1.2 (Synapses) Flashcards
How do signals get from an axon to a dendrite if they don’t touch
Synapses
If action potentials are all the same, what about synapses?
In discussing the action potential we mentioned that it is a largely stereo- typical signal, the action potentials from a neuron all have roughly the same amplitude and shape. The synapses, in contrast, are diverse. They have different strengths, which can change over time. Beyond these variations in strength, synapses can have different dynamics, with differences in the time course of how the synapse responds to a spike, or in how the synapse responds to spikes coming in quick succession.
What are gap junctions and which animals are they found
Fast and direct transfer: The complicated and variable behaviours of synapses are possible because synapses do not simply connect the axon to the dendrite, they are not simply holes or pores through which ions flow. In fact, there are synapses, called gap junctions that are like that, these gap junctions are the only synapses in some simple creatures like jellyfish and are found in the mammalian brain.
What is a pre-synaptic axon
A pre-synaptic axon is the part of a neuron that releases neurotransmitters into the synaptic cleft to transmit a signal to the next neuron (the post-synaptic cell). It is the axon terminal of the sending neuron at a synapse, initiating communication with the receiving neuron.
What is a post-synaptic dendrite
A post-synaptic dendrite is the part of a receiving neuron that contains receptors to detect and respond to neurotransmitters released by the pre-synaptic axon. It receives signals across the synapse, allowing information to pass from one neuron to the next.
What are chemical synapses
Chemical synapses are junctions between neurons where signals are transmitted using neurotransmitters. In these synapses, the pre-synaptic neuron releases neurotransmitters into the synaptic cleft, which then bind to receptors on the post-synaptic neuron, initiating an electrical response. This process allows controlled, directional communication between neurons.
What is the gap between the dendrite and axon called
Synaptic cleft
Charge doesn’t flow directly from dendrite to axon, describe the synaptic process.
Importantly, electrical charge does not flow directly from dendrite to axon. When a spike arrives at the synapse it triggers a chain of events. The sud- den change in voltage opens channels in the membrane of the synapse that allow calcium to flow into the terminal bouton, the part of the synapse on the axon side of the cleft (it is an amazing property of neurons that they contain ion-specific channels). Calcium flows into the synapses and, by way of com- plicated chemical reactions, this causes some little (≈40 nm) membrane- bound spheres called vesicles to fuse with the wall of the cleft and burst, releasing specialised molecules called neurotransmitters into the cleft.
Draw a synapse and label the parts
What is the terminal bouton
The terminal bouton is the end of a neuron’s axon that releases neurotransmitters into the synapse to communicate with a post-synaptic cell.
What are vesicles
Vesicles are small membrane-bound sacs within cells that store and transport molecules, such as neurotransmitters, for release into the synapse during neuronal communication.
What are neurotransmitters
Neurotransmitters are chemical messengers released by neurons to transmit signals across synapses to other neurons, muscles, or glands, enabling communication within the nervous system.
What is the role of neurotransmitters, and what is the difference between the excitatory and inhibitory effect.
These neurotransmitters, in turn, bind with channels (“receptors”) on the opposite face of the cleft, that is, with channels in the membrane of the post- synaptic dendrite. These channels then open in response to binding with the neurotransmitter. Depending on the type of synapse, they either allow ions to flow into, or out of, the dendrite, either increasing its voltage, or de- creasing it. As a crude first approximation, we might summarise the im- mediate effect of a synapse as either excitatory: increasing the voltage of the post-synaptic neurons, or inhibitory: decreasing it.
What is the flow of ions for exicatory and inhibitory neurotransmitters
Each type of synapse has different channels in the dendritic face of the cleft and different neurotransmitters that bind to these channels. In an excita- tory synapses these channels allow sodium ions into the cell; Since sodium ions are positive ions this increases the charge inside the cell. Some excita- tory channels may also allow influx of positively charged calcium ions. In an inhibitory synapse the channels either allow chlorine ions into the den- drite (chlorine ions are negative so this decreases the voltage), or they allow potassium ions out of the cell (potassium ions are positive, so this decreases the voltage).
What is the difference between ligand-gated channels and voltage-gated channels
Ion channels that open because they have bonded with a neurotransmitter are called ligand-gated channels; a ligand is a molecule that binds to things. These channels act as gates, sometimes allowing ions through and sometimes not and they do so depending on whether or not they are bound to a ligand. This is in contrast with the voltage-gated channels that open and close depending on voltage. We will see later that voltage gated channels are im- portant in understanding how spiking happens.
What are reuptake pumps
Reuptake pumps are proteins in neuron membranes that retrieve neurotransmitters from the synaptic cleft back into the pre-synaptic cell, helping to regulate signal duration and recycle neurotransmitters.
What is a EPSP and IPSP. Draw it
What is the tipping point (voltage) for inbound PSPs, and which part of the cell controls this
However, if lots of PSPs arrive at around the same time, the voltage in the soma will increase un- til it reaches a tipping point, around -55 mV is typical value of where this tipping point is. At the tipping point the opening of voltage-gated channels will cause a spike, usually at the point the axon joins the soma, and this spike will head off down the axon
Will a single EPSP, cause the soma to release an action potential?
No (need loads inbound)
Physically, describe the difference between a single axon and dentrite
Dendrites are typically shorter than axons and thicker, so this conductance allows the change in voltage at the dendrite to propagate in to the soma
Do dentrites contain voltage gated channels?
In general dendrites lack the voltage-gated channels needed for action potentials and the PSPs in dendrites propagate passively towards the axon.
Where are voltage gated channels found in the neuron
Voltage-gated channels are primarily found along the axon, especially at the axon hillock and nodes of Ranvier. These locations enable the initiation and rapid propagation of action potentials along the axon toward the terminal bouton.
What is the role of voltage-gated channels
Voltage-gated channels regulate ion flow in response to changes in membrane potential, enabling the initiation and propagation of action potentials in neurons.
