Module 1.3: Neuron, Neural Firing, Neurotransmitters, and Psychoactive Drugs Flashcards
What is a neuron?
It is a nerve cell that is the basic building block of the nervous system
What are the parts of a neuron?
- Dendrites
- Cell body
- Axon
- Myelin Sheaths
- Terminal branches of axon
What are dendrites?
Branching extensions of neurons that receive messages from other neurons
What is the soma?
AKA cell body - contains the nucleus, the cell’s life-support center
What is the axon?
it passes electrical messages from the cell body to the axon terminals; attached to the soma
What is the myelin sheath?
It is a fatty layer that protects the axons of certain neurons and makes messages within a neuron travel faster
When does the myelin sheath begin to develop?
Before birth and continues into adulthood
What is myelination? When does it occur?
Myelination is the process of formation of myelin sheath - it helps with planning, logic, decision-making, and impulse control
It occurs during preteen years in the brain’s frontal lobes (which fully develop around age 25)
What is Multiple Sclerosis?
It is an autoimmune disease that results from myelin sheath deterioration, causing muscle control loss
What do terminal branches of the neuron do?
Contain terminal buttons, which hold vesicles ; found at the ends of each axon
What are vesicles?
The sacs that hold neurotransmitters
What do glial cells do?
Support, nourish and protect neurons; provide nutrients and myelin, guide neuron connections, and clean up ions and neurotransmitters
Why do glial cells provide nutrients to neurons?
Because neurons cannot feed themselves or do these functions for themselves
What is the synapse?
It is the gap or space between the tip of the sending (presynaptic) neuron and the dendrite of the receiving (postsynaptic) neuron
What is the synapse also known as?
Synaptic gap - synaptic cleft
What is a neurotransmitter?
It is the chemical messenger of the nervous system; it travels across the synapse and binds to receptor sites on the receiving (postsynaptic) neuron
What is a neural impulse?
It is the influx of the +ve ions moving like falling dominos in the axon of the neuron
How is a neural impulse generated?
If the combination of chemical signals received by a neuron’s dendrites exceed a minimum strength or threshold, the neuron fires, transmitting an action potential down its axon in a chemical-to-electrical process
What is a threshold?
It is the level of stimulation required to trigger a neural impulse
When is a threshold reached?
When the excitatory “go” messages overwhelm the inhibitory “stop” messages
What is the threshold value?
-55 mV (millivolts)
What is an all-or-none response mean?
Neural impulses are not “strong” or “weak” = action potentials have the same strength
therefore, neural firing happens at full response or not at all
What does a “strong” sensation equate to?
A large quantity of action potentials
What are neurotransmitters divided into?
Excitatory and Inhibitory Signals
What do excitatory signals do?
Provoke an action
What do inhibitory signals do?
Stop an action
What happens when excitatory signals greatly outnumber inhibitory?
The threshold is reached and action potential occurs
What is the resting potential?
Polarized state - no messages are sent; axon gates are closed
What happens in the neuron during resting potential?
Positive sodium (Na+) ions are on the outside of the cell; positive potassium (K+) ions are inside the cell along with many -ve charged protein ions
What is the resting potential value?
-70 mV
What does the axon membrane being selectively permeable mean?
It contains voltage-gated ion channels that either open to allow ion exchange (depolarization) or close to prevent it (polarization)
What is an action potential?
It is a brief electrical charge that travels down an axon (neural impulse, nerve firing, depolarization)
How is an action potential generated?
It is generated when positive sodium (Na+) ions move into the axon and potassium ions (K+) move out
When does an action potential start?
It starts when receptor sites of dendrites are stimulated
What are the steps of an action potential?
Step 1: The semipermeable axon opens its gates once threshold is met
Step 2: Na+ ions flood in through the channels -> inside becomes +ve
Step 3: Gates open in the 1st part of the axon, allowing K+ ions to flow out (repolarizes that section of the axon)
Step 4: Sodium/potassium pump continues to depolarize new sections of the axon and repolarize the previous ones
Step 5: Refractory period
What is a refractory period?
It is a resting pause after an action potential where subsequent action potentials cannot occur until the axon returns to resting state
What is a refractory period also known as?
Repolarization - reestablishing -ve charge in neuron -> Na+ is pushed out
What is an absolute refractory period?
It is a time when neural impulses CANNOT be sent, as +ve sodium ions are being pushed out of the cell
What is a relative refractory period?
It is when a neuron will only respond to a stronger than normal impulse; follows the absolute refractory period
What can happen when action potentials go wrong?
Multiple Sclerosis - a disease that leads the immune system to attack and destroy myelin sheath throughout the nervous system
- causes muscle weakness, vision changes, and numbness and memory issues
Myasthenia Gravis - a disease that leads to a weakening of voluntary muscles by destroying acetylcholine receptor sites
