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

Glial Cells

• 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

Types of Neurons

• 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

Transmission

• 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

Neurotransmitters

• 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

Types

Endorphins

• Natural pain killers

• Elevates mood (euphoria)

• Runners high, acupuncture

• Morphine, heroin, opioids

Acetylcholine (ACh)

• Muscle contractions, organ function, learning, implicit memory

• Botox (antagonist), black widow venom, nicotine (agonist)

• Alzheimer's

Dopamine

• Learning, movement, attention, emotion

• Cocaine, ketamine, Adderall (R.I.)

• Schizophrenia (too much), Parkinson's (too little)

• Emotional euphoria

• High concentration in teen years

Serotonin

• Both excitatory and inhibitory

• Regulates mood, hunger, sleep, arousal

• Job is to reach equilibrium

• Prozac, Zoloft (S.S.R.I.), ecstasy (R.I.)

• Depression (too little)

Gamma-Aminobutyric Acid (GABA)

• Inhibitory

• Controls anxiety, sleep, growth

• Cocaine, Marijuana (antagonists), Xanax, Valium, Librium (agonists)

• Huntington's (too little)

Glutamate

• Excitatory

• Controls anxiety, memory formation, inflammatory response

• Anticonvulsants, OCD drugs (antagonists)

• Migraines, some seizure conditions (too much)

• Impacted greatly by diet

• Too much or too little is harmful

Norepinephrine

• Both a hormone and a neurotransmitter

• Alertness and arousal

• Elevated in manic state

• Caffeine (R.I.)