BBB - Neural Firing Lesson

Learning Target:

• Identify the basic process of transmission of a signal between neurons. 

AP psychology course and exam description, effective fall 2020. (n.d.). https://apcentral.collegeboard.org/media/pdf/ap-psychology-course-and-exam-description.pdf

Neural Transmission

Neurons transmit information throughout the nervous system, but they also communicate within themselves, thus creating an electrochemical process. Electrical within the neuron, and chemical between neurons. Two types of neurons are involved in the transmission of messages between neurons: the presynaptic neuron which sends the message and the postsynaptic neuron which receives the message.

 

Communication within the Neuron

The process of communication within the neuron is called an action potential (a brief electrical impulse by which information is transmitted along the axon of a neuron). The action potential is an all-or-none response meaning it fires all the way or not at all. It is a brief electrical impulse created by the movement of ions. The action potential begins when messages are gathered by dendrites (the fibers that extend from a neuron's cell body and receive information) and the cell body of a receiving neuron. Axon membranes act as the gatekeeper controlling the balance of negative and positively charged ions in and outside of the axon. The membranes open and close allowing ions to flow in and out of the axon.

There is a minimum amount of stimulation needed to ignite the process. The stimulation comes from other neurons or sensory receptors. While waiting, the neuron is said to be polarized (in a polarized state there is a difference in the electrical charge inside and outside of the axon). During this state, it sits with an electrical charge of -70 millivolts. In its resting state, the neuron retains a larger concentration of potassium ions on the inside and is surrounded by sodium ions on the outside.

Once the neuron has been sufficiently stimulated depolarization (the initial phase of the action potential) begins starting the action potential. During depolarization, the gates of the axon open and the sodium ions rush in while potassium rushes out. The charge of the neuron changes briefly from -70 millivolts to +30 millivolts. This change creates an electrical impulse that continues down the length of the axon.

Again, this process is self-sustaining, meaning it either happens all the way or not at all. There is no partial potential. After the action potential has taken place, the neuron enters what is called a refractory period. During this time, the neuron is unable to fire and works to reestablish or repolarize itself to its negative inside/positive outside state.

Communication between Neurons

The electrical impulses created by the action potential travel from neuron to neuron across a tiny gap known as the synapse (the point of communication between neurons). The action potential reaches the axon terminal buttons, stimulating the release of chemical molecules called neurotransmitters. These molecules cross the synaptic gap and bind to the receptor sites of a new receiving neuron. This process will either excite or inhibit a new action potential. Any excess neurotransmitter left in the synaptic gap is usually reabsorbed by the sending neuron in a process called reuptake (the process by which a neurotransmitter molecule detaches from a postsynaptic neuron and is reabsorbed by the presynaptic neuron).

Certain drugs can be taken that will create similar processes and cause changes in behavior through their interaction in the synapse. Drugs that excite or mimic the neurotransmitters are called agonists and will make a neuron fire. Drugs that inhibit or block receptor sites and reuptake are called antagonists. Other drugs called reuptake inhibitors block the reuptake of neurotransmitters, causing them to remain in the synapse.

Neurotransmitters

Neurotransmitters are linked to our ability to interact with our environment. They guide our feelings, actions, movement, and the way we think. Too much or too little of certain neurotransmitters have been linked with psychological, physical, and behavioral problems. Additionally, the complex interaction between neurotransmitters can also drive behavior. In AP Psychology there are a few important neurotransmitters you should know.

Review neurotransmitters and their functions in the table below.

Neurotransmitter	Role or Function	Additional Information
Acetylcholine (ACh)	Learning, memory, and motor movement	Lack of it is linked to Alzheimer's disease. Too much can cause muscle spasms.
Dopamine	Movement, reward sensations, and alertness	Lack of it is associated with Parkinson's disease. Too much of it has been linked to schizophrenia.
Endorphins	Pain perception and emotions	Linked to addictions (opiate)
Serotonin	Sleep and emotional states	A lack of it is linked to depression.
GABA	Inhibits brain activity	Anxiety disorders. Anti-anxiety medication increases GABA activity.

Participate in the vocabulary activity below to check for understanding of the parts of the neuron and action potential.

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