How signals are sent through the nervous system Synapse Synapse Junction between two connecting neurons Synaptic cleftbetween the neurons signal has to go across this space Signals need to be sent ID: 314240
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Slide1
Membrane Potentials and Impulses
How signals are sent through the nervous systemSlide2
Synapse
Synapse = Junction between two connecting neurons
Synaptic 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 muscleSlide3Slide4
Synapse
Presynaptic Neuron: sender of the signal; axon end (Before synapse)
Postsynaptic Neuron:
receiver of the signal (After synapse
); dendrite endSlide5
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?Slide6Slide7
Neurotransmitters
Distal end of axons have synaptic knobs with synaptic vesicles
(store neurotransmitter)Slide8Slide9
Neurotransmitters
Can be:Excitatory: increase signal transmittance
More of this type =
sending of signal
Inhibitory:
decrease signal
transmittance
More of this type =
no signalSlide10
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
-2Slide11
Neurons at restSlide12
Neurons at rest
Resting potential: inside is more negative than outside of the cell
AKA
POLARIZED
(think polar opposites)Slide13
Why?Slide14
Resting Neuron
To keep the cell in resting
potential,
a
Sodium-Potassium pump
restores ions to where they belongSlide15
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?Slide16Slide17
Depolarization
Environmental Stimuli (odor, touch, sound,etc
.)
Receptor cell releases
neurotransmitter
ONLY
Na
+
channels open,
Na
+
ions go into cell
= DEPOLARIZATION Slide18Slide19
Depolarization
Inside of cell becomes more POSITIVEThis triggers an
ACTION POTENTIAL
Will continue down rest of membraneSlide20Slide21
Repolarization
Quickly after the previous step, K+ is able to move across membrane through its channels; sodium can no longer moveSlide22
Repolarization
Inside is negative again (repolarized)Slide23Slide24
Refractory period
Sodium – Potassium pump uses active transport to move Na+ & K+ back to where they startedDuring this time, the neuron cannot transmit an impulse
Known as
REFRACTORY PERIOD
Membrane returns to true
resting potentialSlide25Slide26
All or None Response
Just like muscles if a nerve responds, it responds completelyGreater
intensity of stimulation triggers more impulses per second
Not
a greater intensity of impulseSlide27
Nerve Impulse
This “wave” of action potentials from one neuron to the next is known as a NERVE IMPULSE
Moves
from dendrites
down through axonSlide28
Nerve Impulses
Unmyelinated neurons conduct impulses over their entire membrane surface-
SLOW
Myelinated
neurons conduct impulses from
node of Ranvier to node of Ranvier - FASTSlide29
Synaptic Transmission
1. 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.Slide30
Neurotransmitters
Excitatory NTs: cause depolarizationInhibitory NTs:
lessen depolarizationSlide31
Last Step
Neurotransmitters are broken down by
enzymes
, or
Reabsorbed
by presynaptic
cell
Called
re-uptake