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11 Feb 2011
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Chapter 4
Conduction and Neurotransmission
-all thoughts, emotions, and behaviours occur because of chemical processes that occur in neurons
-human nervous system has approx. 85 billion neurons
-neurons have a communication network that involves two main processes:
1.Conduction
changes within a neuron that allow information to be transmitted from one part of the neuron to
another
2.Neurotransmission
changes in neuron caused by release of biologically active chemicals from adjacent neurons
The Neuron
-each neuron has numerous excitatory and inhibitory inputs/synapses
-main body of neuron is called soma
-has extensions called dendrites (several) and axons (one)
axon hillock: region where axon emerges from soma
myelin sheath: coating around the axons (works like insulation)
Nodes of Ranvier:
-gaps in myelin sheath where axons come into direct contact with ECF
-speeds up electrical transmission
Axon terminal: an enlargement at the branch of axons
Conduction
4 primary ions important for conduction:
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1.Sodium (Na+)
2.Potassium (K+)
3.Chloride (Cl -)
4.Calcium (Ca 2+)
5.Large negatively charged protein molecules
2 processes that influence concentration of ions across neuronal membranes:
1.Concentration gradient
ions flow from high concentration region to low concentration region
2.Electrostatic pressure
the force exerted by attraction of oppositely charged ions or by repulsion of similarly charged ions
Neuron can be in one of 2 states
1.Polarized
-resting potential state
-more negative charged ions on the inside of the membrane than on the outside of the membrane
2.Depolarized
-rapid exchange of ions across the neuron membrane
-results in action potential
-Resting potential of neuron is -70 mV
-if stimulus causes neuron to hit threshold potential (around -60 mV), it triggers an action potential
Steps involved in action potential:
oNeuron goes from resting potential to threshold potentialopening of ion channels
oVoltage gates channels open and allow Na+ to enter the cell –causes further depolarization
oTriggers opening of K+ channels which drives membrane back towards resting potential
(repolarization)
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Document Summary

All thoughts, emotions, and behaviours occur because of chemical processes that occur in neurons. Each neuron has numerous excitatory and inhibitory inputs/synapses. Has extensions called dendrites (several) and axons (one) axon hillock: region where axon emerges from soma myelin sheath: coating around the axons (works like insulation) Gaps in myelin sheath where axons come into direct contact with ecf. Axon terminal: an enlargement at the branch of axons. 4 primary ions important for conduction: www. notesolution. com: sodium (na+, potassium (k+, chloride (cl -, calcium (ca 2+, large negatively charged protein molecules. Neuron can be in one of 2 states: polarized. More negative charged ions on the inside of the membrane than on the outside of the membrane: depolarized. Rapid exchange of ions across the neuron membrane. If stimulus causes neuron to hit threshold potential (around -60 mv), it triggers an action potential. Axon hillock is the decision maker in producing action potentials.

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