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Summary Integrative Neuroscience, second year Biology (English)

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Rijksuniversiteit Groningen (RuG)

This is a summary for the Integrative Neuroscience course in the second year of the Biology program provided by the RuG. In this summary the entire course is explained in such a way that makes the material easy to understand. I passed this course using only my summary, and I hope you will too!

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Integrative neuroscience
1. Chemical senses:
For survival, the detection of environmental cues is very important. This is done with
multiple receptors, among which are the cells sensitive to chemicals, called
chemoreceptors.

Taste and smell are examples of the detection of environmental chemicals. They help us
distinct between new nutrient sources and potential toxins.

There are also chemoreceptors in the internal milieu. Each cell has the ability to detect
chemical substances. The detection of internal stressors are essential for preserving the
internal homeostasis.

Wilder Penfield:
This is a guy. A pioneering brain surgeon to be exact. He mapped the motor cortex using a
mild electric current. While he was operating on epileptic patients, Penfield applied electric
currents to the surface of the patients brain in order to find problem areas. Since, his
patients were awake (because then brain cannot feel pain), they could tell Penfield what
they experienced. He found that some areas trigger smell, taste and sometimes whole
memory sequences.
With this information, he was able to map the somatosensory and motor cortex.

Somatosensory cortex:
This is the area where the reception of touch perception takes place.

This is a physical stimuli of neutral substances, that results in the perception of touch,
pressure, pain, taste and smell. 40% of all sensation come from the mouth and the face.

Tasting:
In the mouth, there are 5 basic tastes; sweetness, saltiness, sourness, bitterness and
umami. A bitter taste is caused by the molecule; phenylthiocarbamide (PTC). Not
everyone has receptors to taste this, and thus some people can and others cannot taste
PTC.
When you eat something, it is a bundle of all different types of flavors. It is the pattern of
flavors that the brain can recognize, rather than the a single labeled line. factors like,
temperature, texture and moisture also play a big part in tasting.

Not only that, but memory can also determine whether you like or dislike something. If you
ate something and got very sick afterwards, you can develop a severe dislike for that kind
of food. Even though, the food may not have been the causation for the sickness.

Less commonly known, is that one can also taste fat. You can taste fat on the CD36, this
is a scavenger receptor. It binds to collagen, LDL, phospholipids and long-chain fatty
acids. A snp (single nucleotide polymorphism) in the CD36 can lead to a preference of
high fat foods, which increases the risk towards obesity (the joke is that I made the word
obesity in bold/fat letters).

On the tongue, there are different regions that are able to taste different flavors. The
tongue consists of many papillae, also known as taste buds. One taste bud is a cluster of
taste cells, with gustatory afferent axons and their synapses.
Page 1

,Most receptor cells (±90%) react to 2 or more flavors.
Different receptors acquire different action potentials, with
different flavors. Where one might create a higher action
potential for sweetness, it might create a low action potential
for bitterness. This way you are able to differentiate between
flavors.

Taste transduction:
This is done by 3 cell types; with either ion channels or G-
protein coupled receptors.

- Type I: glial like cells. The ion channels, can detect saltiness by the passage of Na+
through the channels, causing membrane depolarization.

- Type II: receptor cells. The G-protein coupled receptor, can detect sweetness and
bitterness through the binding to the GPCR. This activates phospholipase, IP3 and
releases Ca2+, which leads to the release of the transmitter.

- Type III: presynaptic cells. It can detect sourness by the passage of H+ through the
channels, and also the blockage of the K+ channel.

The projections from the taste buds of the tongue travel via 3 different cranial nerves;
1. The facial nerve
2. Glossopharylgael nerve
3. Vagus nerve
It travels to the brain stem, the signal comes in to the nucleus of the solitary tract (NST).
From which it travels to the ventral posterial nucleus, and finally to the primary gustatory
cortex.

Smelling:
Smell is detected by the cilia of olfactory nerves in the layer of mucus in the nose. The
signal travels to the olfactory receptor cells, and end in the olfactory nerves that lead to
the glomerulus in the olfactory bulb. Then, via a second-order olfactory neuron, the signal
travels to the brain.

To terminate the response, the odor first has to diffuse away. Then cAMP activates a stop
mechanism.

Each olfactory cell selectively expresses one olfactory receptor protein (ORP), which is
able to discriminate odors. Each ORP can bind to multiple odorants.
Same as for taste, smell also works by the brain recognizing a pattern, rather than one
distinct smell.
Each glomerulus contains synapses from olfactory receptor neurons with the same ORPs.
(Segregation is a bitch)

As you get older, you sense of smell decreases. And with this, your sense of taste. On a
less fun note, people who lose their sense of smell, more often become depressed, then
then who become blind.

Page 2

,Funfact; the olfactory cortex is the only sensory system that is directly bound to the
temporal lobe and limbic system, which are important for memory and emotion.

Vomeronasal organ (VNO):
This is an organ that secretes pheromones. A pheromone is a volatile chemical substance
originating from the body. It is involved in aggression and sexual behavior.

In mice, the presence of a female increases the testosterone production, because of the
pheromones secreted by said female.

Page 3

, 2. The eye:
You use this to see. The bundle of light that reaches
your eyes, is refracted by the lens to create a focal
point on the retina.

There is a blind spot where the optic nerves leaves
the eye. This area contain 0 photoreceptors.

People who are near-sighted, create a focal point
before the retina.
People who are far-sighted create a focal point
behind the retina.
This explains why they are not able to see clearly.

Pupillary constriction can be caused when a bright light is shone at one of the eyes. Then
both pupils constrict. This means that it is consensual and happens in the brainstem.

There is a limitation to whatever you can see. For example, if you look at the stars at night,
you might not be able to see some stars. Since their light reflexs directly between the
photoreceptor cells on the retina.

Retina:
This is the part of the eye that is sensitive to light.
The light comes in on the photoreceptors, it travels through the bipolar cells. Finally,
ganglion cells provide the output of the retina and travels to the brain.

So, light has to travel through these layers of cells, except in the fovea. The fovea only
consists of cones. This creates the focus point on your sight and gives the most clear
image.

You have two photoreceptors; cones and rods
- Cones; are active under photopic conditions. They have 3 different opsin; erythrolabe
detects red, chlorolabe detects green, cyanolabe detects blue.
- Rods; are active under scotopic conditions. They are 1000x more sensitive than cones.

The density of cones decrease the further you move from the fovea, and more rods are
present. So, in an environment with a lower light intensity, it is more sensible look to the
side, and not use the fovea directly.

Phototransduction:
- In rods; Light comes in on a photopigment, this causes a change in protein conformation
(creating of rhodopsin). This allows the G-coupled protein to bind to GTP. This decreases
the second messenger (cGMP) response, closes the sodium channel and decreases the
conductance of Na+.

Page 4

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