W4 Neurotransmission- Action potential and synaptic transmission Flashcards
How does a membrane become more permeable to ions?
Protein channels in the cell membrane will open
e.g. Voltage gated sodium ion channels for Na+
What is compound action potential? (lab)
Action potentials are generated in individual axons whereas a compound action potential (CAP) is the sum of action potentials recorded between 2 external electrodes.
What is the Somatic nervous system?
(SNS)
What does it consist of?
How does information travel?
The voluntary nervous system.
In this system, information from the periphery travels to the CNS along afferent sensory nerves and responses travel directly to skeletal muscles along effector motor nerves.
Includes Brain, Spinal cord, Neurones, Nerves, Muscle
What does the CNS consist of?
The brain and spinal cord.
What does the Peripheral nervous system consist of?
Sensory nerves
Nerves from spine to muscles
Basic description of a neurone function:
Transmits action potential from dendrite to axon terminal
Many have a lipid sheath called myelin
Neurones form networks
What is a synapse
Where 2 neurones connect
What is glia?
Where are they found?
A type of cell in the PNS and CNS
What is membrane potential (difference) a result of?
Ion gradients
(Ion conc outside vs inside a cell)
An action potential is a form of…
Bioelectricity
In most cells there are more positive ions….. the cell than…. the cell
So there is a negative potential difference
Outside
Inside
(around -70 mV)
What are excitable cells?
Where their membrane potential changes in response to stimuli
e.g. neurons
The cell membrane is highly… to ions
impermeable- ions can’t cross it easily
(more on outside)
What does the Membrane potential allow?
Electrical signalling and excitability
What are the types of transport across cell membranes
Passive diffusion
Facilitated diffusion
Active transport
Osmosis
What is transported during passive diffusion?
Ethanol, O2, CO2, weak acids and bases
What is transported during passive diffusion?
Ethanol, O2, CO2, weak acids and basesWhat
What is transported during passive diffusion?
Ethanol, O2, CO2 (gases), weak acids and bases
What is transported during facilitated diffusion?
Ions (Cl-, Ca2+, H2O, polar molecules)
What is transported during active transport?
High Ca2+, High Na+, Low K+
What does an excitable membrane need?
A negative membrane potential
Ion concentration gradients
Ion channels
- Voltage gated and Ligand gated
(Na+, K+, Ca2+)
What are ligand gated channels?
They open when they bind to a certain molecule
What is a ligand?
A molecule that binds
Neurones brief description:
Highly specialised cells
Transmit information as electrical signals (nerve impulses or action potentials)
AP/signal received from other neurones or receptors
Propagated by axon (begins at axonal hillock)
What is the resting membrane potential of a neuron?
Maintained by?
-70mV
The permeability of the membrane to K+
An energy dependent pump which moves the ions across the membrane.
What does an action potential change the membrane potential to?
+30mV - It is depolarised
(more positive)
What are the meanings of depolarised and repolarised?
Depolarised= Membrane potential becomes more +ve
Repolarised= Membrane potential becomes more -ve
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 is unidirectional:
- 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 is unidirectional:
- 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
Myelination in CNS vs PNS
CNS- Oligodendrocytes generate myelin
PNS- Schwann cells generate myelin
How are myelinated neurones more efficient?
Only nodes of Ranvier are exposed so action potential jumps from node to node.
Much faster neurotransmission
Much more energy efficient
Saltatory conduction
What is the structure of a synapse?
Pre-synaptic neuron, Synaptic cleft, Post synaptic neurone
What happens when an action potential
reaches the end of a neurone?
- 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
What are the functions of neurotransmitters?
How are they synthesised?
- “A substance that transmits nerve impulses across a synapse (20nm)” : allows the information to flow!
- Synthesised endogenously
- Available in sufficient quantity in the pre-synaptic neuron to exert an effect on the postsynaptic neuron
- If externally administered, it mimics the endogenously-released substance
What are the different types of synapses?
- Synapse between two neurones
- Sensory receptor and a neurone
- Neuromuscular Junctions
- Skeletal muscle, e.g. biceps
- Smooth muscle, e.g. bronchioles
What clinical pharmacologically relevant events occur at synapses? (5)
- Drug action
- Action of neurotoxins
- Formation of memories
- Drug addiction
- Neurodegeneration
What do post-synaptic effects depend upon?
The transmitter and the receptor it binds to
( Ionotropic/ ligand gated)
( Metabotropic/ GPCR/ G-protein coupled)
Some neurotransmitters will bind to both kinds of receptors, e.g. glutamate, GABA
* Ionotropic responses are faster
* Metabotropic responses can have more diverse effects
What are the 2 types of receptors?
Ligand-gated ion channel receptors (fast)
G-protein-linked receptors (slower)
Receptors: Ligand gated (ionotropic) and
GPCRs
- Ligand gated ionotropic receptors fast
- Metabotropic (G-protein coupled/ GPCRs)
- Metabotropic responses can have more diverse effects
Describe Cholinergic neurotransmission in the neuromuscular junction
