6.5 - Neurons and synapses
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The nervous system consists of the Central Nervous System (CNS) and the Peripheral
Nervous System (PNS).
Neurons are the cells that make up the nervous system. These cells transmit electrical impulses
(nerve impulses).
Neuronal Anatomy:
We will be talking
about the
movement of
signals from one
end of a neuron to
the other.
Key Terminology For Nervous Unit:
Nerve Impulse: An electrical signal that travels from one end of a neuron to the other in
order to convey a message.
Potential: The difference in charge across the membrane of a neuron.
Resting Potential: The negative charge registered when the nerve is not conducting a nerve
impulse
Depolarization: The change from the negative resting potential to the positive action
potential.
Repolarization: The change in electrical potential from positive during an action potential,
back to the resting potential.
Neurons pump sodium (Na+) and potassium (K+) ions across their membranes to maintain a
resting potential.
Resting potential is maintained by sodium-potassium
pumps.
Remember these? ECG of an
Action Potential
These pumps use active transport to move ions across the
neuronal membrane to maintain a constant resting
potential of -70mV.
Works through the activity of a Sodium/Potassium Pump:
Fun Exercise: How long can
you go without thinking of
anything? Does this make
sense with what you know
about how nerves maintain
RP?
An action potential consists of depolarization and repolarization of the neuron.
An action potential is created through the opening of
Voltage-Gated Ion Channels.
These channel proteins open and close in finely tuned
procedure to change the potential across the membrane
of the neuron.
The stimulus must increase the potential beyond the
threshold potential to initiate an action potential.
Click the pictures to the right to access the
PHET simulation of a neuron.
Use the simulation to observe how local
currents change in a single part of an axon.
Nerve impulses are action potentials propagated along the axons of neurons.
Propagation of nerve impulses is the result of local
currents that cause each successive part of the axon
to reach the threshold potential.
Steps to an Action Potential:
1. Stimulus causes the membrane potential to
exceed the threshold potential, leading to the
opening of Na+ Voltage-Gated channels.
2. Influx of Na+ ions leads to change in the
membrane potential to +40mV (depolarization),
causing the K+ Voltage-Gated channels to open.
3. Depolarization of a local section of the neuron
depolarizes neighboring sections of the neuron.
4. Efflux of K+ ions eventually causes potential to
return to -75mV (repolarization) in each section,
closing all channels.
1.
From McGraw Hill: http://goo.gl/tI2MD
Brief period before returning to -70mV is known as
refractory period.
5. Sodium/Potassium pump begins to pump Na+/K+
against concentration gradient to return neuron
to resting potential (-70 mV).
The myelination of nerve fibers allows for saltatory conduction.
Nerve Cells in humans have special
coatings made out of fatty cells,
known as Schwann Cells.
These fatty cells “insulate” our
neurons, allowing them to skip the
action potential process for great
lengths of the axon, in order to
speed up the transmission process.
Schwann Cell
We estimate myelination makes
our nerve cells 5000 times more
efficient. Some organisms do not
have this myelination….like squid!
Nodes of Ranvier
Poor guys…..
Neurons are the cells that make up the nervous system. These cells transmit electrical
impulses.
http://www.blackwellpublishing.com/matthews/channel.html
http://outreach.mcb.harvard.edu/animations/synaptic.swf
The Endocrine System
A stimulus is received and processed.
Hormones are secreted directly into the blood.
They are carried to the target tissues (the place of intended action).
The action of the hormone changes the condition of the tissue.
This change in monitored through feedback.
Most hormonal change results in negative feedback.
Key endocrine glands:
1.
2.
3.
4.
5.
6.
7.
8.
Endocrine glands from: http://en.wikipedia.org/wiki/Endocrine_gland
The Endocrine System
A stimulus is received and processed.
Hormones are secreted directly into the blood.
They are carried to the target tissues (the place of intended action).
The action of the hormone changes the condition of the tissue.
This change in monitored through feedback.
Most hormonal change results in negative feedback.
Key endocrine glands:
1.
2.
3.
4.
5.
6.
7.
8.
Pineal gland
Pituitary gland
Thyroid gland
Thymus
Adrenal gland
Pancreas
Ovary (female)
Testes (male)
Endocrine glands from: http://en.wikipedia.org/wiki/Endocrine_gland
A simple diabetes animation
http://gxs.home.texas.net/work_samples/animations/2_diabetes/diabetes.swf
Diabetes Research Activity
Use the following websites to gather data on the prevalence of diabetes worldwide:
http://www.who.int/mediacentre/factsheets/fs312/en/
http://www.idf.org/atlasmap/atlasmap
Then use this data to evaluate the following statement:
77% of people worldwide with diabetes are in low or middle income countries.
Suggest a hypothesis as to why this statement is true, and search through the data to
see if you can derive a correlation.
Design a one page report on this topic, detailing the information that you found and
whether it supports or refutes .
Your Task: To design and record the most efficient negative feedback loop model of a
hormone in a small group using only the space equivalent to one desktop.
Steps you must include (for example): Digestion of starch by mouth
Digestion of sugar by stomach/small intestine
Assimilation of sugar into blood stream
(upon a certain concentration of
Pancreas stimulating release of insulin
glucose being reached)
Cells receiving insulin from pancreas
Cells then up-taking glucose from blood stream
Particles you should make sure to include:
Glucose
Starch
Beta Cells
Record your pathway using Vine and post it under #profbiohl2.
+
= Awesome!