Submitted by: Submitted by shiva3
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Words: 391
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Category: Philosophy and Psychology
Date Submitted: 11/29/2010 06:51 PM
Modern view of neural conduction
Electrical changes inside single nerve cell
Depolarization-inside less negative (-) than outside until certain voltage level (threshold)
Rapid change-action potential (all or none law) once threshold is reached
Implications of:
Threshold-could be all of kinds of energy that do not affect nervous system
All-or-none law- places limit on our ability to respond to different levels of intensity
Refractory period-limits action potentials, ceiling
Speed of neural conduction-limits reaction time
Not all nerves are alike
Bell-Magendie Law(1822)
If you cut the ventral roots of a dog, it can’t move (Motor nerves)
Cut dorsal roots-limbs numb, doesn’t experience sensation (Sensory nerves)
So far:
Philosophers: questions about nature of mind
Physiologists: experimental studies of neural conduction
Now: the link
Johannes Mueller(1838) “Doctrine of Specific Nerve Energies”
Internal causes (as well as external ones) can give rise to sensation (ex: dreams, itch, ringing in ears)
A single “cause” can give rise to many sensations, depending on which nerve is stimulated (ex:effects of pressure on nerves of: skin-touch or pain, eye-pressure phosphate (visual nerve), ear-hear)
A single nerve can be excited by different causes. Each time the sensation is the same. (ex: stimulate visual nerve by light, pressure, electricity, or chemicals. What is the effect? Seeing)
Volta’s tongue sandwich:
Galv-electricity comes from frog
Volta-No, from battery-bitter taste of battery
Brass+iron generate electric current
Electricity from brass + iron stimulate nerves of tongue to get taste (Based on Mueller)
Sensations consist of knowledge of the qualities or conditions of the nerves themselves, not of external bodies. Or, we only know the states of the nerves. (experience comes only from nervous system)
Mueller asks:
What makes nerves different?
Place of termination in brain?
Or, the pattern of signals carried?
Relate Mueller...