Week 3 - Cells of the brain Flashcards
What are the pathological changes that are prevalent in the brains of patients with Alzheimer’s disease?
- Amyloid plaques
- Neurofibrillary tangles
What two types of cells can brain cells be broadly categorised as?
- Glial cells
- Neurons
Roughly how many neurons are there in the brain?
86 billion
Is the ratio of glial cells to neurons constant across the brain?
No, it varies from region to region
Where are the cell bodies of motor neurons located?
Within the brain or spinal cord
Where do the axons of motor neurons carry information from and to?
From the brain to the spinal cord and out to effector organs (eg muscles/glands)
Where are granule cells found?
In the cerebellum and other brain regions
Which type of cell is one of the most numerous cell types in the brain?
Granule cells
Where are pyramidal cells mainly located?
- Cerebral cortex
- Hippocampus
- Amygdala
What is the function of pyramidal cells?
They carry information long distances within and outside of the brain
Which part of the brain are purkinje cells found in?
The outer layer of the cerebellum
Where do purkinje cells transmit information to?
Deep within the cerebellum
Which are among the largest cells within the brain?
Purkinje cells
What is the function of purkinje cells?
They receive and transmit information from other brain areas
What is the function of the dendrites of a neuron?
They receive information and pass it on to the cell body for processing
What does the cell body of a neuron do?
It integrates information received from neighbouring neurons and processes it before passing it on to other neurons via the axon
What is the myelin sheath?
The fatty substance which surrounds and insulates the axon
What is the function of the myelin sheath?
It increases the speed that an action potential can travel along the axon
What is a synapse?
The junction between neurons which enables information to be passed from one neuron to another
What are the axon terminals?
The branches of the axon which form connections with neighbouring neurons
What is the function of an axon?
It passes the information from the cell body to the axon terminal
What is an action potential?
It is an electrical impulse that allows information to be passed from the cell body to the axon terminal
How large are axons?
They can vary widely, some stretch from the foot all the way to the spinal cord, others travel just within one brain region
What is the axon hillock?
The area of the neuron where the cell body and the axon form a junction
What is the function of the axon hillock?
It is where action potentials are initiated
What is the function of dendrites?
They are the main information receivers of the neuron
What are dendrites?
They are small branching extensions of the cell body of neurons and receive synaptic connections from other neurons
What is an action potential?
An electrical signal which travels along the axon and allows presynaptic neuron to communicate with postsynaptic neuron
How is an action potential often described as?
The language of the nervous system
What is a synapse?
The junction between the axon terminal of a presynaptic neuron and the dendrite of a postsynaptic neuron
Complete this:
information received at the ____________ is passed on to the ____________ for processing
- Dendrites
- Cell body
The information from the cell body is passed along which structure to the axon terminal?
The axon
In the form of what is information passed from the axon to the axon terminals?
An action potential
What feature of a neuron can increase the speed at which an action potential can travel along the neuron?
Myelin sheath
At the axon terminal, information is passed from one neron to the dendrites of the next neuron via what?
A synapse
Name the four main types of glial cell
- Astrocyte
- Ependymal cell
- Oligodendrocyte
- Microglial cell
Name a function of astrocytes
Any of the following:
- Form part of the blood-brain barrier
- Regulate concentration of ions and neurotransmitters around neurons
- Help regulate oxygen and nutrient supplies to neurons
- Play a protective and structural role
- Help regulate the immune and inflammatory responses
Which type of glial cell plays a part in regulating oxygen and nutrient supplies to neurons?
Astrocytes
Name a function of ependymal cells
Any of the following:
- Filter plasma from the blood to produce CSF
- Aid the circulation of CSF around the central nervous system
Which type of glial cell plays a part in the production of CSF?
Ependymal cells
What is the function of oligodendrocytes?
They form myelin around axons, which increases the speed of transmission of electrical information
Which type of glial cell is repsonsible for the production of myelin?
Oligodendrocytes
Name a function of microglial cells
Any of the following:
- Remove bacteria and debris from dead and dying brain cells
- Involved in immunological response to foreign invaders
- Provide growth factors for formation of blood vessels and glial cells
Which type of glial cell is involved in the immunological response to foreign invaders?
Microglial cells
Which type of glial cell is involved in providing growth factors for the formation of blood vessels and glial cells?
Microglial cells
Why are astrocytes important in the brain?
Any of the following:
- Form part of the neurovascular unit
- Influence synaptic transmission
- Mediate immune and inflammatory response
- Involved in the generation of new synapses
- Cause dilation of blood vessels in active brain regions in order to increase blood supply
Which type of glial cell has the most diverse role?
Astrocytes
Brains of some patients with major depressive disorder were found to have a reduction in which type of glial cell?
Astrocytes
How many other neurons can one neuron form connections with?
Up to 15000
What does the term presynaptic refer to?
The neuron that is sending out the information
What does the term postsynaptic refer to?
The neuron which receives information
What is meant by the term synaptic transmission?
The flow of information across a synapse from the presynaptic neuron to the postsynaptic neuron
When an action potential reaches the axon terminal, what are the two potential things it could do (depending on the nature of the synapse)?
- Pass from one neuron to the next via gap junctions
- Trigger the release of neurotransmitter that influences the postsynaptic neurons
What is a synaptic cleft?
The very small space between the presynaptic and postsynaptic neuron
Neurotransmitter is released into the synaptic cleft from what?
The presynaptic neuron
What is a synaptic vesicle?
The small vesicles at presynaptic terminals which store neurotransmitters
Neurotransmitter is released into the synapse from where?
Synaptic vesicle
What is the enlarged region at the end of an axon where neurotransmitter is released?
Axon terminal
Which area of the postsynaptic neuron receives a signal from the presynaptic neuron?
Dendrite
What is the name for the packages which contain neurotransmitter ready for release at the synapse?
Synaptic vesicles
What is neurotransmitter?
The signalling molecule that communicates information between neurons via the synapse
What are the proteins that are located on the dendrites of the postsynaptic neuron that bind neurotransmitters?
Postsynaptic receptors
What is the difference between a hormone and a neurotransmitter?
A hormone is generally released into the bloodstream and travels round the body to work on organs whereas a neurotransmitter is released from a neuron and acts on neighbouring neurons or other cells in close proximity
Where are neurotransmitters synthesised?
Either in the axon terminal or in the cell bodies of neurons
After being synthesised in either the axon terminal or the cell bodies of neurons, where are neurotransmitters then transported to?
The axon terminal
After being transported to the axon terminal, why are neurotransmitters then packaged into synaptic vessels?
So they can be released in response to an action potential
The neurotransmitter dopamine is synthesised from which molecule in the axon terminal?
Tyrosine
What are neuromodulators?
Chemicals which are found in the synaptic cleft which can influence synaptic transmission
As well as influencing synaptic transmission, what else can neuromodulators influence?
The responsiveness of postsynaptic neurons
What are some of the key neurotransmitters?
Any of the following:
- GABA
- Glutamate
- Catecholamines such as dopamine and noradrenaline
- Serotonin
The neurotransmitter GABA has which type of effect, inhibitory or excitatory?
Inhibitory
The neurotransmitter glutamate has which type of effect, inhibitory or excitatory?
Excitatory
What is excitatory postsynaptic potenial (EPSP)?
An electrical charge in a postsynaptic neuron which brings it closer to the threshold for firing an action potential
What is inhibitory postsynaptic potential?
An electrical charge in a postsynaptic neuron which takes it further from the threshold for firing an action potential
Which type of postsynaptic potential takes the postsynaptic neuron further away from firing an action potential?
Inhibitory postsynaptic potential
Which type of postsynaptic potential brings a postsynaptic neuron closer to the threshold for firing an action potential?
Excitatory postsynaptic potential
How is the frequency of action potential firing defined as?
The number of action potentials produced in a given time period
What is the frequency of action potential firing used as a measure for?
The level of activity in a neuron
Does the size of an action potential ever change?
No
Rather than the size of an action potential changing, what else does instead?
- The frequency of action potentials
- The number of action potentials produced in a given time
What is the order of events which take place at the synapse?
- Action potential reaches the axon terminal
- Synaptic vesicles fuse with the membrane of the axon terminal, releasing neurotransmitter into the synaptic cleft
- Neurotransmitter diffuses across the synaptic cleft and binds on the postsynaptic neuron
- Neurotransmitter is bound to receptors which results in a change in the excitability of the postsynaptic neuron
- If the excitation is great enough, an action potential is initiated in the postsynaptic neuron
Does dopamine have an inhibitory or excitatory effect?
It can be either
What is the background firing rate?
The low frequency level at which a neuron fires action potentials in the absence of any stimulation
What is the effect of making the presynaptic inhibitory neuron more active?
The frequency of action potentials in the postsynaptic neuron decreases
Along with neurotransmitters influencing the postsynaptic neuron, what else can they influence and how?
The presynaptic neuron, by binding to autoreceptors
What are autoreceptors?
Receptors which are found on the axon terminal of presynaptic neurons which can regulate the release of neurotransmitter
What can autoreceptors regulate?
The release of neurotransmitter
Where are autoreceptors found?
On the axon terminals
Binding of neurotransmitters to autoreceptors decreases what?
The amount of neurotransmitter which is released
Can neurotransmitters regulate their own release?
Yes
How many different ways can neurotransmitters be removed from synapses?
Three
What is synaptic reuptake?
One process by which neurotransmitter can be removed from synapses
What are the three mechanisms in which neurotransmitters can be removed from synapses?
- Synaptic reuptake
- Enzymatic degradation
- Diffusing away from the synapse, being taken up into astrocytes and metabolised into their constituent molecules
What is enzymatic degradation?
The process by which enzymes present in the synaptic cleft break down neurotransmitters
Excessive levels of neurotransmitter can ______________ to neurons?
Be toxic
What happens if a drug that blocks the reuptake of a neurotransmitter is introduced into the synapse?
The neurotransmitter remains in the synaptic cleft for longer and can therefore have a prologned effect on the postsynaptic neuron
What does the term synaptic reuptake mean?
The process which helps terminate the action of neurotransmitter
How does the process of synaptic reuptake terminate the action of neurotrasmitter?
It removes it from the synaptic cleft via specialist channels in the axon terminal
How does the process of enzymatic degradation remove neurotransmitter from synapses?
Enzymes in the synaptic cleft break down neurotransmitter
Neurons which utilise acetylcholine as the principal neurotransmitter are known as what type of neurons?
Cholinergic neurons
Reduced activity in the cholinergic pathway which originates in the pons and projects towards the hippocampus results in what?
Impairment of hippocampal functioning
Reduced hippocampal functioning is often a feature of which disease?
Alzheimer’s disease
How many principal dopaminergic pathways are there in the brain?
3
What is the dopaminergic pathway which runs from the substantia negra to the caudate nucleus and the putamen important for?
The production of movement
What is the route of the nigrostriatal pathway?
From the substantia nigra in the midbrain to the caudate nucleus and the putamen in the striatum
Loss of activity in the nigrostriatial pathway underlies which disease?
Parkinson’s disease
Where does the mesolimbic pathway run?
From the ventral tegmental area of the midbrain to the nucleus accumbens in the ventral striatum
What is the name of the dopaminergic pathway which runs from the ventral tegmental area of the midbrain to the nucleus accumbens in the ventral striatum?
The mesolimbic pathway
What is the route of the mesocortical pathway?
It starts in the ventral tegmental area of the midbrain and projects to the prefrontal cortex
Together, what are the mesolimbic and mesocortical pathways known as?
The reward pathways
The reward pathways are involved in which type of behaviour?
Addictive behaviour
Where do the noradrenergic pathways originate in the brain?
A region of the brain stem known as the locus coeruleus
Where do the noradrenergic pathways project?
From the locus coeruleus in the brain stem down the spinal cord and upwards through many regions of the brain
What are the descending noradrenergic pathways involved in the control of?
Responses of the autonomic nervous system
Descending noradrenergic pathways are important in which type of response?
Stress response
Where do the ascending noradrenergic pathways project?
To the hypothalamus, amygdala, thalamus and widely throughout the cortex
The projection of the noradrenergic pathway to the prefrontal cortex is of particular importance in the context of what?
Mood disorders
Where in the brain do the serotinergic pathways originate?
In the raphe nuclei of the brain stem
Which regions of the brain do serotinergic pathways project to?
- Cerebellum
- Hippocampus
- Prefrontal cortex
- Widely through the cortex
What are some of the roles that serotonergic pathways are involved in?
- Sleep/wake cycle
- Emotions
- Mood
Selective serotonin reuptake inhibitor drugs act how?
By preventing the reuptake of serotonin, so that it remains active in the synapse for longer and continues to exert its effects
If more receptors are occupied by serotonin, what happens to the EPSP generated?
It increases
Increased EPSP due to serotonin reuptake inhibitors has what effect on the action potential firing rate in the postsynaptic neuron?
It increases
How does the type of drug known as an antagonist exert its effect?
It binds to the receptor on the postsynaptic neuron, which can prevent neurotransmitter from binding, meaning that the neurotransmitter cannot exert its effect
What are antagonists?
Chemical substances which bind to receptors and prevent binding of the neurotransmitter
Too much activity in certain pathways might be treated with which type of drug?
Antagonists
If a dopamine antagonist is present, what happens to the action potential firing rate in the postsynaptic neuron?
It is lower
If there is a deficit of activity in a certain pathway, which type of drug would be helpful?
Agonist
Which aspects of synaptic transmission could potentially be altered by drugs?
- Drugs which bind to postsynaptic receptors and autoreceptors
- Drugs that interfere with the processes which terminate the activity of a neurotransmitter
What is meant by the term neuroplasticity?
Changes that occur in the brain as a result of:
- Development and ageing
- Learning and experiences
- Disease processes
- Recovery from brain injury
What is synaptogenesis?
The formation of new synapses between neurons
What is the name of the process which removes dendrites from neurons during adolescence and into early adulthood?
Denritic pruning
What is dendritic pruning?
The process by which dendritic spines are removed from dendrites, thus reshaping the connectivity between neurons
During which period of life does dendritic pruning peak?
Adolescence and into early adulthood
What is Hebbian plasticity?
A type of neuroplasticity which occurs from prolonged or intense activity in one neuron, which leads to increased responsiveness of the next neuron in the pathway
What is the friendly explanation of Hebbian plasticity?
“Neurons that fire together, wire together”
Which brain imaging technique allows activity across the brain to be measured?
fMRI - functional magnetic resonance imaging
How do we measure brain activity directly?
Electoencephalography (EEG)
What is electroencephalography?
Recording of electrical activity from the cortex of the brain using an array of sensors applied to the scalp
What three things have made the study of consciousness scientifically possible?
- A better definition of consciousness
- The discovery that consciousness can be experimentally manipulated
- A new respect for subjective phenomena
Correlational studies are used for what purpose?
To evaluate relationships between two observations
What are some of the techniques that can be used to visualise brain structures?
- Microscopy
- Brain imaging
- Electrophysiology
What is the name for the process in which a chemical neurotransmitter communicates activity from one neuron to another?
Synaptic transmission
