Brains, Neurons and Neural Coding I

Question 1

What are the three promary brain vesicles from embryonic develoment? What are the 6 major divisions of the adult CNS do we get from these?

Answer 1

Forebrain: Cerebral cortex, thalamus

Midbrain: midbrain

Hindbrain: Cerebellum, pons, medulla

Question 2

What is neural processing dependent on?

Answer 2

Neural coding are forms of patterns of electrical activity where individual action potential does not differ but coding is based on space and time

Question 3

What are the 2 neural codings?

Answer 3

Space and time

Question 4

What is neural coding in terms of space?

Answer 4

They are nerual circuits which have speciifc synaptic connections bewteen nerve cells from circuits/networks

• 86billion neurons in the human brain, up to 10,000 synaptic contacts per neuron

Question 5

What is neural coding in terms of time?

Answer 5

The time taken for spike trains

Question 6

What are the two types of time codes?

Answer 6

• Rate code: the average spike frequency | number of spikes over time
• Temporal code: the precise timing of spikes is important

Question 7

What is the conduction of spikes?

Answer 7

range: <1m`s to >100ms
majority <10ms

Question 8

What is the generation of spikes?

Answer 8

Varies with cell type and species but the fastest action potentials can take place within 1-2ms

Question 9

What are the different ways to record electrical activity of the nervous system?

Answer 9

• EEG
• ECoG
• Extracellular recording
• Intracellualr recording

Question 10

How do EEGs work?

Answer 10

• Electrodes are used to amplify and record small voltage changes from the surface of the head
• Can be done prior to neurosurgery

Question 11

How do ECoGs work?

Answer 11

Electrodes attached directly on cortical surface and records local fields potentials due to summed neural activity

Invasive!!

Question 12

How does extracellular recording work?

Answer 12

Microelectrodes are inserted into extracellular space. APs in nearby neurons generate small extracellular currents that can be amplified and picked up as spikes.

Question 13

How does intracellular recording work?

Answer 13

Microelectrodes are inserted through the cell membrane and records voltage difference between intra and extracellular space

Question 14

Which of the 4 methods of recording has highest resolution?

Answer 14

Intracellular recording, then extra, then ECoG and EEG has lowest resolution

Question 15

What is Event Related Potentials (ERP)?

Answer 15

Using EEGs to study responses to sensory stimuli

since the signal from a single electrode due to acticity of thousands to millions of neurons, any response which is lost in noise may be unrelated to the stimulus

• If stimulus is repeated multiple times and averaged random activity cancels out so the activity observed is due to the stimulus.

Question 16

Describe the fundamental divisions of the vertebrae CNS:

Answer 16

During embryonic development, neural tube subdivides into the primary brain vesicles (Forebrain, Midbrain, Hindbrain)
Which divide into the secondary brain vesicles (telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon)
And then the structures of the adult brain

FB – Telencephalon – Cerebral cortex

FB – Diencephalon – CC + Thalamus

MB – Mesencephalon – Pituitary

HB – Metencephalon – Cerebellum + pons

HB – Myelencephalon – Medulla

Question 17

Define the neural code:

Answer 17

Hypothetical relationship between stimulus and response from a neuron or group of neurons and the relationship of electrical activity of neurons in group

Question 18

Describe the importance of having the same action potential:

Answer 18

Individual AP do not differ from each other = can’t have different AP for different information

The code is based on space = which neurons and the time = precise time sequence of series of spikes or spike trains

Question 19

What is a neural circuit – give an example:

Answer 19

Specific synaptic connections between nerve cells that form networks or circuits

An example is reciprocal inhibition = generates alternating rhythmic bursts of activity

Question 20

Describe how the neural code is measured:

Answer 20

Measured in spike trains = average number of spikes between a short interval, t + t+Δt divided by duration of the interval

Question 21

Define the rate code:

Answer 21

Average spike frequency – average number of spikes over some integration time

Question 22

Define the temporal code:

Answer 22

When precise spike timing (within a spike train) or high frequency firing rate fluctuations are found to carry information

The neural code is often identified as the temporal code

Question 23

Define conduction in terms of nerves with range of and conduction of most nerves:

Answer 23

How quickly APs travel along nerves

Range: <1 ms-1 to >100 ms-1,
majority <10 ms-1

Question 24

Describe the implication of generation on maximum firing rate

Answer 24

Varies with cell type/species but fastest AP can take place in 2ms (spike + absolute refractory period)

Implies a maximum firing rate of 500 spikes s-1

Question 25

Describe the experiment Helmholtz conducted to investigate the speed of thought and its limitation:

Answer 25

Mid 19thC, elements were in place for neuroscientific study of perception Helmholtz set out to demonstrate that nerves conduct signals at finite velocity Used crude reaction time technique, so results variable and not very accurate Answer: 10s of m/s (seemed shockingly slow)

Question 26

Describe the area that has most of photoreceptors:

Answer 26

Distributed throughout the retina, greater density in area centralis = acute vision

Question 27

Briefly describe the visual pathway:

Answer 27

Begins with the retina, outermost layer = photoreceptors, dendritic processes of rod and cone neurons Excitation by light – bipolar neurons (second neuron in visual pathway synapsed with PR) interact w/third neuron of visual pathway = ganglion neurons RGC axons coalesce to form optic disc + course in optic nerve At optic chiasm, axons originating from medial (nasal) retina decussate and continue as contralateral optic tract Axons from lateral (temporal) retina remain ipsilateral (do not cross at the chiasm) and course in the ipsilateral optic tract

Question 28

Describe horizontal cells and their role:

Answer 28

Laterally interconnecting neurons with cell bodies in inner nuclear layer of retina of vertebrae eyes Increase contrast via lateral inhibition and adapting both to bright and dim light conditions Important for the antagonistic center-surround property of receptive fields of many types of RGC