Brains, neurons and neural codes

Question 1

Describe the fundamental divisions of the vertebrae CNS:

Answer 1

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 2

Define the neural code:

Answer 2

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

Question 3

Describe the importance of having the same action potential:

Answer 3

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 4

What is a neural circuit – give an example:

Answer 4

Specific synaptic connections between nerve cells that form networks or circuits

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

Question 5

Describe how the neural code is measured:

Answer 5

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

Question 6

Define the rate code:

Answer 6

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

Question 7

Define the temporal code:

Answer 7

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 8

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

Answer 8

How quickly APs travel along nerves

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

Question 9

Describe the implication of generation on maximum firing rate

Answer 9

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 10

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

Answer 10

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 11

Describe the area that has most of photoreceptors:

Answer 11

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

Question 12

Briefly describe the visual pathway:

Answer 12

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 13

Describe horizontal cells and their role:

Answer 13

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