Lecture 16: Synaptic Transmission, Learning and Memory Flashcards
Hypothesised that memories are formed by
connections between neurons
Memories and the brain
Connections of an ensemble of neurons is strengthened when memories are formed - connections are strengthened and these will represent an engram (memory trace) in the brain
Memory is not static, goes through the process of consolidation over time and can be retrieved and then reconsolidated and then retrieved again etc
encoding phase is an active state
encoding - consolidation - retrieval - reconsolidating - retrieval …
How are memories stored in the brain
release of neurotransmitter - activation of postsynaptic receptors - trafficking of receptors to the PSD - local translation of new proteins - altered gene expression
rapid, intermediate, long term changes (have rapid, intermediate and long term changes that underpin the storage of memories in the brain)
This rapid response needs to be transformed into a long-lasting response because we want our memories to last for a long time
The process of information transfer at synapses is called ……which involves
synaptic transmission which involves a change in the membrane potential
synapse communication changes
electrical signal propagated down an axon which results in neurotransmitter release and this neurotransmitter activates the second neuron and the cycle continues
this is a way that information can be transferred between neurons
Electrical synapses allow
allows the rapid propagation of a signal in the form of ions
membrane potential
Definition: electrical potential difference across the membrane
• Nerve cells are “polarised”
the reference point is the outside the cell (neurons are therefore said to be inside negative)
• Sometimes Vm is “at rest”
The resting membrane potential
-65 mV (range −30, −90 mV)
• Other times it is not
e.g. during an action potential
measuring membrane potential
micro electrode made of glass which is filled with salt solution which allows measurement of the electrical potential across the membrane with a voltmeter
What causes the resting membrane potential
- Phospholipid membrane is impermeable to ions.
2. There is an uneven distribution of ions between inside and outside of the cell
Ions and membrane potential
Potassium high concentration inside at a ratio of 1:20 by contrast sodium and chloride ions are concentrated outside of neurons at 10:1 or 11.5:1 respectively, calcium is highly concentrated outside the cell at a ratio of 10000:1 which is important because changing the level of calcium inside the cell is one of the most important ways to changes the response/activity of a neuron
Potassium ion and neuron
Conc outside in mM 5
Conc inside in mM 100
ration out:in = 1:20
Sodium ion and neuron
Conc outside in mM 150
Conc inside in mM 15
ration out:in = 10:1
Calcium ion and neuron
Conc outside in mM 2
Conc inside in mM 0.0002
ration out:in = 10000:1
Chlorine ion and neuron
Conc outside in mM 150
Conc inside in mM 13
ration out:in = 11.5:1
What causes the uneven distribution of ions?
Sodium-Potassium pump (within the physical membrane)
Calcium pump
Sodium-Potassium Pump
Is an integral membrane protein
• Concentrates K+ inside the neuron and Na+ outside
- If Na+ levels are high “inside” the pump breaks down ATP to produce energy
- This drives the pump
- The pump drives ions against their concentration gradients
Sodium leaves cells and potassium enters the cell
Calcium pump
Actively transports Ca2+ out of the cytosol across the cell membrane.
Additional mechanisms methods of calcium homeostasis include:
• intracellular calcium-binding proteins and
• organelles - endoplasmic reticulum and mitochondria
It is very important to control the amount of calcium within the cell
Depolarised
If the membrane potential becomes more positive than it is at the resting potential, the membrane is said to be depolarized.
Hyperpolarised
If the membrane potential becomes more negative than it is at the resting potential, the membrane is said to be hyperpolarized.
Change in membrane potential allows
communication between neurons
Influx of NEGATIVE ions
Hyperpolarisation
Inhibits the neuron
IPSP
chlorine for example
Influx of POSITIVE ions
Depolarisation
Excites the neuron
EPSP
via the influx of sodium ions for example
Action potentials
crucial to neuronal communication
(nerve impulse, spike, discharge)
“Information is encoded in the frequency of action potentials of individual neurons as well as in the distribution and number of neurons firing action potentials in a given nerve.”
Information flows via electrical signals (charged atoms)
An important method of conveying information over distances
Signals do not diminish over distance; they are signals of fixed size and duration
Occur when “changes” meet “threshold”
Membrane potential and action potential
membrane potential changes rapidly during an action potential