Saltatory and Continuous Conduction & Differences and Similarities Seen in Action & Graded Potentials 12.17, 12.18

continuous conduction

conduction occurs in unmyelinated axons. This process involves the sequential opening of voltage gated Na+ and K+ channels located within the axon membrane along the entire length of the axon to propagate an impulse.

factors affecting axon regeneration

depend on the cell body and a critical amount of the neurilemma being intact, the extent of the damage to the axon, and the distance between site of damaged axon and the structure it innervates.

action potential

segment: axon channels: voltage-gated direction of v change: + or - amount of v change: large; temporary reversal of polarity degree of v change: does not vary duration: self-propagating along axon distance traveled: length of axon change in intensity: same intensity with gates opening in sequence

graded potential

segment: dendrites and cell body channels: chemically gated channels direction of v change: + or - amount of v change: small degree of v change: based on magnitude of stimulus duration: 1 ms to a few ms distance traveled: short change in intensity: decrease with distance

saltatory conduction

conduction occurs in myelinated axons. Nerve signals transmit much faster than in continuous conduction because an action potential is generated only at the neurofibrils (segments of axon without myelination) of myelinated axon rather than along the entire length of unmyelinated axon. Many voltage gated Na+ and K+ channels are located at the nodes for propagation of the impulse. Na+ diffuses through the axoplasm of the electrically insulating myelinated regions at a much faster rate than the events at the node. The decrease in number of channels used in saltatory conduction compared to continuous conduction leads to a decrease in delay (from waiting for channels to open and close) and a quicker impulse transmission. Saltatory is also more efficient because less energy is used by pumps to maintain the resting membrane potential.

axon regeneration

1. Axon is severed 2. Proximal portion of each severed axon seals and swells; distal portion and myelin sheath degenerate; neurilemma survives 3. Neurilemma and endoneurium form a regeneration tube 4. Axon regenerates and remyelination occurs 5. Innervation to effector is restored

IPSP

1. Neurotransmitter binds to chemical receptors on postsynaptic membrane 2. Ligand-gated K+ (or Cl-) channels open 3. K+ flows out of (Cl- flows into) the postsynaptic neuron 4. Inner membrane of neuron becomes more negative, causing an IPSP (graded potential) 5. Local current of K+ (or Cl-) propagates towards axon hillock, decreasing in strength as it travels

EPSP

1. Neurotransmitter binds to chemical receptors on postsynaptic membrane 2. Ligand-gated Na+ channels open 3. Na+ flows into the postsynaptic neuron 4. Inner membrane of neuron becomes less negative, causing an EPSP (graded potential) 5. Local current of Na+ propagates towards axon hillock, decreasing in strength as it travels