Neural Conduction

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...