Psychobiology Flashcards
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Degrees of reductionism (3)
Macro-anatomical (brain areas)
Micro-anatomical (brain cells)
Macro molecular (individual protein molecules)
Blindsight
Patients with damage to the visual cortex declare they cannot see but can actually instinctively reach for objects
(superior colliculus intact - where sight functions)
Function of 1) Broca’s area 2) Wernicke’s area
1) Speech production
2) Speech perception
Three characteristics of neurons
Fully differentiated
Cannot undergo mitosis (cell division)
Generally, cannot be replaced in a mature nervous system
Dendrites
Branch like processes that receive information from other neurons
Axons
Long filament like processes that convey information away from the cell body to other neurons (through the terminals)
Longest axon in body
Sciatic nerves’ axons run from the end of the spinal cord to the toes
Myelin Sheath
Insulating fatty layer that coats the axons to speed transmission
How does myelin sheath speed transmission
Made from oligodendrocytes, it enables the action potential to decrease as it travels underneath the sheath and fully regenerate at each node (conserving energy)
Schwann cells
Makes the Myelin in the peripheral nervous system (PNS) - similar to oligodendrocytes
Nucleus (3 functions)
Contains chromosomes and DNA, produces neurotransmitters and receptors, makes modifications to dendrites
Microtubules
Transport system moving proteins up and down axons (damage can cause Alzheimer’s)
Mitochondria function
Takes in nutrients, breaks it down and converts it into energy to be used
Function of cell body
Cell maintenance, one way being protein production
How information is passed through a neuron to the other
Electrical signal (action potential) comes in through dendrites into cell body, then passes through the axon to the terminals where neurotransmitters are released into the synapse ready for the neighbouring neurons receptors to pick up
A multipolar neuron
One axon and many dendrites
Bipolar neuron
One axon, one dendrite tree (usually in sensory systems)
Unipolar neuron
One axon divided into 2 branches. One branch receives info and the other sends it
Afferent neuron
Carries information towards the CNS (A for arrival)
Efferent neuron
Carries information away from the CNS (E for exit)
Types of glial cells (3)
Astrocytes
Oligodendrocytes
Microglia
Function of glial cells (3)
Support neurons
Take away waste
Give neurons nutrients
Astrocytes function (2)
Some limit exchange of substances between blood and brain (barrier)
Others regulate ion concentration and extracellular concentration of neural signalling
(are star shaped)
Oligodendrocytes function
To wrap around axon to create myelin sheath (multiple layers of cell membrane)
Microglia funtion
To remove waste, viruses and fungi
mostly inactive unless repair is needed
Cell membrane and function
A barrier surrounding cells made up of membrane lipids (not perfect, a bit leaky)
Can open its channels to certain chemicals and not others in particular circumstances
Resting membrane potential (full explanation)
When the neuron is inactive, it is a state in which neurons can become active at any moment (requites a lot of energy for the brain).
Inside the cell is more negatively charged (-70mV).
There is electrostatic pressure of positively charged ions (Na+) from out to inside the cell
Force balanced by the K+ inside the cell attempting to diffuse outwards
Electrostatic pressure
Ions with a different charge to nearby them naturally move towards or away to balance the charges (attract like magnets)
Action potential (full explanation)
The mV shifts from -70 to -55 due to neighbouring action potentials or sensory inputs. This causes the Na+ channels to open and positively charged ions to flood the cell. Then the K+ channels open and it diffuses out. Once the mV is +40, repolarisation begins as charge inside cell now more than outside. Na+ leaves the cell and K+ enters.
mV overshoots -70 slightly before returning to the resting membrane potential state
How is cognition speed often measured
Action potentials per second
Diffusion
Movement of ions from a high to low concentration area
Why depolarisation of neuron occurs (3) - mV from -70 to -55
Action potential in neighbouring neuron
Sensory receptors
Chemical transmission between neurons
Synaptic cleft
Gap (20nm) between a neurons terminals and another’s dendrites
Synapse
Gap between neurons, including receptors etc.
What is different in an electrical synapse compared with a chemical one
Neurons touch each other (no cleft), so ions diffuse across adjoining pours
Pre-synaptic neuron
Input neuron that brings information to the synapse
Vesicle
A bubble type thing that neurons package molecules in to transport them
How neurotransmitters are released from the neuron into the cleft
The vesicle is encapsulated by the cell membrane and the neurotransmitters are then released onto the other side into the cleft
What happens when a neurotransmitter bind to a receptor
Certain ion channels open, allowing the conductance of the neuron to change
Post-synaptic neuron
Receives information at the synapse from the receptors on the dendrites
Hypopolarisation
Opening of the cation channels (+ve) - is excitatory
similar to depolarisation
Hyperpolarisation
Opening of anion channels (-ve), is inhibitory
Ligand and two examples
Chemical that interacts with a receptor (E.g. neurotransmitters, drugs)
Binding site
Location on receptor that ligands interact
Why will only some ligands bind to some receptors
They need to match each others 3D shape (at least roughly)
Affinity
How well a ligand binds to a receptor
high affinity receptors are saturated by very dilute ligands
Types of receptors (2)
Ionotropic
Metabotropic
Ionotropic receptor
Directly coupled to ion channel (ligand binds and ion channel opens)
Metabotropic receptor
The ligand binding changes its 3D shape and activates a G-protein inside its neuron, causing a signalling cascade which can change excitability and protein synthesis
Why are there receptors at pre-synaptic neurons as well
To provide negative feedback in order to stop neurotransmitter release when beneficial (called retrograde signalling, important for plasticity)
Glutamate neurotransmitter characteristics (4)
Derived from glutamic acid
Excitatory
Most abundant in brain
Bind to at least 8 receptor types
GABA neurotransmitter characteristics (3)
Made from glutamate
Most abundant inhibitory neurotransmitter in brain
Binds ionotropic and metabotropic GABA receptors
Glycine neurotransmitter characteristics (3)
An amino acid (unusual)
Binds to inhibitory receptors in the spinal cord
A co-agonist
Monamine neurotransmitter characteristics (3)
Includes dopamine, serotonin and neuropeptides
Mostly bind to metabotropic receptors
Found in a restricted group of neurons
Synaptic transmission explanation in steps
1) Neurotransmitter made in cell body, stored in vesicles
2) When action potential arrives, vesicle fuses with cell membrane and releases transmitter into cleft
3) Binds with post-synaptic neuron’s receptor
4) Ion channel opens or closes
5) Excess neurotransmitters then recycled, vesicles reconstructed
What receptor does 1) caffeine 2) alcohol 3) nicotine bind to
1) Adenosine receptors
2) GABA and NMDA receptors
3) Nicotinic receptors
Pharmacokinetics
How drugs get to their site of action and are handled by the body
Stages of pharmacokinetics (4)
Absorption
Distribution
Metabolism
Elimination
Absorption, and method of absorption
How drugs get into the body, always through a membrane (nasal, intestine, skin) or injected
How do water soluble drugs absorb into the body
Not by membranes, but cross pores in capillaries
How do lipid soluble drugs absorb into the body (3)
Pores in capillaries, cell membranes and blood-brain barrier
Slower routes of drug absorption (4)
Oral, suppository, topical (skin), mucous membranes (nasal, chewing etc)
Faster routes of drug absorption (3)
Inhalation, Injection, directly into brain (the fastest)
Methods of injection (3)
Subcutaneous (under skin), Intramuscular (in muscles) and intravenous (in vain)
Blood-brain barrier
Made of astrocytes, it separates the brain from the bloodstream
How drugs become less likely to pass the blood-brain barrier
They bind to plasma proteins, making them too big to get through capillary pores
Why do fat soluble drugs take longer for the body to eliminate
Get deposited in fat tissue (e.g. THC)
Metabolizing a drug
Converting it into another compound (can be inactive, active or even more active) - often essential for elimination
(Mainly in liver, but everywhere)
Methods of eliminating a drug (4)
Urine, Breath (e.g. alcohol), sweat and hair
Drug half life
Measures the duration of action of a drug by the time taken for blood plasma levels of the drug to fall by half
Pharmacodynamics
The effect the drug has on the body
Direct agonist drug and example
Mimics the effect of a particular neurotransmitter (nicotine)
Indirect agonist drug and example
Enhances the action of a natural neurotransmitter (not affecting the binding) - (cocaine blocks dopamine reuptake/recycling)
Direct antagonist drug and example
Binds to receptor with no physiological effect (blocks endogenous transmitters (meloxone - used to treat opium, an agonist, overdoses)
Indirect antagonist drug
Inhibits neurotransmitter release and synthesis without binding
Allosteric modulator drug and example
Alters the action of a binding natural neurotransmitter, binding to a secondary binding site (alcohol increases the effect of principle ligand on GABA receptors)
Inverse agonist drug
Has the opposite effect of a natural neurotransmitter on the receptor
Therapeutic index
Quantifies the difference in doses for desirable and toxic effects of a drug
Therapeutic index equation
Doses that produce desirable effects in 50% of animals (ED50) / Doses that produce toxic effects in 50% of animals (LD50)
Alcohols effect on the brain (3)
Enhances GABA transmission by binding to GABAA receptor (secondary binding site), increasing the flow of Cl- ions
Acts as antagonist at NMDA receptor, reducing Na+ into neuron
Indirectly increases neurotransmission in serotonin and dopamine systems (at cannabinoid receptors)
Long-term brain effects of alcohol consumption (2)
Korsakoff’s syndrome (damage to thalamus and hypothalamus)
Withdrawal (addiction)
What happens to the brain when alcoholics try to detoxify
Becomes overactive to try and regain its normal state. Causing: anxiety, hyperexcitability, tremors etc
Cocaine’s effects on the brain (2)
Blocks dopamine transporter, reducing reuptake/recycling and prolonging duration of dopamine in the synapse (repeatedly binding)
Indirectly increases dopaminergic transmission
Why is methamphetamine one of the most addictive amphetamines?
Is more liquid soluble so can cross the membrane more easily
Amphetamines effects on the brain (2)
Blocks dopamine and noradrenaline reuptake (indirect agonist)
Doubles release of dopamine and noradrenaline by reversing transporters to push more out into synapse
Effect of nicotine on the brain
A direct agonist, it mimics nAChRs receptors in the presynaptic neuron - increasing neurotransmitter release
Why desensitisation to nicotine is so easy
nAChRs receptors change shape every time they are activated, it binds worse the more it is taken, building up a tolerance
Effect of caffeine on the brain
Direct antagonist, it binds to adenosine receptors (which inhibit dopamine receptors activation through co-localisation), caffeine reduces this inhibition, increasing dopamine signalling
Why heroin is more addictive than morphine
Crosses blood-brain barrier more easily, then is metabolised into morphine in the brain
Opiates effects on the brain (3)
Direct agonist, naturally produced opiod ligands bind to mu and kappa receptors
Inhibits neurotransmitter’s responsible for pain release
Indirectly inreases dopamine release: by inhibiting GABA neurons, reducing dopamine inhibition
How is THC eliminated in the body
In urine, lipid soluble so metabolism is essential for elimination (some in fat stores makes elimination slow)
Cannabis effects on the brain (3)
Direct agonist, it binds to CB1 and CB2 receptors
Complex interactions with cannabinoid and opioid systems
Results in dopamine release