Transcript The role of the Central Nervous System and Neurotransmitters in

GHG 114-115
OBB 255-265
Neurons and synaptic
transmission
Biopsychology
Specification details
The structure and function of sensory, relay and motor
neurons.
The process of synaptic transmission, including reference to
neurotransmitters, excitation and inhibition.
consider
the
importance
of the
brain
We need to understand that the
brain is ‘localised’ – meaning
different areas do different things
The brain is also ‘lateralised’ –
meaning the left and right
hemispheres are slightly different
Homework: ensure that you have labelled the different
parts of the brain
The Brain
Click here>>> to check out the brain tutorial
Learn some more about the CNS
• Neurotransmitters and the CNS
Don’t sit there passively – make
notes…how many neurones? How
many connections? etc.
Neurons
• Cells that conduct nerve impulses are called
neurons
• The things that people think and feel, say and
do are caused, one way or another, by
electrochemical events occurring within and
between the neurons that make up the
nervous system, particularly those in the brain
(80%)
Label your diagram
Terminal buttons Terminal
buttons
Dendrite - Receives the nerve impulse
or send signals to an
adjacent cell
signal from adjacent neurons
Nodes of ranvierThese speed
up the transmission of the
impulse by forcing it to ‘jump’
Myelinsignals
sheathpass
Insulates
Axon Where the electrical
along/protects
from external influences
Nucleus - the control centre of athe
cell,axon
which
contains the cell's chromosomalthat
DNAmight effect the transmission of
the nerve impulse down the axon
Three types
of neurons
Relay Neuron
Different types of neurons
The cellular structure of all neurons is the same. There are
anatomical differences in size, depending on their function
1. Motor
2. Relay
3. Sensory
neuron
(Interconnecting) neuron
neuron
Function
Carries messages
from the CNS to
effectors such as
muscles and
glands
Transfers messages
from sensory neurons
to other
interconnecting
neurons or motor
neurons
Carries messages
from the PNS to
the brain and
spinal cord
Length of fibres
Short dendrites
and long axons
Short dendrites and
short or long axons
Long dendrites and
short axons
Structural and functional differences
1. Motor neuron 2. Relay (Interconnecting) neuron
Function Carries messages Transfers messages from sensory
from the CNS to neurons to other interconnecting
effectors such as neurons or motor neurons
muscles and
glands
Lets apply this…(AO2)
Sensory neuron- oh
that’s hot!
Takes message along
PNS to the spinal
cord - brain (CNS)
Connects to a relay
neuron
Message transferred
to motor neuron
Message sent to
muscle to move
hand!
3. Sensory neuron
Carries messages
from the PNS to the
brain and spinal
cord
Knee Jerk
In a reflex arc, like the kneejerk reflex, a stimulus, such
as a hammer hitting the
knee, is detected by sense
organs in the peripheral
nervous system, which
conveys a message along a
sensory neuron. The
message reaches the
central nervous system
where it connects with a
relay neuron. This then
transfers the message to a
motor neuron. This then
carries the message to an
effector such as a muscle,
which causes the muscle to
contract and, hence, the
knee to move or jerk.
Neurotransmitters
• Neurotransmitters are chemical messengers that act between
the neurons in the brain. This allows the brain to process
thoughts and memories.
• Neurons receive and transmit messages, passing them from
cell to cell.
Dopamine
Serotonin
noradrenaline
How Synapses work
You need to be able to explain how messages
are passed via neurotransmitters
One more
animation
Lets break that down!
The synapse
Words in Bold are key!
So what are we looking at here?
That blue bulbous portion that
looks like a nose is the
presynaptic neuron.
The smiley below it in pink is the
postsynaptic neuron.
And neurotransmission is what
gets a signal from one side to
the other.
The distance between a
presynaptic and postsynaptic
neuron is about 20-40
nanometers!
Action potential
Now the presynaptic neuron
has a signal.
This stimulus is transmitted
as an action potential
electrically down the
neuron until it gets to the
bulge in the picture, the
synaptic button.
Vesicles
But the electrical signal cannot
just bounce on to the next
neuron. There’s too much
space in between the two
neurons.
The change in potential is going
to affect little vesicles, little
blobs of membrane inside the
presynaptic neuron. These
vesicles contain the
neurotransmitters, which
are synthesized in the
presynaptic cell, and stored
in the vesicles until
stimulated.
Into the synapse
The electrical signal (via its
effects on calcium ions)
causes the vesicles to
begin to migrate to the cell
membrane.
Then they either dump all of
their neurotransmitter into
the synapse or just
release a little of it.
Reception
So now the neurotransitting chemicals
are in the synapse. They float
across the tiny space in a random
way, and in the process, bump into
receptors on the other side
The receptors here are important.
This is because there tend to be
many different types of receptor
for one type of neurotransmitter
Depending on which receptor type the
neurotransmitter hits, the result will
usually be either excitation or
inhibition of the postsynaptic
neuron’s action potential.
Breakdown/reuptake
So what happens then? You don’t want to
leave the neurotransmitter sitting
around in the synapse. Because this
means it will continue to bump into
receptors and pass signals on to the
post-synaptic neuron.
So the signal must be terminated
Depending on the neurotransmitter you’re
dealing with, there are various things
that can happen.
An enzyme can break down the
neurotransmitter chemical into its
component parts, or the presynaptic
neuron can have transporters, which
suck the neurotransmitter up back
into the synaptic button, either to be
shoved back into vesicles, or to be
degraded
Neurotransmitters continued:
• RECEPTORS can be thought of as locks – if a certain
chemical (neurotransmitter) fits like a key, then the
message is passed on: if it does not fit then the
message is blocked
Excitation and inhibition
• Synaptic connections can be excitatory or
inhibitory – the difference lies in the action
of the neurotransmitter at the postsynaptic
receptor
• Excitatory - they make it more likely the next
neuron will fire (such as acetylcholine)
• Inhibitory - they make it less likely the next
neuron will fire (such as GABA)
• Normal brain function depends upon a
regulated balance between excitatory and
inhibitory influences
Complete the
synaptic
transmission
flow chart
Synaptic transmission - answers
•
•
•
•
nerve impulse travels down an axon
nerve impulse reaches synaptic terminal
this triggers the release of neurotransmitters
the neurotransmitters are fired into the synaptic
gap
• neurotransmitter binds with receptors on the
dendrite of the adjacent neuron
• if successfully transmitted the neurotransmitter is
taken up by the post-synaptic neuron
• the message will continue to be passed in this way
via electrical impulses
Synapse: The gap between the end of one neuron and
the dendrites of the next neuron.
What you need to
label:
1. Direction of
impulse.
2. Axon terminal
3. Synaptic vesicles
containing
neurotransmitter
4. Synaptic gap
5. Dendrite
6. Receptor site
This is an interesting site that will
add to your understanding
of the brain
• http://outreach.mcb.harvard.edu/animations/
synaptic.sw
To end the session on the CNS
and the Brain