Nervous System (NS)

Central Nervous System (CNS)

Peripheral Nervous System (PNS)

  • Somatic (Voluntary) Nervous System - Reacts with External Environment
    - Sensory neurons - Get signals from senses (sight, sound, touch, ...)
    - Motor neurons - Control skelital muscles.
  • Autonomic (Involuntary) Nervous System - Reacts with Internal Environment.
    (internal organs and glands. Largely involuntary muscles.)
    • Sympathetic Branch
      - Causes release of neurotransmitter noradrenaline, which among other things stimulates the heartbeat and raises blood pressure. The release of adrenaline from the adrenal medulla on the kidneys into the blood ensures that all the cells of the body will be exposed to sympathetic stimulation even if no neurons reach them directly.
    • Parasympathetic Branch
      - Mainly the vagus nerves, which returns the body functions to normal after they have been altered by sympathetic stimulation. The vagus nerves also help keep inflammation under control.
See: Adrenergic Receptor Database at Beijing Medical

Brain Anatomy

The brain is made up of many cells, but the neurons are the primary players in brain functions. There are 100 Billion neurons in the brain. A typical neuron has about 1,000 to 10,000 synapses (that is, it communicates with many other neurons, muscle cells, glands, etc.). It has been estimated that there are 1 quadrillion synapses in the human brain. That's 1015.
This wiring system surpasses by many orders of magnitude the complexity of even the most advanced supercomputers.

In the 4th century BC Hippocrates concludes the brain was involved in sensation and was the seat of intelligence. Plato agrees.
In the 17th century English anatomist and physician Thomas Willis did work on the anatomy of the brain, and published Pathologicae cerebri, et nervosi generis specimen, an important work on the pathology and neurophysiology of the brain. See Neuroscience History

But there is still a lot that is unknown.

The brain is divided into the left and right hemispheres and with the exception of the pineal gland in the center, every brain module below is duplicated in each hemisphere.

  • Left Hemisphere - Communicates by using words, has highly developed verbal abilities, is logical and systematic, concerned with matters as they are.
  • Right Hemisphere - Communicates using images (pictures), has highly developed spatial abilities, is intuitive and imaginative, concerned with emotions and feelings.
Sensory and motor neurons on the left side of the body are connected to the right hemisphere of the brain and vice versa.
So, a stroke in the left hemisphere may cause speech problems and paralysis of the right side of the body.
Whereas a stroke in the right hemisphere may cause paralysis to the left side and problems with spatial and perceptual abilities causing misjudgement of distances and instability. See Effects of Stroke.

The main components of the brain are most apparent in the embryonic development of the brain, where three swellings occur for the forebrain, midbrain and hindbrain. All vertibrates have these 3 parts.

Simplified version:
    Neocortex - Thought (including planning, language, logic & will, awareness), most developed in humans.

    Limbic System - Emotion (feelings, relationship/nurturing, images and dreams, play), shared by mammals.

    Reptilian Brain - Instinct (survival, breathing/swallowing/heartbeat, startle response), entire brain in reptiles.

The following section is more about psychology than anatomy, but it is integrally linked with brain function.
In work started in the 1960s, neurologist Dr. Paul MacLean (director of the Laboratory of Brain Evolution and Behaviour (now NIMH) at the NIH, discovered that each layer can become dominant depending on the circumstances.
Previous to MacLean's work it was assumed that the neocortex dominates the limbic and the reptilian brains.This assumption is anulled by the finding that the mental functions of the neo-cortex can be hijacked by the functions of the other two brain layers.
The Three-Layered Brain at
Human Nature - Fundamentals | The Future of Human Evolution |
Relationships/The Evolution of the Human Brain - Wikibooks
Transactional Analysis and the Triune Brain

Brain systems:
Forebrain | Midbrain | Hindbrain

The Forebrain
(Telencephalon, Diencephalon)

* Telencephalon

* Cerebrum (also called the Cerebral Cortex, Cerebral Hemispheres or Neo-Cortex) (Telencephalon) - The cerebrum consists of the cortex, large fiber tracts (corpus callosum) and some deeper structures (basal ganglia, amygdala, hippocampus). It integrates information from all of the sense organs, initiates motor functions, controls emotions and holds memory and thought processes (emotional expression and thinking are more prevalent in higher mammals).

Source: Rice U.
See Also: Functional brain map below

The neopallium is the top layer of the cerebral hemispheres, about 2 mm thick, and is involved in higher functions such as sensory perception, generation of motor commands, spatial reasoning, and in humans, language and conscious thought. Other names for the neopallium include neocortex , isocortex and homotypical cortex.

* Corpus Callosum - A bundle of nerve fibers (millions of axons from the cerebral cortex) that allows the two hemispheres to communicate.

Cerebral Lobes:

Source: Anatomy of the Brain
at The American Health Assistance Foundation

See The hindbrain for the Medulla, Pons and Cerebellum.
See brain map below for specific functional areas.

  • Frontal lobe - Involved in motor skills (including speech) and higher cognitive functions, conscious thought, short-term memory. The left frontal cortex seems to be the language area.
    Expressive functions - Personality, emotions, and long-term memory. Reasoning, problem solving, and high-level thinking are also believed to be controlled by this area of the brain.
    The left frontal lobe is active in doing exact math calculations.
  • Parietal lobe - Receives and processes all somatosensory input from the body (touch, pain)
    Left parietal lobe performs analytical functions. Math approximations.
  • Temporal lobe - The processes auditory information from the ears, relates it to areas of the parietal lobe and the motor cortex of the frontal lobe. Also processes olfactory input.
    Sensual information, aesthetics, beauty and form.
  • Occipital lobe - Receives and processes visual information directly from the eyes and relates this information to Wernicke's area in the parietal lobe and frontal lobe.
  • Limbic system - More evolutionarily primitive brain structures deep inside the brain. They are involved in many of our emotions and motivations, particularly those that are related to survival, such as fear, anger, and emotions related to sexual behavior. The limbic system is also involved in feelings of pleasure that are related to our survival, such as those experienced from eating and sex.
    (Sometimes the Limbic System is classified as distinct from the Cerebrum)
  • Hippocampus - Control of the emotional response to a given situation. Also 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.
  • Amygdala - Reaction to fear. Receives signals of the potential danger and begins to set off a series of reactions that will help you protect yourself.
  • Cingulate Gyrus - Coordinates Sensory Input With Emotions. Emotional Responses to Pain. Regulates Aggressive Behavior.
  • Fornix - Connects the Hippocampus to the Hypothalamus
* Diencephalon - Inner Brain - Part of Forebrain next to Midbrain
  • thalamus - Involved in sensory perception and regulation of motor functions (i.e., movement). It connects areas of the cerebral cortex that are involved in sensory perception and movement with other parts of the brain and spinal cord that also have a role in sensation and movement
  • Hypothalamus and pituitary gland - These control visceral functions, body temperature and behavioral responses such as feeding, drinking, sexual response, aggression and pleasure.
  • Posterior lobe of the pituitary - Receives antidiuretic hormone (ADH) and oxytocin from the hypothalamus and releases them into the blood.
    See Cervical Xray on the spine page.


- The brainstem connects the brain and the spinal cord. It consists of the medulla (an enlarged portion of the upper spinal cord), pons and midbrain (lower animals have only a medulla). The brainstem controls the reflexes and automatic functions (heart rate, blood pressure), limb movements and visceral functions (digestion, urination).

The Midbrain (mesencephalon)

The midbrain (mesencephalon) occupies only a small region in humans (it is relatively much larger in "lower" vertebrates).

  • Tectum - Controls Auditory and Visual Responses.
  • Tegmentum - Attention Control Mechanism and awareness. Controls Motor Functions. Regulates Some Autonomic Functions.
  • Ventral Tegmental Area (VTA): Packed with dopamine-releasing neurons, which relay messages about pleasure through their nerve fibers to nerve cells in a limbic system structure called the nucleus accumbens. Still other fibers reach to a related part of the frontal region of the cerebral cortex. So, the pleasure circuit, which is known as the mesolimbic dopamine system, spans the survival-oriented brainstem, the emotional limbic system, and the frontal cerebral cortex.
  • Isthmus - midbrain-hindbrain junction

The Hindbrain (rhombencephalon)

Cranial Nerves
  • Pons - Contains many cranial nerves (Nerves such as the facial nerves, which emerge from the brainstem rather than the spinal cord). It contains the Pontine Sleep Center, which is important for the level of consciousness, and the Respiratory Centers, which along with the Medullary Respiratory Centers help control Respiratory Movements.
  • Cerebellum - The cerebellum is located behind the brain stem. The cerebellum integrates information from the vestibular system (region of the inner ear that helps with balance) that indicates position and movement and uses this information to coordinate balance, posture and limb movements.
  • Medulla Oblongata - Controls autonomic functions (such as breathing, heartbeat, sneeze, cough, swallow, vomiting). Processing of inter-aural time differences for sound localization.
    The Vagus nerve is the tenth cranial originating from the medulla oblongata. See Cervical Xray on the spine page.

Vagus Nerve

The vagus nerve is the longest of the cranial nerve. Its name is derived from Latin meaning "wandering". It does not go thru the spinal cord, but from the medula (part of the brainstem) down the neck, to the chest and abdomen.
The pharyngeal branch travels between the internal and external carotid arteries and enters the pharynx at the upper border of the middle constrictor muscle. It supplies the all the muscles of the pharynx and soft palate except the stylopharyngeas and tensor palati.
The superior laryngeal nerve branches distal to the pharyngeal branch and descends lateral to the pharynx.
The third branch is the recurrent branch of the vagus nerve and it travels a different path on the left and right sides of the body.
Speech is permitted through a branch of the vagus nerve, the laryngeal nerve, which innervates the larynx.
In the thorax branches go to the lungs for bronchoconstriction, the esophagus for peristalsis and the heart for slowing of heart rate. In the abdomen branches enter the stomach, pancreas, small intestine, large intestine and colon for secretion and constriction of smooth muscle.
See Vagus nerves at Medical Look Human Anaatomy
Vagus nerve in health.
Brain Map:

Source: The Columbia College of Physicians and Surgeons Complete Home Medical Guide
See also the Functional brain map from Science Daily

Other Maps:
Hidden Talents-- 113 Brain Maps
Gray's Anatomy
Brain Map - Broca's Area -

Techers Guide at
Divisons of the Nervous System System at Neuroscience for Kids

A new brain atlas and database developed by the International Consortium for Brain Mapping (ICBM), uses an anatomically labeled brain template. The Laboratory of Neuro Imaging (LONI) at UCLA has a Data Immersive Visualization Environment (DIVE) for Brain Visualization.
Logic+Emotion: Creativity 2.E by David Armano
See Also:
Central Nervous System at Human Physiology by Frank Orme at aol Hometown
How your brain works at
Comparative Mammalian Brain Collections at
Functional brain map from Science Daily by Daniel Oldjira Fufa.
Other Brain Maps at:, Hidden Tallents
The NIH Blueprint - Non-Human Primate (NHP) Atlas will generate an atlas of gene expression in the developing rhesus macaque brain. They have contracted with the Allen Institute for Brain Science in Seattle and the UC Davis MIND Institute for this project.
Brain Structures and their Functions at Bryn Mawr College.

Brain Waves

The brain functions by sending electrical signals from one place to another. Very small charges pass between nerve cells, accompanied by changes in electrical potential, in voltage. This activity can be measured and displayed as a wave form called brain wave or brain rhythm.

Brain waves are measured with an electroencephalogram (EEG) by placing electrodes on the scalp and measuring voltage differences.
Frequency band (cycles/second) Name of Wave Band Description
1 - 3 Delta Generally strongest when a person is in a deep dreamless sleep.
4 - 7 Theta May be associated with dreamy, creative, intuitive states.
8 - 12 Alpha Associated with a calm and relaxed state when the person is not thinking.
12 - 16 SMR Sensorimotor rhythm (SMR) is associated with physical stillness and body presence.
15 - 30 Beta Associated with being alert, with normal thinking, with processing information.
40+ Gamma (Sometimes included in Beta). Associated with intensely focused thought. Brain state of hyperalertness, perception, and integration of sensory input. Tibetan Buddhist monks had high Gamma activity during meditation.


The brain and spinal cord are made up of many cells, including neurons and glial cells.
90% of the brain is glial cells; they provide support functions for the neurons.
Source: NIH
There are 100 Billion neurons in the brain.

The neuron body contains organelles such as mitochondria, endoplasmic reticulum,
and a nucleus (which contains DNA).
The dendrites radiate out from the cell body. They are specialized for
receiving information from other neurons. Dendrites act like antennae for nerve cells.

The axon generally carries nerve impulses away from the cell body.
Usually only one axon sprouts off of the cell body, but it may have many branches.
Axons convey information from one part of the brain to antoher.
They may be up to a meter long.  
(A Giraffe's primary afferent axon (from toe to neck) is 15 feet long.)
The Synapse is the point of connection between two neurons (axon
 and dendrite) or between a neuron (axon) and a muscle or gland. 
 Boutons are where synapes occur.
Different Types Of Neurons
There are different types of neurons. They all carry electro-chemical nerve signals, but differ in structure (the number of processes, or axons, emanating from the cell body) and are found in different parts of the body.
  • Sensory neurons or Bipolar neurons carry messages from the body's sense receptors (eyes, ears, etc.) to the Central Nervous system (CNS). They include the senses, sight, hearing, taste and feeling, touch, pain, temperature. Sensory neuron account for 0.9% of all neurons. (Examples are retinal cells, olfactory epithelium cells.)
  • Motoneurons or Multipolar neurons carry signals from the CNS to the muscles and glands. These neurons have many processes originating from the cell body. Motoneurons account for 9% of all neurons. (Examples are spinal motor neurons, pyramidal neurons, Purkinje cells.)
  • Interneurons or Pseudopolare (Spelling) cells form all the neural wiring within the CNS. These have two axons (instead of an axon and a dendrite). One axon communicates with the spinal cord; one with either the skin or muscle. These neurons have two processes. (Examples are dorsal root ganglia cells.)

Source: NIH
Note: Some articles state that appendages of a sensory neuron that comes from the nerve ending is a dendrite.
Women have 10% more neurons.
You loose 10% over a lifetime.
A typical neuron is 10 microns (µm) (.01 mm) in diameter. (See size)
They vary in size from 4 microns (.004 mm) to 100 microns (.1 mm) in diameter.
Their length varies from a fraction of an inch to several feet.
The cell body of a motor neuron is approximately 100 microns (0.1 millimeter) in diameter.

Source: Rn Continuing Education

When a dendrite is stimulated in a certain way, the neuron to which it is attached suddenly changes its electrical polarity and may fire, sending a signal out along its single axon where it may be picked up by the dendrites of other neurons.

A typical neuron has about 1,000 to 10,000 synapses (that is, it communicates with 1,000-10,000 other neurons, muscle cells, glands, etc.). It has been estimated that there are 1 quadrillion synapses (the gap between the axon terminal and the receiving cell) in the human brain. That's 1015.
The synapses therefore constitute an exceedingly complex wiring system that surpasses by many orders of magnitude the complexity of even the most advanced supercomputers.

A computer model constructed from an actual 3-d microscopic photo of a single cortical neuron.
The cell body (soma) is represented in blue.
Dendrites appear in green, and the axons are red.
The white dots represent the locations of boutons, where synapses occur.

Source: Visualizing Neurons at the U. of Alabama

Spinal Cord


See other diagrams at: Spine under health,

Mapping the Mind, by Rita Carter
The Human Brain: An Introduction to Its Functional Anatomy by John Nolte
Synaptic Self: How Our Brains Become Who We Are, by Joseph Ledoux.

See Also:
Brain Anatomy and Parts of the Brain
History of Neuroscience including Nobel Prize winners
Brain Cranium issues in health
Brain Facts at the Society for Neuroscience
Human Nature - Fundamentals | The Future of Human Evolution |
Interviews - Clotaire Rapaille, The Reptillian Brain and Persuasion | FRONTLINE | PBS
neurons at Georgia Perimeter College
Neuroscience for kids at U. of Washington
Brain Cells at
Pittsburgh Supercomputing Center (PSC) Visualizations for Gray Matters: The Brain Movie
Introduction to Neuroanatomy
Cranial Nerves
Overview of Neuron Structure and Function at the NIH
Mental and neurological diseases
Neuroscience Glossaries at,, Society for Neuroscience (SFN) (, Neuroscience at a Glance (
Neuroscience for Kids at U. of Washington
Nervous System - Human Brain |
Organization of the Nervous System at John W. Kimball's Biology Pages HR> Return to NeuroScience

last updated 14 Mar 2010