Neuronal Networks and Behaviour
Lecture 1 : Introduction
The brain has specific area’s for specific tasks. These area’s are able to transmit and receive information
through neurons. Neurons have chemical electrical signalling, that make them able to process information.
The human brain has 1011 neurons, each consisting of 1000 – 10 000 synapses.
Communication between neurons happens through synaptic transmission.
Most of the cells in the cortex are pyramidal neurons. They have many dendrites and axons to transmit
information. The dendrite has many spikes that are able to receive information. The information is given by
axons, that release neurontransmitters that connect to synapses. There is a great range of axons that cause
different reactions. For instance the excitatory or inhibitory axons.
- AP arrives at the axon, which depolarizes it’s membrane.
- Depolarization opens voltage-gated Ca2+-channels: calcium ions flow in
- Neurotransmitter release is triggered: they bind to post synaptic receptors
- Depolarization/hyperpolarization of post synapse
o Depolarization: travels to cell body, which causes excitatory postsynaptic potential (EPSP)
▪ NT: glutamate, receptors: AMPA, NMDA
o Inhibitory causes hyperpolarization, inhibitory postsynaptic potential (IPSP)
▪ NT: GABA, receptor: GABAergic receptors
Neurons can generate action potentials with this communication. APs are generated through the build-up of
EPSPs. APs are generated at the Axon Initial Segment of the neuron. APs are different from EPSPs in several
ways: APs are all-or-nothing events where EPSPs can be graded, APs are extremely short.
Frequency of AP firing conveys the signal of the neurons. Drugs can bind to receptors and simulate action of
neurotransmitter.
General plan of sensory systems
Components that are needed to perceive the outside world:
- Receiver and translator of information:
o Sensory receptors/axons receive information and translate energy of the stimulus into
electrical signals
- Transporter of information:
o axons transport the signal to the series of relay nuclei
▪ Cell bodies of skin neurons are located in dorsal root ganglia, close to the spine.
However their long axons stretch out to the skin where they are able receive the
information. They then transport the information to the cell body.
- Integrator and processor of information:
o interneurons and local circuitry in nuclei process the signal. The information ultimately
reaches the brain.
- Giver of output (this is not discussed in the course.
Reception sites of sensory systems
Sensory receptors translate the energy of the stimulus into electrical signals, four attributes are important in
the receptors: modality, location, intensity and timing.
- Modality: the type of stimulus. These potentials are summed up to either form or not form an AP.
Non-sensory neurons receive this information from axons of other neurons. Receptors in sensory
neurons work differently. Each sensory system has a specific receptor to receive information, for
instance in the visual system receptors can receive light.
Types of sensory receptors:
o Mechanical (touch and proprioception, hearing, balance): physical stretch or tension on the
receptor deforms the membrane and opens the channels.
o Chemical (pain, itch, smell, taste): binding of a chemical to the receptor
o Photoreceptors (vision): photoreceptor in retina change in conformation of a photosensitive
protein
o Thermal (temperature)
Receptor activation results in the change of postsynaptic potential.
, There are several different mechanoreceptors in the skin
for touch: Merkel cells, Ruffini corpuscle, Pacinian corpuscle,
Meissner corpuscle. Each receptor receives different information.
This is seen in the figure: the finger moves across braille and the
receptors are active at a different moment.
Proprioception: sense of the position of muscles and joints
of the body. They are axons wrapped around different structures,
just like the mechanoreceptors in the skin. When wrapped around a
muscle, they can perceive the muscles stretch.
- Location of receptors: what is the position of the stimulus
relative to the body?
o Topographical arrangement of neuronal receptive
fields: dermatomes devide the body in different
recepteive fields, that all receive and perceive
information of the body in a different area of the
spinal chord and brain.
▪ Retinatopy in retina, tonotopy in cochlea, gustotopy in gustatory
cortex.
o Spatial resolution is determined by the size of the receptive field and density of receptors.
▪ Fingertips are very sensitive to small changes, where the wrist has larger receptive
fields and is not as sensitive. This is found in all sensory systems.
- Intensity of the stimulus: how strong is the stimulus (touch is becoming stronger)?
o Sensory thershold is determined by the sensitivity of the receptors. How much stimulation is
needed to trigger APs
o Change in energy of the stimulus:
▪ Change in membrane potential
▪ Translation into digital code of APs.
- Timing of the stimulus: how does the stimulus change in time?
o Slowly adapting responses: changes in stimulus are coded in frequency
o Rapidly adapting responses: start and end of the stimulus are most important,
react to either the start or end of the stimulus. Most of the neurons are like this.
▪ Adaptation: a constant stimulus fades from consiousness
o Sensory systems are able to detecet contrasts and motion
Transport of the information
Axons transport the signal to the series of relay nuclei. All sensory systems have
complicated pathways.
- Multiple parallel pathways increase the speed of processing
o Different receptors for touch work together
- Topograpical representation is maintained (upper limbs have lateral position
in dorsal column, lower limbs are positioned more medial)
- Cross over of all sensory information to the opposite hemisphere
(decussation), this happens mostly in the medula.
- Feedback connections/descending projections: predictions of how the reality
is, is done by these feedback connections.
Processing of information
Interneurons and local circuitry in nuclei process the signal.
- Before reaching the cortex, all information passes
through the thalamus. This is a major relay station
for sensory and motor information. The thalamus is
organised neatly, it has a y-shaped division into
anterior, lateral and medial thalamus. It projects to
the middle layers of the cortex.
, - Information is projected to primary sensory cortices, yellow
coloured.
The cortex a stereotypical structure:
Columns: cells are organised in functional columns, one cell has
information from different locations from for instance the skin.
Layers: six layers, all have different function. Most information
from thalamus enters in layer IV. This information then spreads
through the other layers.
Topographical representation is maintained in the sensory cortex, seen in the
example of touch. This is also for different functional columns. So slowly and
rapidly adapting neurons in one of the fingers all have their own presentation in
the functional columns.
This is for instance also seen in the Ocular Dominance Columns!
Less than ¼ of the human cortex contains projection area’s, the rest is involved
with language, reasoning, moral thoughts et cetera.
Lecture 2: The Visual System – part 1
Reception of the visual system
Photons enter the eye and will be converted into neural impulse in the retina. The information goes through
the thalamus and is projected on the primary visual cortex. Eventually the information will go to other more
specific area’s of the brain. The eye focusses and adapts the incoming light and it inverts the projection of the
image. Wertheimer was one of the first ones to study the visual system. He found Gestalt psychology:
- What we see represents the properties of objects and the organization of sensations by the brain.
- The brain makes assumptions about what is seen in the world. It makes expectations that seem to
derive in part from experience and in part from the built-in neural wiring for vision.
Vision is based on interrelationship: relationships between the components of the image can be recognized in
different images. It works like a melody. When a song is played, we can recognize a song when sung in a
different note, because the interrelationship between the notes is recognized.
The eye cannot see both the vase and the two faces at the same time. The eye can only focus on one object
at the time and regards other information background noise.
In the picture on the left, a pattern cannot really be detected by the brain. However, the
occluded object in the backround is now constructed as a visual image accordingly, the letter B
arrises. The integration of distinctive objects into a coherent visual scene is aided by another
central fact of vision: closer structures cover those that are more distant.
Muller-Lyer illusion: assumptions about visual objects are also based on the surroundings of the object.
The size of the object is wrongfully detected by the brain because of the shape of the surroundings.
The perceived size of the object depends on other objects in the visual field. We judge the size of an
object by comparing it to its immediate surroundings. This is the illusion in the room, where two people differ
greatly in size.
The visual image we see is already enhanced and adapted by the neuron circuitry in retina, thalamus and
cortex. Our visual system is constantly making assumptions about the outside worlds based on experience and
build in neuronal wiring, the modulating infleunce of descending projections.
, The human eye
The retina is the most important part of the eye, it’s where the ligth is collected and eventually sent
off to the brain. The retina contains a retinotopic map of the visual field. At the back of the retina,
photoreceptors in rods and cones are activated by the light. A chemical reaction activates bipolar
cells, ganglian cells and eventually information is sent to the visual cortex via the thalamus. In the
blind spot all the information is gathered and clustered in the optic
nerve. This part of the retina is completely blind.
Rods and cones differ in size and shape and contain photoreceptors
that are activated by light. The cells have an inner segement
containing the nucleus and biosynthetic machinery and an outer
segment containing light-transducing apparatus. This apparatus
consist of membraneous disks, which have lightabsorbing
photopigments.
Pigment epithelium: removal of disk and regeneration of photopigment. Verder verwerken met
aantekingen Ster, Marit.
The two cells are specialized in different kinds of light.
- Rods
o Very good in detecting (small amounts of) light
o Distributed mostly in periphery of the retina
o Many rods converge on one bipolar cell, so the vision is less
specific than that of the cones
o Have longer responses
- Cones
o Detect large amount of light, day
o Distributed in fovea: small spot on retina, densely packed with
cones. Very little distributed in the periphery of the retina
o Responsible for visual acuity and colour: they have one-to-one connections to bipolar cells
o Have sharp-short responses
When one looks at a star and try to focus on it, it will disappear: cones are not active enough yet,
rods are. Rods are however only found in the periphery, so one can’t focus on the star.
Rods and cones respond to light with graded hyperpolarization. The more intense the light, the more
hyperpolarized the cell will become.
Phototransduction – dark current, absence of light:
- Intracellular cGMP keep cation channels open in rods and cones: conduct inward current, carried
by Na+ and Ca+. This leads to depolarization of the membrane.
Phototransduction – light current, presence of light:
- Light is absorbed by the pigment, activates pigement molecules: opsin or rhodopsin
(rods)
- Activated pigment stimulated G-protein (transducin), activates cGMP
phosphodiesterase. This enzyme catalyzes the breakdown of cGMP→ 5-GMP.
- cGMP concentration is lowered, cGMP-gated channels close, which reduces the
inward current and causees the photoreceptor to hyperpolarize.
The light must be indirectly involved in the closing and opening of the channels, because
with the second messengers its signal can be amplificated largely.
Ca2+ concentration decrease plays a key role in the modulation of photoreceptor sensitivity.
Take notes from Sterre and Marit to complement this statement.
Lecture 1 : Introduction
The brain has specific area’s for specific tasks. These area’s are able to transmit and receive information
through neurons. Neurons have chemical electrical signalling, that make them able to process information.
The human brain has 1011 neurons, each consisting of 1000 – 10 000 synapses.
Communication between neurons happens through synaptic transmission.
Most of the cells in the cortex are pyramidal neurons. They have many dendrites and axons to transmit
information. The dendrite has many spikes that are able to receive information. The information is given by
axons, that release neurontransmitters that connect to synapses. There is a great range of axons that cause
different reactions. For instance the excitatory or inhibitory axons.
- AP arrives at the axon, which depolarizes it’s membrane.
- Depolarization opens voltage-gated Ca2+-channels: calcium ions flow in
- Neurotransmitter release is triggered: they bind to post synaptic receptors
- Depolarization/hyperpolarization of post synapse
o Depolarization: travels to cell body, which causes excitatory postsynaptic potential (EPSP)
▪ NT: glutamate, receptors: AMPA, NMDA
o Inhibitory causes hyperpolarization, inhibitory postsynaptic potential (IPSP)
▪ NT: GABA, receptor: GABAergic receptors
Neurons can generate action potentials with this communication. APs are generated through the build-up of
EPSPs. APs are generated at the Axon Initial Segment of the neuron. APs are different from EPSPs in several
ways: APs are all-or-nothing events where EPSPs can be graded, APs are extremely short.
Frequency of AP firing conveys the signal of the neurons. Drugs can bind to receptors and simulate action of
neurotransmitter.
General plan of sensory systems
Components that are needed to perceive the outside world:
- Receiver and translator of information:
o Sensory receptors/axons receive information and translate energy of the stimulus into
electrical signals
- Transporter of information:
o axons transport the signal to the series of relay nuclei
▪ Cell bodies of skin neurons are located in dorsal root ganglia, close to the spine.
However their long axons stretch out to the skin where they are able receive the
information. They then transport the information to the cell body.
- Integrator and processor of information:
o interneurons and local circuitry in nuclei process the signal. The information ultimately
reaches the brain.
- Giver of output (this is not discussed in the course.
Reception sites of sensory systems
Sensory receptors translate the energy of the stimulus into electrical signals, four attributes are important in
the receptors: modality, location, intensity and timing.
- Modality: the type of stimulus. These potentials are summed up to either form or not form an AP.
Non-sensory neurons receive this information from axons of other neurons. Receptors in sensory
neurons work differently. Each sensory system has a specific receptor to receive information, for
instance in the visual system receptors can receive light.
Types of sensory receptors:
o Mechanical (touch and proprioception, hearing, balance): physical stretch or tension on the
receptor deforms the membrane and opens the channels.
o Chemical (pain, itch, smell, taste): binding of a chemical to the receptor
o Photoreceptors (vision): photoreceptor in retina change in conformation of a photosensitive
protein
o Thermal (temperature)
Receptor activation results in the change of postsynaptic potential.
, There are several different mechanoreceptors in the skin
for touch: Merkel cells, Ruffini corpuscle, Pacinian corpuscle,
Meissner corpuscle. Each receptor receives different information.
This is seen in the figure: the finger moves across braille and the
receptors are active at a different moment.
Proprioception: sense of the position of muscles and joints
of the body. They are axons wrapped around different structures,
just like the mechanoreceptors in the skin. When wrapped around a
muscle, they can perceive the muscles stretch.
- Location of receptors: what is the position of the stimulus
relative to the body?
o Topographical arrangement of neuronal receptive
fields: dermatomes devide the body in different
recepteive fields, that all receive and perceive
information of the body in a different area of the
spinal chord and brain.
▪ Retinatopy in retina, tonotopy in cochlea, gustotopy in gustatory
cortex.
o Spatial resolution is determined by the size of the receptive field and density of receptors.
▪ Fingertips are very sensitive to small changes, where the wrist has larger receptive
fields and is not as sensitive. This is found in all sensory systems.
- Intensity of the stimulus: how strong is the stimulus (touch is becoming stronger)?
o Sensory thershold is determined by the sensitivity of the receptors. How much stimulation is
needed to trigger APs
o Change in energy of the stimulus:
▪ Change in membrane potential
▪ Translation into digital code of APs.
- Timing of the stimulus: how does the stimulus change in time?
o Slowly adapting responses: changes in stimulus are coded in frequency
o Rapidly adapting responses: start and end of the stimulus are most important,
react to either the start or end of the stimulus. Most of the neurons are like this.
▪ Adaptation: a constant stimulus fades from consiousness
o Sensory systems are able to detecet contrasts and motion
Transport of the information
Axons transport the signal to the series of relay nuclei. All sensory systems have
complicated pathways.
- Multiple parallel pathways increase the speed of processing
o Different receptors for touch work together
- Topograpical representation is maintained (upper limbs have lateral position
in dorsal column, lower limbs are positioned more medial)
- Cross over of all sensory information to the opposite hemisphere
(decussation), this happens mostly in the medula.
- Feedback connections/descending projections: predictions of how the reality
is, is done by these feedback connections.
Processing of information
Interneurons and local circuitry in nuclei process the signal.
- Before reaching the cortex, all information passes
through the thalamus. This is a major relay station
for sensory and motor information. The thalamus is
organised neatly, it has a y-shaped division into
anterior, lateral and medial thalamus. It projects to
the middle layers of the cortex.
, - Information is projected to primary sensory cortices, yellow
coloured.
The cortex a stereotypical structure:
Columns: cells are organised in functional columns, one cell has
information from different locations from for instance the skin.
Layers: six layers, all have different function. Most information
from thalamus enters in layer IV. This information then spreads
through the other layers.
Topographical representation is maintained in the sensory cortex, seen in the
example of touch. This is also for different functional columns. So slowly and
rapidly adapting neurons in one of the fingers all have their own presentation in
the functional columns.
This is for instance also seen in the Ocular Dominance Columns!
Less than ¼ of the human cortex contains projection area’s, the rest is involved
with language, reasoning, moral thoughts et cetera.
Lecture 2: The Visual System – part 1
Reception of the visual system
Photons enter the eye and will be converted into neural impulse in the retina. The information goes through
the thalamus and is projected on the primary visual cortex. Eventually the information will go to other more
specific area’s of the brain. The eye focusses and adapts the incoming light and it inverts the projection of the
image. Wertheimer was one of the first ones to study the visual system. He found Gestalt psychology:
- What we see represents the properties of objects and the organization of sensations by the brain.
- The brain makes assumptions about what is seen in the world. It makes expectations that seem to
derive in part from experience and in part from the built-in neural wiring for vision.
Vision is based on interrelationship: relationships between the components of the image can be recognized in
different images. It works like a melody. When a song is played, we can recognize a song when sung in a
different note, because the interrelationship between the notes is recognized.
The eye cannot see both the vase and the two faces at the same time. The eye can only focus on one object
at the time and regards other information background noise.
In the picture on the left, a pattern cannot really be detected by the brain. However, the
occluded object in the backround is now constructed as a visual image accordingly, the letter B
arrises. The integration of distinctive objects into a coherent visual scene is aided by another
central fact of vision: closer structures cover those that are more distant.
Muller-Lyer illusion: assumptions about visual objects are also based on the surroundings of the object.
The size of the object is wrongfully detected by the brain because of the shape of the surroundings.
The perceived size of the object depends on other objects in the visual field. We judge the size of an
object by comparing it to its immediate surroundings. This is the illusion in the room, where two people differ
greatly in size.
The visual image we see is already enhanced and adapted by the neuron circuitry in retina, thalamus and
cortex. Our visual system is constantly making assumptions about the outside worlds based on experience and
build in neuronal wiring, the modulating infleunce of descending projections.
, The human eye
The retina is the most important part of the eye, it’s where the ligth is collected and eventually sent
off to the brain. The retina contains a retinotopic map of the visual field. At the back of the retina,
photoreceptors in rods and cones are activated by the light. A chemical reaction activates bipolar
cells, ganglian cells and eventually information is sent to the visual cortex via the thalamus. In the
blind spot all the information is gathered and clustered in the optic
nerve. This part of the retina is completely blind.
Rods and cones differ in size and shape and contain photoreceptors
that are activated by light. The cells have an inner segement
containing the nucleus and biosynthetic machinery and an outer
segment containing light-transducing apparatus. This apparatus
consist of membraneous disks, which have lightabsorbing
photopigments.
Pigment epithelium: removal of disk and regeneration of photopigment. Verder verwerken met
aantekingen Ster, Marit.
The two cells are specialized in different kinds of light.
- Rods
o Very good in detecting (small amounts of) light
o Distributed mostly in periphery of the retina
o Many rods converge on one bipolar cell, so the vision is less
specific than that of the cones
o Have longer responses
- Cones
o Detect large amount of light, day
o Distributed in fovea: small spot on retina, densely packed with
cones. Very little distributed in the periphery of the retina
o Responsible for visual acuity and colour: they have one-to-one connections to bipolar cells
o Have sharp-short responses
When one looks at a star and try to focus on it, it will disappear: cones are not active enough yet,
rods are. Rods are however only found in the periphery, so one can’t focus on the star.
Rods and cones respond to light with graded hyperpolarization. The more intense the light, the more
hyperpolarized the cell will become.
Phototransduction – dark current, absence of light:
- Intracellular cGMP keep cation channels open in rods and cones: conduct inward current, carried
by Na+ and Ca+. This leads to depolarization of the membrane.
Phototransduction – light current, presence of light:
- Light is absorbed by the pigment, activates pigement molecules: opsin or rhodopsin
(rods)
- Activated pigment stimulated G-protein (transducin), activates cGMP
phosphodiesterase. This enzyme catalyzes the breakdown of cGMP→ 5-GMP.
- cGMP concentration is lowered, cGMP-gated channels close, which reduces the
inward current and causees the photoreceptor to hyperpolarize.
The light must be indirectly involved in the closing and opening of the channels, because
with the second messengers its signal can be amplificated largely.
Ca2+ concentration decrease plays a key role in the modulation of photoreceptor sensitivity.
Take notes from Sterre and Marit to complement this statement.
