In 1937, John
Zachary Young suggested that the squid giant axon could be used to
study neuronal electrical properties. Being larger human neurons than but similar in
nature to human neurons , squid cells were easier to study. human neurons By inserting
electrodes into the giant squid axons, accurate measurements human neurons were made
of the membrane potential. human neurons The
cell membrane of the axon and soma contain voltage-gated ion channels
that allow human neurons the neuron to generate and propagate an electrical signal (an
action potential). human neurons These signals are generated and propagated by
charge-carrying ions including sodium (Na+), potassium (K+), chloride
(Cl-), and calcium (Ca2+).
Thin neurons
and axons require less metabolic expense to produce and carry action
potentials, but thicker axons human neurons convey impulses more rapidly. To minimize
metabolic expense while maintaining rapid conduction, many neurons have
insulating sheaths of myelin around their axons. The sheaths are formed
by glial cells: oligodendrocytes in the central nervous system and
Schwann cells in the peripheral nervous system. The sheath enables
action potentials to travel faster than in unmyelinated axons of the
same diameter, whilst using less energy. human neurons The myelin sheath in peripheral
nerves normally runs along the axon in sections about 1 mm long,
punctuated by unsheathed nodes of Ranvier, which contain a high density
of voltage-gated ion channels. Multiple sclerosis is a neurological
disorder that results from demyelination of axons in the central nervous
system.
Some
neurons do not generate action potentials, but instead generate a
graded electrical signal, which in turn causes graded neurotransmitter
release. human neurons Such nonspiking neurons tend to be sensory neurons or
interneurons, because they cannot carry signals long distances.
