Week 8 neurotransmission Flashcards
Neurones
Neurone: Responsible for
communication
-Action potential / neurotransmission
-Information transmits from dendrite to axon terminal -> many have a lipid sheath called
myelin
-Action potential generated in axonal hillock and travels down axon ->excitable membrane
Bioelectricity
Membrane potential (difference) is fundamental to all cells
Membrane potential is a result of ion gradients
Excitable cells (bioelectricity)
Membrane potential changes in response to stimuli
Nerve impulses (bioelectricity)
Changes in membrane potential that travel down nerves
Ion gradients
-Cell membrane is highly impermeable to ions -> allows formation of ion gradients (membrane potential difference)
-Allows electrical signalling and excitability
Membrane potential is the basis of;
–Neurotransmission
–Muscle contraction
–Secretion -> hormones, neurotransmitters, digestive enzymes, mucus,
surfactant
–Immune responses
Inside the cell
Low Ca2+, Low Na+, High K+
Outside the cell
High Ca2+, High Na+, Low K+
Charge across membrane
-70mV
An excitable membrane needs;
-A negative membrane potential
-Ion concentration gradients
-Ion channels
->Voltage gated
->Ligand gated
Sodium Na+
Potassium K+
Calcium Ca2+
Negative membrane potential (ion gradient)
Neurons have a negative membrane potential
More negative on the INSIDE of the cell than the outside -> when at rest
Membrane potential is due to unequal ion distribution
->A gradient of ions across the membrane which provides a DIFFUSION gradient and a MEMBRANE POTENTIAL
Neurones (nerve cells)
-Neurones are highly specialised cells
-Transmit information as electrical signals (nerve impulses or action potentials)
-Action potentials only travel one way
-Propagated by axon (begins at axonal hillock)
Neurone at Rest
-Resting membrane potential
of a neuron is -70 mV
Maintained by:
-An energy dependent
pump which moves the
ions across the membrane
Neurone: Action potential
An action potential changes the membrane potential to +30mV
Action Potential
Electrical impulses formed by ions moving into the neurone
The axonal action potential (depolarization and repolarization) is made up
of movement in sodium (+ charged ion) and potassium (+ charged ion)
Signal received at dendrites causes dendritic depolarisation
Dendritic depolarisation
-Ligand gated ion channels
-Metabotropic channels (involves a chain of other molecules to open channel)
This depolarisation opens voltage gated sodium channels
Action potential propagation
-Dendrite: ligand gated ion
channels open
-Axon: voltage gated ion
channels open
Action potential detail
Stimulus = electrical,
mechanical or chemical
Axon AP = electrical
Stimulus has to be strong
enough to reach threshold
potential
->Enough depolarisation to open
first NaV
->Sodium channels in the
membrane are sensitive to
voltage and open when the
THRESHOLD membrane potential is reached
The AP is all or Nothing
Action potential direction
The action potential is propagated
down the axon by voltage sensitive channels
-When as action potential occurs, Na+ voltage sensitive channels open due to the local change in membrane potential
->This causes more Na+ channels to open
-Na+ channels behind the action potential become inactive
-Therefore the action potential can only move in ONE direction
Action potential phases
-Depolarisation ->Na+ channels
open
-Repolarisation ->K+ channels
open
-Refractory period->Re-establishment of resting potential - Na+/K+ exchange
-Return to resting state
Myelination CNS
Central nervous system ->
Oligodendrocytes
Myelination PNS
Peripheral nervous system ->
Schwann Cells
Saltatory conduction
Axons in most vertebrate
neurones are myelinated
Mostly covered in fatty substance –> myelin
Only nodes of Ranvier are
exposed
Action potential ‘jumps’ from
one node to the next
-Much faster neurotransmission
-Much more energy efficient
Action potential at end of neurone
At the end of the axon is the synapse
-Presynaptic neuron, synaptic cleft, post synaptic neurone
->Presynaptic terminal contains synaptic vesicles
->Post synaptic terminal has receptors that neurotransmitter binds to
Synpase
-Impulse dependent release
-Membrane depolarisation opens voltage gated calcium channels
-Calcium influx triggers vesicles to move to the presynaptic
membrane
-Vesicles fuse with the membrane and release their content into the synapse
Neurotransmission at the synapse
-AP depolarises terminal (opens
voltage gated calcium channels)
-Calcium enters cell
-Triggers vesicles to move to the
presynaptic membrane. Vesicles fuse with the membrane and leading to exocytosis of synaptic vesicles
-Neurotransmitter diffuses across cleft
-Binds with receptors on the
postsynaptic cell
-Initiates a response in the
postsynaptic cell
Neurotransmitter Receptors
Post-synaptic effects depend upon the transmitter and the receptor it binds to;
-Ionotropic/ligand gated
-Metabotropic (G-protein coupled /GPCR
Some neurotransmitters will bind to both kinds of receptors;
-Ionotropic responses are faster
-Metabotropic responses can have more diverse effects
Receptors: Ligand gated (ionotropic) and GPCRs
Ligand gated ionotropic receptors fast
-Metabotropic (G-protein coupled/ GPCRs)
-Metabotropic responses can have more diverse effects
