Download How Neurons and Synapses Work

November 7, 2016
Journal: What is the difference
between dendrites and the axon
terminal?
How Neurons and Synapses Work
Excitable Cells
 Neurons, glands, and muscle cells
 Can carry an electrical charge when stimulated
Local Potential
 A stimulus causes a response in a cell called a
local potential aka graded potential
 If its big enough it causes action potential
Action Potential
Occurs in response to an internal or
external change
Series of permeability changes within
the neuron that carry the electrical
impulse down the axon
Impulse conduction
How Action Potential Works
 When a cell is not excited it is said to be at rest
 A resting cell is considered to be polarized
 Meaning that there is a difference in charge across
the cell membrane with more negative charges
inside the cell
How Action Potential Works
 When a neuron becomes stimulated, sodium ion channels
open and let Na+ ions to travel into the neuron, making the
cell more positive
 This is called depolarization
How Action Potential Works
 Then K+ leaves the cell through potassium ion channels
 These positive charges leaving the cell begin to return the
cell back to a resting state.
 This is called repolarization.
How Action Potential Works
 Hyperpolarization - cell
becomes more negative then
when at rest
 Sodium-potassium pump
works to restore equilibrium
 Refractory Period – Cell is
unable to accept another
stimulus until it returns to
rest
How Action Potential Moves Down the Axon
 As the Na+ comes into one section of the axon, it triggers the
sodium ion channels in the neighboring section to open
 Continues in a domino effect
Myelin Sheath Speeds up Impulse
Conduction
 If a myelin sheath is present around the axon the impulse
conduction will move faster
Axon Diameter Speeds up Impulse
Conduction
 The wider the axon diameter the faster the ions will flow because
there is more room for the ions to flow
 Action Potential Video:
https://www.youtube.com/watch?v=OZG8M_ldA1M
November 7, 2016
 Journal: Explain how an impulse is
conducted down the axon of one
neuron.
Chemical Synapses
Chemical Synapses
 Step 1: Sodium arrives at the axon terminal
Chemical Synapses
 Step 2: The terminal depolarizes and calcium enters through
calcium ion channels
Chemical Synapses
 Step 3: Neurotransmitters are released from vesicles via
exocytosis and are released into the synapse
Chemical Synapses
 Step 4: Neurotransmitters bind to the cell receiving signal
and causes gates to open or close, either exciting or calming
down the receiving cell
Chemical Synapses
 Step 5: Neurotransmitter is taken away from the synapse by
an inactivator, usually an enzyme, to stop the
neurotransmitter from continuously binding to the receiving
cell
Important Neurotransmitters
 Acetylcholine: Controls skeletal muscles
 Norepinephrine: Control visceral and cardiac muscle
 Dopamine: Controls motivation and mood
 Epinephrine: Adrenaline; Increased fight or flight response
 Serotonin: Regulates mood and anxiety
 Endorphins: Increase pleasure and decrease pain
Synapse Video
 https://www.youtube.com/watch?v=p5zFgT4aofA