Organization of the
Nervous System
The nervous system is divided into the
peripheral nervous system (PNS) and the central nervous system (CNS)
Link to discussion of the central nervous system.
2013
Index to this page
The Sensory-Somatic Nervous System
The Cranial Nerves
The Autonomic Nervous System
The Sympathetic Branch
The Parasympathetic Branch
The PNS consists of
sensory neurons running from stimulus receptors that inform the CNS of the stimuli motor neurons running from the CNS to the muscles and glands - called effectors - that take action.
The CNS consists of the
spinal cord and the brain The peripheral nervous system is subdivided into the
sensory-somatic nervous system and the autonomic nervous system
The Sensory-Somatic Nervous System
The sensory-somatic system consists of
12 pairs of cranial nerves and
31 pairs of spinal nerves.
NERVOUS SYSTEM
2013
The Cranial Nerves
Nerves
Type
Function
I
Olfactory Nerve
Sensory
olfaction (smell)
II
Optic Nerve
Sensory
vision
(Contain 38% of all the axons connecting to the brain.)
III
Oculomotor Nerve
Motor*
eyelid and eyeball muscles
IV
Trochlear Nerve
Motor*
eyeball muscles
V
Trigeminal Nerve
Mixed
Sensory: facial and mouth sensation
Motor: chewing
VI
Abducens Nerve
Motor*
eyeball movement
VII
Facial Nerve
Mixed
Sensory: taste
Motor: facial muscles and salivary glands
VIII
Auditory Nerve
Sensory
hearing and balance
IX
Mixed
Glossopharyngeal Nerve
Sensory: taste
Motor: swallowing
X
Vagus Nerve
Mixed
main nerve of the parasympathetic nervous system (PNS)
XI
Accessory Nerve
Motor
swallowing; moving head and shoulder
XII
Motor*
tongue muscles
Hypoglossal Nerve
*Note: These do contain a few sensory neurons that bring back signals from the muscle spindles in the muscles they control.
The Spinal Nerves
All of the spinal nerves are "mixed"; that is, they contain both sensory and motor neurons
[View].
All our conscious awareness of the external environment and all our motor activity to cope with it operate through the sensory-somatic division of the PNS.
Link to a discussion of the mechanism by which the commands of the motor neurons of the sensory-somatic system are executed by skeletal muscles.
NERVOUS SYSTEM
2013
The Autonomic Nervous System
The autonomic nervous system consists of sensory neurons and motor neurons that run between the central nervous system (especially the hypothalamus and medulla oblongata) and various internal organs such as the:
heart lungs viscera glands (both exocrine and endocrine) It is responsible for monitoring conditions in the internal environment and bringing about appropriate changes in them. The contraction of both smooth muscle and cardiac muscle is controlled by motor neurons of the autonomic system.
The actions of the autonomic nervous system are largely involuntary (in contrast to those of the sensory-somatic system). It also differs from the sensory-somatic system is using two groups of motor neurons to stimulate the effectors instead of one.
The first, the preganglionic neurons, arise in the CNS and run to a ganglion in the body.
Here they synapse with postganglionic neurons, which run to the effector organ (cardiac muscle, smooth muscle, or a gland).
The autonomic nervous system has two subdivisions, the
sympathetic nervous system and the
NERVOUS SYSTEM
2013
parasympathetic nervous system.
The Sympathetic Nervous System
The preganglionic motor neurons of the sympathetic system (shown in black) arise in the spinal cord.
They pass into sympathetic ganglia which are organized into two chains that run parallel to and on either side of the spinal cord.
The preganglionic neuron may do one of three things in the sympathetic ganglion:
synapse with postganglionic neurons
(shown in white) which then reenter the spinal nerve and ultimately pass out to the sweat glands and the walls of blood vessels near the surface of the body. pass
