Week 4 Flashcards
Synapses
-Fluid filled spaces between the terminal button of a pre-synaptic neuron and the dendrite of a post-synaptic neuron
- 20-30 nanometers
Presynaptic Neuron
Typically an axon transmitting an axon potential
Axon Terminal
-Contains vesicles that contains molecules of neurotransmitter
- Vesicles ‘docked’ near presynaptic membrane
Neurotransmitter
-Chemical signals that transmit signal from one neuron to another neuron/cell
- When activated, they will travel across the synaptic gap
- Transmitter substances are powerful molecules that make us change our behaviours
Post-Synaptic Neuron
- Typically a dendrite on another neuron, could also be a muscles/gland cell
- Membrane of postsynaptic neuron/cell contains receptors for a specific transmitter substance
Transmitter Substances
- Controls the behaviour or response of other cells or organs
- Cross the synaptic cleft and bind to/ interact with receptors on the post-synaptic membrane
Lock and Key Model
Transmitter molecules will only affect the postsynaptic membrane if their shape fits the shape of certain receptor molecules in the membrane
Receptors
In neurons, specialised protein molecules on the postsynaptic membrane; neurotransmitter molecules bind to these molecules after passing through the synapse
Acetylcholine
Learning
Memory
Sleeping
Dreaming
Norepinephrine
Arousal
Vigilance
Attention
Serotonin
Dreaming
Emotional States
Impulsiveness
Dopamine
Motor control over voluntary movement
GABA
Reduced anxiety
Reduced action potential
Glutamate
Learning and memory
Increased action potential
Endorphins
Pain Reduction and reward
How do neurotransmitters make communication possible
- Crossing the synapse
- Latching onto receptors on the postsynaptic cell
- Triggering a response in that cell
Neurotransmitter Release
- Action Potential arrives at axon terminal
- Voltage gated Ca channels open
- Ca enters the presynaptic neuron
- Ca signals to neuron transmitter vesicles
- Vesicles move to the membrane and dock
- Neurotransmitters release via exocytosis
- Neurotransmitters bind to receptors
- Signal initiated in postsynaptic cell
Post-Synaptic Potentials
-An alteration in membrane potential of the post synaptic neuron, produced by movement of ions at the synapse
- Once psp’s are activated, they produce either an excitatory or inhibitory effect
Excitatory PSP’s examples
Chemical; excitatory neurotransmitters i.e. epinephrine and histamine
Physical; In sensory neurons, external signals may trigger an action potential i.e. light, sound, pressure or temperature
Pacemaker Potentials; Some excitable cells require no external stimulus to fire i.e. cardiac pacemaker cells on the sinoatrial cell in heart
Inhibitory PSP’s examples
Chemical; Inhibitory neurotransmitters i.e. GABA, Glycine and several neurotoxins and drugs
Physical; In sensory neurons, weak stimuli ma not reach the threshold of excitation to fire an action potential
What happens at excitatory synapses
- Na channels open and Na enters the cell making action potential more likely
- Reduction of membrane potential towards 0 from RMP makes AP more likely
- Negative charge decreases i.e. -70 mv to -50mv
What happens at inhibitory synapses
- K ion channels open, allowing K to leave the cell making AP less likely
- Increase in membrane potential relative to RMP makes AP less likely
- Occurs when negative charge inside the axon increases i.e. -70mv becomes -80mv
Conflicting Messages
- Multiple neurons may synapse at any given time so there can be a mix of IPSP’s and EPSP’s
Neural Integration
The algebraic summation of PSP’s
- AP will only happen when membrane potential reaches the threshold of excitation
- Excitatory effects must win
