Dr.
Gerald S. Hecht
Assistant Professor of
Psychology
College
of
Sciences
webmaster@psiwebsubr.org
PSYC
488 – History & Systems Exam 2 Study Guide
EARLY
STUDIES OF THE SPINAL CORD AND THE BELL-MAGENDIE LAW OF SPINAL NERVE
FUNCTION
Bell-1811
Published Idea for a New Anatomy of the Brain Published for Friends
in which he speculated about the functional significance of parts of
the brain AND described some experiments on the spinal cords of
“stunned rabbits”
- Stimulating
the POSTERIOR spinal nerves = NO MUSCLE MOVEMENT
- Stimulating
the ANTERIOR spinal nerves = YES MUSCLE MOVEMENT
Bell
speculated that there was a FUNCTIONAL DIVISION of the SPINAL NERVE
ROOTS:
- ANTERIOR
ROOTS send messages to muscles “telling” them to move
- POSTERIOR
ROOTS carry messages about sensations into the cord
- Used
Conscious subjects
- ANTERIOR
ROOT severed: NO limb movement when the subjects limb was pinched –
YES vocalizing in response to the pinch
- POSTERIOR
ROOT severed: YES limb movement when pinched – NO vocalizing to
the pinch.
Magendie
concluded that SENSORY NERVES enter through the POSTERIOR ROOTS and
MOTOR NERVES
exit through the ANTERIOR ROOTS.
Big
Brouhaha ensues--- Bell’s brother-in-law John Shaw challenges
the priority of Magendie’s discovery—yelling all over
Europe about Bell’s pamphlet published for his friends…
Magendie claims to have never seen it (probably really hadn’t)
… Controversy (and international incident) settled by experts
agreeing that Bell’s use of “STUNNED” rabbits
precluded proof of VOLUNTARY motor responses. In the end BOTH were
given credit and the BELL-MAGENDIE LAW of spinal reflexes still
stands today.
Bell-Magendie
Law provided PHYSIOLOGY with specific knowledge of the anatomical and
functional specificity of spinal root function and PSYCHOLOGY with
one of its first and longest lasting paradigms: THE STIMULUS AND
RESPONSE (S-R) (the idea that sensations precede behavior).
SENSORY
PHYSIOLOGY
17th
century: Luigi Galvani attached a wire from the roof of his lab into
the “frog room” and attached the other end of the wire to
a frog’s leg… the muscles would contract when the
atmospheric conditions (weather, etc.) changed. Galvani believed that
electricity was generated by the brain and distributed throughout the
body by the “wires” that are the nervous system…
he was wrong about the last part (the brain as a powerplant)
Alessandro
Volta challenged Galvani’s theory: He said that the muscle
contractions observed by Galvani were due to a potential difference
(today known as voltage… get it?) across the membranes of
nerve cells. Volta said that Galvani’s frog’s nervous
systems had not generated electricity, they had alternately stored
and conducted it…. BASICALLY STATED THAT NERVES WERE
BATTERIES! (turns out to be true!!)
- 1850-
Emil du Bois-Reymond
- developed
a very sensitive amp/volt meter… attached one of the
electrical leads into a nerve and the other to the outside membrane
of the nerve. When the muscle was stimulated.. he was able to DETECT
the spread of current down the nerve…It took a “moment”
for the meter to register… so Du Bois Reymond suggested that
it could be POSSIBLE TO MEASURE THE SPEED OF NEURAL IMPULSE AFTER
ALL!!
- THE
ROLE OF THE GERMAN UNIVERSITY SYSTEM IN NEURAL/SENSORY PHYSIOLOGY AND
ACCEPTANCE OF PSYCHOLOGY AS A SEPARATE SCIENCE--Germany
was more conductive to this type of research than other countries
because:
- England
and U.S. Religious beliefs would not have the “HUMAN SOUL
MEASURED BY SCALES AND ELECTRODES”
- England,
France and the U.S. Practiced the manner of the so called “GENTLEMAN
SCIENTIST”… living on an independent income.
- Wave
of reform over German Universities encouraged research, outstanding
academic freedom, reputation for scientific excellence and academic
rigour… the “publish or perish” ethic,
fellowships, scholarships, graduate assistantships, postdoctoral
research positions, grants and tenure based on ability rather than
socioeconomic or family background.
- Product
of the aforementioned German University system
- Improving
upon Du Bois-Reymond’s method measured the time from electrical
stimulation of a nerve until the occurrence of a muscle contraction.
The time from stim to contrac in a 60mm section of nerve was 0.0015
seconds… so the speed of the neural impulse was around 50-90
meters per second
- This
is MUCH, MUCH slower than the speed of light or speed of electrical
current in a wire which is around 300 MILLION METERS/SECOND.
- The
implications of this in detail are the subject of another course…
but suffice it to say… it showed that whatever the nervous
system was doing, it was slow enough to study
- Helmholtz
opened up an AMAZING DOOR… The interval between THOUGHT and
ACTION was MEASURABLE!!!… the machinery of the “mind”
could be understood…. A science of psychology was possible!
- DOCTRINE OF SPECIFIC NERVE ENERGIES
- Either
the nerves themselves must communicate different impressions to brain
OR…
- The
nerves must project to different parts of the brain and it is the
brain area which imposes the specificity.
- Mueller
thought that it was impossible to know if 1 or 2 was the correct
answer BUT… today we know that it is the latter—Different
sensory projection areas of the brain impose the specific quality.
- The
reason that Mueller thought it impossible was because the
“electricity” traveling down the nerves was moving faster
than could be measured (it was naturally assumed be like electrical
current traveling close to the speed of light… physics hadn’t
reached that point yet).
- Gustav Fechner and Psychophysics
- The
division between mind and body (the mental realm and the physical
realm) was an illusion caused by the nervous system refracting or
distorting physical properties of the outside world.
- Discovered
the exact quantitative relationships between the magnitudes of
physical stimuli and magnitudes of the resulting mental sensations.
- The
relationship fits a logarithmic function for all of the senses S=k
log R
- where S=change in sensation
(JND),
- R
is the magnitude of the physical stimulus
-
k is the constant derived from
Weber’s law :
The effects of stimulus
intensities are relative to baseline amounts of sensation (i.e., the
perceived brightness of dashboard lights are dependent upon how
bright it is outside even though the amount of “physical light”
emitted by the lights does not change).
Fechner proposed two ways to
measure sensation: 1) the presence or absence of a stimulus (for the
physical side of things) and 2) the absolute threshold of perception
OF the stimulus (the mental side of the equation)
In
brief, Fechner 1) provided the final prerequisites for a science of
psychology with precise and elegant measurement, and 2) was one of
most amazing beings to stomp on the planet and the more you know
about his way of thinking the more you’ll know the “heart”
of psychology as a science…
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