Introduction - Neural Conduction and Synaptic Transmission Flashcards
Neurons resting potential
-70mV
Ionic basis of resting potential
Random motion of ions
Electrostatic pressure
Ions which contribute to resting potential
Chloride
Potassium
Sodium
Negatively charged proteins
Properties of neural membrane responsible for uneven distribution of ions
Differential permeability of ions (K+ and Cl- pass readily through, Na+ with difficulty, proteins not at all)
Sodium potassium pump (3 Na+ for 2 K+)
Depolarisations are
EPSPs
Hyperpolarisations are
IPSPs
Post synaptic responses are what type of response?
Graded
Weak signals elicit small potentials and vice versa
Postsynaptic potentials characteristics
Rapid
Decremental - decrease in amplitude as they travel through the neuron
Action potentials are
All or nothing
Threshold of excitation
-65mV
Ionic basis of AP
Na+ channels open and Na+ moves into cell
Triggers opening of K+ which moves out of the cell
Na+ channels close
Repolarisation occurs due to continued efflux of K+
K+ channels gradually close causing hyperpolarisation for a brief time
Absolute refractory period
Period where it is impossible to cause an action potential
Relative refractory period
Period where an AP can be initiated but only with higher than normal levels of stimulation
Antidromic conduction
If an electrical stimulation of sufficient intensity is applied to the terminal end of the axon, an AP will be generated and travel back along the axon to the cell body
Orthodromic conduction
Axonal conduction in the natural way from cell body to terminal buttons
Conduction is faster when
Axons are myelinated
Axons are larger in diameter
Two categories of neurotransmitter
Small
Large
Small neurotransmitters
Several types
Typically synthesised in the cytoplasm of the terminal button and packaged into synaptic vesicles by the button’s Golgi complex
Stored in clusters next to the presynaptic membrane
Large neurotransmitters
Neuropeptides
Assembled in the cytoplasm on ribosomes and packaged into vesicles by Golgi complex
Transported by microtubules to the terminal buttons at a rate of 40cm per day
Don’t congregate as close to the presynaptic membrane as small vesicles do
Release of neurotransmitter molecules
AP causes Ca2+ channels to open
Ca2+ entry causes vesicles to fuse with the presynaptic membrane and empty their contents into the synaptic cleft
Small-molecule neurotransmitters tend to be released in a pulse each time there is an influx of Ca2+
Neuropeptides tend to be released gradually in response to gradual increase in Ca2+ which may occur due to a general increase in neuron firing rate
Activation of receptors by neurotransmitters
Neurotransmitters produce signals in postsynaptic neuron by binding to receptors on the postsynaptic membrane
Many neurotransmitters can bind to multiple receptor types
Allows different messages to be transmitted in different parts of the brain by one neurotransmitter
Ionotropic receptors
Ligand-activated ion channels
Binding causes opening or closing of channel
Metabotropic receptors
Associated with signal or G-proteins
Slower effects
Longer lasting
More diffuse and varied
Binding causes subunit of g-protein to break away
Subunit may bind to nearby ion channel and induce IPSP or EPSP
Or may trigger synthesis of second messenger which influences the neuron in many ways
What is an autoreceptor?
Metabotropic receptor
Binds to neuron’s own neurotransmitter molecules
Regulate the amount of neurotransmitter molecules in the synapse - reduces release when too high, increases it when too low
Astrocytes have been shown to communicate with neurons and other cells using…
Gap junctions
Neurotransmitter types
Amino acids Monoamines Acetylcholine Soluble gas neurotransmitters Neuropeptides Endocannabinoids
Amino acids
Glutamate - most prevalent neurotransmitter in mammalian CNS
GABA - most prevalent inhibitory neurotransmitter in mammalian CNS
Monoamines
Catecholamines
- Dopamine
- Norepinephrine
- Epinephrine
Indolamines
- Serotonin (5-HT)
Acetylcholine
Neurotransmitter at neuromuscular junction
Soluble gas neurotransmitters
Nitric oxide
Carbon monoxide
Endocanabinoids
Similar to THC (main psychoactive constituent of marijuana)
Neuropeptides
Pituitary peptides Hypothalamic peptides Brain-gut peptides Opioid peptides Miscellaneous peptides
What is an agonist?
Drug that facilitates the effect of a particular neurotransmitter
What is an antagonist?
Drug that inhibits the effects of a particular neurotransmitter
Atropine
Receptor blocker which exerts antagonistic effect by binding to muscarinic receptors, blocking ACh’s effect on them
Curare
Receptor blocker at cholinergic synapses at nicotinic receptors
Binding blocks transmission at neuromuscular junction, paralysing recipient and killing them by blocking respiration
Used to prevent muscle contraction during surgery when patient is maintained by a ventilator
Botox
Blocks release of ACh at neuromuscular junction and is therefore a deadly poison
Injected in minute doses has applications in medicine and cosmetics
The existence of opioid receptors in the brain suggests that
Opioid chemicals occur naturally in the brain
Families of endogenous opioids
Enkephalins
Endorphins
