Download Action Potentials

Chapter 2
Nerve Cells and Nerve
Impulses
Cells of the Nervous System
Neurons
• Cells in the nervous system
that communicate info
Glial Cells
Glial Cells
• Nonneural cells in nervous
system
• Outnumber neurons 10 to 1
• Provide myelin, nutrition,
communicate info, etc.
Glial Cells
Four Classes Of Glial
Cells
1. Oligodendrocytes
2. Schwann cells
3. Astrocytes
4. Microglia
Anatomy of Neurons
Cell Membrane
• Lipid Bilayer (fat
molecules)
• Water repelling
• Protein channels allow
ions in and out of the
cell
Cells of the Nervous System
Interneurons
• Small neurons whose axons
and dendrites are all confined
within a given structure
Cells of the Nervous System
Afferent Nerves (Approach)
• Carry signals from muscles,
organs, etc toward the CNS
Efferent Nerves (Exit)
• Carry signals out of CNS to
muscles, skin, organs, etc.
Module 2.2: The Nerve Impulse
Ions and Electrical Charges
Ions
• Positively or negatively
charged particles
Electrical Gradient
• Neg. charged ions want to
move to positive areas
Concentration Gradient
• Ions naturally move from high
to low concentration
Resting Potential
Resting Potential
• Steady electrical charge
• -70 mV (millivolts) – mostly
due to neg. charged proteins
Illustration
“Like all salts in a solution, the
salts in neural tissues separate into
positively and negatively charge
particles called ions.” –Pinel, p. 78
Resting Potential
Sodium-Potassium Pump
• Actively transports sodium
ions out and potassium ions in
the cell
• Pushes more sodium out
than lets potassium in
• Many locations in a neuron
Resting Potential
Why do neurons have a resting potential,
which takes energy to maintain?
• Prepares the neuron to respond rapidly
• By maintaining a negative charge, the cell is prepared to respond
strongly and rapidly
• Like a archer poised with the arrow pulled back
Action Potentials
Threshold of Excitation
-65 mV (typically)
Action Potentials
Action Potentials
• Reversal of the
membrane potential,
signal travels down
the axon, contains
neural message
(-70 to +30)
• Lasts 1 millisecond
• All-or-nothing
Action Potentials: How are they
Produced?
Sodium Ion Channels
• When threshold of
excitation is reach Sodium Ion
Channels open wide
• Na+ rushes in
Potassium Channels
• Influx of Na+ triggers
opening of Potassium channels
• K+ rushes out
• After cell has been
repolarized, they close slowly
Action Potential
Video: Lecture 4 Action Potential 2
Local anesthetic drugs, such as Novocain
attach to the sodium channels of the
membrane, preventing sodium ions from
entering. In doing so, the drugs block
action potentials. If the anesthetics are
applied to sensory nerves carrying pain
messages, they prevent the messages
from reaching the brain.” –Kalat, p. 42
Action Potential
Refractory Period
• Hyperpolarization
• 1-2 milliseconds
• Keeps action potential
moving in one direction
Absolute Refractory Period
• Impossible to fire
Relative Refractory Period
• Higher than normal amount
of stimulation necessary to
fire
Action Potential
This electrochemical process can
be repeated 100 times per second!