PSY100H1 Chapter Notes - Chapter 3: Acetylcholine, Peripheral Nervous System, Monoamine Neurotransmitter

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12 Apr 2012
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Psychology chapter 3
Monday, February 06, 2012
1:05 PM
Neurons: the basic unit of the nervous system; it operates through electrical impulses,
which communicate with neurons, through chemical signals. Neurons receive integrate and
transmit information in the nervous system.
There are 3 types of neurons:
1. Sensory neurons: they detect information from the physical world and pass information
along to the brain, usually via the spinal cord. They are also called afferent neurons,
meaning they carry information to the brain. The sensory nerves that provide information
from the muscles are called as somatosensory.
2. Motor neurons: direct muscles to contract or relax, thereby producing movement. Motor
neurons are therefore efferent neurons , neurons that transmit signals from the brain to the
muscles throughout the body.
3. Interneurons: communicate within local or short distance circuits. They communicate with
other neurons typically within a specific brain region.
Neurons do not communicate randomly they; they selectively communicate with other
neurons to form circuits, or neural networks.
The neuron structure:
1. The cell body: in the neuron where information from thousands of other neurons is
collected and processed.
2. Dendrites: branchlike extensions of the neuron that detect information from other neurons.
They also increase the neurons receptive field.
3. Axon: a long narrow out growth where the information is transmitted to other neurons.
4. Terminal buttons: small nodules at the ends of the axons that release chemical signals from
the neuron to the synapse.
5. Synapse/synaptic cleft: the site for chemical communication between neurons, which
contains extracellular fluid.
6. Myelin sheath: a fatty material, made up of glial cells , that insulates the axon and allows
for rapid movement of electrical impulses along the axon.
7. Nodes of Ranvier: small gaps of exposed axons, between segments of myelin sheath,
where action potentials are transmitted.
Action Potential: the neural impulse that Impulse that passes along the axon and
subsequently causes the release of chemicals from the terminal buttons.
Usually when a neuron is polarized it is at a state of rest, at about -70mV. And its charge
inside is slightly more negative compared to outside the neuron. This is because there are
more potassium ions inside ( k is -ive) and there are more sodium ions outside ( Na +ive).
For an action potential to occur, the dendrites first receive information, the information
received is either excitatory signals or inhibitory signals.
Excitatory signals depolarize the cell membrane, increasing the likelihood that the neuron
will fire ( action potential) or the inhibitory signals hyperpolarize the cell, decreasing the
chance of an action potential.
When the dendrites do receive an excitatory signal, the sodium gates in the axon are
opened allowing a rush of sodium to go into the neuron, changing the charge from negative
to positive. A fraction of a second later the sodium gates close and the potassium gates are
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