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Chapter 2

BIOL 4309 Chapter Notes - Chapter 2: Semipermeable Membrane, Axon Terminal, Neuroglia


Department
Biology
Course Code
BIOL 4309
Professor
qing lin
Chapter
2

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Chapter 2: Structure and Function of the Nervous System
A) Cells of the Nervous System
Two primary types of cells:
1) Neurons: nerve cells
- Function: to transmit information in the form of electrical signaling over long
distances
2) Glial Cells: supporting cells that provide metabolic support, protection, and
insulation for neurons
Sensory neurons sensitive to environmental stimuli, convert the physical stimuli in the world
around us and in our internal environment into an electrical signal and transmit the info to
Interneurons nerve cells within the brain and spinal cord
- Form complex interacting neural circuits and are responsible for:
Conscious sensations, recognition, memory, decision making, and
cognition
Motor neurons direct a biobehavioral response appropriate for the situation
Neurons have 3 major external features
1) the soma (cell body)
- contains the nucleus and other organelles
that maintain cell metabolic function
2) the dendrites
- treelike projections from the soma that
receive information from other cells
3) the axon
- the single tubular extension that conducts
the electrical signal from the cell body to
the terminal buttons on the axon
terminals
Cytoplasm a semipermeable membrane filled with a salty, gelatinous fluid that encloses the
neuron

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Extracellular fluid a salty fluid that surrounds neurons from which they take oxygen,
nutrients, and drugs and into which they secrete metabolic waste products that reach the
blood and then filtered out by the kidneys
Mitochondria responsible for generating energy from glucose in the form of ATP
- found throughout the cell but particularly where energy needs are great
- critical for survival because neurons use large quantities of ATP and is
synthesized continually to support neuron function
(Dendrites)
- on the dendrites of a single neuron as well as on
the soma there may be thousands of receptors
which respond to neurochemicals released by
other neurons
- depending on the changes, the overall effect
may be excitatory or inhibitory
- the dendrites and their spines exhibit the special
feature of being constantly modified and can
change shape rapidly in response to changes in
synaptic transmission
Synapse the gap between two neurons
Three major types of the synapse:
1) Axodendritic synapse
2) Axonsomatic synapse
3) Axonaxonal synapse
Convergence each neuron receives and integrates a vast amount of information from many
cells
Divergence the information can then be transmitted to a few neurons or thousands of other
neurons
Dendritic spines covering dendrites that dramatically increase the receiving surface area
(Axons and terminal buttons)

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Axons
- Tubular in structure and are filled with axoplasm (the cytoplasm within the
axon)
- Axons vary significantly in both length and diameter
- Function: to transmit the action potential (electrical signal) that’s generated at
the axon hillock down the length of the axon to the terminals
Axon hillock the portion of the axon that’s adjacent to the cell body
Axon collaterals when axons split or bifurcate into numerous branches, providing the
capacity to influence many more cells
Terminal buttons (axon terminals) small enlargements at the end of the axons located near
other cells’ dendrites or somas
- These contain small packets (synaptic vesicles) of neurochemicals
(neurotransmitters) that provide the capacity for chemical transmission of
information across the synapse to the adjacent cells or target organ
Domaminergic neurons neurons that release dopamine
Serotonergic neurons neurons that release serotonin
Myelin fatty insulating coating that wraps most axons, created by concentric layers of glial
cells
- The myelin sheath provided by the glial cells is not continuous along the axon
but has breaks where the axon is bare to the extracellular fluid
- The thicker the myelin, the quicker the conduction
- Myelination saves energy by reducing the effort required to restore the
neuron to its resting state following the transmission of the electrical signal
Node of Ranvier the breaks between glial cells which are the sites where the action potential
if regenerated during the conduction of the electrical signal along the length of the axon (leaps
and bounds, saltatory conduction)
Two glial cells:
Schwann cells glial cells that myelinate peripheral nerves that serve muscles, organs, and
glands
Oligodendroglia glial cells that myelinate nerves within the brain and spinal cord
(a small number of neurons are unmyelinated and conduct slowly, others are thinly wrapped,
and some rapidly conducting neurons have a hundred or more wraps)
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