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How signals are sent through the nervous system. Membrane Potentials and Impulses. Synapse. Synapse = Junction between two connecting neurons Synaptic cleft-between the neurons, signal has to go across this space - PowerPoint PPT Presentation
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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
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