Describe the functions and the functioning of the nervous system
Neurons – are the nerve cells – three main classes
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Sensory -translate information into electrochemical information
Interneurons – collect and relay information, sensory neurons
Motor – carry directions to the muscles
What does it look like?
http://www.google.ca/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/a/a9/C
omplete_neuron_cell_diagram_en.svg/500pxComplete_neuron_cell_diagram_en.svg.png&imgrefurl=http://en.wikiped
Neurons are either afferent, moving impulses to the brain, or efferent, moving impulses from the brain.
How do neurons work?
-move electric currents, either positive or negative, along the line
-Use of an impermeable membrane and ions on either side to develop an electrical potential, causing a
flow to reduce the potential
-Neurons use a sodium/potassium pump to pump sodium out, potassium in. The problem is that the
membrane leaks, potassium diffuses out. Because there is more potassium and sodium outside, the
charge is positive outside relative to inside. This is resting potential.
-information is carried by causing a disturbance in this resting potential. Gated ion pores open and close
causing a disturbance in two ways:
1. Electrically controlled – open or close when electric potential changes allowing sodium to
rush in.
2. Chemically Controlled – open when a chemical messenger binds – like adrenalin
Action Potentials – brief changes in the electrical potential moves along the neurons, passing the
message – not electrical charges.
An impulse occurs when part of a neuron is depolarized, causing the sodium channels to open and
sodium to rush in. Why?
1. Attracted to negative charge
2. Repel potassium outside
3. Diffuse from high sodium to low sodium
When sodium rushes in, it becomes positive inside which triggers the potassium channels to open so it
can rush out making the in the inner charge negative again. Please note the that the sodium channel are
all or nothing, when one opens the next is triggered to open as well. This passes the impulse.
Quick Picture
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html
As the impulse moves along the neuron, it moves towards the axon end. The axon, the long part of the
neuron, is surrounded by the Myelin Sheath, or the Schwan Cells. These insulate the axon against
disturbance of the impulse, and have small gaps between them known as the Nodes of Ranvier ot allow
depolarization. What happens when the impulse reaches the end of the neuron?
The space between axons, neurons, is known as the synapses. There is the presynaptic neuron that
carries the action potential, the synaptic cleft in the middle, and postsynaptic neuron that is receiving
the impulse on the other side of the synapses. How does the impulse pass?
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2.
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Action potential triggers opening of Ca channels
Ca rushes in
Because of Ca ions, a neurotransmitter is releases from the presynaptic neuron to the synapse
Neurotransmitter moves across and binds to receptors on the post neuron
Causes opening of chemically gated ion channels, influx of sodium, impulse started on next.
Transmitter in synapse is eliminated.
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter14/animation__transmission_across_a_synapse.html
Within our body
Central Nervous System – consists of the brain and spinal cord and receives the impulses from the rest
of the body. These parts of the nervous system are enclosed by bone.
Peripheral Nervous System – consists of all nerves not enclosed by bone and found in all of limbs and
areas outside of the spine and skull. The job is carry impulses to and from the limbs.
Not all organisms have the same system as we do. To compare nervous systems, we look at;
http://faculty.washington.edu/chudler/invert.html
Human Brain versus Reptile Brain
Please answer the following questions:
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How is a human brain different?
Why do they say the human/mammal brain has evolved from the reptilian brain?
What is the reptilian brain responsible? Thoughts, responsibilities, etc.
What extra things can the human brain do?