18-11-21 - Synapse 2 Flashcards
Learning outcomes
- Review the EPSP and IPSP, their propertineuronalaxon response
- Recall additional mechanisms that regulate dendritic integration including dendritic morphology and synaose distribution
- Describe LTP and synaptic plasticity with examples
- Explain the role of synaptic plasticity in memory formation
- Recall the different basic patterns of circuitry found in the nervous system
- Describe specific examples of micro-circuitry and outline their role in neuronal network functions
What are 3 factors that determine if a neuron will reach its threshold potential and fire an action impulse?
1) The inherent excitability of the neuron (e.g number of ion channels, high or low resting membrane potential)
2) The frequency or amount of incoming excitatory impulses (from one or may snaptic connections)
3) The frequency or amount of incoming inhibitory impulses (from one or many synaptic connections
How does the system of descending modulation of pain function?
1) Sensory pain neuron that enters the spinal cord is activated
2) It synapses with an ascending pain neuron, which crosses to the other end of the spinal cord and ascends to the thalamus
3) In emergency situations, if the brain decides to not feel this pain, the brain can send a descending pain modulatory neuron down to this level of the spinal cord, where it synapses with an excites an inhibitory interneuron
4) This counteracts the incoming pain excitation, and only takes a small amount of interneuron activity to bring the membrane potential of the sensory pain neuron to below the threshold potential
What is computation in chemical synapses?
What is rectification?
What does it allow?
- Computation is the summation of EPSPS and IPSPS from potentially many different sources by neuron which decides if the threshold potential is reached and an action potential is generated
- Rectification refers to the fact that chemical synapses can only transmit information in one direction, which allows for the channelling and control of flow of information
What is plasticity?
How can this be done?
What might plasticity be involved in?
What are the 4 synaptic changes involved in long term potentiation (LTP)?
How are these synaptic changes controlled?
What is an example of LTP in memory?
What is an example of LTP in learning?
- Plasticity refers to the idea that the brain can reinforce particular pathways in the brain through synaptic changes
- This can be done through long term potentiation (LTP), and in some cases, long term depression (LTD) of these particular pathways
- Plasticity may be involved in learning and memory
• 4 synaptic changes involved in long term potentiation:
1) Increase neurotransmitter release through vesicle numbers (A)
2) Formation of new synapses and synaptic zones – may be a smaller area that can be polarised by ion changes (B)
3) Increased post-synaptic receptor density and mitochondria – leads to greater sensitivity to excitatory and inhibitory information from neurotransmitters (C)
4) Formation of new dendritic spines – more receptors (D)
• Control of these synaptic changes is done in part by neuromodulators, such as encephalins
• These small peptides modulate the transmission of pain at the level of the spinal cord
• Holidays, such as Christmas, are an example of LTP in memory
• Memories lie dormant for most of the year, but sights, smell, and sounds trigger these post-synaptic changes, which bring the memories back to the front of our mind
• Reason we are able to store these memories is long term potentiation
• The baby’s learned behaviour of putting things in their mouth is done by the long-term potentiation of the motor pathways responsible for putting things in their mouth
• This allows them to understand their environment, and so it is developed early.
What is the process of Long term depression (LTD) in the model of addiction?
What are the 3 different types of circuits in the neuron networks?
• In the neuron network there is:
1) Neuronal convergence
2) Neuronal divergence
3) Feedback
• Examples of these circuits:
1) Feedforward excitation
• One excitatory cell with an excitatory synapse onto a 2nd cell, which becomes excitatory as well
2) Feedforward inhibition
• Excitation in 1st cell causes excitation in the 3rd cell
• Excitatory cell with excitatory synapse onto an inhibitory cell
• When exciting an inhibitory cell, it passes an inhibitory signal to the next cell, in this case an excitatory cell
3) Convergence/divergence
• Signals from multiple cells converge on a singla cell/ small number of cells
• 3 excitatory cells passing information to a singla neuron
• This cell becomes excited and passes an action potential along its axon, which has 3 branches
• This is in a parallel configuration, so 3 equally potent action potentials go onto to excite 3 more cells
4) Lateral inhibition
5) Feedback/recurrent inhibition
• Excitatory cell passes excitatory signal onto excitatory cell which feedback to an interneuron, which is inhibitory
• Can be ain a circuit where all cells inhibit each other
6) Feedback/recurrent excitation
• Forms excitation circuit
• Can have a spiralling excitation
How does neuronal convergence work?
What will this generate?
What determines the degree of convergence?
What are the range of inputs on a single neuron in the mammalian brain?
What are 2 examples of cells with a high degree of convergence?
What is an example of where convergence occurs?
- When a cell has several neurons converging on it, the input from these cells will be integrated within the cell body
- This will either generate or not generate an action potential
- The more dendrites a neuron has, the high degree of convergence and integration of the signals
- The mammalian brain ranges from 1 to 100,000 inputs
- An example of cells with many inputs are cortical pyramid cells and cerebellar purkinje cells
- Convergence of signals from cone cells occurs in the eye, otherwise, the optical nerve would be huge
How does neuronal divergence occur in neurons?
- When the axon of a neuron has multiple branches, an action potential can be transmitted simultaneously in a parallel fashion along each branch to synapse with multiple neurons
- The action potential along each branch is equally potent, and there is no loss of strength
What are the 2 different forms of divergent neurons?
What are examples of when each type is used?
1) Spatially focussed divergent neurons
• Branching from the original neuron goes to specific number of neurons
• Information is channelled tightly
• Proprioceptive information about a muscle or joint can be diverged to several different other neurons, potentially each with different functions
2) Widely divergent neurons
• A lot of branching from the original neuron onto a wide area of neurons
• Different messages computed in different ways
• Sensory information arriving at the somatosensory cortex can be diverged widely throughout the cortex
What are the 10 steps of how the knee jerk reflex works?
Is this process a passive relaxation?
1) Stimulation of the patellar tendon causes unexpected stretch in the quadriceps (extensor muscle)
2) This unexpected stretch is interpreted as something that needs to be corrected by the body
3) There is a reflex response where the stretch receptors in the quadriceps send sensory signals through the dorsal horn of the spinal cord
4) This sensory signal diverges into 2 branches
5) The first branch is an excitatory branch that goes on to motor neurons int the anterior horn, which are excited and generate an action potential
6) This action potential is quickly sent down tot eh quadriceps, which causes them to contract
7) The tension in the antagonist muscle also has to be turned off
8) The 2nd branch of the sensory signal is also excitatory, as you cant have 2 different signals from the same branch
9) The other branch of the sensory signal excites an inhibitor interneuron, which sends an inhibitory signal
10) The inhibitory interneuron sends a signal that inhibits the normal tension of the antagonistic muscle (flexor muscle) by inhibiting the motor neurons of the flexor muscle
• This process is not a passive relaxation, as excitation is turned off by turning off a motor neuron that is active
How does the Golgi tendon organ reflex compare to the knee jerk reflex?
When does this process occur?
Why does it occur?
What are the steps of the Golgi tendon organ reflex?
What kind of mechanism is this?
- This is a similar process to the knee jerk reflex, but in the opposite direction for the Golgi tendon
- This process occurs when there is too much strain on a muscle, causing it to relax
- This is done to the muscle can’t be damaged easily
1) Active shortening of the muscle can cause the golgi tendon to become active to prevent damage
2) It sends sensory information tot eh spinal cord, which splits into 2 signals
3) The first signal is an excitatory signal which goes onto an inhibitory interneuron, which inhibits the motor neuron that is activating the extensor muscle (quadriceps)
4) At the same time, the 2nd sensory signal excited in interneuron, which excites the antagonist muscle (flexor)
5) This causes the flexor muscle to tense, and the muscle that was being actively shortened (quadricep) to relax to prevent any further damage
• This is a safety mechanism, while the knee jerk reflex is an involuntary reflex
Describe the 3 steps involved in local neuronal feedback.
Why is this process done?
Where is this process used?
1) As N1 generates an action potential, information is passed to N2
2) If N2 crosses the threshold potential, an action potential is fired and it inhibits its target cell, but also feedbacks to inhibit N1
3) N1 is moderated by negative feedback from N2
• This process is done because we don’t want neuron 1 to be excited all the time
• This process is used in the thalamus a lot of e.g for turning down descending pain information
What are 2 systems used to control the excitation of the motor cortex?
• Systems used to control the excitation of the motor cortex:
1) Visual feedback
2) Somatosensory (proprioceptive) system
• Involved in gripping and feeling
• This feedback can be long distance or local control
