Introduction to neurones, nerve conduction and synaptic transmission Flashcards
What is the purpose of a dendrite?
To receive inputs from other neurones and convey graded electrical signals passively to the soma
What is the purpose of the soma?
It is the synthetic and metabolic centre
Contains the nucleus, ribosomes, mitochondria and ER
It integrates incoming electrical signals that are conducted passively to the axon hillock
What is the axon hillock?
Site of initiation of the “all or nothing” action potential
What is the function of the axon?
Conducts output signals as action potentials to the presynaptic terminal
Mediates transport of materials between the soma and presynaptic terminal and vice versa by slow and fast axonal transport
What is the function of the synapse?
Point of chemical communication between neurones
What viruses will exploit retrograde transport to infect neurones?
Herpes
Polio
Rabies
What are the different types of neurones?
Unipolar
Pseudounipolar
Bipolar
Multipolar
Where can unipolar neurones be found?
Peripheral autonomic system
Where can pseudounipolar neurones be found?
Dorsal root ganglion
Where can bipolar neurones be found?
Retina
Where can multipolar neurones be found?
Lower motor system
What is the resting potential for a neurone?
-70 mV
What is the threshold for a neurone?
-60 mV
What channels allow for the upstroke and downstroke of the action potential in neurones?
Upstroke = Na+ Downstroke = K+
Why do passive signals in neurones not spread far from their site of origin?
Current loss across the membrane accompanied by a reduced change in potential
What are strategies utilised to increase passive current speed and therefore action potential velocity?
Decreased axial resistance of the axoplasm via increased axon diameter
Increased membrane resistance - addition of myelin provided by schwann cells in PNS and oligodendrocytes in CNS
What is saltatory conduction?
Action potential jumping from one node of ranvier to the next
What are examples of demyelinating disorders?
MS (CNS)
Guillan-Barre (PNS)
What separates the pre and post synaptic membranes?
Synaptic cleft
What holds the pre and post synaptic membranes together?
A matrix of fibrous extracellular protein within the cleft
Where are the neurotransmitters stored in the neurone?
Vesicles within the presynaptic terminal
What are the different types of synapses?
Axodendritic
Axosomatic
Axoaxonic
What is the most common type of synapse?
Axodendritic
What is the most common neurotransmitter of excitatory synapses in the CNS?
Glutamate
What will glutamate activate?
Post synaptic, cation selective, inotropic glutamate receptors resulting in a depolarisation; excitatory postsynaptic potential
What are the major amino acid neurotransmitters in the CNS?
Glutamate
GABA
Glycine
What is the most common neurotransmitter of inhibitory synapses in the CNS?
GABA or glycine
What will GABA/glycine activate?
Postsynaptic, anion selective, inotropic, GABA or glycine receptors generating a local, graded hyperpolarizaing post synaptic potential
What is spatial summation?
Many inputs converge upon a neurone to determine its output
What is a temporal summation?
A single input may modulate output by variation in action potential frequency of that in put
What are the major amine neurotransmitters?
Dopamine
Histamine
Noradrenaline
Serotonin
What are the major peptic neurotransmitters?
Cholecystokinin Dynorphin Enkephalins Neuropeptide Y Somatostatin Substance P Thyrotropin releasing hormone Vasoactive intestinal polypeptide
Which neurotransmitters are released from synaptic vesicles?
Acetylcholine
Amino acids
Amines
Which neurotransmitters are released from secretory vesicles?
Peptides
Which neurotransmitters mediate fast neurotransmission via inotropic ligand gated ion channels?
Glutamate GABA Glycine Acetylcholine Serotonin
Which neurotransmitters mediate slow neurotransmission via metabotropic G-protein coupled receptors?
All except glycine
What are the modes of neurotransmission?
Direct
Indirect
How does direct neurotransmission work?
Ionotropic receptors
The receptor is an integral component of the molecule that forms the channel is controls
Gating of channel is rapid
How does indirect neurotransmission work?
Mediated by activation of metabotropic receptors
Receptor and the channel it controls are distinct
Gating of channel is slower
Which channels does fast EPSP utilise?
Activation of nicotinic ACh receptors
Conduction of Na+ and K+
Which channels does slow EPSP utilise?
Activation of muscarinic G coupled ACh receptors
Close of M-type K+ channels
Which is the major excitatory neurotransmitter?
Glutamate
What channels will glutamate bind to?
Non-NMDA receptors to bind the agonist kainate or AMPA controlling Na+ and K+
NMDA receptors controlling channels permeable to Na+ , Ca 2+, K+
Which mode of transmission will non-NMDA ionotropic receptors (AMPA and kainate) mediate?
Fast excitatory synaptic transmission in the CNS
Which mode of transmission will NMDA mediate?
Slow component to excitatory synaptic potential
Which ion will NMDA receptors have a high permeability to?
Ca 2+
Which drugs act on NMDA receptors?
Ketamine
Psychotomimetic agents such as phencyclidine
Which pathway relies on ionotropic and metabotropic glutamate receptors?
Retinal
