Transcript chapter 3 cells of the nervous system

Chapter Three
Cells of the
Nervous System
CHAPTER 3
CELLS OF THE NERVOUS SYSTEM
Neurons and Glia
• The Structure of neurons
– Neuron membranes separate intracellular fluid
from extracellular fluid
– The neural cytoskeleton provides structural
support that maintains the shape of the neuron
Figure 3.2 The Neural Membrane
Figure 3.3 Three Fiber Types Compose the
Cytoskeleton of Neurons
Figure 3.4 Tau Phosphorylation Leads to
Cell Death
Neurons and Glia
• Structural Features of Neurons
– Cell body (soma) contains nucleus and other
organelles
– Dendrites – branches that serve as locations at
which information from other neurons is received
– Axons are responsible for carrying neural
messages to other neurons
• Vary in diameter and length
• Many covered by myelin
Figure 3.5 The Neural Cell Body
Figure 3.6 Axons and Dendrites
Structural Variations in Neurons
• Unipolar
– Single branch extending from the cell body
• Bipolar
– Two branches extending from the neural cell body: one
axon and one dendrite
• Multipolar
– Many branches extending from the cell body; usually one
axon and many dendrites
Figure 3.8 Structural and Functional
Classification of Neurons
Functional Variations in Neurons
• Sensory Neurons
– Specialized to receive information from the outside world
• Motor Neurons
– Transmit commands from the CNS directly to muscles and
glands
• Interneurons
– Act as bridges between the sensory and motor systems
Glia
• Macroglia: Largest of the glial cells
– Astrocytes
– Oligodendrocytes
– Schwann cells
• Microglia: Smallest of the glial cells
Table 3.1 Types of Glia
Figure 3.9 Astrocytes
Figure 3.10 Oligodendrocytes and Schwann Cells
The Generation of the Action Potential
• Ionic Composition of the Intracellular and
Extracellular Fluids
– The difference between these fluids provides the neuron
with a source of energy for electrical signaling
– Differ from each other in the relative concentrations of
ions they contain
Figure 3.12 The Composition of Intracellular and
Extracellular Fluids
Figure 3.13 Measuring the Resting Potential
of Neurons
The Generation of the Action Potential
• The Movement of Ions
– Diffusion is the tendency for molecules to distribute
themselves equally within a medium
– Electrical force is an important cause of movement
• Like electrical charges repel
• Opposite electrical charges attract
Figure 3.14 Diffusion and Electrical Force
The Generation of the Action Potential
• The Resting Potential
– Membrane allows potassium to cross freely
– Measures about -70mV
– If potassium levels in extracellular fluid increase, resting
potential is wiped out
The Action Potential
• Threshold
– When recording reaches about -65mV
• Channels open & close during action potential
– Sodium flows into neuron , potassium flows out around
the peak of the action potential
• Refractory period
– Recording returns to resting potential
– Absolute versus relative refractory periods
• The action potential is all-or-none
Figure 3.15 The Action Potential
The Propagation of the Action Potential
• Propagation
– Signal reproduces itself down the length of the neuron
– Influenced by myelination
• Passive conduction = propagation in unmyelinated axon
• Saltatory conduction = propagation in myelinated axon
Figure 3.16 Action Potentials Propagate Down
the Length of the Axon
Figure 3.17 Propagation in Unmyelinated and
Myelinated Axons
The Synapse
• Electrical synapses
– Directly stimulate adjacent cells by sending ions across the
gap through channels that actually touch
• Chemical synapses
– Stimulate adjacent cells by sending chemical messengers
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Neurotransmitter release
Neurotransmitters bind to postsynaptic receptor sites
Termination of the chemical signal
Postsynaptic potentials
Neural Integration
Table 3.2 A Comparison of Electrical and
Chemical Synapses
Figure 3.19 The Electrical Synapse
Figure 3.21 Exocytosis Results in the Release of
Neurotransmitters
Figure 3.22 Ionotropic and Metabotropic
Receptors
Figure 3.23 Methods for Deactivating
Neurotransmitters
Figure 3.24 Neural Integration Combines
Excitatory and Inhibitory Input
Table 3.3 A Comparison of the Characteristics of
Action Potentials, EPSPs and IPSPs
Neuromodulation
• Synapses between an axon terminal and
another axon fiber
– Axo-axonic synapses have modulating effect on the release
of neurotransmitter by the target axon
• Presynaptic facilitation
• Presynaptic inhibition
Figure 3.26 Synapses Between Two Axons
Modulate the Amount of Neurotransmitter
Released