The difference in voltage charge between the inside and outside of the membrane. Such a membrane is referred to as polarized.

in the plasma membrane allow ions to flow across the membrane

What are the 2 types of ion channels?

Passive: nongated, allow leakage of ions both ways, these are always open.

Gated channels: 2 types,

Ligand: channels open when the appropriate neurotransmitter binds, (sodium/pot. gates).

Voltage gated: channels respond to changes in the membrane potential

Reversed Polarization

The process of producing action potentials

Pot. gates open and membrane becomes highly permeable to K+ ions.

-The sodium gates close

-Inside looses pos ions to outside, and outside of membrane gains pos. charge.

Membrane will repspond to another stimulus, but the stimulus threshold is higher than for a resting neuron, corresponding to period of repolarization.

requires a stronger stimulus to complete restoration of the original resting potential.

must be a threshold stimulus if it will trigger depolarization. A stronger stimulus will make no difference, propagation will occur if threshold.

In myelin encased fibers, myelin acts as an insulator, and does not conduct an action potential. Depolarization jumps from node of Ranvier to node.Since the whole nueron does not have to depolarize, energy is conserved.

The action potential is actually carried by local currents.

greatest diameter nerve fiber, always meylinated, have strong ionic pumps and short refractory periods. Speeds up to 130 m/sec Always exhibit saltatatioin. Found where speed is important

1. Afferents connecting sensory receptors that warn the body of danger to the CNS

2. Efferents that do something about it.

B Fibers:

medium diameter nerve fiber, myelinated, long refractory perids. Speed around .5 m/sec

1. most of visceral sensory and motor fibers

nuerons do not actually make contact with one another, the impulse is transmitted from the azon ending of one to the dendrite ending of another.

Physical Gap=synaptic cleft.

Pre and postsynaptic clefts

neuron transmitting the impulse

nueron receiving the impulse

*presynaptic nueron secretes nuerotransmitter chemical sucstance; diffuses across synaptic cleft where it has an effect on post..dendrite.

If presynaptic nueron is excitatory it secretes a chemical neurotransmitter that can depolarize the dendrite ending of postsynaptic. That neuron cont. to transmit that impulse.

Depolarization is called: excitatory postsynaptic potential(EPSP).

releases an inhibitory neurotransmitter chemical. This chem. causes an increase in the resting polarization of the postsynaptic neuron, thus increasing the threshold stimulus level.

=Hyperpolarization.

Electrical Synapse

There is no true physical gap, but direcct protein channels connecting the cytosol of the two neurons, resulting in electrical coupling. Provides for synchronization of neuron activity, because the transmission from neuron to neuron is so rapid. Found in regions of the brain controlling rapid stereotyped movements, eg eye movements.

Refers only to receptors. Receptors do not appear to have refractory periods. All or none principle does not apply, and repeated stimuli can increase depolarization, and the strength of stimulus transmitted to the sensory neuron dendrite ending.

Action potentials are not produced in short dendritess or on the membrane of the perikaryon.Local electrical currents set in cytosol of the dendrite or neuron cell body.

- After threshold stimulation at dendrite endings, local currents in cytosol carry the message through the dendrite to the cell body. At axon hillock the local currents, if threshold will trigger an action potential, which then runs the length of the axon as described. Not all or none, depends on strength.