PSYB65H3 Chapter Notes - Chapter 4: Hermann Von Helmholtz, Luigi Galvani, Richard Caton

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PSYB65 CHAPTER 4 NOTES– FALL 2015 – JESSICA DA CUNHA 1
Chapter 4 – How Do Neurons Use Electrical Signals to Transmit
Information
Rene Descartes – Treatise on Man -> proposed that the carrier of information is the CSF
flowing through nerve tubes
En fire burns the man’s toe it stretches the skin, which tugs on the nerves leading to the brain
A valve in a ventricle if the brain opens and CSF flows down the tube, filling the leg muscles and
causing them to contract and pull the toe back from the fire
Flow of fluid through other tubes to muscles of the body causes the head to turn toward the
painful stimuli’s and the hands to rub the toe
Isolated the 3 questions that underlie a behavioural response to stimulation
o1 – How do our nerves detect a sensory stimulus and inform the brain about it?
o2 – How does the brain decide what response it should make?
o3 – How does the brain command muscles to move to produce a behavioral response?
Clinical Focus 4-1 – Epilepsy
Epilepsy is the most common neurological disease worldwide – 1 in 20 people experiences a
seizure in their lifetime
Synchronous stimuli can trigger a seizure -> strobe lights are used in diagnosis
Some seizures can be linked to a specific symptom – infection, tumor, damage to brain – or
spontaneously
Three symptoms common to many kinds of epilepsy
o1 – aura: warning of impending seizure which may be a sensation (odor/sound) or a
feeling
o2 – abnormal movements: twitching, repeated shaking or chewing, may start in a limb
and spread across the body – total loss of muscle tone and postural support causes the
person to collapse
o3 – loss of consciousness and later unawareness that the seizure happened
If they occur frequently and cannot be controlled by drugs – surgery may happen
oGoal of surgery is to remove damaged or scarred tissues that is the focal point of
seizure -> prevents seizures from spreading to other brain regions
Epilepsy reveals that the brain is electrically active and when this activity is abnormal – severe
consequences
4.1 Searching for Electrical Activity in the Nervous System
Early discoveries about the nature of electricity led to proposals that it plays a role in conducting
information in the nervous system
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PSYB65 CHAPTER 4 NOTES– FALL 2015 – JESSICA DA CUNHA 2
Early Clues That Linked Electricity and Neuronal Activity
Stephen Gray – rubbed a rod with a piece of cloth to accumulate electrons on the rod. Then
touched the rot to the feet of a boy suspended on a rope and brought a metal foil to the boy’s
nose.
oThe foil was attracted to the boys nose and bend on approaching it – as they touched
electricity passed from the rod through the boy to the file
oThe boy could not feel it
Gray hypothesized that electricity might be the messenger that spreads information through the
nervous system
Electrical Stimulation Studies
Luigi Galvani – frog legs twitched when hit by lightning -> if an electrical current is applied to a
dissected nerve, the muscles connected to that nerve contracts
Galvani discovered electrical stimulation -> passing an electrical current from the uninsulated
tip of an electrode onto a nerve produces behaviour -> contraction
Gustave Fritsch + Eduard Hitzig – electrical stimulation of the neocortex causes movement
oStudied several animals and well as a person who was being treated for war injuries
omovements of arm and legs respond to the stimulation of particular parts of the
neocortex
Robert Barthlow – wrote first description of the effects of human brain stimulation (on Mary
Raffetry)
oGirl had a skull defect that exposed part of her neocortex -> did not go well with rest of
community
oDemonstrated that the brain of a conscious person could be stimulated electrically to
produce movement of the body
Electrical Recording Studies
Richard Caton – first to measure the electrical currents of the brain with a sensitive voltmeter
(device that measure the flow and the strength of electrical voltage by recording the difference
in electrical potential between two bodies)
oWhen he placed the electrodes on the skull of a human subject – could detect
fluctuations in his voltmeters recordings
oThis kind of brain recording (electroencephalogram EEG) is a standard tool used to
monitor sleep stages and recording waking activity and diagnosing disruptions (like in
epilepsy)
Hermann von Helmholtz – stimulated a nerve leading to a muscle and measured the time the
muscle took to contract
oNerve conducted information at 30-40 meters per second, while electricity flows along a
wire faster than the speed of light -> flow of neuron messages is too slow to be an
electric flow
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PSYB65 CHAPTER 4 NOTES– FALL 2015 – JESSICA DA CUNHA 3
Julius Bernstein – chemistry of neurons produces an electric charge, the charge can change
and act as a signal
oSuccessive waves of electric charge make up the message sent by the neuron
Tools for Measuring a Neuron’s Electric Activity
Waves that carry messages are very small and restricted to the surfaces of neurons
Can measure the waves using electrical stimulation and electrical recording techniques and
determine how they are produced
If a single axon Is stimulate -> produces a wave of excitation, if a voltmeter is placed on the
axon, it can detect a change in the electrical charge on that axon’s membrane as the wave
passes
This may seem simple but it requires a large neuron, and a very sensitive device
Giant Axon of the Squid
The neurons of many animals are too small to see by the eye and too small to perform
experiments easily
Loligo vulgaris – Atlantic quit – has giant axons (1000 micrometers/1 mm in diameter)
Loligo is not a giant squid – only about a foot long, but its axons are as big as possible
Each axon is formed by the fusion of smaller axons – they properly messages faster and allow
the quid to jet away from predators
Axon is big enough to be dissected out of the squid and kept functional in a bath of salty liquid
like body fluids – Hodgkin and Huxley
Oscilloscope
Oscilloscope voltmeter sensitive enough to record the small electrical signals from the nerve
An electron beam leaves a trace on a screen, deflections of the beam can be used to record
voltage changes on an axon
Microelectrodes
Needs to be small enough to be able to be placed into an axon
Deliver an electrical current to a single neuron or record from it
To make on is to etch the tip of a piece of thin wire to a fine point
The tip of a glass one can be as small as 1 micrometer, remains hollow
Is filled with salty water which is the conducting medium that an electrical current can travel –
electrode
A were placed in the salt solution connects the electrode to a simulation or recording devices
Use to record from an axon in different ways:
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Document Summary

Chapter 4 how do neurons use electrical signals to transmit. 4. 1 searching for electrical activity in the nervous system: early discoveries about the nature of electricity led to proposals that it plays a role in conducting information in the nervous system. Early clues that linked electricity and neuronal activity: stephen gray rubbed a rod with a piece of cloth to accumulate electrons on the rod. Julius bernstein chemistry of neurons produces an electric charge, the charge can change and act as a signal: successive waves of electric charge make up the message sent by the neuron. Tools for measuring a neuron"s electric activity: waves that carry messages are very small and restricted to the surfaces of neurons, can measure the waves using electrical stimulation and electrical recording techniques and determine how they are produced. Giant axon of the squid: the neurons of many animals are too small to see by the eye and too small to perform experiments easily.

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