|Adventures in Neuroanatomy: Parts of the Nervous System|
Contents of this Page|
Central Nervous System
Peripheral Nervous System
Divisions of the Nervous System
Brain Structure Poll
|Neuroanatomy: the structure of the nervous system. To learn how the nervous system functions, you must learn how the nervous system is put together.|
nervous system can be divided into several connected systems that function
together. Let's start with a simple division:|
The Nervous System is divided into:
|The central nervous system is divided into two parts: the
brain and the spinal cord. The average adult human brain weighs 1.3 to
1.4 kg (approximately 3 pounds). The brain contains about 100 billion nerve cells (neurons) and trillons of "support
cells" called glia. The spinal cord is about 43 cm long in adult women and 45 cm
long in adult men and weighs about 35-40 grams. The vertebral column, the
collection of bones (back bone) that houses the spinal cord, is about 70
cm long. Therefore, the spinal cord is much shorter than the vertebral
For brain weights of other animals, see brain facts and figures.
The Central Nervous System
(Brain and Spinal Cord)
|Did you know?||A stegosaurus dinosaur weighed approximately 1,600 kg but had a brain that weighed only approximately 70 grams (0.07 kg). Therefore, the brain was only 0.004% of its total body weight. In contrast, an adult human weighs approximately 70 kg and has a brain that weighs approximately 1.4 kg. Therefore, the human brain is about 2% of the total body weight. This makes the brain to body ratio of the human 500 times greater than that of the stegosaurus. See "My Brain is Bigger than Your Brain" for more on brain size.|
|Peripheral Nervous System|
|The peripheral nervous system is divided into two major parts: the somatic nervous system and the autonomic nervous system.|
The somatic nervous system consists of peripheral
nerve fibers that send sensory information to the central nervous system
AND motor nerve fibers that project to skeletal muscle.
The picture on the left shows the somatic motor system. The cell body is
located in either the brain or spinal cord and projects directly to a
The picture on the left shows the somatic motor system. The cell body is located in either the brain or spinal cord and projects directly to a skeletal muscle.
The autonomic nervous
system is divided into three parts: the sympathetic nervous system,
the parasympathetic nervous system and the enteric nervous system. The
autonomic nervous system controls smooth muscle of the viscera (internal
organs) and glands.
This picture shows the general organization of the autonomic nervous
system. The preganglionic neuron is located in either the brain or the
spinal cord. This preganglionic neuron projects to an autonomic ganglion.
The postganglionic neuron then projects to the target organ.
Notice that the somatic nervous system has only one neuron between
the central nervous system and the target organ while the autonomic
nervous system uses two neurons.
The enteric nervous system is a meshwork of nerve fibers that innervate
the viscera (gastrointestinal tract, pancreas, gall
This picture shows the general organization of the autonomic nervous system. The preganglionic neuron is located in either the brain or the spinal cord. This preganglionic neuron projects to an autonomic ganglion. The postganglionic neuron then projects to the target organ.
Notice that the somatic nervous system has only one neuron between the central nervous system and the target organ while the autonomic nervous system uses two neurons.
The enteric nervous system is a meshwork of nerve fibers that innervate the viscera (gastrointestinal tract, pancreas, gall bladder).
|The following table shows how the nervous
system can be divided. The
bottom row of the table contains the names of specific areas within the
Click on any word in the bottom two
rows to hear how the term is pronounced. These are ".wav" files (about
|Here is a quick look at one way to divide the brain.|
Click on a word to hear how it is pronounced. These are "wav" files.
|From a top view, notice how the brain is divided into two halves, called hemispheres. Each hemisphere communicates with the other through the corpus callosum, a bundle of nerve fibers. (Another smaller fiber bundle that connects the two hemispheres is called the anterior commissure).|
|Hear IT!||Cerebral Cortex||Cerebellum||Corpus Callosum|
Some differences between the Peripheral Nervous System (PNS) and the
Central Nervous System (CNS):|
In the Peripheral Nervous System, neurons can be functionally divided in 3 ways:
(afferent) - carry information INTO the central nervous system
from sense organs.|
Cranial - connects the brain with the
|3||Somatic - connects the
skin or muscle with the central nervous system.|
|The word "cortex" comes from the Latin word for "bark" (of a tree). This is because the cortex is a sheet of tissue that makes up the outer layer of the brain. The thickness of the cerebral cortex varies from 2 to 6 mm. The right and left sides of the cerebral cortex are connected by a thick band of nerve fibers called the "corpus callosum." In higher mammals such as humans, the cerebral cortex looks like it has many bumps and grooves. A bump or bulge on the cortex is called a gyrus (the plural of the word gyrus is "gyri") and a groove is called a sulcus (the plural of the word sulcus is "sulci"). Lower mammals, such as rats and mice, have very few gyri and sulci.|
|The word "cerebellum" comes from the Latin word for "little brain." The cerebellum is located behind the brain stem. In some ways, the cerebellum is similar to the cerebral cortex: the cerebellum is divided into hemispheres and has a cortex that surrounds these hemispheres.|
|Brain stem |
|The brain stem is a general term for the area of the brain between the thalamus and spinal cord. Structures within the brain stem include the medulla, pons, tectum, reticular formation and tegmentum. Some of these areas are responsible for the most basic functions of life such as breathing, heart rate and blood pressure.|
|The hypothalamus is composed of several different areas and is located at the base of the brain. Although it is the size of only a pea (about 1/300 of the total brain weight), the hypothalamus is responsible for some very important functions. One important function of the hypothalamus is the control of body temperature. The hypothalamus acts as a "thermostat" by sensing changes in body temperature and then sending signals to adjust the temperature. For example, if you are too hot, the hypothalamus detects this and then sends a signal to expand the capillaries in your skin. This causes blood to be cooled faster. The hypothalamus also controls the pituitary.|
|The thalamus receives sensory information and relays this information to the cerebral cortex. The cerebral cortex also sends information to the thalamus which then transmits this information to other areas of the brain and spinal cord.|
|Limbic System |
|The limbic system (or the limbic areas) is a group of structures that includes the amygdala, the hippocampus, mammillary bodies and cingulate gyrus. These areas are important for controlling the emotional response to a given situation. The hippocampus is also important for memory.|
|The hippocampus is one part of the limbic system that is important for memory and learning.|
|Basal Ganglia |
|The basal ganglia are a group of structures, including the globus pallidus, caudate nucleus, subthalamic nucleus, putamen and substantia nigra, that are important in coordinating movement.|
|The midbrain includes structures such as the superior and inferior colliculi and red nucleus. There are several other areas also in the midbrain.|
Now that you have read about many of the areas of the
brain, here is where
some of these areas are located:
Check out the glossary for definitions of other brain areas.
|Travel through the brain with the incredible Brain Fly-Through game. (Requires the FLASH plug-in for your browser.)|
|Did you know?||John Adams (2nd President of the US) and his son, John Quincy Adams (6th President of the US), were both born in Braintree, Massachusetts.|
|BACK TO:||Exploring the Nervous System||Table of Contents|
Neuroscience for Kids