Neurotransmission Flashcards
What does the whole idea of chemical neurotransmission and the vesicle hypothesis rest on?
- The whole idea rests on two classes of molecule: chemical messengers and chemically-gated (ligand-gated) receptors
What compromises one motor unit? What happens if the alpha motor neuron fires an impulse? What allows for reliable transmission of excitation from neurons to cells? What does the post-synaptic part contain?
- Alpha motor neuron and all of the skeletal muscle fibres it innervates are one motor unit
- All motor units fire together if the alpha motor neuron fires an impulse
- High fidelity junction that allows for reliable transmission of excitation from a neuron to one cell type (e.g. a muscle fibre)
- Post-synaptic part contains lipid-bound vesicles loaded with neurotransmitter molecule (e.g. Ach)
When is latency shortest (see diagrams)? What happens as AP is propagated away from that site?
- Shows that latency is shortest at the site of neuromuscular junction
- As AP is propagated away from that site, they get later and later
What is caused in the post-synaptic cell by neurotransmitter release in the CNS?
- Neurotransmitter release in the CNS causes…. o EPSPs o (excitatory post-synaptic potentials) o & o IPSPs o (inhibitory post-synaptic potentials) - …in the post-synaptic cell
How do the potentials inside an outside of cells differ in EPP, EPSP and IPSP?
See diagrams in lecture notes (and try to somehow make sense of them)
What are the primary sensory neurons? What are the main neurotransmitters in CNS neurons?
- Primary sensory neurons: Glutamate
- CNS neurons:
Acetylcholine
o Amino acids:
Gamma-aminobutyric acid (GABA) (inhibitory)
Glycine (inhibitory)
o Biogenic Amines:
Noradrenaline
5-HT
Dopamine
What is utilised by the stretch-reflex and reciprocal antagonist inhibition to allow for contraction of the triceps?
- Utilises INHIBITORY INTERNEURON – releases glycine to inhibit activity and therefore contraction at the triceps, at the same time as the biceps is activated
How are IPSPs recorded?
In an antagonistic motoneuron
What are the three types of signals in neurons and what is the speed of each?
Neurotransmitter (fast - ms)
Neuromodulator (slower - secs-minutes)
Neurotrophic factor (slowest - mins-hours)
What types of signals are sent by the major neurotransmitters in the CNS?
- Primary sensory neurons: Glutamate (Fast + Modulator)
- CNS neurons:
- Acetylcholine (F + M)
o Amino acids:
Glutamate (F + M)
Gamma-aminobutyric acid (GABA) (F + M)
Glycine (F)
o Biogenic Amines:
Noradrenaline (M)
5-HT (F + M)
Dopamine (M)
What type of receptors are employed by fast neurotransmission?
- Fast neurotransmission employs multimeric (pentameric and tetrameric) receptors that incorporate ion channels
- G-protein coupled receptors comprise 7 transmembrane spanning segments
What are the two classes of action from neurotransmitters?
Direct gating of ion channel
Activation of G-protein coupled receptor
Which neuromodulators are not fast neurotransmitters?
- co-transmitter neuropeptide o substance P - e.g. inflammatory mediators etc o prostaglandin E2 o bradykinin
Which mechanisms are involved in the termination of transmitter action?
- Transmitter breakdown
- Reuptake using selective transport mechanisms
What is the mechanism of neurotransmitter breakdown?
- e.g. Acetylcholine esterase, present in the synaptic cleft (e.g. at nerve-muscle junction)
o can be inhibited by organophosphate nerve agents (e.g. sarin (nerve gas), insecticides)
o medicinally inhibited by neostigmine, physostigmine etc for treatment of myasthenia gravis (pyridostigimine in Gulf War Syndrome) - BUT ACh is unusual
What is an example of the process of neurotransmitter reuptake?
- Glutamate transporters in both neurons and glia
- GABA reuptake into presynaptic terminals and astrocytes by GATs
- Biogenic amine reuptake into presynaptic terminals (e.g. for noradrenaline uptake 1 and uptake 2 mechanisms)
- All amine/amino-acid transporters utilize the
- energy stored in the Na+ gradient
- Summarized in Chapter 9 of Rang, Dale, Ritter and Moore
What happens in the Na+/K+ dependent glutamate transporter?
Glutamate is taken up into pre and post-synaptic terminals, and into the adjacent glia, terminating its neurotransmitter action. The transporter uses energy stored in the transmembrane Na+ gradient to uptake glutamate.
What are muscle action potentials recorded by electrical stimulation of the peripheral nerve?
- M-wave, direct activation of motor units by electrical stimulation
- H-reflex, electrical equivalent to stretch-reflex
- F-wave, antidromic motor nerve action potentials bouncing off the a-motoneurons
What sort of abnormalities might one detect in a nerve conduction study?
- Record evoked muscle action potentials – o Peripheral demyelination o Look for giant motor units (MND/ALS) o Lambert-Eaton myasthenic syndrome o Myasthenia Gravis o Carpal tunnel entrapment o Record sensory nerve volley by recording in the digits- o Peripheral demyelination
