AP PSYCH 2.4 Neural Firing

Structure of the Neuron

There are two types of cells that make up the nervous system, the neuron itself and glial cells
Most neurons have several dendrites which are the point of intake for chemical information from adjacent neurons
- Dendrites look like tree branches, reaching out towards other nearby neurons
The soma, or the cell body, contains the nucleus and other structures which all work toward maintaining the health of the neuron
The axon is a long bundle of fibers which carries information away from the cell body
- The longest axons are in the spinal cord
The typical axon has several myelin sheath coverings, but some do not
- The myelin sheath is a fatty, insulating cover that regulate the speed of the electrical impulse
The gaps between the myelin sheaths are called the Nodes of Ranvier, which help promote action potential
- Action potential is the moment in which electrical impulse moves through the cell after having reached it’s threshold
The final structure is the axon terminal which has several names
- These can be called terminal buttons, branches, knobs, and end buttons
- These are at the end of the neuron and axon, branching off to connect with another neuron’s dendrite
- The two do not touch, but leave a very small space called the synapse
- These buttons harbor the neurotransmitters

The most abundant cell in the body is the glial cell
Their job is to protect and provide nutrients for neurons
There are approximately 85 billion and they make up about half the volume of the brain and spinal cord
Unlike the neuron, glial cells have no part in processing information
One type of glial cell is the Schwann cell, which forms the myelin sheath of the neuron

The impulses inside neurons move at speeds of 330 miles and hour, meaning messages can travel throughout the body in milliseconds
There are several types of neurons in the nervous system
- Sensory neurons or afferent neurons receive information from sensory receptors and send it inward
- Motor neurons or efferent neurons send information from the brain to glands and muscles
- Interneurons transmit information from sensory to motor neurons
- Mirror neurons activate when we watch others complete an activity like yawning
- These neurons are in both humans and other animals

At resting potential, when neurons are not actively firing, there is a majority of Sodium (Na+) surrounding them, and Potassium (K+) inside the cell
Through a permeable membrane, (Na+) moves into the cell and depolarizes it, moving it into action potential, when it fires
Neurons do not half-fire; they have to reach their threshold and action potential before firing, which they do at only one intensity
After firing, neurons under go a refractory period where they essentially prepare for the next impulse
At the site of the buttons, where neurotransmitters are stored and released, there is also reuptake
- After the neurotransmitters have been released into the synapse, hopefully binding with the dendrite, the neurotransmitters are taken back up into the button

There are hundreds of individual types of neurotransmitters, but we will cover the most important categories
Neurotransmitters are used for communication between neurons to perform mental or physical activities
Messages are carried in both directions, from the brain to the body or vice versa, via afferent and efferent neurons
These little chemical messengers are stores in sacs in the axon terminals/buttons
There are two general types of neurotransmitters
- Excitatory, which stimulate firing, sending messages
- Inhibitory, slowing firing and stopping messages