The nervous system can be separated into divisions on the basis of anatomy and physiology. The anatomical divisions are the central and peripheral nervous systems. The CNS is the brain and spinal cord. The PNS is everything else. Functionally, the nervous system can be divided into those regions that are responsible for sensation, those that are responsible for integration, and those that are responsible for generating responses. All of these functional areas are found in both the central and peripheral anatomy.
Considering the anatomical regions of the nervous system, there are specific names for the structures within each division. A localized collection of neuron cell bodies is referred to as a nucleus in the CNS and as a ganglion in the PNS. A bundle of axons is referred to as a tract in the CNS and as a nerve in the PNS. Whereas nuclei and ganglia are specifically in the central or peripheral divisions, axons can cross the boundary between the two. A single axon can be part of a nerve and a tract. The name for that specific structure depends on its location.
Nervous tissue can also be described as gray matter and white matter on the basis of its appearance in unstained tissue. These descriptions are more often used in the CNS. Gray matter is where nuclei are found and white matter is where tracts are found. In the PNS, ganglia are basically gray matter and nerves are white matter.
The nervous system can also be divided on the basis of how it controls the body. The somatic nervous system (SNS) is responsible for functions that result in moving skeletal muscles. Any sensory or integrative functions that result in the movement of skeletal muscle would be considered somatic. The autonomic nervous system (ANS) is responsible for functions that affect cardiac or smooth muscle tissue, or that cause glands to produce their secretions. Autonomic functions are distributed between central and peripheral regions of the nervous system. The sensations that lead to autonomic functions can be the same sensations that are part of initiating somatic responses. Somatic and autonomic integrative functions may overlap as well.
A special division of the nervous system is the enteric nervous system, which is responsible for controlling the digestive organs. Parts of the autonomic nervous system overlap with the enteric nervous system. The enteric nervous system is exclusively found in the periphery because it is the nervous tissue in the organs of the digestive system.
autonomic nervous system (ANS)
functional division of the nervous system that is responsible for homeostatic reflexes that coordinate control of cardiac and smooth muscle, as well as glandular tissue
axon
single process of the neuron that carries an electrical signal (action potential) away from the cell body toward a target cell
brain
the large organ of the central nervous system composed of white and gray matter, contained within the cranium and continuous with the spinal cord
central nervous system (CNS)
anatomical division of the nervous system located within the cranial and vertebral cavities, namely the brain and spinal cord
dendrite
one of many branchlike processes that extends from the neuron cell body and functions as a contact for incoming signals (synapses) from other neurons or sensory cells
enteric nervous system (ENS)
neural tissue associated with the digestive system that is responsible for nervous control through autonomic connections
ganglion
localized collection of neuron cell bodies in the peripheral nervous system
glial cell
one of the various types of neural tissue cells responsible for maintenance of the tissue, and largely responsible for supporting neurons
gray matter
regions of the nervous system containing cell bodies of neurons with few or no myelinated axons; actually may be more pink or tan in color, but called gray in contrast to white matter
integration
nervous system function that combines sensory perceptions and higher cognitive functions (memories, learning, emotion, etc.) to produce a response
myelin
lipid-rich insulating substance surrounding the axons of many neurons, allowing for faster transmission of electrical signals
nerve
cord-like bundle of axons located in the peripheral nervous system that transmits sensory input and response output to and from the central nervous system
neuron
neural tissue cell that is primarily responsible for generating and propagating electrical signals into, within, and out of the nervous system
nucleus
in the nervous system, a localized collection of neuron cell bodies that are functionally related; a “center” of neural function
peripheral nervous system (PNS)
anatomical division of the nervous system that is largely outside the cranial and vertebral cavities, namely all parts except the brain and spinal cord
process
in cells, an extension of a cell body; in the case of neurons, this includes the axon and dendrites
response
nervous system function that causes a target tissue (muscle or gland) to produce an event as a consequence to stimuli
sensation
nervous system function that receives information from the environment and translates it into the electrical signals of nervous tissue
soma
in neurons, that portion of the cell that contains the nucleus; the cell body, as opposed to the cell processes (axons and dendrites)
somatic nervous system (SNS)
functional division of the nervous system that is concerned with conscious perception, voluntary movement, and skeletal muscle reflexes
spinal cord
organ of the central nervous system found within the vertebral cavity and connected with the periphery through spinal nerves; mediates reflex behaviors
stimulus
an event in the external or internal environment that registers as activity in a sensory neuron
tract
bundle of axons in the central nervous system having the same function and point of origin
white matter
regions of the nervous system containing mostly myelinated axons, making the tissue appear white because of the high lipid content of myelin
In 2003, the Nobel Prize in Physiology or Medicine was awarded to Paul C. Lauterbur and Sir Peter Mansfield for discoveries related to magnetic resonance imaging (MRI). This is a tool to see the structures of the body (not just the nervous system) that depends on magnetic fields associated with certain atomic nuclei. The utility of this technique in the nervous system is that fat tissue and water appear as different shades between black and white. Because white matter is fatty (from myelin) and gray matter is not, they can be easily distinguished in MRI images. Visit the Nobel Prize website to play an interactive game that demonstrates the use of this technology and compares it with other types of imaging technologies. Also, the results from an MRI session are compared with images obtained from x-ray or computed tomography. How do the imaging techniques shown in this game indicate the separation of white and gray matter compared with the freshly dissected tissue shown earlier?
MRI uses the relative amount of water in tissue to distinguish different areas, so gray and white matter in the nervous system can be seen clearly in these images.
Visit this site to read about a woman that notices that her daughter is having trouble walking up the stairs. This leads to the discovery of a hereditary condition that affects the brain and spinal cord. The electromyography and MRI tests indicated deficiencies in the spinal cord and cerebellum, both of which are responsible for controlling coordinated movements. To what functional division of the nervous system would these structures belong?
They are part of the somatic nervous system, which is responsible for voluntary movements such as walking or climbing the stairs.
1. Which of the following cavities contains a component of the central nervous system?
A) abdominal
B) pelvic
C) cranial
D) thoracic
C
2. Which structure predominates in the white matter of the brain?
A) myelinated axons
B) neuronal cell bodies
C) ganglia of the parasympathetic nerves
D) bundles of dendrites from the enteric nervous system
A
3. Which part of a neuron transmits an electrical signal to a target cell?
A) dendrites
B) soma
C) cell body
D) axon
D
4. Which term describes a bundle of axons in the peripheral nervous system?
A) nucleus
B) ganglion
C) tract
D) nerve
D
5. Which functional division of the nervous system would be responsible for the physiological changes seen during exercise (e.g., increased heart rate and sweating)?
A) somatic
B) autonomic
C) enteric
D) central
B
1. What responses are generated by the nervous system when you run on a treadmill? Include an example of each type of tissue that is under nervous system control.
Running on a treadmill involves contraction of the skeletal muscles in the legs, increase in contraction of the cardiac muscle of the heart, and the production and secretion of sweat in the skin to stay cool.
2. When eating food, what anatomical and functional divisions of the nervous system are involved in the perceptual experience?
The sensation of taste associated with eating is sensed by nerves in the periphery that are involved in sensory and somatic functions.