NEUROSCI 101 Lecture Notes - Lecture 3: Axon Hillock, Sodium-Potassium Alloy, Chemical Synapse
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2-4-16
Ch. 4: Neurochemistry
Pre-Lecture Questions:
● Why don’t action potentials occur in dendrites?
○ EPSPs are smaller in the dendrites than in the axon and receive the impulse that
comes from the axon hillock. Dendrites also don’t have voltage-gated Na/K
channels to allow ion flow.
● What normally causes sodium to rush in and initiate an action potential at the axon
hillock?
○ At the axon hillock, graded potentials such as EPSP/IPSPs are being summed
up. Na+ wants to pass through the cell membrane because of the principle of
electrostatic attraction (opposite charges attract) to make the inside of the cell
less negative.
● In giant squid axon, action potentials are faster than graded potentials.
○ F, giant squid axons are unmyelinated
○ myelination speeds action potentials but doesn’t make action potentials faster
than graded potentials
○ GRADED POTENTIALS ARE ALWAYS FASTER
● A +3 mV charge is administered to a giant squid axon. How would the voltage change
after the charge was given?
○ The voltage reading would decrement as it moves away from the site of
stimulation. This charge is considered a graded potential because it hasn’t
reached threshold (minimum requirement for +20 mV) yet.
(types of neurotransmitters, types of receptors/receptor binding, packaging, enzyme
deactivation discussed in paper notes)
Modern Memory Research
● Carl Lashley (1940s) - searched for the “engram,” the region in the cortex associated
with memory creation, unable to find it, he declared that memories were distributed
throughout the cortex
● Donald Hebb (1949)
○ learning and its retention (memory) involves strengthening of synapses
○ when an axon in cell A is near enough to excite cell B and repeatedly takes part
in firing it, some growth process or metabolic change takes place such that A’s
efficiency as a cell firing B is increased > learning occurs
○ over time, cont. firing must strengthen connection b/w A, B
●how to “strengthen” a synapse (EPSPs increase when synapses get stronger):
○ increase NT release from presynaptic terminal
○ increased sensitivity of postsynaptic terminal
○ combination of both
●long-term learning causes any of the following:
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