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
What do we see in Huntington’s disease?
Degeneration of GABA cells
How do opioids work?
Interfere with release of neurotransmitters from presynaptic neurones transmitting pain info - thus we have reduced PERCEIVED pain, although the pain info probably still reaches the brain as actual pain receptors are not directly being influenced
What is a drawback of the high degree of specialisation of neurones?
Metabolic machinery/capabilities are very limited - susceptible to problems when blood supply interrupted as no capacity to store energy; need continuous replenishment of glucose and oxygen via blood
What are oligodendrocytes and schwann cells?
Oligodendrocytes - support and insulate axons in CNS by creating myelin sheath
Schwann - support and insulate axons in PNS; cell body wraps around the axon and physically becomes the sheath
What are the ionic characteristics of a neuronal membrane at rest?
Impermeable to large proteins (-ve) so they remain inside cell
Resting membrane more permeable to potassium than sodium i.e. fewer sodium ions through leak channels
Greater conc of potassium inside, more sodium, chloride and calcium outside (both conc and elec gradient for sodium INTO cell)
Membrane more positive outside
Sodium kept out by sodium/potassium pumps
What is meant by the equilibrium potential of potassium?
Initially conc gradient means net movement outside - difference in charge across the membrane isnt enough initially to create a gradient
Eventually enough ions have moved out such that the inside of the membrane is significantly negative and electro and chemical gradients balance out –> no further net movement
What is meant by signal integration?
At any one point, the membrane potential is determined by the SUM of all individual depolarising and hyperpolarising events originating nearby (spatial summation)
