Week 11: Spikes, brains and the senses

Question 1

List the different parts of a neuron.

Answer 1

Dendrite
Nucleus
Axon
Nodes of Ranvier
Axon terminal
Schwann cell
Myelin sheath

Question 2

Sketch and label a neuron cell.

Answer 2

(62)

Question 3

What is the Myelin sheath?

Answer 3

A protective fatty substance that electrically insulates the axons of neurons.

Question 4

What is the function of the myelin sheath?

Answer 4

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.

Question 5

What is the effect of disease on the myelin sheath?

Answer 5

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.

Question 6

A summary sentence for myelin sheath.

Answer 6

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.

Question 7

What is a Schwann cell?

Answer 7

A type of glial cell. It plays a crucial role in the peripheral nervous system (PNS).

Question 8

What is the function of Schwann cells?

Answer 8

i) Produce the myelin sheath.

ii) Participate in nerve regeneration and repair.

iii) Contribute to the maintenance and nourishment of peripheral nerves.

Question 9

A summary of Schwann cells.

Answer 9

The primary function of Schwann cells is to provide insulation and support to peripheral nerve fibres, allowing for the efficient transmission of electrical signals.

Question 10

What is a dendrite?

Answer 10

Branched extension of a neuron that receives incoming signals from other neurons.

Question 11

What is an axon?

Answer 11

A long slender extension of a neuron that transmits electrical signals, including action potentials (AP’s), away from the cell body.

Question 12

What are action potenitals?

Answer 12

The rapid and brief electrical impulses responsible for long-distance communication.

They are all or nothing events, either occurring fully or not at all.

Question 13

What happens when an AP is triggered?

Answer 13

AP propagates down the axon without decreasing in strength until it reaches the axon terminals.

Question 14

How are APs generated?

Answer 14

Depolarisation
Repolarisation
Hyperpolarisation

Question 15

What is depolarisation?

Answer 15

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.

Question 16

What is repolarisation?

Answer 16

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.

Question 17

What is hyperpolarisation?

Answer 17

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.

Question 18

Sketch a graph of voltage against time for the action potential and label it.

Answer 18

(63)

Question 19

How does the AP vary across neuron regions?

Answer 19

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.

Question 20

What does closed time refer to when talking about ion channels?

Answer 20

The length of time that an ion channel remains in a closed state during its normal functioning within a neuron.

Question 21

Sketch a graph showing the relationship between number of events and closed time of an ion channel.

Answer 21

(65)

Question 22

What do ion channels do?

Answer 22

Ion channels undergo a series of conformational changes, transitioning between open and closed states.

Question 23

What does the Nernst equation do?

Answer 23

Relates the voltage across a membrane to the difference in ion concentration across the membrane.

Question 25

What is the equation for the flux across a semi-permeable membrane? How is it calculated?

Answer 25

It is a sum of the terms due to diffusion and the electric field. (67)

Question 26

What is the Boltzmann distribution and when can it be assumed?

Answer 26

Can be assumed in thermodynamic distribution. (68)

Question 27

Derive the diffusion coefficient from the Boltzmann distribution.

Answer 27

(69)

Question 28

From the equation for flux, derive the Nernst equation.

Answer 28

(70)

Question 29

Sketch a basic circuit model of a cell membrane.

Answer 29

(71)

Question 30

What equation for the electrical circuit model of a cell membrane does Kirchhoff's first law give?

Answer 30

(72)

Question 31

What equation for the electrical circuit model of a cell membrane does Kirchhoff's second law give?

Answer 31

(73)

Question 32

Sketch a circuit model for the total membrane potential.

Answer 32

(74)

Question 33

What does Kirchhoff's first law give for a total membrane potential?

Answer 33

(75)

Question 34

From Kirchhoff's first law, derive the resting potential for a total membrane.

Answer 34

(76)

Question 35

How do you calculate the resting potential of a cell?

Answer 35

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.

Question 36

What is the cable equation?

Answer 36

(77)

Question 37

What is the solution of the cable equation in the steady state?

Answer 37

(78)

Question 38

For the Hodgkin-Huxley equations, what does Kirchhoff's first law give?

Answer 38

(79)

Question 39

What are the three expressions used for the conductivity of each of the ion channels in the Hodgkin-Huxley equations?

Answer 39

(80)

Question 40

Sketch a graph showing how the time constants change with potential.

Answer 40

(81)

Question 41

Sketch a graph showing how the parameter value for the different ion channels, changes with potential.

Answer 41

(82)

Question 42

What are spikes? How are they described?

Answer 42

Spikes are travelling waves that are transmitted along an axon. A combination of the HH model with the cable equation allows for the description.

Question 43

What are Glia?

Answer 43

Glia are a group of non-neuronal cells that provide support and essential functions within the nervous system.

Question 44

What are the types of glial cells?

Answer 44

Astrocytes Oligodendrocytes Microglia Schwann cells

Question 45

What are Astrocytes?

Answer 45

Star-shaped, abundant in the CNS.

Question 46

What is the function of astrocytes?

Answer 46

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.

Question 47

What are oligodendrocytes?

Answer 47

Glial cells found in the CNS.

Question 48

What is the function of oligodendrocytes?

Answer 48

Producing and maintaining the myelin sheath. Each oligodendrocyte can myelinate multiple axons.

Question 49

What are the four basic types of neurons?

Answer 49

Bipolar Unipolar Multipolar Pyramidal

Question 50

Describe unipolar neurons.

Answer 50

Cells have a single process that extends from the cell body. This process divides into two branches: an axon and a dendritic process.

Question 51

Describe bipolar neurons.

Answer 51

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.

Question 52

Describe multipolar neurons.

Answer 52

Cells have multiple processes originating from the cell body, typically including one axon and multiple dendrites.

Question 53

Describe pyramidal neurons.

Answer 53

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.

Question 54

How can the process of encoding be separated?

Answer 54

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)))

Question 55

Sketch the a diagram representing the process of encoding.

Answer 55

(83)

Question 56

What is the simple model for neural encoding?

Answer 56

(84)

Question 57

Sketch a simple neural network.

Answer 57

(85)

Question 58

What are the three types of neural network architectures?

Answer 58

Pattern association network Autoassociation network Competitive network

Question 59

What is a pattern association network?

Answer 59

Associate a set of input patterns with corresponding output patterns (memory recall or pattern recognition).

Question 60

What is an Autoassociation network?

Answer 60

A type of neural network architecture used for unsupervised learning.

Question 61

What is a competitive network?

Answer 61

Neural network used for clustering and visualisation of high-dimensional data.

Question 62

For pattern association networks, what is the activation of a neuron, h, given by?

Answer 62

(86)

Question 63

What does the neuron activation equation for pattern association networks describe?

Answer 63

The process of memory recall.

Question 64

What is the Hebbian learning rule?

Answer 64

It is an update rule for the array of synaptic coupling strengths. (87)

Question 65

Sketch the non-linear relationship between voltage and firing rate.

Answer 65

(88)

Question 66

Why are the pattern association, autoassociation and competitive neural networks thought to be a reasonable description of naturally occurring brains?

Answer 66

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.