Electrical Signals 1
BIOL 1407
Electrical Signals
• Changes in
membrane
potential 
currents
• Used by cells for
quick
communication
Chemical vs. Electrical Signaling
• Type of Signals
– Chemical
– Electrical + Chemical = Electrochemical
• Types of Chemicals Used
– Hormones
– Neurotransmitters
Chemical vs. Electrical Signaling
• Speed of Transmission
– Slow
– Fast
• Duration of Response
– Long
– Short
Functions of Nervous Systems
Neuron
• Cell body = Soma
• Dendrites
• Axon
– Axon Hillock
– Axon Terminals =
Synaptic Knobs =
Synaptic Terminals
Types of Neurons
Supporting Cells = Neuroglia
Schwann Cells
Neural Pathways Example
Membrane Potential
• Electrical Difference = Potential
• Membrane at Rest = Resting Membrane Potential (RMP)
Membrane Proteins
• Sodium Potassium Pump
– Maintains Resting Membrane Potential
• Leak Channels
– Na+ and K + Leak Channels
• Chemically-Regulated (Gated) Channels
– Also called Ligand-Gated Channels
• Voltage-Regulated (Gated) Channels
– Na+ and K + Voltage-Regulated Channels
• Chemically-Regulated
Channels
• Gated
• On dendrites and cell
body
• Responds to
chemicals
• Graded potentials
• Voltage-Regulated
Channels
• Gated
• On axons
• Respond to changes
in voltage
• Action potentials
(APs)
Voltage-Regulated
+
Na
Channel
Na+ Channel is
Closed and Activated
Na+ Channel is Closed
and Inactivated
Na+ Channel is Open;
Stays Open for Short
Amount of Time
Voltage-Regulated
K+ Channel is Closed
K+ Channel is Open
+
K
Channel
Changes in Membrane Potential
• Resting Membrane Potential (RMP)
• Depolarization
– Membrane becomes more + than RMP
• Hyperpolarization
– Membrane becomes more – than RMP
• Action Potential: pattern of MP changes
– Depolarization
– Repolarization
– Undershoot: Brief Hyperpolarization
Changes in Membrane Potentials
Graded Potentials
• Occur at dendrites
and cell bodies
• Response to changes
in chemicallyregulated channels
• Strength diminishes
over distance
• Vary in strength
Graded Potentials
• Can be depolarizing
event or
hyperpolarizing event
Action Potentials
• Occur only along
axons
• Strength is always the
same
• Strength of signal
stays the same along
the entire length
• All-or-none
Threshold Stimulus
• Threshold Stimulus –
Enough depolarization
to generate an AP
– Usually -55 mV
• Subthreshold Stimulus
– Insufficient
depolarization to
generate an AP
The End
Unless otherwise specified, all images in this presentation came from:
Campbell, et al. Biology, 7th ed. and 8th ed. Pearson Benjamin Cummings.