Neuron Neuron PhysiologPhysiologyy

Functional Properties of NeuronsFunctional Properties of Neurons

Irritability – ability to respond to stimuli

Conductivity – ability to transmit an impulse

A nerve impulse does not flow like electricity because:

1. Neurons conduct impulses at a slower rate than electric current

2. Neuron provides energy for transmission once it’s been stimulated. Wire is a passive conductor and requires a steady, outside energy source for continuous flow of electrons.

Characteristics of Nerve Impulses

• How can stimuli of different intensities be identified?

Ex: light tap on arm vs. punch

-vary the # of impulses sent

-vary the # of neurons triggered

(the speed & duration of nerve impulse is always the same)

Characteristics of Nerve Impulses• What is saltatory conduction?

-fastest method of nerve impulse conduction; nerve impulse jumps from one node of Ranvier to another; occurs only in myelinated neurons

(like the difference between flying & driving)

Transmission of a Nerve Impulse

• See diagram & graph

Starting a Nerve ImpulseStarting a Nerve Impulse

The plasma membrane at rest is polarized

Fewer positive ions are inside the cell than outside the cell

Starting a Nerve ImpulseStarting a Nerve Impulse Depolarization – a

stimulus depolarizes the neuron’s membrane

A deploarized membrane allows sodium (Na+) to flow inside the membrane

The exchange of ions initiates an action potential in the neuron

The Action Potential (Nerve The Action Potential (Nerve Impulse)Impulse)

If the action potential (nerve impulse) starts, it is propagated over the entire axon

Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane

The sodium-potassium pump restores the original configuration This action requires ATP

Nerve Impulse PropagationNerve Impulse Propagation

The impulse continues to move toward the cell body

Continuation of the Nerve Impulse Continuation of the Nerve Impulse between Neuronsbetween Neurons

Impulses are able to cross the synapse to another nerve

Neurotransmitter is released from a nerve’s axon terminal

The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter

An action potential is started in the dendrite

Synaptic Transmission• Synapse - a junction or gap between the axon of one neuron with the dendrites of another neuron

• Neurotransmitter - a chemical that changes the permeability of the cell membrane to a specific type of ion - initiates an action potential

Ex: acetylcholine, serotonin, norepinephrine, GABA

• Diagram of Synaptic Transmission

(synaptic cleft, vesicle, neurotransmitter, axon,

dendrite, & receptor)

Synaptic Transmission

• animation/tutorial

How Neurons Communicate at How Neurons Communicate at SynapsesSynapses

Review: Video Clip

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

The End!