Test 2 Material: Brain and Behavior; Neuro
I. Gross Organization of the Nervous System
The nervous system is the organ system responsible for producing, controlling and guiding our acts, thoughts and
responses to the world around us. During embryological development it is derived from cells similar to those which go on
to form our skin, but those precursor cells to the nervous system become incredibly specialized and diverse, working
together more complexly and intricately than any other organ system in the body. The basic plan arises from the form of a
simple hollow tube that expands and differentiates itself into something that looks and functions very different from the
tube it once was. We will examine its major divisions (the central, CNS, and peripheral, PNS, nervous systems) and its
subdivisions, both in architecture and in function.
The most "available" division of the nervous system to the early anatomists for examination is the
(PNS). It consists of the nerves which directly connect to the skin, muscles, blood vessels and organs of the body.
As a general simplification, if nerve tissue not encased in bone (skull, spinal column), it is part of the PNS.
1. Somatic (Voluntary)
somatic nervous system
at one time was called the
voluntary nervous system
. This accurately describes the role and
distribution of its connections. The somatic nervous system innervates the muscles, and connective tissues attached to the
skeleton and our skin. It is responsible for our voluntary movements and the physical sensations (heat, cold, pressure,
vibration, pain) we experience. The individual nerves are typically made up of both
Such a nerve can be roughly thought of as a bidirectional cable that has wires, some of which send impulses out to the
body from the nervous system and some of which carry impulses from the body to the nervous system.
a. Afferent Nerves
To describe a nerve fiber as afferent means simply that the direction of the impulses it transmits go
system from the body's muscles and skin. Therefore, afferent nerves conduct
information towards the nervous
b. Efferent Nerves
An efferent nerve fiber sends impulses
from the nervous system in the direction of the body's muscles. The
efferent fibers generate movements of the skeleton and hence are
nerve fibers since their activation causes the
locomotion of our limbs, torso and facial features.
2. Autonomic (Involuntary)
autonomic nervous system
used to be called the
involuntary nervous system
. The autonomic system is responsible
for sensory and motor functions outside of our voluntary control, such as internal organs and glands, smooth muscles in
our gastrointestinal tract and blood vessels and the smooth muscles attached to our skin. Its subdivisions, the sympathetic
and parasympathetic, have opposite and complementary actions on our bodies' organs and tissues. Autonomic nervous