Lecture 24: Neuronal Physiology Part 2

What is true of the AP waveforms of different neuron types?

all the waveforms are all different

What are the spiking patterns in cerebral cortex neurons?

• no adaption

  • no slowing of AP firing rate with prolonged stimulation

• stronger adaption

• rhythmic bursts

What does each neuron express?

different complement of ion channels with slow kinetics

What is true of the no adaption spike pattern?

there is only fast Na⁺ channels and delayed-rectifier K⁺ channels

What is true of the stronger adaption spiking pattern?

has another set of K⁺ channels that activate slowly

What is true of the rhythmic bursting spiking pattern?

interplay between two or more voltage-gated currents with slow kinetics

What is the diversity of firing patterns?

Where are action potentials initiated?

axon initial segment

What is true of Na_v channels?

they activate at more negative voltages

What is orthodromic action potential conduction?

forward, into axon

What is antidromic action potential conduction?

• backward, into soma and dendrites

• strongly attenuated

  • dendrites filter fast signals like APs much more strongly

• may trigger biochemical changes, potential role in plasticity of synapses and intrinsic membrane properties

What is the most common demyelinating disease of the CNS?

multiple sclerosis

What is shown in MS?

distributed zones of demyelination in brain and spinal cord

What are the effects of demyelination on axonal conduction?

• same action current at node of Ranvier distributed across longer, leakier, stretches of membrane

• impaired ability of axons to transmit high frequency trains of impulses

  • decreased conduction velocity

  • conduction blockade - total blockade of propagation

• generation of ectopic action potentials

  • APs arise spontaneously without input from upstream part of axon

How would an AP in one axon be transmitted to an adjacent non-myelinated axon?

K⁺ efflux and local current depolarize the neighbor to threshold (crosstalk / ephaptic transmission)

Why would the AP in the adjacent axon propagate in both directions?

It starts mid-axon, and Naᵥ channels on both sides are resting/available, not inactivated