Week 11: Spikes, brains and the senses Flashcards
List the different parts of a neuron.
Dendrite
Nucleus
Axon
Nodes of Ranvier
Axon terminal
Schwann cell
Myelin sheath
Sketch and label a neuron cell.
(62)
What is the Myelin sheath?
A protective fatty substance that electrically insulates the axons of neurons.
What is the function of the myelin sheath?
i) Increases the speed and efficiency of electrical impulses along the axons.
ii) Provides structural support to the axon helping maintain its integrity and preventing damage or degeneration.
What is the effect of disease on the myelin sheath?
In diseases, damaged myelin leads to impaired nerve function.
Loss of myelin disrupts the normal conduction of electrical impulses causing a range of neurological symptoms.
A summary sentence for myelin sheath.
Myelin sheath is a critical component of the nervous system that enhances the conduction speed of nerve impulses and provides protection and support to the axons of neurons.
What is a Schwann cell?
A type of glial cell. It plays a crucial role in the peripheral nervous system (PNS).
What is the function of Schwann cells?
i) Produce the myelin sheath.
ii) Participate in nerve regeneration and repair.
iii) Contribute to the maintenance and nourishment of peripheral nerves.
A summary of Schwann cells.
The primary function of Schwann cells is to provide insulation and support to peripheral nerve fibres, allowing for the efficient transmission of electrical signals.
What is a dendrite?
Branched extension of a neuron that receives incoming signals from other neurons.
What is an axon?
A long slender extension of a neuron that transmits electrical signals, including action potentials (AP’s), away from the cell body.
What are action potenitals?
The rapid and brief electrical impulses responsible for long-distance communication.
They are all or nothing events, either occurring fully or not at all.
What happens when an AP is triggered?
AP propagates down the axon without decreasing in strength until it reaches the axon terminals.
How are APs generated?
Depolarisation
Repolarisation
Hyperpolarisation
What is depolarisation?
A stimulus causes the axon’s membrane potential to become more positive.
This rapid change in membrane potential triggers the opening of voltage-gated sodium channels.
This leads to an influx of sodium ions into the axon.
The influx of positive ions further depolarises the membrane, creating a positive feedback loop and results in the rising phase of the action potential.
What is repolarisation?
After reaching its peak, the membrane potential rapidly repolarises.
Voltage-gated potassium channels open, allowing potassium ions to exit the axon.
This brings the membrane potential back to its resting state and contributes to the falling phase of the action potential.
What is hyperpolarisation?
Following repolarisation, there is a brief period of hyperpolarisation during which the membrane potential temporarily becomes more negative than the resting potential.
It is caused by the prolonged opening of potassium channels and serves a refractory period, preventing the immediate generation of another action potential.
Sketch a graph of voltage against time for the action potential and label it.
(63)
How does the AP vary across neuron regions?
The shape of an AP is generally consistent across different regions of a neuron, including the cell body, dendrites and axon, but can be slightly varied depending on the specific location within the neuron.
What does closed time refer to when talking about ion channels?
The length of time that an ion channel remains in a closed state during its normal functioning within a neuron.
Sketch a graph showing the relationship between number of events and closed time of an ion channel.
(65)
What do ion channels do?
Ion channels undergo a series of conformational changes, transitioning between open and closed states.
What does the Nernst equation do?
Relates the voltage across a membrane to the difference in ion concentration across the membrane.
What is the equation for the flux across a semi-permeable membrane?
How is it calculated?
It is a sum of the terms due to diffusion and the electric field.
(67)
What is the Boltzmann distribution and when can it be assumed?
Can be assumed in thermodynamic distribution.
(68)
Derive the diffusion coefficient from the Boltzmann distribution.
(69)
From the equation for flux, derive the Nernst equation.
(70)
Sketch a basic circuit model of a cell membrane.
(71)
What equation for the electrical circuit model of a cell membrane does Kirchhoff’s first law give?
(72)
What equation for the electrical circuit model of a cell membrane does Kirchhoff’s second law give?
(73)
Sketch a circuit model for the total membrane potential.
(74)
What does Kirchhoff’s first law give for a total membrane potential?
(75)
From Kirchhoff’s first law, derive the resting potential for a total membrane.
(76)
How do you calculate the resting potential of a cell?
The resting potential of a cell is the sum of the Nernst potentials for all of the ions in the cell’s environment weighted by the conductivities of the cell membrane and normalised by the sum of the conductances.
What is the cable equation?
(77)
What is the solution of the cable equation in the steady state?
(78)
For the Hodgkin-Huxley equations, what does Kirchhoff’s first law give?
(79)
What are the three expressions used for the conductivity of each of the ion channels in the Hodgkin-Huxley equations?
(80)
Sketch a graph showing how the time constants change with potential.
(81)
Sketch a graph showing how the parameter value for the different ion channels, changes with potential.
(82)
What are spikes? How are they described?
Spikes are travelling waves that are transmitted along an axon.
A combination of the HH model with the cable equation allows for the description.
What are Glia?
Glia are a group of non-neuronal cells that provide support and essential functions within the nervous system.
What are the types of glial cells?
Astrocytes
Oligodendrocytes
Microglia
Schwann cells
What are Astrocytes?
Star-shaped, abundant in the CNS.
What is the function of astrocytes?
Provides structural support to neurons, regulating the extracellular environment, maintaining ion balance and participating in the formation and regulation of synapses.
Astrocytes also play a role in regulating blood flow to the brain and are involved in processes like synaptic plasticity and the blood-brain barrier.
What are oligodendrocytes?
Glial cells found in the CNS.
What is the function of oligodendrocytes?
Producing and maintaining the myelin sheath.
Each oligodendrocyte can myelinate multiple axons.
What are the four basic types of neurons?
Bipolar
Unipolar
Multipolar
Pyramidal
Describe unipolar neurons.
Cells have a single process that extends from the cell body.
This process divides into two branches: an axon and a dendritic process.
Describe bipolar neurons.
Cells have two distinct processes extending from the cell body: one axon and one dendrite, which are located at opposite ends of the cell body.
Describe multipolar neurons.
Cells have multiple processes originating from the cell body, typically including one axon and multiple dendrites.
Describe pyramidal neurons.
A specific type of multipolar neuron found in the cerebral cortex, particularly in the neocortex.
They are named for their characteristic triangular/pyramidal shape of the cell body.
How can the process of encoding be separated?
Into two consecutive functions:
-The creation of the neuronal current (J(x(t)))
-The creation of spikes from the neuronal current G(J(x(t)))
Sketch the a diagram representing the process of encoding.
(83)
What is the simple model for neural encoding?
(84)
Sketch a simple neural network.
(85)
What are the three types of neural network architectures?
Pattern association network
Autoassociation network
Competitive network
What is a pattern association network?
Associate a set of input patterns with corresponding output patterns (memory recall or pattern recognition).
What is an Autoassociation network?
A type of neural network architecture used for unsupervised learning.
What is a competitive network?
Neural network used for clustering and visualisation of high-dimensional data.
For pattern association networks, what is the activation of a neuron, h, given by?
(86)
What does the neuron activation equation for pattern association networks describe?
The process of memory recall.
What is the Hebbian learning rule?
It is an update rule for the array of synaptic coupling strengths.
(87)
Sketch the non-linear relationship between voltage and firing rate.
(88)
Why are the pattern association, autoassociation and competitive neural networks thought to be a reasonable description of naturally occurring brains?
All of these models use local learning rules (only small parts of the network need to be activated for a memory) and are thus efficient and biologically relevant.
Some popular neural network models in computer science (e.g. perceptrons) are thought to be less biologically relevant for this reason.
