NEURONAL SIGNALLING:
INTRODUCTION:
The neurone is the principle unit
of signal transduction
Synaptic Transmission:
Synapse--the small spaces between
neuronal cells (~20 nm). The point
where electrical conduction is
converted to chemical conduction (in most cases).
Neurotransmitter is released into the synaptic cleft, between
the pre and post-synaptic neurons. This NT release is
triggered by invading action potential signal which arrives at
the pre-synaptic neurone.
Two types of Synapses
1) Electrical (less common, simple)
2) Chemical ( common, more complex)-
in mammalian neurons, the most common type
of synapse is one which converts an
electrical signal to a chemical signal
which crosses the synapse.
There is an enormous number, distribution
and density of synapses on a nerve cell.
The arrangement of synapses in the NS is
extremely intricate, with thousands of
different synaptic terminals contacting a single neurone.
Neurones ‘integrate’ information form thousands of synapses
from many different sources, and the behavioural response of
the post-synaptic neurone depends on the many inputs it
receives.
Electric charge of cytoplasm:
All activity within the
neurone is based on
changes in electric
charge of the cytoplasm.
This is due to movement
of positive or negative
ions across the cell
membrane.
Binding of
neurotransmitters to
receptors on dendrites
, causes opening of ion channels in the membrane, permitting ion
passage through the channel and changing membrane potential.
Types of electrical responses:
Neurones can be divided into categories depending on how
frequently they are activated to send signals/ messages.
Intristic:
-- Silent
-- Beating
-- Bursting – brief periods of much activity followed by rest
periods
Extrinsic (response to external stimuli – another connected
neurone inducing a response):
-- Sustained response
-- Accommodation
-- Delay
Measuring neuronal activity:
Activity is measured by treating membrane as part of an
circuit
Charge separation caused by the membrane’s ability to
selectively prevent movement of ions
Section of the brain
placed in culture,
and electrodes are
placed to make
electric contact with
nerves (like having
an extra pre-synaptic
cell connected to the
neurone being
measured).
A complete electric
circuit must be made
with the neurone as
the limiting
resistance
Impalement - charge
movement. Intrusion of electrode directly into the cell and
measurements made.
Patch clamping - channel activity. Electrode forms a seal with
the surface of the neurone, so activity of a small area of the
cell surface can be measured.
Changes occurring as a result of stimulating the neurone
depend on potential difference, which is calculated by current
INTRODUCTION:
The neurone is the principle unit
of signal transduction
Synaptic Transmission:
Synapse--the small spaces between
neuronal cells (~20 nm). The point
where electrical conduction is
converted to chemical conduction (in most cases).
Neurotransmitter is released into the synaptic cleft, between
the pre and post-synaptic neurons. This NT release is
triggered by invading action potential signal which arrives at
the pre-synaptic neurone.
Two types of Synapses
1) Electrical (less common, simple)
2) Chemical ( common, more complex)-
in mammalian neurons, the most common type
of synapse is one which converts an
electrical signal to a chemical signal
which crosses the synapse.
There is an enormous number, distribution
and density of synapses on a nerve cell.
The arrangement of synapses in the NS is
extremely intricate, with thousands of
different synaptic terminals contacting a single neurone.
Neurones ‘integrate’ information form thousands of synapses
from many different sources, and the behavioural response of
the post-synaptic neurone depends on the many inputs it
receives.
Electric charge of cytoplasm:
All activity within the
neurone is based on
changes in electric
charge of the cytoplasm.
This is due to movement
of positive or negative
ions across the cell
membrane.
Binding of
neurotransmitters to
receptors on dendrites
, causes opening of ion channels in the membrane, permitting ion
passage through the channel and changing membrane potential.
Types of electrical responses:
Neurones can be divided into categories depending on how
frequently they are activated to send signals/ messages.
Intristic:
-- Silent
-- Beating
-- Bursting – brief periods of much activity followed by rest
periods
Extrinsic (response to external stimuli – another connected
neurone inducing a response):
-- Sustained response
-- Accommodation
-- Delay
Measuring neuronal activity:
Activity is measured by treating membrane as part of an
circuit
Charge separation caused by the membrane’s ability to
selectively prevent movement of ions
Section of the brain
placed in culture,
and electrodes are
placed to make
electric contact with
nerves (like having
an extra pre-synaptic
cell connected to the
neurone being
measured).
A complete electric
circuit must be made
with the neurone as
the limiting
resistance
Impalement - charge
movement. Intrusion of electrode directly into the cell and
measurements made.
Patch clamping - channel activity. Electrode forms a seal with
the surface of the neurone, so activity of a small area of the
cell surface can be measured.
Changes occurring as a result of stimulating the neurone
depend on potential difference, which is calculated by current
