membrane just down-stream of the action potential. As a result, an
action potential is generated in the adjacent region and is quickly followed by a
return to resting potential. The action potential travels down the neuron like
dominoes falling over; each reversal in charge triggers the opening of ion channels in
the adjacent membrane.
Action potentials are the same no matter what stimulus caused them. Your central
nervous system (CNS) can detect different intensity of different stimuli by interpreting the frequency of action
potentials traveling down the neuron. For example, if you tap your finger on your desk softly, your CNS will receive
fewer action potentials per second than if you tapped your finger very hard
Passing a signal from one neuron to another – Chemical synapse
If the nervous system is going to function properly, neurons must be able to communicate with each other by
passing signals to one another. This occurs at a synapse, or relay point between two cells. The most common type
of synapse in the nervous system of animals is chemical synapse. Chemical synapse occurs in the narrow space
between the axon terminal of the sending neuron and the dendrite of the receiving neuron.
When action potential reaches the axon terminal, it is converted into a chemical signal. This chemical signal comes
in the form of a neurotransmitter (a chemical that carries information from one nerve cell to another). Once the
action potential arrives at the end of the neuron, it stimulates vesicles containing a neurotransmitter. The vesicle
will then fuse with the cell membrane and release the neurotransmitter into the synaptic cleft using the process of
exocytosis. The released neurotransmitters diffuse across the synaptic cleft and bind to receptor molecules, which
are proteins attached to ion channels within the membrane of the receiving cell. The binding of the
neurotransmitters to the receptor molecules causes the ion channels to open, allowing Na+ to diffuse into the cell.
This influx of Na+ ions causes an action potential in the receiving neuron. The neurotransmitter is then either
broken down or transported back to the sending neuron to be reused. The absence of neurotransmitters in the
synaptic cleft causes the ion channels to close and the signal to end.
Analysis Questions
Directions: Answer question based on readings
1. Sending neuron is also known as _______Dendrite_____________
2. Receiving neuron is also known as _______Axon_____________
3. What term is used to describe a neuron that is not transmitting a signal?
The neuron is at rest, this difference responsible is named because the resting potential.
4. Assume that the neuron is at rest, where is potassium (K+) higher, inside or outside of the cell?
The inside of the cell and also the outside of the cell are separated by a membrane with K channels, that
are at first closed. there's a higher concentration of potassium ions on the inside of the cell than on the surface.
5. Assume that the neuron is at rest, where is sodium (Na+) higher, inside or outside of the cell?
6. Describe the conditions inside and outside of a neuron during action potential.
Inside the neuron has charged because of the presence of positively charged sodium
ions and outside the neuron negatively charged due to the dearth of as several
sodium ions.
7. What causes a neuron to change from resting potential to action potential?
A stimulus causes metal ion-channels inside the cell membrane to open and permit sodium ions to
diffuse into the cell. This changes the charge of the neuron to positive.
8. What causes a neuron to return to a resting potential from an action potential?
Sodium channels close, preventing any additional Na from getting into the neuron. Meanwhile, K
channels open, permitting positively charged K ions to diffuse out.
9. How is a signal transmitted through a single neuron?
The action potential is generated within the adjacent region and is quickly followed by a come back to
potential drop. The action potential travels down the neuron like dominoes falling over; every reversal in
charge triggers the gap of ion channels within the adjacent membrane.
10. What is a neurotransmitter?
Neurotransmitter is a chemical that carries info from one nerve cell to a different.
11. How are neurotransmitters secreted into the synaptic cleft?
Through exocytosis
12. How does a neurotransmitter cause an action potential in a receiving neuron?
The neurotransmitter binds to a receptor on the particle channel. once the neurochemical is sure to the
receptor, the particle channel opens and permits Na+ to diffuse into the cell, inflicting associate action
13. How is the signal between neurons stop?
The neurotransmitter is either reabsorbed by the causation somatic cell or with chemicals countermined
within the conjunction cleft.
14. What is saltatory conduction?
Saltatory conduction describes the method associate degree electrical impulse skips from node to node
down the complete length of an axone, dashing the arrival of the impulse at the nerve terminal as
compared with the slower continuous progression of change spreading down associate degree
unmyelinated axone.
Use the lecture slides and/or Julien’s Primer of Drug Action text to help answer the following questions.
Use the diagram (numbers) to identify the stages of an action potential.
Which section of the graph represents depolarization?
Which of the following segments of the graph shows a phase where the neuron will be less likely to
fire an action potential? ________2______
Which of the following segments of the graph shows repolarization?
Which section of the graph represents a neuron at rest?
At what membrane voltage is a neuron at rest? Use the Y axis on graph to answer.
Na+ has the highest concentration ____________ the cell while K+ has the highest concentration of
the ______________ of the cell.
What membrane potential is considered threshold membrane potential? ________5________ mV
When all the K+ Voltage-Gated channels are open (-90mV), the cell is considered to be
hyperpolarized. Which segment of the graph represents this? ________5________
At what stage are all the Na+ Voltage-Gated Channels open? ___________2____________
Match each term to the appropriate description.
Action potential
Refractory period
Potassium ions (K+)
Sodium-potassium pump
Sodium ions (Na+)
____E_____ Period of repolarization of the neuron during which it cannot respond to a second stimulus
__B_______ State in which the resting potential is reversed as sodium ions rush into neuron
____C_____ Electrical condition of the plasma membrane of a resting neuron
____G_____ Period during which potassium ions rush out of the neuron
____A_____ Transmission of the depolarization wave along a neuron's membrane
____F_____ The chief positive intracellular ion in a resting neuron
____D_____ Process by which ATP is used to move sodium ions out of the cell and potassium ion back into
cell; restores the resting conditions of the neuron
Directions: The diagram represents the final stages of synaptic transmission. Answer the following questions
related to synaptic transmission
1.Synaptic vesicles store varied neurotransmitters that are released at the synapse. the discharge is regulated
by a voltage-dependent Ca channel. Vesicles are essential for propagating nerve impulses between neurons
and are perpetually recreated by the cell.
2.Voltage gated Ca channels play crucial roles in several bodily functions including: cardiac action potentials,
neurotransmitter release, contraction. throughout neurological functions, these Ca channels produce action
potentials. At resting state,voltage-gated Ca channels are during a closed conformation.
3. The message travels from the presynaptic terminal of 1 synapse to the synaptic cleft to the postsynaptic
terminal of following synapse. The synaptic cleft is principally used to transport neurotransmitters from one
synapse to a different in order to continue carrying the nerve impulse till it reaches its destination.
4. Calcium channels are membrane-spanning proteins that regulate the intracellular concentration of Ca ions
(Ca2+). once getting into the cell, Ca2+ activates specific Ca receptor proteins, calmodulin, troponin-C, or Caactivated calcium, potassium, and chloride channels.
5. Neurotransmitter vesicles store numerous neurotransmitters that are free at the conjunction. the discharge
is regulated by a voltage-dependent metallic element channel. Vesicles are essential for propagating nerve
impulses between neurons and are constantly recreated by the cell.
6.Neurotransmitter receptors transmit the actions of sure neurotransmitters, therefore enabling cell-to-cell
communication within the nervous system. Most receptors are integral membrane proteins classified as
ligand-gated ion channels or G protein-coupled receptors .
Neurotransmitters (NTs: How Does the Brain Communicate?
The brain contains billions of nerve cells (neurons) that are always talking to each other. Neurons pass
messages back and forth within the brain and the spinal column. These nerve networks control everything
we feel, think, and do.
Neurotransmitters—The Brain's Chemical Messengers
To make messages jump from one nerve cell to another it creates chemical messengers, called
neurotransmitters. The end of one nerve cell releases neurotransmitters that travel to nearby nerve cell. Then
the transmitter binds to receptors on the nearby nerve cell, giving
Directions: Use your textbook to fill in information about the chemicals listed below.
Indicate (1) whether each neurotransmitter is excitatory, inhibitory, or both and (2) briefly describe
its function.
Acetylcholine is a chemical that is observed among the nerve synapses, or gaps, among nerve cells. When
activated, it causes the contraction of skeletal muscles and turns on glandular functions inside the endocrine
system.Like mail persons who can each supply and select up envelopes and packages, acetylcholine
capabilities inside the peripheral nervous gadget and crucial nervous device both as an activator and
inhibitor. In the peripheral nervous gadget, it reasons skeletal muscle groups to contract. In the important
nervous device, it inhibits the activation of the cholinergic
Acetylcholine (ACh)
Glutamate is a effective excitatory neurotransmitter that is launched with the aid of nerve cells in the brain. It
is accountable for sending signals among nerve cells, and under normal situations it performs an important
position in getting to know and
Gamma aminobutyric acid is a naturally happening amino acid that works as a neurotransmitter in your
brain. Neurotransmitters feature as chemical messengers. GABA is considered an inhibitory
neurotransmitter because it blocks, or inhibits, sure brain alerts and decreases activity on your fearful
Gamma aminobutyric acid (GABA)
Collectively with adrenaline, norepinephrine will increase heart price and blood pumping from the heart. It
also increases blood strain and allows ruin down fats and boom blood sugar tiers to provide more power to
the body._____________________________________________________________________________________
Norepinephrine (NE)
Dopamine is a chemical discovered naturally within the human frame. It is a neurotransmitter, which means
it sends alerts from the body to the brain. Dopamine performs a element in controlling the movements a
person makes, as well as their emotional responses. The right stability of dopamine is crucial for both bodily
and mental
Dopamine (DA)
Serotonin is an critical chemical and neurotransmitter inside the human body. It is believed to assist modify
mood and social behavior, appetite and digestion, sleep, memory, and sexual choice and function. There may
be a link between serotonin and
Endorphins act as analgesics, because of this they diminish the belief of pain. They additionally act as
sedatives. They are synthetic in your brain, spinal cord, and many other elements of your body and are
released in reaction to brain chemicals referred to as
Answer the following questions:
What is monoamine oxidase?
Monoamine oxidase is concerned in removing the neurotransmitters catecholamine, serotonin and
intropin from the brain. MAOIs prevent this from happening, that makes a lot of of those brain chemicals on
the market to result changes in each cells and circuits that are wedged by depression.
What is an monoamine oxidase inhibitor (MOAI)?
MAOIs were the primary category of antidepressants to be developed. They fell out of favor owing
to issues regarding interactions with sure foods and diverse drug interactions. once MAO is restrained,
noradrenaline, serotonin, and Intropin don't seem to be countermined, increasing the concentration of all 3
neurotransmitters within the brain. MAOIs are used for the treatment of Parkinson's sickness.
How do MOAI’s work at the synapse?
MAOIs increase synaptic norepinephrine, serotonin, and dopamine by inhibiting the protein enzyme
from metabolizing these amine transmitters. Adverse effects embody hypotension, weight gain, sexual
disfunction, edema, and sleep disorder.
What is the precursor to serotonin, i.e. what amino acid is it made form?
Hydroxytryptophan is associate organic compound precursor employed in the formation of 5hydroxytryptamine. 5-HTP has been used as associate oral supplement various to spice up 5hydroxytryptamine.22 it's been shown in studies to boost depression, however solely preliminary proof is
offered suggesting that 5-HTP conjointly could improve anxiety.
Serotonin can be metabolized (broken down) into what sleep related hormone?
What is the precursor to dopamine i.e. what amino acid is it made form?
Dopamine is one in every of the 3 main sign molecules from the hormone family. the opposite 2 are
the known fight-or-flight response molecules hormone and noradrenaline.Dopamine is created within the
brain. It’s additionally created in and utilized by alternative systems within the body, wherever it acts as a
very important chemical courier. Dopastat is attached the center, modulating vessel perform, stimulating
muscular tissue contraction, and promoting the widening of blood vessels required for correct blood flow.
Dopastat is employed within the kidneys to assist them perform properly, stimulating inflated excretion, and
evacuation excess Na.
What is the precursor to epinephrine and norepinephrine?
Epinephrine and norepinephrine are two neurotransmitters that additionally function hormones, and they
belong to a category of compounds called catecholamines. As hormones, they influence totally different
elements of your body and stimulate your central nervous system.Chemically, epinephrine and
norepinephrine are very similar. However, epinephrine works on each alpha and beta receptors, whereas
catecholamine solely works on alpha receptors. Alpha receptors are only found within the arteries. Beta
receptors are within the heart, lungs, and arteries of skeletal muscles. It’s this distinction that causes
epinephrine and norepinephrine to have slightly totally different functions.