The Nervous System Is Composed of Cells
• Types of cells in the nervous system
– Neurons, or nerve cells
• are the most important part of the nervous system
• There are many types of neurons
– Glial cells provide support for neurons
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Microglia
Astrocytes
Oligodendrocytes
Schwann cells
• Neuron doctrine states that:
– The brain is composed of independent cells.
– Information is transmitted from cell to cell across synapses.
Scale of Things
Figure 2.2 The Major
Parts of the Neuron
Figure 2.5 A Classification of Neurons into
Three Principal Types
Figure 2.7 Glial Cells
Neuron Classification
• By Function into three groups, which is all but useless
– Sensory Neurons
– Interneurons
– Motor Neurons
• By Structure into three groups, not much better
– Unipolar: dendrite and axon emerging from same process.
– Bipolar: axon and single dendrite on opposite ends of the soma.
– Multipolar: more than two dendrites:
• Golgi I: neurons with long-projecting axonal processes; examples are
pyramidal cells, Purkinje cells, and anterior horn cells.
• Golgi II: neurons whose axonal process projects locally; the best
example is the granule cell.
• Most neurons are named as they are discovered which is
not classification and results in a very long list
• There currently is no useful classification system for
neurons
Box 2.1 Neuroanatomical Methods Provide Ways to Make Sense of the Brain
Figure 2.1 Nineteenth-Century Drawings of Neurons
Retinal Circuits
Retinal Circuits
http://webvision.med.utah.edu/book/part-vi-development-of-cell-types-and-synaptic-connections-in-theretina/development-of-cell-types-and-synaptic-connections-in-the-retina/
Figure 2.3 Variety in the Form
of Nerve Cells
Diversity of Neurons
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Thousands of different types of neurons
Improves information processing
Perception under a range of circumstances
Flexible processing to assess unexpected things
Circuit diagram of sensory neocortex
– Yuste lab composite diagram of circuits in the sensory
neocortex
Synapses
• Neurons are interconnected through synapses
– Individual neurons do not have specific behavioral or
cognitive functions
– neurons connected into a circuit have function
• The neuronal cell body and dendrites receive
information across synapses.
• Dendrites have a branched arborization pattern to
facilitate contacts.
• Information is transmitted from the presynaptic neuron
to the postsynaptic neuron. (Mostly)
– There are chemical signals from postsynaptic neuron to
presynaptic neuron called “retrograde” which is some sort of
feedback signal
Figure 2.6 Synapses
EM of Chemical synapse
mitochondria
Figure 5.3, Bear, 2001
Active Zone
EM of synapses on cell body
A segment of pyramidal cell dendrite from stratum radiatum (CA1)
with thin, stubby, and mushroom-shaped spines from rat
hippocampus. Found at Synapse Web
http://synapses.clm.utexas.edu/anatomy/compare/compare.stm
Neurophysiology
• The electrical and chemical processes within
neurons
– An action potential is a rapid electrical signal that
travels along the axon of a neuron.
– A neurotransmitter is a chemical messenger
between neurons.
– Electrical and chemical processes work together
• Chemistry produces the electrical activity
• Electrical activity modulates the chemistry
Figure 3.3 The Ionic Basis of the Resting Potential
Fig 3.4 Distribution of Ions
Fig 3.4
Fig 3.6 Action Potential Mediated by Voltage-Gated Na Channels
Ion Channels
• The cell membrane is a lipid bilayer, with two layers of
lipid molecules.
• Ion channels are proteins that span the membrane and
allow ions to pass.
– There are many types of ion channels
– Usually classified based on gating and type of ion
• Gating
– Voltage-Gated ion channels open and close in response to membrane
potential.
– Ligand-gated ion channels open or close depending on binding of ligands
to the channel
• Type of Ion
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Sodium (Na)
Potassium (K)
Chloride (Cl)
Calcium (Ca)
FIGURE 2 | General structural topology of voltage-gated ion channels.
The distribution and targeting of neuronal voltage-gated ion channels Helen C. Lai and Lily Y. Jan
Nature Reviews Neuroscience 7, 548-562 (July 2006)
Animation of voltage gated Na channel, when the outside is depolarized
the gate on the inside of the channel opens.
Voltage-gated sodium channel Function
Potassium Channels
Potassium channel in membrane You Tube video
Action Potential Animations
• Action Potential Animation You Tube video
•
Action Potential animation, advanced with detailed
explanation You Tube video
Fig 3.8a Conduction along Axons
Fig 3.8b Conduction along Axons