How Neurons Communicate


The Action Potential: The Brain's Electrical Signal

  • nerve impulses that travel along the axons in neurons are bioelectrical currents that result from the movement of four common ions- sodium, potassium, calcium and chloride
  • positive ions=sodium, potassium and calcium
  • negative ions=chloride
  • channels in the neuron membrane allows ions to move from one side of the cell membrane to the other
  • inside of neuron has a slightly negative charge; outside has a slightly positive charge
  • resting potential = difference in charge between outside and inside
  • quiet -neuron sends impulses at a slow rate down the axon
  • neuron stimulated - positively charged sodium ions enter the cell and creates "action potential" along the axon. They travel from cell to cell like a "row of dominoes falling" to send messages/commands through the brain. Interesting: Action potentials can travel at a speed of up to 220 mph.

Chemical Signals:

The brain has chemical messengers known as neurotransmitters. There may be possibly as many as 100 neurotransmitters. Some are generated in the cell bodies of neurons, while others are produced in axon terminals. The neurotransmitters are either excitatory or inhibitory. They increase or decrease the probability that a neron will fire. Inhibiting activity prevents the event of all neurons in the motor cortex firing all the time.

The Synapse is how the electrical and chemical components come together to allow information to be passed from cell to cell within the central nervous system. This happens at the junction of the axon terminal of one neuron and a dendrite of another neuron.

How does the information travel from cell to cell within the central nervous system?
The action potential reaches the axon terminal, which opens some vesicles and triggers the release of the neurotransmitters into the gap between the axon terminal and dendrite of two neurons. The neurotransmitter molecules enter the cleft/gap and travel to the postsynaptic or receiving neuron. Receptors, large protein molecules on the dendrite of receiving neuron, are specifically designed to match up with neurotransmitter. Once the signal is received by the dendrite, the target neuron is stimulated and sends an electrical signal to the cell body of the neuron. This neuron adds up the information from the signal and decides what to do with it, use or discard. This is the end of the cycle. See Figure 4.1 Synapse on pg. 54 (Brain Matters) for a visual diagram of a synapse.

What does this mean?
The chemical messengers (neurotransmitters), and their receptors, underpin all behavior. Thoughts and emotions are the results of chemical processes in the brain, and so are the twitches of muscles.

Amino Acids and Amines
Amino acids and amines are two types of neurotransmitters (chemicals that help neurons communicate with other cells).
Amino acids come from protein foods. They help with rapid communication between neurons. Some types of amino acids carry “inhibitory” messages, while some carry “excitatory” messages, which means they either slow down or speed up the speed at which a neuron (brain cell) communicates.
Amines are amino acids that are chemically modified, act slower than other amino acids, and change how amino acids “act.” They have powerful effects on many parts of the brain. For example, epinephrine is a hormone in charge of our fight-or-flight response in our bodies, but also acts in our brains as a neurotransmitter. It is largely responsible for keeping us alert. Norepinephrine is another amine neurotransmitter that works with our fight-or-flight response, especially dealing with wakefulness. Dopamine controls motor functioning, but also mediates maternal behavior AND various types of addiction. Serotonin is a mood enhancer, but also works with memory, sleep, control of appetite, and regulation of body temperature. And finally, acetylcholine is another type of amine that works with REM sleep and memory.

Peptides
  • Peptides are a group of neurotransmitters with act in the body and the brain. For example one peptide, angiotensin, is released into the bloodstream when the body become dehydrated. It causes the kidney to conserve water, body tissues to conserve fluids, and the brain to send messages of thirst.
  • There are over 100 peptides that serve purposes in the body and the brain that act as regulators to stimulate or inhibit other functions.
  • Endorphins are opiate-type neurotransmitters that provide a receptor for opiates. This is why morphine works in the brain. It responds to the natural cite that deadens pain and produces euphoria. Doctors can reinforce the effects of this ‘reward pathway.’ It is used by the brain to to prompt good feelings in response to relieving hunger, thirst, sex, escaping a potentially dangerous situation, social contact, humor and music.
  • Endorphins rise during prolonged, sustained exercise like running, childbirth. This reduces pain levels.
  • Behaviors that are necessary for survival are chemically reinforced in the brain.



The Mind And Body Connection
  • We have many of the same peptides in the brain as we do in our gastrointestinal tract.
  • Our 'gut feelings' are more than mere metaphors...the mental and the physical, the mind, the brain, and the body are intrinsically linked by means of these chemicals"

Understanding Addiction
  • If a chemical substance is synthesized in our brain, we call it a neurotransmitter. If it is synthesized in a laboratory, it's called a drug.
  • Cocaine acts directly on the pleasure centers,producing the user's "high" which helps to explain why it is one of the most addictive substances known.
  • Just because a drug mimics one of the brain's own neurotransmitters, it does not necessarily have the same effect.
  • drug use may be the result of abnormalities in the chemical balance of the brain.
  • depression is often the result of low levels of dopamine in the brain. Afflicted persons aren't aware of the cause of their depression only that cocaine or amphetamine makes them feel better.
  • An effective classroom climate might be described as a climate that allows students to naturally increase the endorphin,dopamine,norepinephrine,or,serotonian levels in their brains,making the students' education experiences more pleasurable and rewarding.