MEMBRANE POTENTIALS AND

IMPULSESHow signals are sent through the nervous system

Synapse Synapse = Junction between two

connecting neuronsSynaptic cleft-between the neurons, signal

has to go across this space

Signals need to be sent from neuron to neuron, not just from neuron to muscle

Synapse Presynaptic Neuron: sender of the signal;

axon end (Before synapse) Postsynaptic Neuron: receiver of the signal

(After synapse); dendrite end

Synaptic Transmission Transmission occurs when the message

crosses the synapse

Neurotransmitters are biochemicals that complete this function

Which neurotransmitter did we learn about during the muscular unit?

Neurotransmitters Distal end of axons have synaptic knobs

with synaptic vesicles (store neurotransmitter)

Neurotransmitters Can be:

Excitatory: increase signal transmittance○ More of this type = sending of signal

Inhibitory: decrease signal transmittance○ More of this type = no signal

Chemistry Review Ions play an important role in the nervous system

signals

What is an ion?

An atom that has lost or gained 1/more electrons

Ions are positive if electrons are lost and negative if electrons are gained

Examples: Na+ K+ Mg+2 Cl- O-2

Neurons at rest

Neurons at rest Resting potential: inside is more

negative than outside of the cell

AKA POLARIZED (think polar opposites)

Why?

Resting Neuron To keep the cell in resting potential, a Sodium-

Potassium pump restores ions to where they belong

Action Potential Conditions must change in order for a

signal to be sent by the neuron

This electrochemical signal = ACTION POTENTIAL

Which part of the neuron is the sender?

Depolarization1. Environmental Stimuli (odor, touch,

sound,etc.)2. Receptor cell releases neurotransmitter3. ONLY Na+ channels open, Na+ ions go

into cell

= DEPOLARIZATION

Depolarization Inside of cell becomes more POSITIVE

This triggers an ACTION POTENTIAL

Will continue down rest of membrane

Repolarization Quickly after the previous step, K+ is

able to move across membrane through its channels; sodium can no longer move

Repolarization Inside is negative again (repolarized)

Refractory period Sodium – Potassium pump uses active

transport to move Na+ & K+ back to where they started

During this time, the neuron cannot transmit an impulse

Known as REFRACTORY PERIOD

Membrane returns to true resting potential

All or None Response Just like muscles if a

nerve responds, it responds completely

Greater intensity of stimulation triggers more impulses per second

Not a greater intensity of impulse

Nerve Impulse This “wave” of action potentials from one

neuron to the next is known as aNERVE IMPULSE

Moves from dendrites down through axon

Nerve Impulses Unmyelinated neurons conduct impulses over their entire

membrane surface- SLOW

Myelinated neurons conduct impulses from node of Ranvier to node of Ranvier - FAST

Synaptic Transmission1. When an impulse reaches the end of an axon, synaptic vesicles release neurotransmitters

2. The neurotransmitters react with receptors on the postsynaptic membrane to open ion channels.

3. Ions flow into the postsynaptic cell, eliciting a response.

Neurotransmitters Excitatory NTs: cause depolarization

Inhibitory NTs: lessen depolarization

Last Step Neurotransmitters

are broken down by enzymes, or

Reabsorbed by presynaptic cell

Called re-uptake