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Neurons & Neuroanatomy
What are the characteristics of
neurons important for Cognitive
Neuroscience?
What is the brain structure
important for CogNeuro?
Classes of neurons
• Unipolar - One process extends from body,
which can contain both dendrites and axon
terminals
• Bipolar - One axon and one dendrite process.
• Multipolar - Many dendrite processes.
• Pseudounipolar - Bipolar cells where the
dendrite and axon processes have merged.
• We’ll be primarily interested in multipolar
cells.
Neural membrane
• There are specialized structures in the neural
membrane that allow various elements to
cross in and out of the cell
– Ion channels: Proteins that cross the cell wall,
creating pores that allow ions (Na+, K+, Cl-) to
pass.
– Specific to particular ions; more K+ channels
– Nongated and gated
– Ion pumps: Actively transport ions across the
membrane, creating an electric gradient across
the membrane (3 Na+ out; 2 K+ in)
Cellular currents
• There are two types of electrical
currents that can pass through a
neuron:
• Active currents are ones that are caused by
explicit chemical activity (opening and closing
of ion channels); ex - at the synapse and
across the surface of the axon
• Passive currents are ones that simply pass
through the cytoplasm, typically as a response
to active currents; ex - within the cell body as a
result of synaptic activity; within the axon as a
result of action potentials.
Action Potential
• The signal a neuron generates down its axon
is called an action potential.
• All action potentials are the same magnitude
(strength), so they are either on or off.
• An action potential is only generated if the
depolarization of the cell membrane crosses
a threshold.
• We determine how excited a neuron is by its
firing rate - how many action potentials per
second it generates.
Depolarization of the AP
• As opposed to the nongated ion
channels discussed so far, action
potentials are driven by gated channels
that open in response to high voltage
levels (the threshold).
• In particular, gated Na+ channels are
opened by membrane depolarization,
which allows Na+ into the cell. This
causes further depolarization, which
opens more channels…..
Repolarization of the AP
• Depolarization also causes voltagegated K+ channels to open, but slightly
after the Na+ channels. This drives K+
out of the cell, reestablishing the resting
potential of the cell; this is called
repolarization.
• Because of the delay, K+ flows out after
Na+ stops flowing in, so there is a brief
period of hyperpolarization
Neurotransmitter
• Neurons communicate by sending chemical
messages called neurotransmitters to other
neurons.
• These neurotransmitters travel from axon to
either the dendrite or the cell body across the
synapse.
• Where a synapse is depends on what the
connection type is
– Excitatory: Axon to dendrite
– Inhibitory: Axon to cell body