Week 2: Biological Brains and Neurons = CHECKED Flashcards
Large scale anatomy of the brain diagram = major subdivisions of brain
(not spinal cord)
The telencephalon consists of: (2)
the olfactory bulb
subcortical structures (e.g., basal ganglia)
The telecephalon is also called as
the cerebum
The diencephalon contains (4)
thalamus
hypothalamus
epithalamus
subthalamus
The mesencephalon contains
tectum and tegmentum
The mesencephalon is the
front portion of the brain stem
The rhombencephalon is the
lower part of the brain stem (i.e., hindbrain)
The rhombencephalon contains the (3)
medulla oblongata
pons
cerebellum
The cerebrum is for
higher (cortical) function
The basal ganglia is important for (6)
Action selection
Attention
Procedural learning
Habit learning
Conditional learning
Eye movements
The thalamus is the
main relay station for the brain between the telencephalon (cerebral cortex) and the brainstem/spinal cord for sensory information
Epithalamus function
Helps to regulate circadian rhythms
Subthalamus function
regulates and coordinates motor function
Hypothalamus function: it regulates (4)
- body temperature
- blood pressure
- caloric intake/expenditure
- water balance
The main function of hypothalamus is to
maintain your body’s internal balance, which is known as homeostasis.
Mesencephalon function (5)
Controls auditory processing (superior colliculus)
Pupil dilation
Eye movement
Hearing
Regulates muscle movement
Rhombencephalon (hindbrain) mostly deals with autonomic functions such as: (5)
breathing
alertness
arousal
digestion
perspiration (Sweating) etc…
Spinal cord function
Transmits nerve signals to the muscles
Spinal cord is not a mere relay as it can produce
complex activity patterns for locomotion based on simple inputs
There are commonalities between the brains of humans and other animals (e.g., cat, pigeon) but…
there is differences in organisation and extent and differences in mental abilities/makeup
Functions of large subdivisions of brain can fit within our brain-enviroment loop
In the human brain, finer subdivisions can be mapped out (compared to higher-level overview of brain - telencephalon etc…)
such as using
Brodman areas (1909)
Brodman areas map out smaller areas of brain based on: (3)
- Connectivity (intrinsic, afference, efferent)
- Cell types (based on cytoarchituere)
- Structure (i.e., are the neurons grouped together?)
afferent neurons
Nerve cells that carry impulses towards the central nervous system
efferent neurons
Nerve cells that conduct impulses away from the central nervous system
Instrinsic Neuron
cell whose axons and dendrites are all confined within a given structure
extrinsic neurons
are autonomic neurons that bring signals from CNS to digestive system
More modern methods of finding finer subdivisions of brain are
gene expression
Sensory organs are neuron interfaces with the exterior environment e.g., hearing (2)
When sound impacts your ear it will excite the hair cells in the inner ear which will translate that into electrical signals
Neurons can form networks either:
locally (local connections) and across the brain (long-range connections)
Grey matter in the brain is
contains the majority of neuron somas (cell body)
White matter in the brain is
fibre tracts connecting the neurons in the brain
White matter can make long-range connections as they have
have fibre tracts connecting neurons from one cortical regions to another
There is also local connections within parts of the brain and this defines a so-called
circuits or microcircuits that are committed/serve one or more particular functions
There is also local connections within parts of the brain and this defines a so-called circuits or microcircuits that are committed/serve one or more particular functions
e.g., parts of brain (2)
cerebellum
hippocampus
Hippocampus circuit (3)
inputs from the EC are processed at successive levels, from the EC layer 2 spiny stellate cells to dentate gyrus (DG) granule cells,
to recurrently connected CA3 pyramidal neurons, onto CA1 and subicular pyramidal cells (along with a direct projection from EC layer 3),
and fed back to the EC layer 5.
The hippocampus is important for memory as in HM they took out his hippocampus and so (2)
could not form any new memories
This puts forward the idea that this circuit is important for memory
Diagram of circuit motifs = different types of artifical neural networks
Feed-forward neural network:
We have a group of neurons that project directly (have excitatory network connections) to another group of neurons
Feed-forward neural network is the simplest
artificial neural network devised
Feedback inhbition neural network
During feedback inhibition, excitatory principal neurons synapse with inhibitory interneurons, which then inhibit those neurons by feeding back to them (negative feedback loop) - Carl & Jong , 2017
Recurrent Neural Networks
neurons inside interconnected circuits send feedback signals to one another
Lateral inhibition network
In lateral inhibition, active neurons suppress neighbouring neurons’ activity through inhibitory synaptic connections - Cao et al., (2018)
Neurons come in all shapes and varieties but the most common types are the
cortical pyramidal neurons
Neurons (cortical pyramidal neurons) have a long axon where
electrical impulses from the neuron travel away to be received by other neurons.
Neurons (cortical pyramidal neurons) have dendrites where it receives
nput (incoming electrical impulses) from other neurons via synaptic connection
Neurons interact with each other via synapses steps (4)
AP travels down the axon of the pre synaptic terminal
This causes vesicles of the pre-synaptic neuron to release NT
The NT diffuses across the synaptic cleft.
The NT is released across the synaptic cleft and binds onto the receptor molecules of the post synaptic terminal of the receving neuron
Neurons interact with each other via synapses
After NT bind to receptor on receiving neuron
If NT is excitatory then (e.g.., noradrenaline)
the post-synaptic neuron is more likely to fire an electrical impulse (i.e., action potential)
Neurons interact with each other via synapses
After NT bind to receptor on receiving neuron
If NT is inhibitory (e.g., serotonin)
post-synaptic neuron is less likely to fire an impulse (i.e., action potential)
What are neurons?
Neurons are cells that
maintain a difference
in electric potential between
the inside of the neuron
and the outside!
In the membrane of neuron (4)
ion-pumps exchange electrically charged atoms (ions) with the
extra-cellular medium.
Some ion pumped in and some pumped out
This charge distribution
generates the membrane potential (or transmembrane potential).
Approximately -80 to -70 mV
The type of ion channels( e.g., Na+ channel, K+ ion channel) and ion pumps a neuron has isbased on the
gene expression of the neuron
Many ion-conducting channels are embedded
within the cell membrane (Dayan et al., 2001)
The ion channels reduce the membrane resistance for ions to flow
what is the membrane resistance
It is a measure of the impediment to the flow of ions across a membrane (Binder et al., 2009)
Most ion channels are highly selective meaning
they only let one single type of ion to pass through them
(Dayan et al., 2001)
The membrane of a neuron has ion pumps and ion channels
Ion pumps are.. (2)
It exchanges ions (i.e., pumping some ions inside and some pumping outside) within the extra-cellular medium
Pumps maintain the separation of charge which generates the resting membrane potential and maintains it
The membrane of a neuron has ion pumps and ion channels
Ion channels are:
Channels are specific to a given type of ion (e.g.. Na+, K-channels)
The resting membrane potential is when the (2)
flow of ions into the cell equals that going out
(Dayan et al., 2001)
The membrane potential can fluctuate if there is an unbalance of ions flowing into and out of the cell due to (2)
opening and closing of ion channels
(Dayan et al., 2001)
Hyperpolarisation is
when there is more positively charged ions outside than inside the cell which causes a change in the membrane potential to be more negative.
resting membrane potential (2) is.. and it is usually…
he electrical charge of a neuron when it is not active
usually around -70 to -80 mV
voltage gated channels are those ion channels that
open (conduct many more ions) and close in response to changes in membrane potential
A lot of charged atoms moving inside or outside of a voltage gated channels this means
a current flows in or out (like Na+ flows in)
The opening and closing of different ionic channels generates a fast change in membrane potential
AP
Action potential generation (8)
- A neuron at rest will typically have a membrane potential of around -70 millivolts.
- An action potential is produced at a particular part of the neuron’s cell membrane when an external stimulus with sufficient electrical value changes the resting membrane potential of the neuron to the neuron’s action potential threshold (also known as threshold potential).
- The threshold potential of a neuron is usually -55 mV.
- The threshold potential activates the voltage-gated Na+ ion channels to open which allows a rapid influx of Na+ ions to enter inside the neuron and causing an increase in the membrane potential towards +40 mV.
- This causes the depolarisation of a small region of the cell membrane.
- The voltage-gated Na+ ion channel begin to close and the influx of Na+ inside the neurons stops.
- The voltage-gated K+ ion channels open with a slight delay and causes an efflux of K+ to move out of the cell which causes the membrane potential to decrease to -90 mV) and causing the neuron to become hyperpolarised.
- Eventually, the voltage-gated K+ ion channels close and eventually the voltage returns back to the resting membrane potential. This is called the refractory period.
How does the AP progagate to other neurons? (5)
- Once the action potential is produced at a particular part of the neuron’s cell membrane it is propagated through the neuron’s axon and every part of the cell membrane becomes sequentially depolarised to initiate synaptic transmission to communicate with other neurons.
- In synaptic transmission, the action potential will travel all the way down to the axon of the neuron’s pre synaptic terminal.
- This will cause the vesicles to form and release a neurotransmitter that will diffuse across a synaptic cleft which will bind to the receptor molecules of the post synaptic terminal of a receiving neuron.
- If the neurotransmitter is excitatory (e.g., noradrenaline) then the post-synaptic neuron is more likely to fire an action potential.
- If the neurotransmitter is inhibitory, then the post synaptic neuron is less likely to fire an action potential.
Ion channels are important because (2)
Several diseases/disorders manifest as a consequence of ion channels disruptions with massive consequences!
Their variety allows for a variety of firing patterns that are important for specific functions
There are many different ion channels and subtypes that
vary in their properties (e.g. time course of opening and closing)
There is a vast zoo of different types of neurons. Differences manifest in (2)
in their firing properties (the number and distribution of action potentials across time).
The different neuronal properties enable information processing specific to a brain area, micro-circuit, or even individual neuron!
The other major factors are synaptic inputs (4) shaping activity pattern of neurons
Different types of neuro-transmitters have different effects on spiking
Changes in synapses are believed to implement learning!
Excitatory neurotransmitters raise the membrane potential(examples: glutamate, NMDA)
Inhibitory neurotransmitters lower the membrane potential(examples: glycine, gaba)
