NATS 1860 Study Guide - Midterm Guide: Sodium Channel, Color Blindness, Receptive Field

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12 Feb 2013
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NATS 1860 2nd Semester Midterm Exam
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Brain Framework:
- We have sensory inputs (vision, hearing, and touch) that feed the inputs into
higher brain areas that make decisions, store them into memory and have
them function for other uses.
- In the case of light, light enters our eye, that then follows to the visual cortex,
that then goes into the planning and decisions and is interchangeable to the
working memory that can then be used for long term memory and emotions
or motor control
o The same process occurs with Ears in terms of the auditory cortex and
skin in terms of the somato cortex.
Sensory and Motor Maps:
- These are two-dimensional surfaces that are developed through electric
brain stimulation in order to figure out which locations do which actions
- These maps are all distorted in the sense that they represent how much
neural activity is coming or going from rather than the physical area of the
body
- Neurons are one nerve cell whereas some nerves typically have millions of
connections to other nerve cells
o Axons are the main part of the nerve cell that come out of the nerve
cell and connect at synapses with other cells.
Axons originate at axon hillocks which are small protrusions of
the soma
o Soma is the body of the nerve cell where axons come from and
dendrites enter (or leave)
In order to measure cell activity, you insert an electrode into
the soma
o Dendrites and axons have different functions from the nerve cells
o The Dendrites and Axons are how the nerve cell dispatches and
receives its information.
- Neuron membranes are made from two layers of lipid molecules
o One layer seeks water, and the other layer avoids water.
Large protein molecules form channels through the membrane.
Channels open and close to let particular ions through.
Spikes and Action Potential
- This occurs when there are the proper conditions for cells to release and
break through their chemical from outside of the cell to the inside of the cell
- This is done through an aspect of ionic charge and forces
o The diffusion force occurs when there is a higher to lower
concentration
o Once there is an equilibrium of negative and positive charges, the cell
returns to norms
- The two ions used for spikes are Na+ and K+ (Sodium and Potassium)
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o Na+ is outside of the cell
o K+ is inside of the cell
- Depolarization occurs when there is a higher amount of positive charge
within the cell than there is negative
o This occurs when the ionic channels of the cell open and allow the
outside Na+ to flow into the cell, causing a diffusion of cells and
sending out a spike (Action Potential)
The action potential occurs because of a created threshold.
A cell can fire a maximum of 300 spikes per second.
o When the cell reaches threshold, the Sodium channels open, allowing
sodium to enter the cell and depolarize it.
Afterwards, the channels for sodium close and the channels
that allow potassium to leave open. The reduction of potassium
allows the cell to balance out
Finally, the cell is ready to be fired again.
- Hyperpolarization occurs when the cell flows K+ out, however is not
replenished with enough Na+. When this occurs, there is no reaction in the
cell.
- Spikes are the same size, and the only thing that differs is how often the
spikes are fired, which depends on the amount of stimulation on that specific
cell.
o The spikes travel down from the axon to the synapses.
It starts from the bottom, travels through the axon, and goes
up.
o Each spike lasts about 1ms and cannot be fired for another 2ms
o Humans require myelin for proper function of spikes in the sense that
myelin helps spikes jump from one gap to another.
- Once the action potential goes through, it latches onto the dendrites or somas
of other bodies.
o Synapses contain neurotransmitters that signal our brain when the
action potential comes into contact.
GLU (Glutamate) is an important neurotransmitter that opens
sodium ion channels in order to open sodium ion channels
This causes EPSP (Excitatory Post-Synaptic Potential) in
which the spikes are generated at the cell body and
transferred up the axons.
EPSP adds electrodes
GABA (Gamma acid) is the important neurotransmitter that
opens potassium channels in the post-synaptic neuron
This allows to hyperpolarize the cell and causes IPSP
(Inhibitory Post-Synaptic Potential)
IPSPs subtract from ESPS
If EPSP subtracted by IPSP still results in the depolarization to
threshold (more positive than negative in the cell) a spike will
be fired
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o Spikes cause calcium to flow out of the synapses and send signals to
the brain
- Excitation and Inhibition is present everywhere in the brain where one cell
re-excites another cell and this relies on constant cooperation within the
brain
Photoreceptors and the Retina
- The blind spot is where the nerve exits the retina is at the back of the eye
and is organized backwards.
- Neurons get stimulated by light:
o Photoreceptors are specialized neurons that have proteins in their
membranes (photopigments) that evolved to capture photons of light
in such wavelength that we can see
- We have Rods and Cones:
o Rods are specialized for night vision in the sense that they’re sensitive
to light, but do not code for colour
o Cones are used for seeing daytime vision in term of brighter intense
sensitivity to light.
50% of cones are red
45% of cones are green
5% of cones are blue
o Colour blindness occurs when there is a certain amount of cones
defective or missing
Largely females are responsible for transferring colour
blindness and males more commonly have colour blindness
(since CB is a hereditary disorder with the X)
People with colour blindness aren’t blind to colour, they simply
cannot discriminate against them.
- M and P Ganglion Cells
o These cells deliver all of their information through a chiasmic method
right side of the primary visual cortex from the left side of the
receptive field, and vice cersa
o These are the photoreceptors that connect to other cells. They send
their axons out of the retina and into the brain.
o M cells are for motion, they have a larger receptive field, have bigger
cells, and respond to a larger area on the retina
They respond to the intensity of light, but do not carry colour
information. They’re active on both rods and cones and can
carry information both during the day and night
M cells have low resolution, but have a higher response rate.
This is because we need faster response to motion than
to details to avoid predators
o P cells (Pattern) have very small receptive fields, are usually smaller
than M cells, but have very high detail in imprinting pagers.
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