PSYC 2015 Chapter Notes - Chapter 2: Reflex Arc, Sympathetic Nervous System, Interneuron

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8 Feb 2017
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Mohit Singh
Bio Psych Notes
Ch. 2
Charles Scott Sherrington demonstrated that communication between one
neuron and the next is different from communication along a single axon.
o He inferred a specialized gap between neurons and called it a synapse.
Circuit from sensory neuron to muscle response is called a reflex arc.
Sherrington observed that:
o Reflexes are slower than conduction along an axon.
o Several weak stimuli presented at nearby places or times produce a
stronger reflex than one stimulus alone does
o When one set of muscles becomes excited, a different set becomes
relaxed.
Temporal summation= repeated stimuli within a brief time have a cumulative
effect.
Presynaptic Neuron= neuron that delivers transmission
Post Synaptic Neuron= neuron that receives transmission
Action potentials are always depolarizations.
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Graded potentials may be either depolarizations (excitatory) or
hyperpolarizations (inhibitory)
A graded depolarization is known as a Excitatory Postsynaptic Potential
(EPSP)
o It results from a flow of sodium ions into the neuron.
o If an EPSP does not cause the cell to reach its threshold, the
depolarization decays quickly.
Sherrington also found that synapses have the property of spatial summation,
which is summation over space.
Temporal summation and spatial summation ordinarily occur together.
o A neuron might receive input from several axons in succession.
Sensory neuron Interneuron Motor Neuron
Inhibitory Postsynaptic Potential (IPSP) is a temporary hyperpolarization of a
membrane.
o Occurs when synaptic input selectively opens the gates for potassium
ions to leave the cell (carrying a + charge with them) or for chloride ions
to enter the cell. (carrying a charge with them)
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