Neuronal function and neuropharmacology Flashcards
What are the two types of brain cells?
Neurones - transmission and integration of information
Glial cells - specialised for mechanical and metabolic support of neurones, and tissue repair
What are the 5 key structural features of neurones?
Cell body - nucleus and organelles
Dendrites - around cell body, specialised for receiving and integrating information
Axon - rapid transmission of electrical signals, often surrounded by a myelin sheath
Axon hillock - point where axon leaves cell body, specialised for generation of action potentials
Synapse - chemical transmission of a signal from one neurone to another
What is the membrane potential in neurones?
a charge/voltage across the membrane, which is 70mV at rest with the inside of the cell more negative than outside - we say the RESTING POTENTIAL of the neurone is -70mV, a charge which is due to uneven distribution of ions across the membrane
How are signals transmitted in neurones?
By changes in the membrane potential
In the dendrites and cell body, how does a change in membrane potential occur?
By passive diffusion, in which the signal strength decays over distance
What is meant by excitatory and inhibitory post-synaptic potentials?
EPSP - depolarisation caused by changes in membrane conductance e.g. opening of sodium channels
IPSP - hyperpolarisation caused by changes in membrane conductance e.g. opening of chloride channels
What is meant by temporal and spatial summation?
TEMPORAL - combining of changes in membrane potential occurring at same time to give a larger membrane potential change
SPATIAL - combining of changes in membrane potential occurring close together spatially to give a larger membrane potential change
How are signals transmitted in axons?
By an “all-or-nothing” reversal of the membrane potential called an action potential
What are 4 key features of action potentials?
Always the same size
Travel very quickly
Do not decay over distance
Mediated by rapid changes in membrane permeability to sodium and potassium
What is the characteristic pattern of an action potential?
Spike lasts around 1msec
3-5msec refractory period during which time the membrane is unresponsive, preventing the signal from travelling backwards
What is conduction velocity along an axon dependent on?
Diameter of the axon and amount of myelination (basic conduction speed is 2-5 m/sec, but in larger axons it is ~200m/sec
What happens when the signal reaches the synapse?
Neurotransmitters released from the terminal button (presynaptic) and bind to receptors in the postsynaptic membrane
Depending on types of receptors present, this binding can have an excitatory or inhibitory effect
What are the different classes of NTs?
Some are always excitatory e.g. glutamate
Some are always inhibitory e.g. GABA - opens chloride channels on postsynaptic membrane so neurone more negative and harder to depolarise
Others can be either depending on the receptor type present e.g. dopamine, noradrenaline, serotonin
On what levels can therapeutic drugs act on neuronal transmission?
Membrane potentials (e.g. local anaesthetics) Neurotransmitter synthesis (e.g. L-Dopa) Neurotransmitter release (e.g. amantadine) Neurotransmitter-receptor interactions (anticonvulsants, antipsychotics) Neurotransmitter clearance (e.g. antidepressants)
Why are inhibitory synapses important?
Control spread of excitatory activity, keeping activity “channelled” - epilepsy is the result of different brain circuits being activated all at the same time
What is acetylcholine like as a neurotransmitter?
Generally excitatory but depends on receptor
Voluntary movement, behavioural inhibition, memory
We see degeneration of ACh-producing neurones in Alzheimer’s disease
How is dopamine connected to brain disease?
Parkinson’s - degeneration of DA-releasing neurones
Schizophrenia - Excess DA