The Nervous System:
Crossing Neural Membranes
Anna Mayersohn, Hannah Medley,
Alex Mitchell, and Zahra Pirani
Electrical Charges in a Neuron
When a neuron is not being disturbed (resting), it maintains a
constant electrical charge across its membrane, where the
cytoplasm is negatively charged, and the extracellular fluids
are positively charged. These charges are reversed by stimuli,
or outside forces. When this happens, the cytoplasm becomes
positively charged compared to the negative extracellular
fluid. The change creates an action potential, which spreads
throughout the rest of the neuron (7).
Electrical Charges in a Neuron
Within a neuron,
information is carried
through action potentials,
which are electrical
signals. To carry
information to another
cell, the electrical signal
needs to be converted to
a chemical signal (7).
http://upload.wikimedia.org/wikipedia/commons/d/d3/Neuron1.jpg (3)
Chemical synapse and Neurotransmitters
Chemical synapse: The narrow cleft
between two neurons or between a
neuron and another cell. The first
neuron is the presynaptic neuron and
the second is the postsynaptic
neuron (7).
.
Neurotransmitters: Signaling
molecules that are packaged in
vesicles at the end of the axon of
the presynaptic neuron (7). Once the
molecules are released, they diffuse
across the chemical synapse and
bind to receptors on the membrane
of the cell on the other side (4, 7).
http://www.neurevolution.net/wpcontent/uploads/Synapse.JPG (1)
Neurotransmitters
Acetylcholine or ACh is a type of neurotransmitter. It acts at a
chemical synapse between a motor neuron and a muscle cell.
ACh is released from the motor neuron, diffuses across the
chemical synapse, and binds to receptors on the muscle
membrane where it finally triggers action potentials which
initiate muscle contraction (7).
Serotonin is a neurotransmitter converted from tryptophan
(an amino acid) that binds to serotonin receptor sites in the
postynaptic neuron. Serotonin acts on neurons in brain regions
that control sleeping and eating habits, sensory perception,
temperature control, and emotions(5).
The Path of a Neurotransmitter
Neurotransmitters start in synaptic
vesicles that float in the
cytoplasm of the presynaptic
neuron.
They require an action potential in
order to diffuse out of the cell and
across the synapse (7).
http://www.daviddarling.info/images/neurotransmitter.jpg
(2)
The Path of a Neurotransmitter
When the action potential arrives at
the end of an axon, it is converted
from an electrical signal to a chemical
one in the form of neurotransmitters.
The synaptic vesicles that
neurotransmitters are packaged in fuse
with the membrane of the presynaptic
neuron and are expelled from
it (exocytosis). The
neurotransmitters then diffuse across
the synaptic cleft (7).
http://www.daviddarling.info/images/neurotransmitter.jpg
(2)
The Path of a Neurotransmitter
The neurotransmitters
bind to protein pumps on
the dendrites of
the postsynaptic
neuron. The ions enter the
neuron by passing through
protein pumps that change
shape and create a
passageway when specific
neurotransmitters bind to
them (7).
https://static.flatworldknowledge.com/sites/all/files/imagecache/book/58757/fwk-stangorfig03_005.jpg
(8)
The Path of a Neurotransmitter
When the neurotransmitter binds to the postsynaptic cell, it
either creates (excitatory neurotransmitter) or inhibits
(inhibitory neurotransmitter) an action potential in that
neuron.
In other words, an electrical signal (action potential) triggers
the release of a chemical signal (neurotransmitter) when it
reaches the output zone. If an excitatory neurotransmitter is
released, it can trigger another action potential, which will
run though the other neuron in a similar fashion (7).
The Path of a Neurotransmitter
http://www.youtube.com/watch?v=HXx9qlJetSU (6)
References
1. Chemical synapse. 8 Apr. 2007. Neurevolutions. N.p., n.d. Web. 25 Oct. 2011.
http://www.neurevolution.net/wp-content/uploads/Synapse.JPG.
2. Darling, David. Neurotransmitter. N.d. Internet Encyclopedia of Science. David Darling, n.d. Web. 25 Oct.
2011.http://www.daviddarling.info/encyclopedia/N/neurotransmitter.html.
3. Gorton, Nick. Neuron1.jpg. N.d. Wikipedia. N.p., 16 Aug. 2005. Web. 25 Oct. 2011.
http://upload.wikimedia.org/wikipedia/commons/d/d3/Neuron1.jpg.
4. Johnson, George B., and Gary J. Brusca. Biology, Visualizing Life. Washington DC: National Academy, 1990.
Print.
5. Landry, Mim J. "Serotonin and impulse dyscontrol: brain chemistry involved in impulse and addictive
behavior." Behavioral Health Management Jan.-Feb. 1994: 35+. General OneFile. Web. 24 Oct.
2011.Document URL. http://go.galegroup.com/ps/i.do?&id=GALE%
7CA15628250&v=2.1&u=mlin_m_wellhigh&it=r&p=ITOF&sw=w. Gale Document Number: GALE|A15628250
6. Neural Synapse. Youtube. jokerwe, 2 Oct. 2007. Web. 25 Oct. 2011. http://www.youtube.com/watch?
v=HXx9qlJetSU.
References (continued)
7. Starr, Cecie, and Ralph Taggart. "34.3 Chemical Synapses." Biology, The Unity and Diversity of Life. 9th
ed. Pacific Grove: Jack C. Carey, 2001. 580-81. Print.
8. The Synapse. Introduction to Psychology. By Charles Stangor. N. pag. Flat World Knowledge. N.p., Nov. 2010.
Web. 25 Oct. 2011. http://www.flatworldknowledge.com/node/285354#stangor-ch03_s01_s02_f01.