BPK 105 Study Guide - Midterm Guide: Paravertebral Ganglia, Celiac Ganglia, Autonomic Nervous System
27 Apr 2018
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● Module 4—Do questions 6, and 11.
6. Explain how a myelinated axon can conduct a signal faster than an unmyelinated axon
of similar diameter. Use and define appropriate terminology in your explanation. [4
marks]
Unmyelinated axons do not have myelin sheaths; they can rest in either Schwann cells or
oligodendrocytes indentations. These axons conduct action potentials by continuous
conduction, meaning that action potentials travel throughout the entire lengths of axons.
Myelinated axons are covered in myelin sheaths. Depending on its location, part of the axon will
will either be covered in layers of Schwann cells (peripheral nervous system) or
oligodendrocytes (central nervous system) repeatedly. The sheaths are formed when an axon is
tightly wrapped by the plasma membrane of either an oligodendrocyte or a Schwann cell. The
insulation properties of the sheath does not allow most ions to move across the plasma
membrane. The spaces in the sheath are also referred to as the nodes of Ranvier; these areas
are where ions may move across the membrane. They are necessary for the conduction of
faster action potentials because they allow action potentials to avoid travelling throughout the
axon’s entire length; instead, the action potentials can ‘jump’ from one node of Ranvier to
another. This can be done because once an action potential is conducted at one node, a local
current eventually travels through the cytoplasm of the another node. For myelinated axons,
action potentials are conducted through saltatory conduction (Van Putte et al., 196).
11. Use the heart and lungs as physiological examples to compare and contrast the
sympathetic and parasympathetic divisions of the autonomic nervous systems. Include
the structure and function of each division in your discussion. [8 marks]
Both the sympathetic and parasympathetic divisions can stimulate particular functions and
inhibit others. The sympathetic division of the autonomic nervous system or the flight-or-flight
system ensures that an individual is ready for physical activity and thus, also ready to respond
to a threat. A sympathetic stimulation, for instance, leads to the increase of blood pressure, as
well as heart rate; it also leads to the dilation of bronchial tubes, leading to an increase in
airflow. The activities that do not help prepare individuals when it comes to physical activity are
inhibited or decreased (ex. digestion).
The parasympathetic division or the rest-and-digest system typically activates functions that are
generally associated with the body when it is at rest. Involuntary actions, like digestion, are
stimulated as this division becomes more active. It decreases heart rate (inhibitions of
contractions), leading to a decrease in blood pressure, and causes the constriction of the
respiratory passages; airflow is reduced.
Some organs are innervated by one of the two mentioned divisions. However, both divisions
typically innervate the organs that receive autonomic neurons and generally, the divisions have
opposite impacts on functions; when these divisions innervate one organ together, the
parasympathetic division will a have a more significant impact when the body is resting and the
sympathetic division will be more impactful when an individual is doing physical activity or is
under pressure.
Document Summary
Module 4 do questions 6, and 11: explain how a myelinated axon can conduct a signal faster than an unmyelinated axon of similar diameter. Use and define appropriate terminology in your explanation. Unmyelinated axons do not have myelin sheaths; they can rest in either schwann cells or oligodendrocytes indentations. These axons conduct action potentials by continuous conduction, meaning that action potentials travel throughout the entire lengths of axons. Depending on its location, part of the axon will will either be covered in layers of schwann cells (peripheral nervous system) or oligodendrocytes (central nervous system) repeatedly. The sheaths are formed when an axon is tightly wrapped by the plasma membrane of either an oligodendrocyte or a schwann cell. The insulation properties of the sheath does not allow most ions to move across the plasma membrane. The spaces in the sheath are also referred to as the nodes of ranvier; these areas are where ions may move across the membrane.
