BGYB30 chapter 8 textbook notes

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18 Feb 2011
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Chapter 8 Neurons: Cellular and Network Properties
Emergent Properties:Complex processes, such as consciousness, intelligence,
emotion, that
cannot be predicted from the properties of individual nerve
The nervous system can be divided into two parts: The central nervous system (the brain
and spinal cord; CNS) and the peripheral nervous system (afferent/sensory neurons and
efferent neurons; PNS)
Efferent neurons can also be divided into two subgroups: somatic motor division (controls
skeletal muscles) and autonomic division (controls smooth/cardiac muscles, exocrine and
some endocrine glands, as well as adipose tissue)
The autonomic division, also called the visceral nervous system, is further subdivided into
the sympathetic and parasympathetic branches
The nervous system is composed primarily of two types of cells: neurons and glial cells
Neurons are the functional unit of the nervous system; they consist of dendrites (which
receive incoming signals), a cell body (called the soma where the nucleus of the cell is
found), and the axon (which carries outgoing signals)
Neurons can be classified structurally, based on the presence or lack of axons and dendrites
1.Pseudounipolar:A neuron where the axon and the dendrite fuse during
They are both found on the same single body. The soma is to
the side of the dendrite/axon fuse
2.Bipolar:There is a single, separate axon and a separate dendrite
on the neuron.
Both are about the same length and are separated by the cell
3.Multipolar:There are many branched dendrites and axons on the neuron
4.Anaxonic:There is no distinguishable axon on the neuron
Axons can also be functionally classified:
1.Sensory (afferent):Neurons that carry information about temperature, pressure,
light, etc.
From sensory receptors to the CNS; usually they are found
close to the CNS with long bodies reaching the receptor in the
limbs and organs
Most sensory neurons have a pseudounipolar structure (the cell body is out of the
direct path of signals along the axon/dendrite). However for smell and vision, they
have a bipolar structure (signal travels through the cell body)
2. Interneurons: Neurons that lie completely within the CNS. They have complex
branching systems that allow them to communicate with other
3.Efferent neurons: Very similar to the model neuron (fig. 8-2, page 247). They
usually are
In terms of afferent and efferent peripheral (sensory) neurons, many axons are
bundled together with connective tissue to for a nerve. Some nerves carry afferent
signals only, some only carry efferent signals, some carry both
The cell is controlled by the soma, where the nucleus of the cell is. The soma is usually very
small (about 1/10th the size of the cell)
Dendrites receive incoming information for other cells. They increase the surface area of the
neurons allowing them to communicate at different locations
In the PNS, dendrites are used primarily to receive information and relay it to other areas
of the neuron that can process the information (usually the soma)
However in the CNS dendrites are more complex, sometimes acting as an independent